γ‐Alumina as a Support for Catalysts: A Review of Fundamental Aspects

Mechanosynthesis of fluorescent magnetic alumina for latent fingerprint detection

A green approach towards the synthesis of both conventional and magnetic fluorescent powders for revealing latent fingerprints (FPs) is disclosed. The powders formulation is based on a biodegradable matrix and fluorescent dyes extracted from commercial felt-tip markers. Two classes of powders are described: one with a fluorescent component, and other with both fluorescent and magnetic components. The incorporation of the magnetic component not only enables easy manipulation but also eliminates the risk of latent print ridge destruction. Optimization of the mechanosynthesis parameters allowed the development of magnetic powders with intense fluorescence emission, avoiding quenching caused by the magnetic component. The new powders proved to be highly efficient in revealing latent FPs on a variety of surfaces of forensic interests. The efficacy of these powders was demonstrated by comparison with commercial fluorescent magnetic and non-magnetic powders. The novel powders, prepared using a green protocol and biodegradable matrices, display excellent fluorescence properties, are cost-effective, easy to manipulate, and offer a significant advancement in fingerprint detection.

Intermediate-Temperature Reverse Water-Gas Shift under Process-Relevant Conditions Catalyzed by Dispersed Alkali Carbonates

Current reverse water-gas shift (RWGS) technologies require extreme temperatures of >900 °C. The ability to perform RWGS at lower temperatures could open new opportunities for sustainable chemical and fuel production, but most catalyst materials produce methane and coke at lower temperatures, especially at elevated pressures targeted for industrial processes. Here we show that transition-metal-free catalysts composed of K2CO3 or Na2CO3 dispersed on commercial γ-Al2O3 supports (K2CO3/γ-Al2O3 and Na2CO3/γ-Al2O3) are highly effective RWGS catalysts in the intermediate-temperature regime. At a high gas hourly space velocity of 30,000 h-1 and operating pressure of 10 bar, K2CO3/γ-Al2O3 reached RWGS equilibrium-limited CO2 conversion at 550 °C and was 100% selective for CO at all temperatures tested (up to 700 °C). Na2CO3/γ-Al2O3 was also 100% CO-selective and only slightly less active. Both catalysts were stable for hundreds of hours on stream at 525 °C and tolerated large quantities of methane and propane impurity in the CO2/H2 feed. The unique performance attributes, combined with the low-cost components and extremely simple synthesis, make dispersed carbonate RWGS catalysts attractive options for industrial application.

Insight into the atomic-level structure of γ-alumina using a multinuclear NMR crystallographic approach

The combination of multinuclear NMR spectroscopy with 17O isotopic enrichment and DFT calculations provided detailed insight into both the bulk and surface structure of γ-Al2O3. Comparison of experimental 17O NMR spectra to computational predictions confirmed that bulk γ-Al2O3 contains Al cations primarily in "spinel-like" sites, with roughly equal numbers of alternating AlVI and AlIV vacancies in disordered "chains". The work showed that overlap of signals from OIV and OIII species complicates detailed spectral analysis and highlighted potential problems with previous work where structural conclusions are based on an unambiguous assignment (and quantification) of these signals. There was no evidence for the presence of H, or for any significant levels of O vacancies, in the bulk structure of γ-Al2O3. Computational predictions from structural models for different surfaces showed a wide variety of protonated and non-protonated O species occur. Assignment of signals for two types of protonated O species was achieved using variable temperature CP and TRAPDOR experiments, with the sharper and broader resonances attributed to more accessible surface sites that interact more strongly with water and less accessible aluminols, respectively. DFT-predicted 1H NMR parameters confirmed the 1H shift increases with denticity but is also dependent on the coordination number of the next nearest neighbour Al species. Spectral assignments were also supported by 1H-27Al RESPDOR experiments, which identified spectral components resulting from μ1, μ2 and μ3 aluminols. Combining these with 1H-27Al D-HMQC experiments showed that (i) μ1 aluminols are more likely to be bound to AlIV, (ii) μ2 aluminols are coordinated to all three types of Al, but with a higher proportion bound to similar types of Al and (iii) μ3 aluminols are most likely bound to higher coordinated Al species. 1H DQ MAS spectroscopy confirmed no aluminols exist exclusively in isolation but showed that the closest proximities are between bridging aluminols coordinated to AlIV and/or AlV species.

Design and engineering of microenvironments of supported catalysts toward more efficient chemical synthesis

Catalytic species such as molecular catalysts and metal catalysts are commonly attached to varieties of supports to simplify their separation and recovery and accommodate various reaction conditions. The physicochemical microenvironments surrounding catalytic species play an important role in catalytic performance, and the rational design and engineering of microenvironments can achieve more efficient chemical synthesis, leading to greener and more sustainable catalysis. In this review, we highlight recent works addressing the topic of the design and engineering of microenvironments of supported catalysts, including supported molecular catalysts and supported metal catalysts. Six types of materials, including oxide nano/microparticle, mesoporous silica nanoparticle (MSN), polymer nanomaterial, reticular material, zeolite, and carbon-based nanomaterial, are widely used as supports for the immobilization of catalytic species. We summarize and discuss the synthesis and modification of supports and the positive effects of microenvironments on catalytic properties such as metal-support interaction, molecular recognition, pseudo-solvent effect, regulating mass transfer, steric effect, etc. These design principles and engineering strategies allow access to a better understanding of structure-property relationships and advance the development of more efficient catalytic processes.

Classification and Identification of Facet- and Edge-Specific γ-Al2O3 Surface Sites from 1H/27Al NMR Cross-Signatures and DFT Modeling

γ-Al2O3 is used as both a catalyst and a support for catalytic active phases. The properties of γ-Al2O3 have been ascribed to specific surface sites, with varying Al coordination number, acidity, and basicity, depending on the morphology of the material. Here, we combine surface-specific 27Al{1H} 2D high-field NMR (28.2T, 1.2 GHz for 1H frequency) at fast MAS (50 kHz) to observe four main distinct families of surface Al-OH sites. Comparing the measured NMR signatures (27Al δiso, CQ, and 1H δiso) to computed values from a large range of structural DFT models enables to identify specific edge and facet Al-OH surface sites in γ-Al2O3, including a distinct [4]Al-OH site with an unprecedented CQ approaching 18 MHz. This molecular-level description of alumina surfaces opens new opportunities to understand its unique properties, such as the stabilization of small particles down to single atoms, central to catalytic processes.

Scale-Up of Nanocorundum Synthesis by Mechanochemical Dehydration of Boehmite

This work presents the scale-up of room-temperature mechanochemical synthesis of nanocorundum (high-surface-area α-Al2O3) from boehmite (γ-AlOOH). This transformation on the 1 g scale using a laboratory shaker mill had previously been reported. High-energy Simoloyer ball mills equipped with milling chambers of sizes ranging from 1 to 20 L were used to scale up the mechanochemical nanocorundum synthesis to the 50 g to 1 kg scale, which paves the way to further increase batch size. Milling chambers made of steel and lined with silicon nitride (Si3N4) and milling balls made of steel, zirconia (ZrO2), and silicon nitride (Si3N4) were investigated to address the abrasion problem, leading to contamination of the alumina. Furthermore, several other process parameters, such as ball-to-powder ratio, degree of chamber filling, and milling speed, were optimized to find the conditions for efficient formation of nanocorundum with minimum contamination. Impact forces were found to be decisive in driving the transformation from boehmite to corundum. The nanocorundum produced in the scaled-up experiments has a high specific surface area >110 m2/g with an average particle size of ∼13 nm at a low level of contamination. The optimal sample was also shown to possess improved stability of surface area when exposed to temperatures up to 1200 °C. These results successfully demonstrate the scale-up of 1 g scale results to up to the 1 kg scale and may serve as a blueprint for scaling up also other mechanochemistry processes.

Unveiling Active Al3+ Sites for Ethanol Dehydration on γ-Al2O3 with Solid-State Nuclear Magnetic Resonance Spectroscopy

γ-Al2O3 is a crucial catalyst widely used in industrial alcohol dehydration processes. However, the specific nature of its active sites has remained unclear. In this study, we utilize two-dimensional heteronuclear correlation solid-state nuclear magnetic resonance and density functional theory calculations to uncover the active Al sites on the surface of γ-Al2O3 that facilitate ethanol dehydration. We show the formation of stable pentacoordinated AlV-ethanol complexes upon the adsorption of ethanol on the tetracoordinated AlIV sites. This interaction significantly enhances synergy with adjacent AlV-OH sites, resulting in a marked reduction of the activation energy barrier for ethene production. Furthermore, we reveal an interchange between AlIV and AlV-OH species, allowing hexacoordinated AlVI-OH sites to participate in the dehydration pathway through the migration of ethanol between these coordination sites.

Study of supported heteropolyacid catalysts for one-step DME synthesis from CO2 and H2

Dimethyl ether (DME) is a versatile molecule, gaining increasing interest as a viable hydrogen and energy storage solution, pivotal for the transitioning from fossil fuels to environmentally friendly and sustainable energy supply. This research explores a novel approach for the direct conversion of CO2 to DME in a fixed-bed reactor, combining the Cu/ZnO/Al2O3 methanol synthesis catalyst with supported heteropolyacids (HPAs). First, various HPAs, both commercially available and custom-synthesized, were immobilized on Montmorillonite K10. Using a wet impregnation procedure an almost ideal mono-layer of HPA on the support was achieved. The catalysts were further evaluated for their efficiency in direct synthesis of DME from CO2/H2 in combination with the Cu/ZnO/Al2O3 catalyst. Among the catalysts tested, tungstosilicic acid (HSiW) supported on K10 exhibited the most promising performance, achieving a DME yield (Y DME) of 7.06% and a molar productivity (P mol) of 77.84 molDME molHPA -1 h-1. In a subsequent step, further tests using HSiW on various support materials identified ZrO2 as the most effective support, increasing the molar productivity to 125.44 molDME molHPA -1 h-1, while maintaining the DME yield. The results highlight the potential of applying HPA-based catalysts for sustainable DME synthesis directly from CO2, emphasizing the critical role of the catalyst support for optimizing catalytic performance.

The role of pentacoordinate Al3+ sites of Pt/Al2O3 catalysts in propane dehydrogenation

Pentacoordinate Al3+ (Al3+ penta) sites on alumina (Al2O3) could anchor and stabilize the active site over the catalyst surface. The paper describes the specific effect of Al3+ penta sites on the structure and the catalytic performance of Al2O3 supported Pt catalysts by modulating the quantity of Al3+ penta sites. The Al3+ penta site content of Al2O3 exhibits a volcano-type profile as a function of calcination temperature due to the structural rearrangement. The loading of Pt and subsequent calcination can consume a significant portion of Al3+ penta sites over the Al2O3 support. We further find that, when the calcination temperature of the impregnated Al2O3 is higher than the calcination temperature of Al2O3 precursor, the structural rearrangement of Al3+ penta sites could make Pt partially buried in Al2O3. Consequently, this partially buried structure leads to relatively low conversion but high stability for propane dehydrogenation. This work further elucidates the stabilization mechanism of the Al3+ penta site over Al2O3 support.

Comparative study of the catalytic performance of physically mixed and sequentially utilized γ-alumina and zeolite in methanol-to-propylene reactions

This study aimed to investigate the catalytic performance of H-ZSM-5 zeolite compared with physically mixed and sequentially used synthesized γ-alumina and zeolite in the methanol-to-propylene (MTP) reaction. A facile, green and cost-effective method was first applied to prepare a mesoporous γ-Al2O3 support using a combination of sol-gel and hydrothermal methods via a few consecutive steps. This process was carried out using aluminium nitrate and polyethylene glycol with different molecular weights as non-ionic surfactants. X-ray diffraction, transmission electon microscopy, thermogravimetric analysis, ammonia temperature programmed desorption and Brunauer-Emmett-Teller analysis were then used to characterize the prepared γ-Al2O3 catalyst. Afterwards, the catalytic activity of the commercial H-ZSM-5 zeolite (Si/Al = 200) and the effect of the presence of the γ-alumina physically mixed and unmixed with the zeolite were also researched in the MTP reaction. Accordingly, methanol conversion and product selectivity were monitored via gas chromatography. The physically mixed mesoporous γ-Al2O3 and H-ZSM-5 zeolite exhibited the highest catalytic activity in terms of both conversion and selectivity at 400°C. To our knowledge, this research represents the first documented use of γ-alumina and zeolite simultaneously as catalysts in the MTP reaction within the English literature. It is hoped that this work will offer valuable insights for advancing the development of catalytic systems in methanol conversion processes.

Interplay Between Ni and Brønsted and Lewis Acid Sites in the Hydrodesulfurization of Dibenzothiophene

Ni-MoS2/γ-Al2O3 catalysts are commonly used in hydrotreating to enhance fossil fuel quality. The extensive research on these catalysts reveals a gap in understanding the role of Ni, often underestimated as an inactive sulfide phase or just a MoS2 promoter. In this work, we focused on analyzing whether well-dispersed supported nickel nanoparticles can be active in the hydrodesulfurization of dibenzothiophene. We dispersed Ni by Strong Electrostatic Adsorption (SEA) method across four supports with different types of acidity: silica (~ neutral acidity), γ-Al2O3 (Lewis acidity), H+-Y zeolite, and microporous-mesoporous H+-Y zeolite (both with Brønsted-Lewis acidity). Our findings reveal that Ni is indeed active in dibenzothiophene hydrodesulfurization, even with alumina and silica as supports, although their catalytic activity declines abruptly in the first hours. Contrastingly, the acid nature of zeolites imparts sustained stability and performance, attributed to robust metal-support interactions. The efficacy of the SEA method and the added mesoporosity in zeolites further amplify catalytic efficiency. Overall, we demonstrate that Ni nanoparticles may perform as a hydrogenating metal in the same manner as noble metals such as Pt and Pd perform in hydrodesulfurization. We discuss some of the probable reasons for such performance and remark on the role of Ni in hydrotreatment.

Catalytic activity of Zr/CeO2-Al2O3 catalyst for diesel soot oxidation: synthesis, characterization, and performance evaluation

Diesel soot is a significant contributor to air pollution. Soot particles present in diesel engine exhaust have a negative impact on the environment and human health. Diesel oxidation catalysts (DOCs) and diesel particulate filters (DPFs) currently use noble metal-based catalysts for soot oxidation. Due to the use of noble metals in the catalyst, the cost of diesel after-treatment systems is steadily rising. As a result, diesel vehicles have become commercially less viable than gasoline vehicles and electronic vehicles. The study focuses on an alternative diesel oxidation catalyst with efficiency similar to that of a noble metal catalyst but with a much lower cost. CeO2-Al2O3 catalysts are known for their oxygen storage capacity and high redox activity, making them suitable for soot oxidation. Adding Zr to these catalysts has been shown to influence their structural and chemical properties, significantly affecting their catalytic behavior. Therefore, the current study is focused on using Zr/CeO2-Al2O3 as a substitute for noble metal-based catalysts to enhance its performance for diesel soot oxidation in automotive exhaust. Evaporation-induced self-assembly (EISA) was used to prepare 1, 3, and 5 weight (wt) % Zr supported mesoporous CeO2-Al2O3 catalysts. Morphological, structural, and physicochemical properties of the synthesized catalysts were examined using Brunauer-Emmett-Teller (BET) absolute isotherm, Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Temperature programmed reduction (TPR), and Temperature-programmed desorption of ammonia (NH3-TPD). XRD, BET, and SEM data confirmed that the catalysts were mesoporous and low-crystalline with a high surface area. The soot oxidation activity of the catalysts was evaluated using a thermogravimetric analysis (TGA) technique. The loose contacts soot oxidation activity test suggested that 50% oxidation of soot occurred at 390 °C in the absence of a catalyst. T50 of CeO2-Al2O3 catalyzed soot oxidation was 296 °C. Adding Zr to the catalyst significantly improved catalytic activity for diesel soot oxidation. We observed a further drastic change in T50 of soot over 1, 3, and 5% Zr/CeO2-Al2O3, which were 220 °C, 210 °C, and 193 °C, respectively. According to these results, incorporating Zr into the CeO2-Al2O3 catalyst significantly improved the oxidation process of soot.

Managing Expectations and Imbalanced Training Data in Reactive Force Field Development: An Application to Water Adsorption on Alumina

ReaxFF is a computationally efficient model for reactive molecular dynamics simulations that has been applied to a wide variety of chemical systems. When ReaxFF parameters are not yet available for a chemistry of interest, they must be (re)optimized, for which one defines a set of training data that the new ReaxFF parameters should reproduce. ReaxFF training sets typically contain diverse properties with different units, some of which are more abundant (by orders of magnitude) than others. To find the best parameters, one conventionally minimizes a weighted sum of squared errors over all of the data in the training set. One of the challenges in such numerical optimizations is to assign weights so that the optimized parameters represent a good compromise among all the requirements defined in the training set. This work introduces a new loss function, called Balanced Loss, and a workflow that replaces weight assignment with a more manageable procedure. The training data are divided into categories with corresponding "tolerances", i.e., acceptable root-mean-square errors for the categories, which define the expectations for the optimized ReaxFF parameters. Through the Log-Sum-Exp form of Balanced Loss, the parameter optimization is also a validation of one's expectations, providing meaningful feedback that can be used to reconfigure the tolerances if needed. The new methodology is demonstrated with a nontrivial parametrization of ReaxFF for water adsorption on alumina. This results in a new force field that reproduces both the rare and frequent properties of a validation set not used for training. We also demonstrate the robustness of the new force field with a molecular dynamics simulation of water desorption from a γ-Al2O3 slab model.

Chemical bonding and electronic properties along Group 13 metal oxides

CONTEXT

The present work provides a systematic theoretical analysis of the nature of the chemical bond in Al2O3, Ga2O3, and In2O3 group 13 cubic crystal structure metal oxides. The influence of the functional in the resulting band gap is assessed. The topological analysis of the electron density provides unambiguous information about the degree of ionicity along the group which is linearly correlated with the band gap values and with the cost of forming a single oxygen vacancy. Overall, this study offers a comprehensive insight into the electronic structure of metal oxides and their interrelations. This will help researchers to harness information effectively, boosting the development of novel metal oxide catalysts or innovative methodologies for their preparation.

METHODS

Periodic density functional theory was used to predict the atomic structure of the materials of interest. Structure optimization was carried out using the PBE functional, using a plane wave basis set and the PAW representation of the atomic cores, using the VASP code. Next, the electronic properties were computed by carrying out single point calculations employing PBE, PBE + U functionals using VASP and also with PBE and the hybrid HSE06 functionals using the FHI-AIMS software. For the hybrid HSE06, the impact of the screening parameter, ω, and mixing parameter, α, on the calculated band gap has also been assessed.

Graphene-based versus alumina supports on CO2 methanation using lanthanum-promoted nickel catalysts

The valorization of CO2 as a biofuel, transforming it through methanation as part of the power-to-gas (P2G) process, will allow the reduction of the net emissions of this gas to the atmosphere. Catalysts with 13 wt.% of nickel (Ni) loading incorporated into alumina and graphene derivatives were used, and the effect of the support on the activity was examined at temperatures between 498 and 773 K and 10 bar of pressure. Among the graphene-based catalysts (13Ni/AGO, 13Ni/BGO, 13Ni/rGO, 13Ni-Ol/GO, 13Ni/Ol-GO, and 13Ni/Ol-GO Met), the highest methane yield was found for 13Ni/rGO (78% at 810 K), being the only system comparable to the catalyst supported on alumina 13Ni/Al2O3 (89.5% at 745 K). The incorporation of 14 wt.% of lanthanum (La) into the most promising supports, rGO and alumina, led to nickel-support interactions that enhanced the catalytic activity of 13Ni/Al2O3 (89.5% at lower temperature, 727 K) but was not effective for 13Ni/rGO. The resistance against deactivation by H2S poisoning was also studied for these catalysts, and a fast deactivation was observed. In addition, activity recovery was impossible despite the regeneration treatment carried out over catalysts. The resistance against deactivation by H2S poisoning was also studied for these catalysts, observing that both suffered a rapid/immediate deactivation and which in addition/unfortunately was impossible to solve despite the regeneration treatment carried out over catalysts.

Luminescence Properties of Al2O3:Ti in the Blue and Red Regions: A Combined Theoretical and Experimental Study

Using jointly experimental results and first-principles calculations, we unambiguously assign the underlying mechanisms behind two commonly observed luminescence bands for the Al2O3 material. Indeed, we show that the red band is associated with a Ti3+ d-d transition as expected, while the blue band is the combination of the Ti3+ + O- → Ti4+ + O2- and VO•+e- → VO× de-excitation processes. Thanks to our recent developments, which take into account the vibrational contributions to the electronic transitions in solids, we were able to simulate the luminescence spectra for the different signatures. The excellent agreement with the experiment demonstrates that it should be possible to predict the color of the material with a CIE chromaticity diagram. We also anticipated the luminescence signature of Al2O3:Ti,Ca and Al2O3:Ti,Be that were confirmed by experiment.

Adsorption of Nickel Ions on the γ-Alumina Surface: Competitive Effect of Protons and Its Impact on Concentration Profiles

Mesoporous γ-alumina is used as an adsorbent in the decontamination of water from heavy metals (e.g., nickel and cobalt) and as a support for heterogeneous catalysts prepared by impregnation. In these cases, alumina extrudates are in contact with aqueous solutions containing precursors of the active metal phase to be deposited. The proton concentration (or pH) in the metal solution in contact with alumina can impact the adsorption efficiency of decontamination processes and the activities of catalysts. Yet, it is difficult to quantify the effect of the pH inside the pores since protons are not detected by classical imaging techniques. In this article, the effect of protons on nickel adsorption on alumina is evaluated using a novel technique coupling liquid analysis (pH, conductivity, and UV/vis) and laser-induced breakdown spectroscopy (or LIBS) analysis of concentration gradients inside the solid. Both methods are in excellent agreement. The results show a slow diffusion of protons inside alumina pores (diffusion continues even after 940 min), yielding high proton concentration gradients. On the other hand, the nickel species penetrate the extrudates faster but are slowly displaced by protons under certain operating conditions. As a result, different metal concentration profiles are obtained, depending on the initial pH and contact time. These findings are interesting in catalysis since they prove the possibility of controlling the deposition of the active metal on catalysts by regulating the operating conditions of impregnation. For typical industrial impregnation times (a few minutes to 1 to 2 h), protons do not have enough time to deeply penetrate inside extrudates, so the initial pH of the metal solution will have nearly no effect on the metal distribution. Conversely, decontamination processes have much longer contact times; therefore, lower initial pH values should have negative impacts on the adsorption efficiency due to the protons displacing the adsorbed nickel.

Exploring a Low-Cost Valorization Route for Amazonian Cocoa Pod Husks through Thermochemical and Catalytic Upgrading of Pyrolysis Vapors

Ecuador as an international leader in the production of cocoa beans produced more than 300 000 tons in 2021; hence, the management and valorization of the 2 MM tons of waste generated annually by this industry have a strategic and socioeconomic value. Consequently, appropriate technologies to avoid environmental problems and promote sustainable development and the bioeconomy, especially considering that this is a megadiverse country, are of the utmost relevance. For this reason, we explored a low-cost pyrolysis route for valorizing cocoa pod husks from Ecuador's Amazonian region, aiming at producing pyrolysis liquids (bio-oil), biochar, and gas as an alternative chemical source from cocoa residues in the absence of hydrogen. Downstream catalytic processing of hot pyrolysis vapors using Mo- and/or Ni-based catalysts and standalone γ-Al2O3 was applied for obtaining upgraded bio-oils in a laboratory-scale fixed bed reactor, at 500 °C in a N2 atmosphere. As a result, bimetallic catalysts increased the bio-oil aqueous phase yield by 6.6%, at the expense of the organic phase due to cracking reactions according to nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry (GC-MS) results. Overall product yield remained constant, in comparison to pyrolysis without any downstream catalytic treatment (bio-oil ∼39.0-40.0 wt % and permanent gases 24.6-26.6 wt %). Ex situ reduced and passivated MoNi/γ-Al2O3 led to the lowest organic phase and highest aqueous phase yields. The product distribution between the two liquid phases was also modified by the catalytic upgrading experiments carried out, according to heteronuclear single-quantum correlation (HSQC), total correlation spectroscopy (TOCSY), and NMR analyses. The detailed composition distribution reported here shows the chemical production potential of this residue and serves as a starting point for subsequent valorizing technologies and/or processes in the food and nonfood industry beneficiating society, environment, economy, and research.

Solvent-Free Aerobic Oxidative Cleavage of Methyl Oleate to Biobased Aldehydes over Mechanochemically Synthesized Supported AgAu Nanoparticles

The performance of mechanochemically synthesized supported bimetallic AgAu nanoalloy catalysts was evaluated in the oxidative cleavage of methyl oleate, a commonly available unsaturated bio-derived raw material. An extensive screening of supports (SiO2 , C, ZrO2 , Al2 O3 ), metallic ratios (Ag : Au), reaction times, temperatures, and use of solvents was carried out. The performance was optimized towards productivity and selectivity for the primary cleavage products (aldehydes and oxoesters). The optimal conditions were achieved in the absence of solvent, using Ag8 Au92 /SiO2 as catalyst, at 80 °C, reaction time of 1 h, substrate to catalyst=555 and 10 bar of molecular oxygen. A strong support effect was observed: the selectivity to aldehydes was best with silica as support, and to esters was best using zirconia. This shows not only that mechanochemical preparation of bimetallic catalysts is a powerful tool to generate useful catalyst compositions, but also that a safe, green, solventless synthesis of bio-derived products can be achieved by aerobic oxidative cleavage.

A Review on 1-D Nanomaterials: Scaling-Up with Gas-Phase Synthesis

Nanowire-like materials exhibit distinctive properties comprising optical polarisation, waveguiding, and hydrophobic channelling, amongst many other useful phenomena. Such 1-D derived anisotropy can be further enhanced by arranging many similar nanowires into a coherent matrix, known as an array superstructure. Manufacture of nanowire arrays can be scaled-up considerably through judicious use of gas-phase methods. Historically, the gas-phase approach however has been extensively used for the bulk and rapid synthesis of isotropic 0-D nanomaterials such as carbon black and silica. The primary goal of this review is to document recent developments, applications, and capabilities in gas-phase synthesis methods of nanowire arrays. Secondly, we elucidate the design and use of the gas-phase synthesis approach; and finally, remaining challenges and needs are addressed to advance this field.

Using the Colloidal Method to Prepare Au Catalysts for the Alkylation of Aniline by Benzyl Alcohol

Using the colloidal method, attempts were made to deposit Au NPs on seven different material supports (TiO2, α and γ-Al2O3, HFeO2, CeO2, C, and SiO2). The deposition between 0.8 and 1 wt% of Au NPs can be generally achieved, apart for SiO2 (no deposition) and α-alumina (0.3 wt%). The resultant sizes of the Au NPs were dependent on the nature as well as the surface area of the support. The catalytic activity and selectivity of the supported Au catalysts were then compared in the alkylation of aniline by benzyl alcohol. Correlations were made between the nature of the support, the size of the Au NP, and the H-binding energy. A minimum H-binding energy of 1100 μV K-1 was found to be necessary for high selectivity for the secondary amine. Comparisons of the TEM images of the pre- and post-reaction catalysts also revealed the extent of Au NP agglomeration under the reaction conditions.

Direct Air Capture of CO2 Using Amine/Alumina Sorbents at Cold Temperature

Rising CO2 emissions are responsible for increasing global temperatures causing climate change. Significant efforts are underway to develop amine-based sorbents to directly capture CO2 from air (called direct air capture (DAC)) to combat the effects of climate change. However, the sorbents' performances have usually been evaluated at ambient temperatures (25 °C) or higher, most often under dry conditions. A significant portion of the natural environment where DAC plants can be deployed experiences temperatures below 25 °C, and ambient air always contains some humidity. In this study, we assess the CO2 adsorption behavior of amine (poly(ethyleneimine) (PEI) and tetraethylenepentamine (TEPA)) impregnated into porous alumina at ambient (25 °C) and cold temperatures (-20 °C) under dry and humid conditions. CO2 adsorption capacities at 25 °C and 400 ppm CO2 are highest for 40 wt% TEPA-incorporated γ-Al2O3 samples (1.8 mmol CO2/g sorbent), while 40 wt % PEI-impregnated γ-Al2O3 samples exhibit moderate uptakes (0.9 mmol g-1). CO2 capacities for both PEI- and TEPA-incorporated γ-Al2O3 samples decrease with decreasing amine content and temperatures. The 40 and 20 wt % TEPA sorbents show the best performance at -20 °C under dry conditions (1.6 and 1.1 mmol g-1, respectively). Both the TEPA samples also exhibit stable and high working capacities (0.9 and 1.2 mmol g-1) across 10 cycles of adsorption-desorption (adsorption at -20 °C and desorption conducted at 60 °C). Introducing moisture (70% RH at -20 and 25 °C) improves the CO2 capacity of the amine-impregnated sorbents at both temperatures. The 40 wt% PEI, 40 wt % TEPA, and 20 wt% TEPA samples show good CO2 uptakes at both temperatures. The results presented here indicate that γ-Al2O3 impregnated with PEI and TEPA are potential materials for DAC at ambient and cold conditions, with further opportunities to optimize these materials for the scalable deployment of DAC plants at different environmental conditions.

Catalytic activity of γ-Al2O3(110) in the NO + H2 reaction: a DFT study

In this work, the interaction of the surface of γ-Al2O3(110) with NO and H2 was studied using density functional theory calculations. Free γ-Al2O3(110) adsorbs NO and binds H atoms, but repels the H2 molecule. A triplet of low-coordinated OII-AlIII-OII atoms provides the catalytic activity of γ-Al2O3(110) along the path: (i) the adsorption of NO/AlIII is followed by the binding of H2 to form a hydroxylamine derivative NHOH through an intermediate NO/AlIII + 2 × H/OII complex; (ii) recombination of NHOH with the release of N2 through an intermediate NHOH/AlIII + NHOH/AlIV or adsorption of NO followed by the release of N2O through the intermediate NHOH/AlIII + NO/AlIV; the pathway ends with the regeneration of γ-Al2O3(110). The calculated adsorption heats ensure the diffusion of H atoms from the deposited Pt to the surface (110), initiating the formation of the NH2/AlIII + H/OII complex, which releases NH3 endothermically and is stable enough to inhibit stage (ii) of the above reaction pathway. An excess of O2 in the NO + H2 mixture excludes H/Pt and eliminates inhibition. The formation of oxynitrides is suppressed, but not excluded by more exothermic surface processes. The N-doped conductivity of bulk and surface oxynitrides Al32O47N and the dependence of the heat of adsorption of H atoms on the band gap width were revealed, which suggests a relationship between the band gap width and catalytic activity.

MAO- and Borate-Free Activating Supports for Group 4 Metallocene and Post-Metallocene Catalysts of α-Olefin Polymerization and Oligomerization

Modern industry of advanced polyolefins extensively uses Group 4 metallocene and post-metallocene catalysts. High-throughput polyolefin technologies demand the use of heterogeneous catalysts with a given particle size and morphology, high thermal stability, and controlled productivity. Conventional Group 4 metal single-site heterogeneous catalysts require the use of high-cost methylalumoxane (MAO) or perfluoroaryl borate activators. However, a number of inorganic phases, containing highly acidic Lewis and Brønsted sites, are able to activate Group 4 metal pre-catalysts using low-cost and affordable alkylaluminums. In the present review, we gathered comprehensive information on MAO- and borate-free activating supports of different types and discussed the surface nature and chemistry of these phases, examples of their use in the polymerization of ethylene and α-olefins, and prospects of the further development for applications in the polyolefin industry.

Inductively Coupled Nonthermal Plasma Synthesis of Size-Controlled γ-Al2O3 Nanocrystals

Gamma alumina (γ-Al2O3) is widely used as a catalyst and catalytic support due to its high specific surface area and porosity. However, synthesis of γ-Al2O3 nanocrystals is often a complicated process requiring high temperatures or additional post-synthetic steps. Here, we report a single-step synthesis of size-controlled and monodisperse, facetted γ-Al2O3 nanocrystals in an inductively coupled nonthermal plasma reactor using trimethylaluminum and oxygen as precursors. Under optimized conditions, we observed phase-pure, cuboctahedral γ-Al2O3 nanocrystals with defined surface facets. Nuclear magnetic resonance studies revealed that nanocrystal surfaces are populated with AlO6, AlO5 and AlO4 units with clusters of hydroxyl groups. Nanocrystal size tuning was achieved by varying the total reactor pressure yielding particles as small as 3.5 nm, below the predicted thermodynamic stability limit for γ-Al2O3.

4,6-Diamino-2-thiopyrimidine-based Cobalt Metal Organic Framework (Co-DAT-MOF): green, efficient, novel and reusable nanocatalyst for synthesis of multicomponent reactions

In this study, Co-DAT-MOF powder was prepared via the solvothermal method using 4, 6-diamino-2-thiopyrimidine as the organic linker and Co(NO₃)₂·6H₂O. The synthesized catalysts are characterized using XRD, FT-IR, TGA, SEM, BET, NH₃-TPD, and ICP-OES techniques. SEM analysis clearly indicated the formation of nanosheet microspheres. NH₃-TPD-MS was employed as a means of identifying the various strengths of acid sites and their relative abundance in an attempt to explain the effect of the catalyst surface acid sites. We identified a new acidic feature in Co-DAT-MOF catalyst, related to the presence of desorption peaks in the NH₃-TPD profiles. The activity of Co-DAT-MOF catalyst for the synthesis of multicomponent reactions correlates with lewis acidity. In addition, Co-DAT-MOF exhibited excellent performance for the synthesis of pyrroloacridine-1(2H)-one and chromeno [2, 3- d] pyrimidin-8-amines, as well as good reusability and recyclability.

How Solid Surfaces Control Stability and Interactions of Supported Cationic CuI(dppf) Complexes─A Solid-State NMR Study

Organometallic complexes are frequently deposited on solid surfaces, but little is known about how the resulting complex-solid interactions alter their properties. Here, a series of complexes of the type Cu(dppf)(L_x)⁺ (dppf = 1,1'-bis(diphenylphosphino)ferrocene, L_x = mono- and bidentate ligands) were synthesized, physisorbed, ion-exchanged, or covalently immobilized on solid surfaces and investigated by ³¹P MAS NMR spectroscopy. Complexes adsorbed on silica interacted weakly and were stable, while adsorption on acidic γ-Al₂O₃ resulted in slow complex decomposition. Ion exchange into mesoporous Na-[Al]SBA-15 resulted in magnetic inequivalence of ³¹P nuclei verified by ³¹P-³¹P RFDR and ¹H-³¹P FSLG HETCOR. DFT calculations verified that a MeCN ligand dissociates upon ion exchange. Covalent immobilization via organic linkers as well as ion exchange with bidentate ligands both lead to rigidly bound complexes that cause broad ³¹P CSA tensors. We thus demonstrate how the interactions between complexes and functional surfaces determine and alter the stability of complexes. The applied Cu(dppf)(L_x)⁺ complex family members are identified as suitable solid-state NMR probes for investigating the influence of support surfaces on deposited inorganic complexes.

Role of structural disorder in the vibrational spectra of sol-gel γ and δ-Al2O3 nanoparticles

Alumina nanopowders belonging to the γ and δ transition phases have been characterized by infrared and Raman spectroscopies. A quantitative interpretation of their vibrational spectra has been provided and related to their crystal structure, with particular emphasis on structural disorder and features not predicted by group-theoretical considerations. Both phases show very similar infrared dielectric functions, but with clear instances of mode-splitting in the δ phase, which are related to ordering in the tetrahedral Al positions. Raman spectroscopy was unable to resolve any modes in the sample identified as γ phase, but the full lattice vibrational region could be measured for the δ sample under UV and red excitation lines. Raman spectra are more complex than those obtained by infrared spectroscopy and cannot be completely explained by factor group analysis, in the absence of dedicated theoretical studies. Finally, the luminescent properties of these materials have been qualitatively explored and linked to disorder and substitutional impurities. In general, the results contained in this work prove that vibrational spectroscopies are powerful tools for quantitative analyses of these disordered nanomaterials and suggest the need for more theoretical work to understand their vibrational properties.

Heterogenization of Heteropolyacid with Metal-Based Alumina Supports for the Guaiacol Gas-Phase Hydrodeoxygenation

Because of the global necessity to decrease CO₂ emissions, biomass-based fuels have become an interesting option to explore; although, bio-oils need to be upgraded, for example, by catalytic hydrodeoxygenation (HDO), to reduce oxygen content. This reaction generally requires bifunctional catalysts with both metal and acid sites. For that purpose, Pt-Al₂O₃ and Ni-Al₂O₃ catalysts containing heteropolyacids (HPA) were prepared. HPAs were added by two different methods: the impregnation of a H₃PW₁₂O₄₀ solution onto the support and a physical mixture of the support with Cs_2.5H_0.5PW₁₂O₄₀. The catalysts were characterized by powder X-ray diffraction, Infrared, UV-Vis, Raman, X-ray photoelectron spectroscopy and NH₃-TPD experiments. The presence of H₃PW₁₂O₄₀ was confirmed by Raman, UV-Vis and X-ray photoelectron spectroscopy, while the presence of Cs_2.5H_0.5PW₁₂O₄₀ was confirmed by all of the techniques. However, HPW was shown to strongly interact with the supports, especially in the case of Pt-Al₂O₃. These catalysts were tested in the HDO of guaiacol, at 300 °C, under H₂ and at atmospheric pressure. Ni-based catalysts led to higher conversion and selectivity to deoxygenated compound values, such as benzene. This is attributed to both a higher metal and acidic contents of these catalysts. Among all tested catalysts, HPW/Ni-Al₂O₃ was shown to be the most promising, although it suffered a more severe deactivation with time-on-stream.

Exploring the Multifunctionality of Mechanochemically Synthesized γ-Alumina with Incorporated Selected Metal Oxide Species

γ-Alumina with incorporated metal oxide species (including Fe, Cu, Zn, Bi, and Ga) was synthesized by liquid-assisted grinding-mechanochemical synthesis, applying boehmite as the alumina precursor and suitable metal salts. Various contents of metal elements (5 wt.%, 10 wt.%, and 20 wt.%) were used to tune the composition of the resulting hybrid materials. The different milling time was tested to find the most suitable procedure that allowed the preparation of porous alumina incorporated with selected metal oxide species. The block copolymer, Pluronic P123, was used as a pore-generating agent. Commercial γ-alumina (S_BET = 96 m²·g^-1), and the sample fabricated after two hours of initial grinding of boehmite (S_BET = 266 m²·g^-1), were used as references. Analysis of another sample of γ-alumina prepared within 3 h of one-pot milling revealed a higher surface area (S_BET = 320 m²·g^-1) that did not increase with a further increase in the milling time. So, three hours of grinding time were set as optimal for this material. The synthesized samples were characterized by low-temperature N₂ sorption, TGA/DTG, XRD, TEM, EDX, elemental mapping, and XRF techniques. The higher loading of metal oxide into the alumina structure was confirmed by the higher intensity of the XRF peaks. Samples synthesized with the lowest metal oxide content (5 wt.%) were tested for selective catalytic reduction of NO with NH₃ (NH₃-SCR). Among all tested samples, besides pristine Al₂O₃ and alumina incorporated with gallium oxide, the increase in reaction temperature accelerated the NO conversion. The highest NO conversion rate was observed for Fe₂O₃-incorporated alumina (70%) at 450 °C and CuO-incorporated alumina (71%) at 300 °C. The CO₂ capture was also studied for synthesized samples and the sample of alumina with incorporated Bi₂O₃ (10 wt.%) gave the best result (1.16 mmol·g^-1) at 25 °C, while alumina alone could adsorb only 0.85 mmol·g^-1 of CO₂. Furthermore, the synthesized samples were tested for antimicrobial properties and found to be quite active against Gram-negative bacteria, P. aeruginosa (PA). The measured Minimum Inhibitory Concentration (MIC) values for the alumina samples with incorporated Fe, Cu, and Bi oxide (10 wt.%) were found to be 4 µg·mL^-1, while 8 µg·mL^-1 was obtained for pure alumina.

Alumina supported copper oxide nanoparticles (CuO/Al2O3) as high-performance electrocatalysts for hydrazine oxidation reaction

Direct hydrazine liquid fuel cell (DHFC) is perceived as effectual energy generating mean owing to high conversion efficiency and energy density. However, the development of well-designed, cost effective and high performance electrocatalysts is the paramount to establish DHFCs as efficient energy generating technology. Herein, gamma alumina supported copper oxide nanocatalysts (CuO/Al₂O₃) are synthesized via impregnation method and investigated for their electrocatalytic potential towards hydrazine oxidation reaction. CuO with different weight percentages i.e., 4%, 8%, 12%, 16% and 20% are impregnated on gamma alumina support. X-ray diffraction analysis revealed the cubic crystal structure and nanosized particles of the prepared metal oxides. Transmission electron microscopy also referred to the cubic morphology and nanoparticle formation. Electrochemical oxidation potential of the CuO/Al₂O₃ nanoparticles is explored via cyclic voltammetry as the analytical tool. Optimization of conditions and electrocatalytic studies shown that 16% CuO/Al₂O₃ presented the best electronic properties towards N₂H₂ oxidation reaction. BET analysis ascertained the high surface area (131.2546 m² g¹) and large pore diameter (0.279605 cm³ g^-1) for 16% CuO/Al₂O₃. Nanoparticle formation, high porosity and enlarged surface area of the proposed catalysts resulted in significant oxidation current output (600 μA), high current density (8.2 mA cm^-2) and low charge transfer resistance (3.7 kΩ). Electrooxidation of hydrazine on such an affordable and novel electrocatalyst opens a gateway to further explore the metal oxide impregnated alumina materials for different electrochemical applications.

Fabrication of γ-Al2O3 Nanoarrays on Aluminum Foam Assisted by Hydroxide for Monolith Catalysts

Heat distribution and good adhesion of the washcoat on monolith catalysts are critical to improving catalytic activity and long-term stability. Compared with cordierite, metal foam presents a high thermal conductivity coefficient. Also, the availability of "washcoat" in situ grown on metal substrates opens the door to eliminating the problem of coating peeling. Generally, hydrothermal or thermal methods are used for the fabrication of in situ grown washcoat on metal substrates. In this research, the aluminum foam monolith vertically aligned Al₂O₃ nanowire array is successfully prepared at ambient temperature in an alkaline solution for the first time. Furthermore, the Pt-loaded Al₂O₃ nanowire array (0.5 g_Pt/L _monolith) is applied to C₂H₄ degradation. The catalyst converts 90% C₂H₄ at 147 °C with a gas hourly space velocity (GHSV) of 20,000 h^-1. And a little decrease (1%) is observed in catalytic activity, even in 15 vol % water vapors. The catalysts show good thermal stability and water resistance property over 36 h at 300 °C. Above all, this study presents a simple way of in situ growth of washcoat on metal-substrate monolith with potentially scaled manufacturing. And the monolith catalyst shows good catalytic performance on C₂H₄, which can be applied for volatile organic compound treatment.

Recent Catalytic Advances on the Sustainable Production of Primary Furanic Amines from the One-Pot Reductive Amination of 5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (5-HMF) represents a well-known class of lignocellulosic biomass-derived platform molecules. With the presence of many reactive functional groups in the structure, this versatile building block could be valorized into many value-added products. Among well-established catalytic transformations in biorefinery, the reductive amination is of particular interest to provide valuable N-containing compounds. Specifically, the reductive amination of 5-HMF with ammonia (NH₃ ) and molecular hydrogen (H₂ ) offers a straightforward and sustainable access to primary furanic amines [i. e., 5-hydroxymethyl-2-furfuryl amine (HMFA) and 2,5-bis(aminomethyl)furan (BAMF)], which display far-reaching utilities in pharmaceutical, chemical, and polymer industries. In the presence of heterogeneous catalysts contanining monometals (Ni, Co, Ru, Pd, Pt, and Rh) or bimetals (Ni-Cu and Ni-Mn), this elegant pathway enables a high-yielding and chemoselective production of HMFA/BAMF compared to other synthetic routes. This Review aims to present an up-to-date highlight on the supported metal-catalyzed reductive amination of 5-HMF with elaborate studies on the role of metal, solid support, and reaction parameters. Besides, the recyclability/adaptability of catalysts as well as the reaction mechanism are also provided to give valuable insights into this potential 5-HMF valorization strategy.

Effect of extrusion-spheronization granulation and manganese loading on catalytic ozonation of petrochemical wastewater

The petrochemical secondary effluent (PSE) is typical refractory wastewater derived from the petrochemical industries, which requires advanced treatment due to the strict environmental protection policies. Catalytic ozonation is one of the most widely used advanced oxidation technologies in wastewater treatment because of its high mineralization rate, in which the alumina-based catalyst usually plays an important role. Extrusion-spheronization is a promising technique for the preparation of alumina spheres because the synthesized alumina particles have high sphericity, high specific surface aera and narrow particle size distribution. In this paper, two kinds of alumina-based catalysts (catalyst A: manganese nitrate added after alumina granulation and catalyst B: manganese nitrate added into alumina powder before granulation) were prepared by the extrusion-spheronization method and used for PSE treatment by catalytic ozonation. The prepared alumina samples were characterized by Brunauer-Emmett-Teller (BET) method, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM), while the wastewater samples were analyzed for Total organic carbon (TOC), UV₂₅₄ and fluorescence spectroscopy. Results showed that manganese was uniformly distributed in both catalysts, and the specific surface area of two catalysts was 318.36 m²/g and 354.95 m²/g, respectively. Catalytic ozonation experiments were repeated nine times with each catalyst under the same conditions. The TOC removal rates for catalysts A and B in the first run were 48.88% and 49.06%, respectively, then it dropped to 28.05% for catalyst A but remained 47.81% for catalyst B after using for nine times. This implied that the long-term performance of catalyst B would be more stable than catalyst A. Similar result were found in three-dimensional fluorescence analysis. UV₂₅₄ results indicated that the removal efficiency of aromatic and unsaturated substances by catalyst B was higher than catalyst A. A possible explanation is that the active component manganese oxide formed a catalyst skeleton in catalyst B, which makes it hard to dissolve. Effect of extrusion-spheronization granulation and manganese loading on advanced oxidant treatment of petrochemical wastewater.

Hydration Structures on γ-Alumina Surfaces With and Without Electrolytes Probed by Atomistic Molecular Dynamics Simulations

A wide range of systems, both engineered and natural, feature aqueous electrolyte solutions at interfaces. In this study, the structure and dynamics of water at the two prevalent crystallographic terminations of gamma-alumina, [110] and [100], and the influence of salts─sodium chloride, ammonium acetate, barium acetate, and barium nitrate on such properties─were investigated using equilibrium molecular dynamics simulations. The resulting interfacial phenomena were quantified from simulation trajectories via atomic density profiles, angle probability distributions, residence times, 2-D density distributions within the hydration layers, and hydrogen bond density profiles. Analysis and interpretation of the results are supported by simulation snapshots. Taken together, our results show stronger interaction and closer association of water with the [110] surface, compared to [100], while ion-induced disruption of interfacial water structure was more prevalent at the [100] surface. For the latter, a stronger association of cations is observed, namely sodium and ammonium, and ion adsorption appears determined by their size. The differences in surface-water interactions between the two terminations are linked to their respective surface features and distributions of surface groups, with atomistic-scale roughness of the [110] surface promoting closer association of interfacial water. The results highlight the fundamental role of surface characteristics in determining surface-water interactions, and the resulting effects on ion-surface and ion-water interactions. Since the two terminations of gamma-alumina considered represent interfaces of significance to numerous industrial applications, the results provide insights relevant for catalyst preparation and adsorption-based water treatment, among other applications.

Hydrodesulfurization of Dibenzothiophene over Ni-Mo-W Sulfide Catalysts Supported on Sol-Gel Al2O3-CeO2

To achieve sulfur content in gas oil at a near-zero level, new catalysts with improved hydrogenation functions are needed. In this work, new Ni-Mo-Mo hydrodesulfurization (HDS) catalysts supported by Al₂O₃-CeO₂ materials were synthesized to evaluate their efficiency in the reaction of HDS with dibenzothiophene (DBT). Al₂O₃-CeO₂ supports different CeO₂ loadings (0, 5, 10 and 15 wt.%) and supported NiMoW catalysts were synthesized by sol-gel and impregnation methods, respectively. The physicochemical properties of the supports and catalysts were determined by a variety of techniques (chemical analysis, XRD, N₂ physisorption, DRS UV-Vis, XPS, and HRTEM). In the DBT HDS reaction carried out in a batch reactor at 320 °C and a H₂ pressure of 5.5 MPa, the sulfide catalysts showed a dramatic increase in activity with increasing CeO₂ content in the support. Nearly complete DBT conversion (97%) and enhanced hydrogenation function (HYD) were achieved on the catalyst with the highest CeO₂ loading. The improved DBT conversion and selectivity towards the hydrogenation products (HYD/DDS ratio = 1.6) of this catalyst were attributed to the combination of the following causes: (i) the positive effect of CeO₂ in forcing the formation of the onion-shaped Mo(W)S₂ layers with a large number of active phases, (ii) the inhibition of the formation of the undesired NiAlO₄ spinel phase, (iii) the appropriate textural properties, (iv) the additional ability for heterolytic dissociation of H₂ on the CeO₂ surfaces, and (v) the increase in Brønsted acidity.

Synthesis and Characterization of α-Al2O3/Ba-β-Al2O3 Spheres for Cadmium Ions Removal from Aqueous Solutions

The search for adsorbent materials with a certain chemical inertness, mechanical resistance, and high adsorption capacity, as is the case with alumina, is carried out with structural or surface modifications with the addition of additives or metallic salts. This research shows the synthesis, characterization, phase evolution and Cd(II) adsorbent capacity of α-Al₂O₃/Ba-β-Al₂O₃ spheres obtained from α-Al₂O₃ nanopowders by the ion encapsulation method. The formation of the Ba-β-Al₂O₃ phase is manifested at 1500 °C according to the infrared spectrum by the appearance of bands corresponding to AlO₄ bonds and the appearance of peaks corresponding to Ba-O bonds in Raman spectroscopy. XRD determined the presence of BaO·Al₂O₃ at 1000 °C and the formation of Ba-β-Al₂O₃ at 1600 °C. Scanning electron microscopy revealed the presence of spherical grains corresponding to α-Al₂O₃ and hexagonal plates corresponding to β-Al₂O₃ in the spheres treated at 1600 °C. The spheres obtained have dimensions of 4.65 ± 0.30 mm in diameter, weight of 43 ± 2 mg and a surface area of 0.66 m²/g. According to the curve of pH vs. zeta potential, the spheres have an acid character and a negative surface charge of -30 mV at pH 5. Through adsorption studies, an adsorbent capacity of Cd(II) of 59.97 mg/g (87 ppm Cd(II)) was determined at pH 5, and the data were fitted to the pseudo first order, pseudo second order and Freundlich models, with correlation factors of 0.993, 0.987 and 0.998, respectively.

High-Field NMR, Reactivity, and DFT Modeling Reveal the γ-Al2 O3 Surface Hydroxyl Network

Aluminas are strategic materials used in many major industrial processes, either as catalyst supports or as catalysts in their own right. The transition alumina γ-Al2 O3 is a privileged support, whose reactivity can be tuned by thermal activation. This study provides a qualitative and quantitative assessment of the hydroxyl groups present on the surface of γ-Al2 O3 at three different dehydroxylation temperatures. The principal [AlOH] configurations are identified and described in unprecedented detail at the molecular level. The structures were established by combining information from high-field 1 H and 27 Al solid-state NMR, IR spectroscopy and DFT calculations, as well as selective reactivity studies. Finally, the relationship between the hydroxyl structures and the molecular-level structures of the active sites in catalytic alkane metathesis is discussed.

Infrared photodissociation spectroscopy of (Al2O3)2-5FeO+: influence of Fe-substitution on small alumina clusters

The infrared photodissociation spectra of He-tagged (Al₂O₃)_nFeO⁺ (n = 2-5), are reported in the Al-O and Fe-O stretching and bending spectral region (430-1200 cm^-1) and assigned based on calculated harmonic IR spectra from density functional theory (DFT). The substitution of Fe for an Al center occurs preferentially at 3-fold oxygen coordination sites located at the cluster rim and with the Fe atom in the +III oxidation state. The accompanying elongation of metal oxygen bonds leaves the Al-O network structure nearly unperturbed (isomorphous substitution). Contrary to the Al₂FeO₄⁺ (n = 1), valence isomerism is not observed, which is attributed to a smaller M:O ratio (M = Al, Fe) and consequently decreasing electron affinities with increasing cluster size.

Coloured hybrid materials: exploiting an emergent surface property of fluorinated Al2O3 containing anthocyanins and betacyanins

Two fluorinated γ-Al₂O₃ series were synthesized by a sol-gel method with two solvents (2-propanol and 2-butanol), two aluminium sources (ATB and ATP) and one fluorine source (Na₃AlF₆). The resulting inorganic matrixes were evaluated to characterize aluminium and fluorine species ([AlO₄^5-], [AlO₅^7-], [AlO₆^9-], [AlF₄^-], [AlF₅^2-] and [AlF₆^3-]) by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ²⁷Al magic angle spinning nuclear magnetic resonance (²⁷Al MAS-NMR) and infrared spectroscopy (IR-ATR). BET and BJH analyses using the nitrogen isotherms of these materials allowed identifying a clear trend in some textural parameters such as specific surface area and fluorine content. These results were confirmed by scanning electron microscopy (SEM). Chemical affinity and acid surface properties were evidenced with colour shifts in two groups of hybrid pigments, prepared with natural anthocyanins (Brassica oleracea) and betacyanins (Bougainvillea glabra).

Unveiling the mechanism of methylcellulose-templated synthesis of Al2O3 microspheres with organic solvents as swelling agents in microchannel

Herein, we report a systematic investigation of the preparation of large-pore-volume Al₂O₃ microspheres using a complex synthesis system with methylcellulose (MC) as the template and gelation initiator and organic solvents as the swelling agent and carrier medium under the flow characteristics of a coaxial microchannel. The adsorption of MC micelles on boehmite colloidal nanoparticles (NPs) was proven and determined by interfacial tension measurements, dynamic light scattering, and cryogenic transmission electron microscopy. Isothermal titration calorimetry demonstrated that the adsorption process was caused by nonspecific hydrophobicity; one binding site was involved, and the affinity constant was 1060 M^-1. When the MC:NPs mass ratio exceeded 0.1, the template-NP bridged each other to form large aggregates, thereby forming large mesopores and enhancing the gelation speed. Alkanes, alcohols, and amines were applied to further enhance the porosity, and the swelling capacities were investigated experimentally and theoretically. Amines were efficient swelling agents owing to their excellent ability to swell MC micelles and insert into the acid colloid network. The coaxial microchannel was subjected to molding; this process significantly influenced the morphology and textural properties owing to the internal circulation during droplet formation. When trihexylamine with suitable steric hindrance, alkalinity, and polarity was used as the swelling agent, the microspheres exhibited an optimal specific surface area of 403 m²/g and a pore volume of 1.85 cm³/g.

Opportunities and Challenges for Alternative Nanoplasmonic Metals: Magnesium and Beyond

Materials that sustain localized surface plasmon resonances have a broad technology potential as attractive platforms for surface-enhanced spectroscopies, chemical and biological sensing, light-driven catalysis, hyperthermal cancer therapy, waveguides, and so on. Most plasmonic nanoparticles studied to date are composed of either Ag or Au, for which a vast array of synthetic approaches are available, leading to controllable size and shape. However, recently, alternative materials capable of generating plasmonically enhanced light-matter interactions have gained prominence, notably Cu, Al, In, and Mg. In this Perspective, we give an overview of the attributes of plasmonic nanostructures that lead to their potential use and how their performance is dictated by the choice of plasmonic material, emphasizing the similarities and differences between traditional and emerging plasmonic compositions. First, we discuss the materials limitation encapsulated by the dielectric function. Then, we evaluate how size and shape maneuver localized surface plasmon resonance (LSPR) energy and field distribution and address how this impacts applications. Next, biocompatibility, reactivity, and cost, all key differences underlying the potential of non-noble metals, are highlighted. We find that metals beyond Ag and Au are of competitive plasmonic quality. We argue that by thinking outside of the box, i.e., by looking at nonconventional materials such as Mg, one can broaden the frequency range and, more importantly, combine the plasmonic response with other properties essential for the implementation of plasmonic technologies.