A sinter-resistant catalytic system fabricated by maneuvering the selectivity of SiO2 deposition onto the TiO2 surface versus the Pt nanoparticle surface

Controlling Pt nanoparticle sintering by sub-monolayer MgO ALD thin films

Metal nanoparticle (NP) sintering is a major cause of catalyst deactivation, as NP growth reduces the surface area available for reaction. A promising route to halt sintering is to deposit a protective overcoat on the catalyst surface, followed by annealing to generate overlayer porosity for gas transport to the NPs. Yet, such a combined deposition-annealing approach lacks structural control over the cracked protection layer and the number of NP surface atoms available for reaction. Herein, we exploit the tailoring capabilities of atomic layer deposition (ALD) to deposit MgO overcoats on archetypal Pt NP catalysts with thicknesses ranging from sub-monolayers to nm-range thin films. Two different ALD processes are studied for the growth of MgO overcoats on Pt NPs anchored on a SiO2 support, using Mg(EtCp)2 and H2O, and Mg(TMHD)2 and O3, respectively. Spectroscopic ellipsometry and X-ray photoelectron spectroscopy measurements reveal significant growth on both SiO2 and Pt for the former process, while the latter exhibits a drastically lower growth per cycle with an initial chemical selectivity towards Pt. These differences in MgO growth characteristics have implications for the availability of uncoated Pt surface atoms at different stages of the ALD process, as probed by low energy ion scattering, and for the sintering behavior during O2 annealing, as monitored in situ with grazing incidence small angle X-ray scattering (in situ GISAXS). The Mg(TMHD)2-O3 ALD process enables exquisite coverage control allowing a balance between physically blocking the Pt surface to prevent sintering and keeping Pt surface atoms free for reaction. This approach avoids the need for post-annealing, hence also safeguarding the structural integrity of the as-deposited overcoat.

Harnessing the Synergy of Fe and Co with Carbon Nanofibers for Enhanced CO2 Hydrogenation Performance

Amid growing concerns about climate change and energy sustainability, the need to create potent catalysts for the sequestration and conversion of CO2 to value-added chemicals is more critical than ever. This work describes the successful synthesis and profound potential of high-performance nanofiber catalysts, integrating earth-abundant iron (Fe) and cobalt (Co) as well as their alloy counterpart, FeCo, achieved through electrospinning and judicious thermal treatments. Systematic characterization using an array of advanced techniques, including SEM, TGA-DSC, ICP-MS, XRF, EDS, FTIR-ATR, XRD, and Raman spectroscopy, confirmed the integration and homogeneous distribution of Fe/Co elements in nanofibers and provided insights into their catalytic nuance. Impressively, the bimetallic FeCo nanofiber catalyst, thermally treated at 1050 °C, set a benchmark with an unparalleled CO2 conversion rate of 46.47% at atmospheric pressure and a consistent performance over a 55 h testing period at 500 °C. Additionally, this catalyst exhibited prowess in producing high-value hydrocarbons, comprising 8.01% of total products and a significant 31.37% of C2+ species. Our work offers a comprehensive and layered understanding of nanofiber catalysts, delving into their transformations, compositions, and structures under different calcination temperatures. The central themes of metal-carbon interactions, the potential advantages of bimetallic synergies, and the importance of structural defects all converge to define the catalytic performance of these nanofibers. These revelations not only deepen our understanding but also set the stage for future endeavors in designing advanced nanofiber catalysts with bespoke properties tailored for specific applications.

Enhancing electron interaction between Pt and support for superior electrochemical performance through atomic layer deposition of tungsten oxide

The stabilization of platinum (Pt) catalysts through strong metal-support interactions is crucial for their successful implementation in fuel cell applications. Tungsten oxide (WO3) has demonstrated excellent CO tolerance and has been recognized as a promising substrate for anchoring and stabilizing Pt nanoparticles (NPs). However, the limited specific surface area of conventional tungsten oxide restricts its effectiveness in dispersing noble metal NPs. In this study, we present a pioneering approach by employing atomic layer deposition (ALD) to create a WO3 interlayer between Pt NPs and a carbon substrate. Using nitrogen-doped carbon nanotubes (NCNT) as the foundation, WO3 nanoparticles (2-5 nm) were selectively synthesized, followed by the subsequent deposition of Pt NPs using a bottom-up approach. The Pt-WO3-NCNT catalyst, with a WO3 bridge layer effectively inserted between the active site and carbon support, has displayed a notable augmentation in electrocatalytic activity and notable stability when compared to commercial Pt catalysts in oxygen reduction reaction (ORR). The detailed microstructure and the enhanced electrochemical reaction mechanism of Pt-WO3-NCNT catalyst has been investigated by X-ray adsorption spectrum and density functional theory (DFT) calculations. This work presents an innovative approach for enhancing the stability of Pt catalysts through the utilization of the ALD technique.

Modelling atomic layer deposition overcoating formation on a porous heterogeneous catalyst

Atomic layer deposition (ALD) was used to deposit a protective overcoating (Al₂O₃) on an industrially relevant Co-based Fischer-Tropsch catalyst. A trimethylaluminium/water (TMA/H₂O) ALD process was used to prepare ∼0.7-2.2 nm overcoatings on an incipient wetness impregnated Co-Pt/TiO₂ catalyst. A diffusion-reaction differential equation model was used to predict precursor transport and the resulting deposited overcoating surface coverage inside a catalyst particle. The model was validated against transmission electron (TEM) and scanning electron (SEM) microscopy studies. The prepared model utilised catalyst physical properties and ALD process parameters to estimate achieved overcoating thickness for 20 and 30 deposition cycles (1.36 and 2.04 nm respectively). The TEM analysis supported these estimates, with 1.29 ± 0.16 and 2.15 ± 0.29 nm average layer thicknesses. In addition to layer thickness estimation, the model was used to predict overcoating penetration into the porous catalyst. The model estimated a penetration depth of ∼19 μm, and cross-sectional scanning electron microscopy supported the prediction with a deepest penetration of 15-18 μm. The model successfully estimated the deepest penetration, however, the microscopy study showed penetration depth fluctuation between 0-18 μm, having an average of 9.6 μm.

Effect of Co-fed Water on a Co-Pt-Si/γ-Al2O3 Fischer-Tropsch Catalyst Modified with an Atomic Layer Deposited or Molecular Layer Deposition Overcoating

Atomic layer deposition (ALD) and molecular layer deposition (MLD) methods were used to prepare overcoatings on a cobalt-based Fischer-Tropsch catalyst. A Co-Pt-Si/γ-Al₂O₃ catalyst (21.4 wt % Co, 0.2 wt % Pt, and 1.6 wt % Si) prepared by incipient wetness impregnation was ALD overcoated with 30-40 cycles of trimethylaluminum (TMA) and water, followed by temperature treatment (420 °C) in an inert nitrogen atmosphere. MLD-overcoated samples with corresponding film thicknesses were prepared by using TMA and ethylene glycol, followed by temperature treatment (400 °C) in an oxidative synthetic air atmosphere. The ALD catalyst (40 deposition cycles) had a positive activity effect upon moderate water addition (P _H2O/P _H2 = 0.42), and compared with a non-overcoated catalyst, it showed resistance to irreversible deactivation after co-fed water conditions. In addition, MLD overcoatings had a positive effect on the catalyst activity upon moderate water addition. However, compared with a non-overcoated catalyst, only the 10-cycle MLD-overcoated catalyst retained increased activity throughout high added water conditions (P _H2O/P _H2 = 0.71). All catalyst variations exhibited irreversible deactivation under high added water conditions.

Highly active Ni/Fe3O4/TiO2 nanocatalysts with tunable interfacial interactions for PH3 decomposition

The mixed-metal oxide Ni/Fe₃O₄/TiO₂ with two metal-oxide interfaces to catalyze sequential chemical reactions was first applied in the decomposition of phosphine gas for yellow phosphorus (P₄) production. The catalyst was prepared with tunable Ni-Fe₃O₄ and Ni-TiO₂ interactions via annealing and subsequent reduction. Ni/Fe₃O₄/TiO₂ exhibited significantly effective activity and good stability in the PH₃ decomposition, which were achieved by modulating the metal-support interaction. The characterizations by scanning electron microscopy(SEM), X-ray diffraction analysis(XRD), BET surface area measurement and X-ray photoelectron spectroscopy(XPS) were carried out. The enhancements of the Ni-Fe₃O₄ and Ni-TiO₂ dual interactions by annealing and reduction were verified and the mechanism of PH₃ decomposition over the modulated Ni/Fe₃O₄/TiO₂ catalyst was investigated. NiOOH as an active catalytic intermediate species is produced by the synergistic catalytical dual interfaces. The catalytic reaction pathways of PH₃ decomposition by the dual interfaces were firstly revealed. The results provide underlying insights in the way to promote the catalytic performance for synergistic catalysis in PH₃ decomposition.

Sabatier principle of metal-support interaction for design of ultrastable metal nanocatalysts

[Figure: see text].

Enhancement of the performance of Pd nanoclusters confined within ultrathin silica layers for formic acid oxidation

The optimized design of highly active and stable anode electrocatalysts is essential for high performance direct formic acid fuel cells (DFAFCs). Herein, a facile and cost-effective strategy was proposed to fabricate a robust ultrasmall Pd nanocluster confined within ultrathin protective silica layers anchored on nitrogen doped reduced GO (NrGO) through generating amine functionalized graphene oxide with 3-aminopropyl triethoxysilane (APTES), followed by tuning the thickness of protective silica layers by precisely controlling the amount of tetraethylorthosilicate (TEOS). Amine functionalized graphene oxide generated by using APTES favors the formation of ultrasmall Pd nanoclusters due to the coordination of amine to PdCl24- while the confinement effect of ultrathin protective silica layers stabilizes ultrasmall Pd nanoclusters and impedes the agglomeration and sintering of ultrasmall Pd nanoclusters during electrocatalysis. As a result, the ultrasmall Pd nanoclusters (∼1.4 nm) confined in silica layers on NrGO (Pd/NrGO@SiO2) demonstrate a very high forward peak current density for formic acid oxidation (FAO) of 2.37 A mg-1, outperforming the Pd/C catalyst (0.30 A mg-1) and the Pd/rGO catalyst obtained by a conventional method (0.42 A mg-1). More importantly, our confined Pd catalysts show the highest stability of only 5% inconspicuous degradation of the initial mass activity after 1000 cycles, compared with Pd/C (almost 100% loss), Pd/rGO (61.5% loss) and Pd/NrGO (73.2% loss). These strategies in this work provide a new prospect for the design of excellent noble catalysts to overcome the challenges in the practical application of DFAFCs.

Encapsulating Pt Nanoparticles inside a Derived Two-Dimensional Metal-Organic Frameworks for the Enhancement of Catalytic Activity

The development of highly active and stable electrocatalysts toward oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is a key for commercial application of fuel cells and water splitting. Here, we report a highly active and stable Pt nanoparticles (NPs) encapsulated in ultrathin two-dimensional (2D) carbon layers derived from the ultrathin 2D metal-organic framework precursor (ZIF-67). Electrochemical tests reveal that our approach not only stabilized Pt NPs successfully but also boosted Pt activities toward ORR and HER. We found that our Pt catalysts encapsulated in ultrathin 2D carbon layers exhibited an ORR activity of 5.9 and 12 times greater than those of the commercial Pt/C and Pt/RGO without 2D carbon layer protection. Our encapsulated Pt catalysts also show more than nine times higher stability than those of Pt/C catalysts. In addition to ORR, our novel encapsulated Pt catalysts display an extraordinary stability and activity toward HER, with a lower overpotential (14.3 mV in acidic media and 37.2 mV in alkaline media) at a current density of 10 mA cm^-2 than Pt/C catalysts (23.1 mV in acidic media and 92.1 mV in alkaline media). The enhanced electrochemical activities and stability of our encapsulated Pt catalysts are attributed to the synergistic effect of Pt-based NPs and ultrathin 2D carbon layers derived from ZIF-67 with enriched active sites Co-N_x. First-principles simulations reveal that the synergistic catalysis of Pt-based NPs and Co-N_x derived from ZIF-67 improves the activity for ORR and HER.

Core–shell structured catalysts for thermocatalytic, photocatalytic, and electrocatalytic conversion of CO2

An in-depth assessment of properties of core–shell catalysts and their application in the thermocatalytic, photocatalytic, and electrocatalytic conversion of CO₂into synthesis gas and valuable hydrocarbons.

Highly Active and Durable Ultrasmall Pd Nanocatalyst Encapsulated in Ultrathin Silica Layers by Selective Deposition for Formic Acid Oxidation

The low performance of palladium (Pd) is a considerable challenge for direct formic acid fuel cells in practical applications. Herein, we develop a simple strategy to synthesize a highly active and durable Pd nanocatalyst encapsulated in ultrathin silica layers with vertically aligned nanochannels covered graphene oxides (Pd/rGO@pSiO₂) without blocking active sites by selective deposition. The Pd/rGO@pSiO₂ catalyst exhibits very high performance for a formic acid oxidation (FAO) reaction compared with the Pd/rGO without protective silica layers and commercial Pd/C catalysts. Pd/rGO@pSiO₂ shows an FAO activity 3.9 and 3.8 times better than those of Pd/rGO and Pd/C catalysts, respectively. The Pd/rGO@pSiO₂ catalysts are also almost 6-fold more stable than Pd/C and more than 3-fold more stable than Pd/rGO. The outstanding performance of our encapsulated Pd catalysts can be ascribed to the novel design of nanostructures by selective deposition fabricating ultrasmall Pd nanoparticles encapsulated in ultrathin silica layers with vertically aligned nanochannels, which not only avoid blocking the active sites but also facilitate the mass transfer in encapsulated catalysts. Our work indicates an important method to the rational design of high-performance catalysts for fuel cells in practical applications.

Large-Pore Mesoporous CeO2 -ZrO2 Solid Solutions with In-Pore Confined Pt Nanoparticles for Enhanced CO Oxidation

Active and stable catalysts are highly desired for converting harmful substances (e.g., CO, NO_x ) in exhaust gases of vehicles into safe gases at low exhaust temperatures. Here, a solvent evaporation-induced co-assembly process is employed to design ordered mesoporous Ce_x Zr_{1- x} O₂ (0 ≤ x ≤ 1) solid solutions by using high-molecular-weight poly(ethylene oxide)-block-polystyrene as the template. The obtained mesoporous Ce_x Zr_{1- x} O₂ possesses high surface area (60-100 m² g^-1 ) and large pore size (12-15 nm), enabling its great capacity in stably immobilizing Pt nanoparticles (4.0 nm) without blocking pore channels. The obtained mesoporous Pt/Ce_0.8 Zr_0.2 O₂ catalyst exhibits superior CO oxidation activity with a very low T₁₀₀ value of 130 °C (temperature of 100% CO conversion) and excellent stability due to the rich lattice oxygen vacancies in the Ce_0.8 Zr_0.2 O₂ framework. The simulated catalytic evaluations of CO oxidation combined with various characterizations reveal that the intrinsic high surface oxygen mobility and well-interconnected pore structure of the mesoporous Pt/Ce_0.8 Zr_0.2 O₂ catalyst are responsible for the remarkable catalytic efficiency. Additionally, compared with mesoporous Pt/Ce_x Zr_{1- x} O₂ -s with small pore size (3.8 nm), ordered mesoporous Pt/Ce_x Zr_{1- x} O₂ not only facilitates the mass diffusion of reactants and products, but also provides abundant anchoring sites for Pt nanoparticles and numerous exposed catalytically active interfaces for efficient heterogeneous catalysis.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Atomic-Scale Structure of Mesoporous Silica-Encapsulated Pt and PtSn Nanoparticles Revealed by Dynamic Nuclear Polarization- Enhanced 29Si MAS NMR Spectroscopy

Mesoporous silica encapsulated Pt (Pt@mSiO₂) and PtSn (PtSn@mSiO₂) nanoparticles (NPs) are representatives of a novel class of heterogeneous catalysts with uniform particle size, enhanced catalytic properties, and superior thermal stability. In the ship-in-a-bottle synthesis, PtSn@mSiO₂ intermetallic NPs are derived from Pt@mSiO₂ seeds where the mSiO₂ shell is formed by polymerization of tetraethyl orthosilicate around a tetradecyltrimethylammonium bromide template, a surfactant used to template MCM-41. Incorporation of Sn into the Pt@mSiO₂ seeds is accommodated by chemical etching of the mSiO₂ shell. The effect of this etching on the atomic-scale structure of the mSiO₂ has not been previously examined, nor has the extent of the structural similarity to MCM-41. Here, the quaternary Q², Q³ and Q⁴ sites corresponding to formulas Si(O_1/2)₂(OH)₂, Si(O_1/2)₃(OH)₁ and Si(O_1/2)₄, in MCM-41 and the mesoporous silica of Pt@mSiO₂ and PtSn@mSiO₂ NPs were identified and quantified by conventional and dynamic nuclear polarization enhanced Si-29 Magic Angle Spinning Nuclear Magnetic Resonance (DNP MAS NMR). The connectivity of the -Si-O-Si-network was revealed by DNP enhanced two-dimensional ²⁹Si-²⁹Si correlation spectroscopy.

Pt-Embedded CuO x-CeO2 Multicore-Shell Composites: Interfacial Redox Reaction-Directed Synthesis and Composition-Dependent Performance for CO Oxidation

Exploring the state-of-the-art heterogeneous catalysts has been a general concern for sustainable and clean energy. Here, Pt-embedded CuO _x-CeO₂ multicore-shell (Pt/CuO _x-CeO₂ MS) composites are fabricated at room temperature via a one-pot and template-free procedure for catalyzing CO oxidation, a classical probe reaction, showing a volcano-shaped relationship between the composition and catalytic activity. We experimentally unravel that the Pt/CuO _x-CeO₂ MS composites are derived from an interfacial autoredox process, where Pt nanoparticles (NPs) are in situ encapsulated by self-assembled ceria nanospheres with CuO _x clusters adhered through deposition/precipitation-calcination process. Only Cu-O and Pt-Pt coordination structures are determined for CuO _x clusters and Pt NPs in Pt/CuO _x-CeO₂ MS, respectively. Importantly, the close vicinity between Pt and CeO₂ benefits to more oxygen vacancies in CeO₂ counterparts and results in thin oxide layers on Pt NPs. Meanwhile, the introduction of CuO _x clusters is crucial for triggering synergistic catalysis, which leads to high resistance to aggregation of Pt NPs and improvement of catalytic performance. In CO oxidation reaction, both Pt^δ+-CO and Cu⁺-CO can act as active sites during CO adsorption and activation. Nonetheless, redundant content of Pt or Cu will induce a strongly bound Pt-O-Ce or Cu-[O _x]-Ce structures in air-calcinated Pt/CuO _x-CeO₂ MS composites, respectively, which are both deleterious to catalytic reactivity. As a result, the composition-dependent catalytic activity and superior durability of Pt/CuO _x-CeO₂ MS composites toward CO oxidation reaction are achieved. This work should be instructive for fabricating desirable multicomponent catalysts composed of noble metal and bimetallic oxide composites for diverse heterogeneous catalysis.

High-efficient catalytic reduction of 4-nitrophenol based on reusable Ag nanoparticles/graphene-loading loofah sponge hybrid

Noble metal nanoparticles (NPs) such as Au and Ag have shown many applications in the field of catalysis, sensing etc. due to their excellent photoelectric properties. But agglomeration and a low recovery rate are big problems for their applications. In this research, a novel Ag NPs/graphene (reduced graphene oxide)-loading loofah sponge (Ag NPs/RGO-LS) was synthesized through a one-step reduction method. Where the RGO is used as a nano-support with the high specific surface area and the high conductivity to prevent the agglomeration of Ag NPs and provide a conductive layer. The natural, green, low-cost and high-yield LS is designed as a macro-support to reduce the loss of Ag NPs during recycling. The as-prepared Ag NPs/RGO-LS is stable, uniform, and exhibits high efficiency and reusability in the catalytic reduction of 4-nitrophenol (4-NP) with a high rate constant of 1.893 min^-1 as well as an average conversion of 98% in 6 min during five cycles. The results have not only paved the way for the wide application of Ag NPs but also provide a new road for the application of other metal NPs.

Visible-light promoted catalytic activity of dumbbell-like Au nanorods supported on graphene/TiO2 sheets towards hydrogenation reaction

In this work, the rationally-designed sharp corners on Au nanorods tremendously improved the catalytic activity, particularly in the presence of visible light irradiation, towards the hydrogenation of 4-nitrophenol to 4-aminophenol. A strikingly increased rate constant of 50.6 g^-1 s^-1 L was achieved in M-Au-3, which was 41.8 times higher than that of parent Au nanorods under dark conditions. The enhanced activities were proportional to the extent of the protruding sharp corners. Furthermore, remarkably enhanced activities were achieved in novel ternary Au/RGO/TiO₂ sheets, which were endowed with a 52.0 times higher rate constant than that of straight Au nanorods. These remarkably enhanced activities were even higher than those of previously reported 3-5 nm Au and 3 nm Pt nanoparticles. It was systematically observed that there are three aspects to the synergistic effects between Au and RGO sheets: (i) electron transfer from RGO to Au, (ii) a high concentration of p-nitrophenol close to dumbbell-like Au nanorods on RGO sheets, and (iii) increased local reaction temperature from the photothermal effect of both dumbbell-like Au nanorods and RGO sheets.

TiO2@Pt@CeO2 nanocomposite as a bifunctional catalyst for enhancing photo-reduction of Cr (VI) and photo-oxidation of benzyl alcohol

An solar-light-driven and bifunctional photocatalyst was designed for photo-reduction of Cr(VI) and selective photo-oxidation of benzyl alcohol into benzaldehyde in the presence of water under ambient conditions. Double-shelled and sandwiched TiO₂@Pt@CeO₂ hollow spheres were prepared by using functionalized polystyrene spheres, sol-gel, hydrothermal reaction, and calcination. The Pt nanoparticles (NPs) were controllably loaded between the TiO₂ shell and CeO₂ shell. Under solar-light irradiation, the photo-reduction rate of Cr(VI) (μmol h^-1) was in the order of TiO₂@Pt@CeO₂ (1.901) > TiO₂@CeO₂ (1.424) > TiO₂ (1.040) > CeO₂ (0.992). Among the above-mentioned photocatalysts, the conversion rate of benzyl alcohol for TiO₂@Pt@CeO₂ was also the best. These results were attributed to the combination of TiO₂ and CeO₂ as photocatalyst and oxygen buffer, the double-shelled and sandwiched nanostructure, and the addition of Pt NPs as cocatalyst and electron trap site, which could store and shuttle photo-generated electrons, reduce the recombination of the electron-hole, and then enhance photo-generation of active radicals. This conclusion was verified by the electron paramagnetic resonance (EPR) spectroscopy. Considering the versatile combination of photocatalyst, oxygen buffer and cocatalyst, this work could provide new insights into the design of high-performance bifunctional photocatalysts for heavy metal removal and selective synthesis.

The physical chemistry and materials science behind sinter-resistant catalysts

This tutorial review highlights recent progress in understanding the physical chemistry and materials science for developing sinter-resistant catalytic systems.

One-Pot Green Synthesis of Ag-Decorated SnO2 Microsphere: an Efficient and Reusable Catalyst for Reduction of 4-Nitrophenol

In this paper, hierarchical Ag-decorated SnO2 microspheres were synthesized by a facile one-pot hydrothermal method. The resulting composites were characterized by XRD, SEM, TEM, XPS, BET, and FTIR analysis. The catalytic performances of the samples were evaluated with the reduction of 4-nitrophenol to 4-aminophenol by potassium borohydride (KBH4) as a model reaction. Time-dependent experiments indicated that the hierarchical microspheres assembled from SnO2 and Ag nanoparticles can be formed when the react time is less than 10 h. With the increase of hydrothermal time, SnO2 nanoparticles will self-assemble into SnO2 nanosheets and Ag nanoparticles decorated SnO2 nanosheets were obtained. When evaluated as catalyst, the obtained Ag-decorated SnO2 microsphere prepared for 36 h exhibited excellent catalytic performance with normalized rate constant (κ nor) of 6.20 min-1g-1L, which is much better than that of some previous reported catalysts. Moreover, this Ag-decorated SnO2 microsphere demonstrates good reusability after the first five cycles. In addition, we speculate the formation mechanism of the hierarchical Ag-decorated SnO2 microsphere and discussed the possible origin of the excellent catalytic activity.

Tuning the Catalytic Activity and Selectivity of Pd Nanoparticles Using Ligand-Modified Supports and Surfaces

The organic moiety plays an essential role in the design of homogeneous catalysts, where the ligands are used to tune the catalytic activity, selectivity, and stability of the transition metal centers. The impact of ligands on the catalytic performance of metal nanoparticle catalysts is still less understood. Here, we prepared supported nanoparticle (NP) catalysts by the immobilization of preformed Pd NPs on the ligand-modified silica surfaces bearing amine, ethylenediamine, and diethylenetriamine groups. After excluding any size effect, we were able to study the influence of the ligands grafted on the support surface on the catalytic activity of the supported nanoparticles. Higher activity was observed for the Pd NPs supported on propylamine-functionalized support, whereas the presence of ethylenediamine and diethylenetriamine groups was detrimental to the activity. Upon the addition of excess of these amine ligands as surface modifiers, the hydrogenation of alkene to alkane was fully suppressed and, therefore, we were able to tune Pd selectivity. The selective hydrogenation of alkynes into alkenes, although a considerable challenge on the traditional palladium catalysts, was achieved here for a range of alkynes by combining Pd NPs and amine ligands.

Probing the toxicity of nanoparticles: a unified in silico machine learning model based on perturbation theory

Nanoparticles (NPs) are part of our daily life, having a wide range of applications in engineering, physics, chemistry, and biomedicine. However, there are serious concerns regarding the harmful effects that NPs can cause to the different biological systems and their ecosystems. Toxicity testing is an essential step for assessing the potential risks of the NPs, but the experimental assays are often very expensive and usually too slow to flag the number of NPs that may cause adverse effects. In silico models centered on quantitative structure-activity/toxicity relationships (QSAR/QSTR) are alternative tools that have become valuable supports to risk assessment, rationalizing the search for safer NPs. In this work, we develop a unified QSTR-perturbation model based on artificial neural networks, aimed at simultaneously predicting general toxicity profiles of NPs under diverse experimental conditions. The model is derived from 54,371 NP-NP pair cases generated by applying the perturbation theory to a set of 260 unique NPs, and showed an accuracy higher than 97% in both training and validation sets. Physicochemical interpretation of the different descriptors in the model are additionally provided. The QSTR-perturbation model is then employed to predict the toxic effects of several NPs not included in the original dataset. The theoretical results obtained for this independent set are strongly consistent with the experimental evidence found in the literature, suggesting that the present QSTR-perturbation model can be viewed as a promising and reliable computational tool for probing the toxicity of NPs.

Embedding Ultrafine and High-Content Pt Nanoparticles at Ceria Surface for Enhanced Thermal Stability

Ultrafine Pt nanoparticles loaded on ceria (CeO₂) are promising nanostructured catalysts for many important reactions. However, such catalysts often suffer from thermal instability due to coarsening of Pt nanoparticles at elevated temperatures, especially for those with high Pt loading, which leads to severe deterioration of catalytic performances. Here, a facile strategy is developed to improve the thermal stability of ultrafine (1-2 nm)-Pt/CeO₂ catalysts with high Pt content (≈14 wt%) by partially embedding Pt nanoparticles at the surface of CeO₂ through the redox reaction at the solid-solution interface. Ex situ heating studies demonstrate the significant increase in thermal stability of such embedded nanostructures compared to the conventional loaded catalysts. The microscopic pathways for interparticle coarsening of Pt embedded or loaded on CeO₂ are further investigated by in situ electron microscopy at elevated temperatures. Their morphology and size evolution with heating temperature indicate that migration and coalescence of Pt nanoparticles are remarkably suppressed in the embedded structure up to about 450 °C, which may account for the improved thermal stability compared to the conventional loaded structure.

Synthesis of gold nanoparticles supported on functionalized nanosilica using deep eutectic solvent for an electrochemical enzymatic glucose biosensor

Engineering of nanoparticle (NP) surfaces offers an effective approach for the development of enzymatic biosensors or microbial fuel cells with a greatly enhanced direct electron transport process. However, lack of control over the surface functionalization process and the operational instability of the immobilized enzymes are serious issues. Herein, we demonstrate a facile and green deep eutectic solvent (DES)-mediated synthetic strategy for efficient amine-surface functionalization of silicon dioxide and to integrate small gold nanoparticles (AuNPs) for a glucose biosensor. Owing to the higher viscosity of the DES, it provides uniform surface functionalization and further coupling of the AuNPs on the SiO₂ support with improved stability and dispersion. The amine groups of the functionalized Au-SiO₂NPs were covalently linked to the FAD-center of glucose oxidase (GOx) through glutaraldehyde as a bifunctional cross-linker, which promotes formation of "electrical wiring" with the immobilized enzymes. The Au-SiO₂NP/GOx/GC electrode exhibits direct electron transfer (DET) for sensing of glucose with a sensitivity of 9.69 μA mM^-1, a wide linear range from 0.2 to 7 mM and excellent stability. The present green DES-mediated synthetic approach expands the possibilities to support different metal NPs on SiO₂ as a potential platform for biosensor applications.

Nanofence Stabilized Platinum Nanoparticles Catalyst via Facet-Selective Atomic Layer Deposition

A facet-selective atomic layer deposition method is developed to fabricate oxide nanofence structure to stabilize Pt nanoparticles. CeO_x is selectively deposited on Pt nanoparticles' (111) facets and naturally exposes Pt (100) facets. The facet selectivity is realized through different binding energies of Ce precursor fragments chemisorbed on Pt (111) and Pt (100), which is supported by in situ mass gain experiment and corroborated by density functional theory simulations. Such nanofence structure not only has exposed Pt active facets for carbon monoxide oxidation but also forms ceria-metal interfaces that are beneficial for activity enhancement. The composite catalysts show excellent sintering resistance up to 700 °C calcination. CeO_x anchors Pt nanoparticles with a strong metal oxide interaction, and nanofence structure around Pt nanoparticles provides physical blocking that suppresses particles migration. The study reveals that forming oxide nanofence structure to encapsulate precious metal nanoparticles is an effective way to simultaneously enhance catalytic activity and thermal stability.

Unusual Hollow Al2O3 Nanofibers with Loofah-Like Skins: Intriguing Catalyst Supports for Thermal Stabilization of Pt Nanocrystals

Recently, hollow nanofibers could be fabricated by coaxis electrospinning method or template method. However, they are limited to applications because of the hardship in actual preparation. In this work, hollow γ-Al₂O₃ nanofibers with loofah-like skins were first fabricated by using a single spinneret during electrospinning. These intriguing nanofibers were explored as new Pt supports with excellently sinter-resistant performance up to 500 °C, attributed to the unique loofah-like surface of γ-Al₂O₃ nanofibers and the strong metal-support interactions between Pt and γ-Al₂O₃. When applied in the catalytic reduction of p-nitrophenol, the Pt/γ-Al₂O₃ calcined at 500 °C exhibited 4-times higher reaction rate constant (6.8 s^-1·mg^-1) over free Pt nanocrystals.

Graphene sheets manipulated the thermal-stability of ultrasmall Pt nanoparticles supported on porous Fe2O3nanocrystals against sintering

This study reports a new sinter-resistant catalyst system, consisting of Pt nanoparticles on Fe₂O₃rhombohedrons isolated by wrinkled graphene sheets.

Hierarchical porous N-doped carbon supported palladium (Pd/NHPC) as a sustainable catalyst for the reduction of 4-nitrophenol with good activity and lifetime

Pd/NHPC synthesized through a facile method exhibited high catalytic activity and reusability toward the reduction of 4-NP.

A novel strategy to fabricate a hierarchical Ni–Al LDH platinum nanocatalyst with enhanced thermal stability

A novel strategy has been proposed to fabricate a hierarchical Ni–Al LDH platinum nanocatalyst (LDH-Pt).

Catalytic Reduction of 4-Nitrophenol: A Quantitative Assessment of the Role of Dissolved Oxygen in Determining the Induction Time

The reduction of 4-nitrophenol to 4-aminophenol by borohydride is one of the foremost model catalytic reactions because it allows for a straightforward assessment of catalysts using the kinetic parameters extracted from the real-time spectroscopic monitoring of an aqueous solution. Crucial to its standing as a model reaction is a comprehensive mechanistic framework able to explain the entire time evolution of the reaction. While much of this framework is in place, there is still much debate over the cause of the induction period, an initial time interval where no reaction seemingly occurs. Here, we report on the simultaneous monitoring of the spectroscopic signal and the dissolved oxygen content within the aqueous solution. It reveals that the induction period is the time interval required for the level of dissolved oxygen to fall below a critical value that is dependent upon whether Au, Ag, or Pd nanoparticles are used as the catalyst. With this understanding, we are able to exert complete control over the induction period, being able to eliminate it, extend it indefinitely, or even induce multiple induction periods over the course of a single reaction. Moreover, we have determined that the reaction product, 4-aminophenol, in the presence of the same catalyst reacts with dissolved oxygen to form 4-nitrophenolate. The implication of these results is that the induction period relates, not to some activation of the catalyst, but to a time interval where the reaction product is being rapidly transformed back into a reactant by a side reaction.

Tracking the shape-dependent sintering of platinum-rhodium model catalysts under operando conditions

Nanoparticle sintering during catalytic reactions is a major cause for catalyst deactivation. Understanding its atomic-scale processes and finding strategies to reduce it is of paramount scientific and economic interest. Here, we report on the composition-dependent three-dimensional restructuring of epitaxial platinum–rhodium alloy nanoparticles on alumina during carbon monoxide oxidation at 550 K and near-atmospheric pressures employing in situ high-energy grazing incidence x-ray diffraction, online mass spectrometry and a combinatorial sample design. For platinum-rich particles our results disclose a dramatic reaction-induced height increase, accompanied by a corresponding reduction of the total particle surface coverage. We find this restructuring to be progressively reduced for particles with increasing rhodium composition. We explain our observations by a carbon monoxide oxidation promoted non-classical Ostwald ripening process during which smaller particles are destabilized by the heat of reaction. Its driving force lies in the initial particle shape which features for platinum-rich particles a kinetically stabilized, low aspect ratio.

Understanding nanoparticle sintering is crucial for designing stable catalysts. Here, the authors use high energy grazing incidence X-ray diffraction as an in situ probe to track the compositiondependent three-dimensional restructuring of supported alloy nanoparticles during carbon monoxide oxidation.

Water-dispersible and magnetically recoverable Fe3O4/Pd@nitrogen-doped carbon composite catalysts for the catalytic reduction of 4-nitrophenol

Water-dispersible and magnetically recoverable Fe₃O₄/Pd@nitrogen-doped carbon catalysts were prepared. The catalysts have good catalytic activity and can be magnetically separated from the reaction solution.

Tuned depositing Ag clusters on ZrO2 nanocrystals from silver mirror reaction of silver–dodecylamine complexes

A series of Ag/ZrO₂ nanocomposites have been synthesized from silver mirror reaction in toluene and show excellent catalytic performance for reduction of 4-NP.

Computational modeling in nanomedicine: prediction of multiple antibacterial profiles of nanoparticles using a quantitative structure-activity relationship perturbation model

AIMS

We introduce the first quantitative structure-activity relationship (QSAR) perturbation model for probing multiple antibacterial profiles of nanoparticles (NPs) under diverse experimental conditions.

MATERIALS & METHODS

The dataset is based on 300 nanoparticles containing dissimilar chemical compositions, sizes, shapes and surface coatings. In general terms, the NPs were tested against different bacteria, by considering several measures of antibacterial activity and diverse assay times. The QSAR perturbation model was created from 69,231 nanoparticle-nanoparticle (NP-NP) pairs, which were randomly generated using a recently reported perturbation theory approach.

RESULTS

The model displayed an accuracy rate of approximately 98% for classifying NPs as active or inactive, and a new copper-silver nanoalloy was correctly predicted by this model with consensus accuracy of 77.73%.

CONCLUSION

Our QSAR perturbation model can be used as an efficacious tool for the virtual screening of antibacterial nanomaterials.

Fabrication of CeO2 nanotube supported Pt catalyst encapsulated with silica for high and stable performance

This communication describes the fabrication of Pt/CeO2 nanotube@SiO2 core-shell catalysts applied to highly efficient water-gas shift reaction, where the initial CO conversion is 30.2% at 250 °C. Pt/CeO2 nanotube@SiO2 core-shell catalysts show outstanding thermal stability, even after accelerated aging under reaction conditions at 450 °C for 6 h, and the morphology is also unchanged after thermal treatment at 800 °C.

Metal hybrid nanoparticles for catalytic organic and photochemical transformations

In order to understand heterogeneous catalytic reactions, model catalysts such as a single crystalline surface have been widely studied for many decades. However, catalytic systems that actually advance the reactions are three-dimensional and commonly have multiple components including active metal nanoparticles and metal oxide supports. On the other hand, as nanochemistry has rapidly been developed and been applied to various fields, many researchers have begun to discuss the impact of nanochemistry on heterogeneous catalysis. Metal hybrid nanoparticles bearing multiple components are structurally very close to the actual catalysts, and their uniform and controllable morphology is suitable for investigating the relationship between the structure and the catalytic properties in detail. In this Account, we introduce four typical structures of metal hybrid nanoparticles that can be used to conduct catalytic organic and photochemical reactions. Metal@silica (or metal oxide) yolk-shell nanoparticles, in which metal cores exist in internal voids surrounded by thin silica (or metal oxide) shells, exhibited extremely high thermal and chemical stability due to the geometrical protection of the silica layers against the metal cores. The morphology of the metal cores and the pore density of the hollow shells were precisely adjusted to optimize the reaction activity and diffusion rates of the reactants. Metal@metal oxide core-shell nanoparticles and inverted structures, where the cores supported the shells serving an active surface, exhibited high activity with no diffusion barriers for the reactants and products. These nanostructures were used as effective catalysts for various organic and gas-phase reactions, including hydrogen transfer, Suzuki coupling, and steam methane reforming. In contrast to the yolk- and core-shell structures, an asymmetric arrangement of distinct domains generated acentric dumbbells and tipped rods. A large domain of each component added multiple functions, such as magnetism and light absorption, to the catalytic properties. In particular, metal-semiconductor hybrid nanostructures could behave as effective visible photocatalysts for hydrogen evolution and CO oxidation reactions. Resulting from the large surface area and high local concentration of the reactants, a double-shell hollow structure showed reaction activities higher than those of filled nanoparticles. The introduction of plasmonic Au probes into the Pt-CdS double-shell hollow particles facilitated the monitoring of photocatalytic hydrogen generation that occurred on an individual particle surface by single particle measurements. Further development of catalysis research using well-defined metal hybrid nanocatalysts with various in situ spectroscopic tools provides a means of maximizing catalytic performances until they are comparable to or better than those of homogeneous catalysts, and this would have possibly useful implications for industrial applications.