Sodium Enhances Ir/TiO2 Activity for Catalytic Oxidation of Formaldehyde at Ambient Temperature

Unravelling High Water Vapor-Induced Inhibitory Effects on Pt/Co3O4 Catalysts toward Benzene Oxidation

Water vapor inevitably exists in the environment, which causes adverse impacts on many crucial chemical reactions. However, high water vapor of up to 10 vol %─relevant to a broad spectrum of industrial practices-for catalytic implications has been less investigated or neglected. As such, we explored an industry-relevant, humidity-highly sensitive benzene oxidation only in the presence of 10 vol % water vapor using the well-established Pt/Co3O4 catalysts, to bring such an important yet ignored topic to the forefront. Results revealed that Pt/Co3O4 catalysts possessing higher contents of Pt nanoparticles exhibited marked tolerance to water vapor interference. Under an incomplete benzene conversion condition, the input of 10 vol % water vapor indeed impaired the catalytic performance of Pt/Co3O4 catalyst significantly, which, in fact, was caused by the unfavorable formation of carboxylate species covering the catalyst's surface engendering irrecoverable activity loss, instead of the well-accepted water competitive adsorption. While such activity loss can be restored by elevating the reaction to a higher temperature. This study helps us to understand the compromised catalytic activity caused by high humidity, urging the systematic evaluation of well-established catalyst systems in high water vapor-contained conditions and pressing the development of water-tolerant catalysts for real-life application consideration.

Low-temperature thermocatalytic removal of formaldehyde in air using copper manganite spinels

The removal of formaldehyde (FA) is vital for indoor air quality management in light of its carcinogenic propensity and adverse environmental impact. A series of copper manganite spinel structures (e.g., CuMn2O4) are prepared using the sol-gel combustion method and treated with reduction or oxidation pretreatment at 300 °C condition. Accordingly, CuMn2O4-O ("O" suffix for oxidation pre-treatment in air) is identified as the best performer to achieve 100% conversion (XFA) of FA (50 ppm) at 90 °C; its performance, if assessed in terms of reaction kinetic rate (r) at XFA = 10%, is 5.02E-03 mmol g-1 h-1. The FA removal performance increases systematically with decreases in flow rate, FA concentration, and relative humidity (RH) or with increases in bed mass. The reaction pathways and intermediates of FA catalytic oxidation on CuMn2O4-A are studied with density functional theory simulations, temperature-programmed characterization experiments, and in-situ diffuse reflectance infrared Fourier transform spectroscopy. The synergistic combination of large quantities of adsorbed oxygen (OA) species and oxidized metal species (e.g., Cu2+) contribute to the enhanced catalytic performance of CuMn2O4-O to oxidize FA into CO2 with the reaction intermediates of H2CO2 (DOM), HCOO-, and CO. The present study is expected to provide valuable insights into the thermocatalytic oxidation of FA over spinel CuMn2O4 materials and their catalytic performances in relation to the key process variables.

Sepiolite-Supported Manganese Oxide as an Efficient Catalyst for Formaldehyde Oxidation: Performance and Mechanism

The current study involved the preparation of a number of MnOx/Sep catalysts using the impregnation (MnOx/Sep-I), hydrothermal (MnOx/Sep-H), and precipitation (MnOx/Sep-P) methods. The MnOx/Sep catalysts that were produced were examined for their ability to catalytically oxidize formaldehyde (HCHO). Through the use of several technologies, including N2 adsorption-desorption, XRD, FTIR, TEM, H2-TPR, O2-TPD, CO2-TPD, and XPS, the function of MnOx in HCHO elimination was examined. The MnOx/Sep-H combination was shown to have superior catalytic activities, outstanding cycle stability, and long-term activity. It was also able to perform complete HCHO conversion at 85 °C with a high GHSV of 6000 mL/(g·h) and 50% humidity. Large specific surface area and pore size, a widely dispersed active component, a high percentage of Mn3+ species, and lattice oxygen concentration all suggested a potential reaction route for HCHO oxidation. This research produced a low-cost, highly effective catalyst for HCHO purification in indoor or industrial air environments.

Efficient and Durable Oxidation Removal of Formaldehyde over Layered Double Hydroxide Catalysts at Room Temperature

Room temperature catalytic oxidation (RTCO) using non-noble metals has emerged as a highly promising technique for removal of formaldehyde (HCHO) under ambient conditions; however, non-noble catalysts still face the challenges related to poor water resistance and low stability under harsh conditions. In this study, we synthesized a series of layered double hydroxides (LDHs) incorporating various dual metals (MgAl, ZnAl, NiAl, NiFe, and NiTi) for formaldehyde oxidation at ambient temperature. Among the synthesized catalysts, the NiTi-LDH catalyst showed an HCHO removal efficiency and CO2 yield close to 100.0%, and exceptional water resistance and chemical stability on running 1300 min. The abundant hydroxyl groups in LDHs directly bonded with HCHO, leading to the production of CO2 and H2O, thus inhibiting the formation of CO, even in the absence of O2 and H2O. The coexistence of O2 effectively reduced the reaction barrier for H2O molecule dissociation, facilitating the formation of hydroxyl groups and their subsequent backfill on the catalyst surface. The mechanisms underlying the involvement and regeneration of hydroxyl groups in room temperature oxidation of formaldehyde were elucidated with the combined in situ DRIFTS, HCHO-TPD-MS, and DFT calculations. This work not only demonstrates the potential of LDH catalysts in environmental applications but also advances the understanding of the fundamental processes involved in room temperature oxidation of formaldehyde.

Understanding the Decomposition of Dimethyl Methyl Phosphonate on Metal-Modified TiO2(110) Surfaces Using Ensembles of Product Configurations

The decomposition of dimethyl methyl phosphonate (DMMP), a simulant for the nerve agent sarin, was investigated on Cu4/TiO2(110) and K/Cu4/TiO2(110) surfaces using a combination of near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and density functional theory calculations (DFT). Mass-selected Cu4 clusters and potassium (K) atoms were deposited onto TiO2(110) as a metal catalyst and alkali promoter to improve the reactivity and recyclability of the TiO2 surface after exposure to DMMP. Surface reaction products resulting from decomposition of DMMP were probed by NAP-XPS measurements of phosphorus (P) 2p and carbon 1s core-level spectra. The Cu4/TiO2(110) surface is found to be very active for DMMP decomposition with highly reduced P-species observed even at room temperature (RT). The codeposition of K atoms and Cu4 clusters further improves the reactivity with no intact DMMP detectable. Temperature-dependent measurements show that the presence of K atoms promotes the removal of residual P-species at temperatures > 600 K. Detailed DFT calculations were performed to determine the surface structures and energetically accessible pathways for DMMP decomposition on Cu4/TiO2(110) and K/Cu4/TiO2(110) surfaces. The calculations show that DMMP and P-containing reaction products preferentially bind to the TiO2 surface, while the molecular fragments, i.e., methoxy and methyl, bind to both the Cu4 clusters and TiO2. The Cu4 clusters make the P-O, O-C, and P-C bond cleavages of DMMP markedly more exothermic. The Cu4 clusters are highly fluxional with atomic structures that depend on the configuration of fragments bound to them. Finally, the manifold of P 2p chemical shifts calculated for a large number of energetically favorable configurations of decomposition products is in good agreement with the observed XPS spectra and provides an alternative way of interpreting incompletely resolved core-level spectra using an ensemble of observed structures.

Formulating the Li sites of Li-CoOx composites for achieving high-efficiency oxidation removal of formaldehyde over the Ag/Li-CoOx catalyst under ambient conditions

Oxide supported noble metals are extensively investigated for ambient formaldehyde oxidation, and the Ag-CoOx complex is one promising combination in terms of cost and activity. Further, we previously observed that cooperating Ag with Li + greatly boosted formaldehyde degradation on CoOx. Yet, there is still room for improvement in removal efficiency, mineralization capacity and resistance to severe conditions. These objectives could be realized via strategically formulating the Li+ sites of Li-CoOx composite in this sister study. Three samples with Li + ---Co3+-O2- connections (L-CO), spinel Li+ (LCO-S) and layered Li+ (LCO-L) were obtained at low (300 °C), moderate (500 °C) and high (700 °C) temperatures, respectively. The specific Li+ positions and componential interaction were demonstrated by Hyperspectral imaging (HSI), XRD, SEM, TEM, HAADF mapping, UV-vis DRS and XPS. Moreover, the effect of reactive oxygen exposure on catalytic oxidation of formaldehyde (330-350 mg/m3) was disclosed through CO-TPR and O2-TPD. Compared with the LCO-S and LCO-L, L-CO exhibited dominant formaldehyde degradation due to the larger content of surface oxygen. After Ag decoration, the Li+---Co3+-O2- connections uniquely caused a strong binding of Ag species with catalyst host, which boosted the amount of reactive oxygen and finally resulted in an even higher elimination of ∼73% (CO2 yield = ∼21%), 47% higher than that of the L-CO (CO2 yield = ∼6%). But in contrast, the Ag@LCO-S only achieved ∼53% removal (CO2 yield = ∼9%) and Ag modification was powerless in altering the inertness of LCO-L, demonstrating that the chemical environment of alkali metal is crucial to effectively tuning the catalyst activity. The advantage of Ag@L-CO in formaldehyde depollution was further reflected from its much better resistance to moisture and aromatic compound omnipresent in indoor air. For the first time, this study extended the understanding of the alkali-metal-promoted formaldehyde oxidation reaction to an in-depth level.

Hydroxyl-Decorated Pt as a Robust Water-Resistant Catalyst for Catalytic Benzene Oxidation

In catalytic oxidation reactions, the presence of environmental water poses challenges to the performance of Pt catalysts. This study aims to overcome this challenge by introducing hydroxyl groups onto the surface of Pt catalysts using the pyrolysis reduction method. Two silica supports were employed to investigate the impact of hydroxyl groups: SiO2-OH with hydroxyl groups and SiO2-C without hydroxyl groups. Structural characterization confirmed the presence of Pt-Ox, Pt-OHx, and Pt0 species in the Pt/SiO2-OH catalysts, while only Pt-Ox and Pt0 species were observed in the Pt/SiO2-C catalysts. Catalytic performance tests demonstrated the remarkable capacity of the 0.5 wt % Pt/SiO2-OH catalyst, achieving complete conversion of benzene at 160 °C under a high space velocity of 60,000 h-1. Notably, the catalytic oxidation capacity of the Pt/SiO2-OH catalyst remained largely unaffected even in the presence of 10 vol % water vapor. Moreover, the catalyst exhibited exceptional recyclability and stability, maintaining its performance over 16 repeated cycles and a continuous operation time of 70 h. Theoretical calculations revealed that the construction of Pt-OHx sites on the catalyst surface was beneficial for modulating the d-band structure, which in turn enhanced the adsorption and activation of reactants. This finding highlights the efficacy of decorating the Pt surface with hydroxyl groups as an effective strategy for improving the water resistance, catalytic activity, and long-term stability of Pt catalysts.

Tunable Interfacial Electronic Pd-Si Interaction Boosts Catalysis via Accelerating O2 and H2O Activation

Engineering the interfacial structure between noble metals and oxides, particularly on the surface of non-reducible oxides, is a challenging yet promising approach to enhancing the performance of heterogeneous catalysts. The interface site can alter the electronic and d-band structure of the metal sites, facilitating the transition of energy levels between the reacting molecules and promoting the reaction to proceed in a favorable direction. Herein, we created an active Pd-Si interface with tunable electronic metal-support interaction (EMSI) by growing a thin permeable silica layer on a non-reducible oxide ZSM-5 surface (termed Pd@SiO₂/ZSM-5). Our experimental results, combined with density functional theory calculations, revealed that the Pd-Si active interface enhanced the charge transfer from deposited Si to Pd, generating an electron-enriched Pd surface, which significantly lowered the activation barriers for O₂ and H₂O. The resulting reactive oxygen species, including O₂ ^-, O₂ ^2-, and -OH, synergistically facilitated formaldehyde oxidation. Additionally, moderate electronic metal-support interaction can promote the catalytic cycle of Pd⁰ ⇆ Pd²⁺, which is favorable for the adsorption and activation of reactants. This study provides a promising strategy for the design of high-performance noble metal catalysts for practical applications.

Formaldehyde oxidation on Pd/USY catalysts at room temperature: The effect of acid pretreatment on supports

The complete catalytic oxidation of formaldehyde (HCHO) to CO₂ and H₂O at room temperature is a green route for indoor HCHO removal. Zeolite is an excellent carrier material for HCHO oxidation due to its large surface area, intricate pores and high adsorption capacity. However, the zeolite-supported noble metal catalysts have currently shown relatively low activity especially at room temperature. In this work, we present a facile acid treatment strategy for zeolite catalysts to improve the hydroxyl concentration and further enhance their catalytic activity for HCHO oxidation. Activity tests illustrated that HCHO could be completely oxidized to CO₂ and H₂O at a nearly 100% conversion rate with a weight hourly space velocity (WHSV) of 150,000 mL/(g∙hr) at 25°C, when the support of Pd/USY catalysts was pretreated by hydrochloric acid with a concentration of 0.20 mol/L. The characterization results revealed that the active hydroxyl groups originated from the dealumination in the acid treatment play a key role in the HCHO oxidation reaction. The deduced reaction mechanism suggests that bridging hydroxyl groups may oxidize HCHO to dioxymethylene (DOM) species and terminal hydroxyl groups are responsible for the transformation of DOM groups to formate (HCOO) species.

Construction of strongly-coupled CeO2/MnO2 heterogeneous catalysts for highly-efficient removal of formaldehyde

Formaldehyde (HCHO) is highly toxic, but its low-temperature elimination is still a pressing challenge nowadays.

Electronic Modification by Transitional Metal Dopants to Tune the Oxidation Activity of Pt-CeO2-Based Catalysts

While utilization of transitional metals as a promoter has been extensively studied to enhance the activity of Pt-based catalysts for the oxidation of formaldehyde (HCHO), there is still a lack of well elucidated property-function relationship for the rational selection of a promoter in catalyst design. Herein, we modified a Pt/CeO₂ catalyst with two transitional metal dopants (i.e., Mn and Cu) that showed negligible influence on the physical structure of the Pt-CeO₂ matrix but distinct effects on the activity of the catalyst. Complementary characterizations combined with density functional theory modeling revealed that the transitional metal dopants significantly modified the electronic structure of the catalyst and shifted the d-band of Pt to higher energy with different extents, which may tune the bonding strength of HCHO/intermediates with the Pt-CeO₂ interface domain. The catalyst with moderate bonding strength (i.e., Pt-Mn/CeO₂) displayed the highest reactivity under the ambient condition, while Pt-Cu/CeO₂ with the highest bonding strength showed a dramatically decreased activity. No correlation was observed between the abundancy of the active oxygen and catalytic activity, likely due to the oxygen supply having a much higher rate than the rate-determining step. This work contributes to the elucidation about the property-function relationship of a transitional metal dopant in Pt-based catalysts for the oxidation of HCHO.

Assembled Organoruthenium(II) for Formaldehyde Decomposition and Hydrogen Production

Formaldehyde decomposition is not only an attractive method for hydrogen production, but also a potential approach for gaseous formaldehyde removal. In this research, we prepare some assembled organoruthenium through coordination reaction between Ru(p-Cymene)Cl₂ and bridge-linking ligands. It is a creative approach for Ru(p-Cymene)Cl₂ conversion into heterogeneous particles. The rigidity of bridge-linking ligand enables assembled organoruthenium to have highly ordered crystalline structure, even show clear crystal lattice with spacing of 0.19 nm. XPS shows the N-Ru bond are formed between bridge-linking ligand and Ru(p-Cymene)Cl₂ . The assembled organoruthenium has high abundant active sites for formaldehyde decomposition at low temperature. The reaction rate could increase linearly with temperature and formaldehyde concentration, with a TOF of 2420 h^-1 at 90 °C. It is promising for gaseous formaldehyde decomposition in wet air or nitrogen. Formaldehyde conversion is up to 95 % over Ru-DAPM is 4,4'-diaminodiphenylmethane at 90 °C in air. Gaseous formaldehyde decomposition is a two-steps process under oxygen-free condition. Firstly, formaldehyde dissolve in water, and be converted into hydrogen and formic acid through formaldehyde-water shift reaction. Then intermediate formic acid will further decompose into hydrogen and carbon dioxide. We also find formaldehyde decomposition is a synergetic catalysis process of oxygen and water in moist air. Oxygen is conducive to formic acid desorption and decomposition on the active sites, so assembled organoruthenium exhibit slightly higher conversion for formaldehyde decomposition in moist air. This work proposes a distinctive method for gaseous formaldehyde decomposition in the air, which is entirely different from formaldehyde photocatalysis or thermocatalysis oxidation.

Effect of Hydroxyl Groups on Metal Anchoring and Formaldehyde Oxidation Performance of Pt/Al2O3

Pt/Al₂O₃ catalysts showing excellent activity and stability have been used in various reactions, including HCHO oxidation. Herein, we prepared Pt-Na/Al₂O₃ catalysts with a Pt content of 0.05 wt % to reveal the key factors determining the anchoring of Pt as well as the catalytic activity and mechanism of HCHO oxidation. Pt-Na/nano-Al₂O₃ (denoted as Pt-Na/nAl₂O₃) catalysts with 0.05 wt % Pt content could completely oxidize HCHO to CO₂ at room temperature, which is the lowest Pt content used in HCHO catalytic oxidation to our knowledge. After Na addition, terminal hydroxyl groups (denoted as HO-μ_ter) on nano-Al₂O₃ were transformed to doubly bridging hydroxyl groups between Na and Al (denoted as HO-μ_bri(Na-Al)), which atomically dispersed Pt species. Pt anchoring further promoted the regeneration of HO-μ_bri(Na-Al) by activating O₂ and H₂O, oxidizing HCHO to CO₂ directly by the fast reaction step ([HCOO^-] + [OH]_a → CO₂ + H₂O). Our study revealed that the HO-μ_bri(Na-Al) synergistically generated by HO-μ_ter and Na species provided anchoring sites for Pt species.

Novel B and N Sites of One-Dimensional Boron Nitride Fiber: Efficient Performance and Mechanism in the Formaldehyde Capture Process

Identification of adsorption centers with atomic levels of adsorbents is crucial to study the adsorption of formaldehyde (HCHO), especially for an in-depth understanding of the mechanism of HCHO capture. Herein, we investigate the HCHO adsorption performance of one-dimensional (1D) nanoporous boron nitride (BN) fiber, and explore the adsorption mechanism by density functional theory (DFT) calculations, including adsorption energy change and Bader charge change, and experimental study as well. Research shows that the 1D nanoporous BN fiber possesses a high concentration of Lewis pairs, which act as Lewis acid and Lewis base sites associated with the fiber's electron-deficient and electron-rich features. It is worth noting that the HCHO removal efficiency of a typical sample is as high as 91%. This work may open the door to the field of adsorption of other pollutants by constructing Lewis pairs in the future.

Distinct Role of Surface Hydroxyls in Single-Atom Pt1/CeO2 Catalyst for Room-Temperature Formaldehyde Oxidation: Acid-Base Versus Redox

The development of highly efficient catalysts for room-temperature formaldehyde (HCHO) oxidation is of great interest for indoor air purification. In this work, it was found that the single-atom Pt₁/CeO₂ catalyst exhibits a remarkable activity with complete removal of HCHO even at 288 K. Combining density functional theory calculations and in situ DRIFTS experiments, it was revealed that the active O_latticeH site generated on CeO₂ in the vicinity of Pt²⁺ via steam treatment plays a key role in the oxidation of HCHO to formate and its further oxidation to CO₂. Such involvement of hydroxyls is fundamentally different from that of cofeeding water which dissociates on metal oxide and catalyzes the acid-base-related chemistry. This study provides an important implication for the design and synthesis of supported Pt catalysts with atom efficiency for a very important practical application-room-temperature HCHO oxidation.

Research Progress of Highly Efficient Noble Metal Catalysts for the Oxidation of 5-Hydroxymethylfurfural

5-hydroxymethylfurfural (HMF) is considered to be one of the most pivotal multifunctional biomass platform chemicals. This Review discusses recent advances in catalytic oxidation of HMF towards high-value products. The reaction mechanism of different noble metals and the path of HMF oxidation to high-value products have been deeply investigated in the noble metal catalytic system. The reaction mechanisms of different noble metals and HMF conversion paths were compared in detail. Moreover, the factors affecting the performance of different noble metal catalysts were summarized. Finally, effective strategies were put forward to improve the catalytic performance of noble metal catalysts. The purpose is to provide a valuable reference for the academic research on the preparation of oxidation products from biomass-based HMF and the industrial application of noble metal catalysts.

Single-atom Ir1 supported on rutile TiO2 for excellent selective catalytic oxidation of ammonia

Gaseous ammonia (NH₃) in the atmosphere is potentially harmful to both human health and the environment. The selective catalytic oxidation of NH₃ (termed as NH₃-SCO) into N₂ and H₂O is a promising method for decreasing NH₃ emissions. A highly efficient catalyst is required for controlling NH₃ emissions by this method in practice. In this study, we prepared Ir/TiO₂ catalysts using different crystal structures of TiO₂ (rutile, P25 or anatase) as supports by a simple impregnation method and evaluated their performance in the NH₃-SCO. We found that the Ir/TiO₂-R (rutile) catalyst performed better than the Ir/TiO₂-P25 (mixed-phase) and Ir/TiO₂-A (anatase) catalyst. High-angle annular dark-field images of the aberration-corrected scanning transmission electron microscopy revealed that the Ir species were mainly atomically dispersed on the TiO₂ support in Ir/TiO₂-R with 1 wt% Ir loading, whereas the Ir species agglomerated to form clusters or nanoparticles in Ir/TiO₂-P25 and Ir/TiO₂-A. The combined results of X-ray absorption fine structure, H₂-temperature-programmed reduction, and in situ diffuse reflectance for infrared Fourier Transform spectroscopy studies suggested that atomically dispersed Ir species had stronger electronic metal-support interaction with rutile TiO₂, which resulted in easier to adsorb and activate O₂ at the interface and thus, better low-temperature activity of the Ir/TiO₂-R catalyst.

Hydrogenated Amorphous Titania with Engineered Surface Oxygen Vacancy for Efficient Formaldehyde and Dye Removals under Visible-Light Irradiation

Hydrogenated crystalized TiO_2−x with oxygen vacant (O_V) doping has attracted considerable attraction, owing to its impressive photoactivity. However, amorphous TiO₂, as a common allotrope of titania, is ignored as a hydrogenated templet. In this work, hydrogenated amorphous TiO_2−x (HAm-TiO_2−x) with engineered surface O_V and high surface area (176.7 cm² g⁻¹) was first prepared using a unique liquid plasma hydrogenation strategy. In HAm-TiO_2−x, we found that O_V was energetically retained in the subsurface region; in particular, the subsurface O_V-induced energy level preferred to remain under the conduction band (0.5 eV) to form a conduction band tail and deep trap states, resulting in a narrow bandgap (2.36 eV). With the benefits of abundant light absorption and efficient photocarrier transportation, HAm-TiO_2−x coated glass has demonstrated superior visible-light-driven self-cleaning performances. To investigate its formaldehyde photodegradation under harsh indoor conditions, HAm-TiO_2−x was used to decompose low-concentration formaldehyde (~0.6 ppm) with weak-visible light (λ = 600 nm, power density = 0.136 mW/cm²). Thus, HAm-TiO_2−x achieved high quantum efficiency of 3 × 10⁻⁶ molecules/photon and photoactivity of 92.6%. The adsorption capabilities of O₂ (−1.42 eV) and HCHO (−1.58 eV) in HAm-TiO_2−x are both largely promoted in the presence of subsurface O_V. The surface reaction pathway and formaldehyde decomposition mechanism over HAm-TiO_2−x were finally clarified. This work opened a promising way to fabricate hydrogenated amorphous photocatalysts, which could contribute to visible-light-driven photocatalytic environmental applications.

FeCo alloy encased in nitrogen-doped carbon for efficient formaldehyde removal: Preparation, electronic structure, and d-band center tailoring

Formaldehyde is a typical indoor air pollutant that has posed severely adverse effects on human health. Herein, a novel FeCo alloy nanoparticle-embedded nitrogen-doped carbon (FeCo@NC) was synthesized with the aim of tailoring the transition-metal d-band structure toward an improved formaldehyde oxidation activity for the first time. A unique core@shell metal-organic frameworks (MOFs) architecture with a Fe-based Prussian blue analogue core and Co-containing zeolite imidazole framework shell was firstly fabricated. Then, Fe and Co ion alloying was readily achieved owing to the inherent MOF porosity and interionic nonequilibrium diffusion occurring during pyrolysis. High-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectra confirm that small FeCo alloys in situ form in FeCo@NC, which exhibits a higher formaldehyde removal efficiency (93%) than the monometallic Fe-based catalyst and a remarkable CO₂ selectivity (85%) at room temperature. Density functional theory calculations indicate the number of electrons transferred from the metal core to the outer carbon layer is altered by alloying Fe and Co. More importantly, a downshift in the d-band center relative to the Fermi level occurs from - 0.93 to - 1.04 eV after introducing Co, which could alleviate the adsorption of reaction intermediates and greatly improve the catalytic performance.

Acid pretreatment of support promotes Pd/SiO2 activity for formaldehyde oxidation at room temperature

Hydroxyl groups on SiO2 produced by acid pretreatment favored the anchoring of Pd particles and increased their dispersion, which induced more oxygen vacancies on the surface of catalysts and further enhanced H2O activation.

Water-induced gaseous formaldehyde decomposition using ruthenium organic crystalline particles

Novel ruthenium organic crystalline particles are prepared for providing two distinctive approaches for formaldehyde decomposition: catalytic oxidation or water-induced formaldehyde decomposition.

A simple method to regulate surface hydroxy groups on Al2O3 for improving catalytic oxidation performance for HCHO on Pt/Al2O3

For supported noble metal catalysts, the properties of the support had great influence on the state of noble metals. Herein, we chose Al2O3 as model to find a simple method...

Fabrication of More Oxygen Vacancies and Depression of Encapsulation for Superior Catalysis in the Water-Gas Shift Reaction

Fabrication of sufficient oxygen vacancies and exposure of active sites to reactants are two key factors to obtain high catalytic activity in the water-gas shift (WGS) reaction. However, these two factors are hard to satisfy spontaneously, since the formation of oxygen vacancies and encapsulation of metal nanoparticles are two inherent properties in reducible metal oxide supported catalysts due to the strong metal-support interaction (SMSI) effect. In this work, we find that addition of alkali to an anatase supported Ni catalyst (Ni/TiO₂(A)) could well regulate the SMSI to achieve both more oxygen vacancies and depression of encapsulation; therefore, more than 20-fold enhancement in activity is obtained. It is found that the in situ formed titanate species on the catalyst surface is crucial to the formation of oxygen vacancies and depression of encapsulation. Furthermore, the methanation, a common side reaction of the WGS reaction, is successfully suppressed in the whole catalytic process.

Engineering oxygen vacancies via amorphization in conjunction with W-doping as an approach to boosting catalytic properties of Pt/Fe-W-O for formaldehyde oxidation

Engineering functional defects in support materials has gained ever-increasing attention as a novel approach to boosting the catalytic performance of oxide-supported catalysts. Herein, we demonstrate the feasibility of engineering oxygen vacancy in iron oxide through amorphization in conjunction with foreign cation doping and elucidate the important role of support functionality in the catalytic oxidation of formaldehyde (HCHO). A supported Pt catalyst on Fe-W-O amorphous nanosheets (denoted as Pt/a-Fe-W-O) was synthesized using a one-step solvothermal method. This simple method allowed us to simultaneously create abundant oxygen vacancies in the substrate and to ensure uniform dispersion of tiny Pt nanoparticles with an average diameter of 1.4 nm on the high-surface-area substrate. This renders an increased possibility of Pt/O-vacancy coexistence in close proximity, which synergistically boosts the formation of active oxygen and surface hydroxyl species. Consequently, the Pt/a-Fe-W-O catalyst with an optimal W/Fe molar ratio of 0.08:1 and a 1.51 wt% Pt loading exhibited a high specific reaction rate of 68.3 μmol g_Pt^-1 s^-1 and excellent stability during 24 h continuous test, outperforming most existing HCHO oxidation catalysts. Our study highlights the importance of functional oxygen defects in construction of synergistic active sites for promoting the reactions requiring multiple active species.

Tuning the shape and crystal phase of TiO2 nanoparticles for catalysis

Synthesis of TiO₂ nanoparticles with tunable shape and crystal phase has attracted considerable attention for the design of highly efficient heterogeneous catalysts. Tailoring the shape of TiO₂, in the crystal phases of anatase, rutile, brookite and TiO₂(B), allows tuning of the atomic configurations on the dominantly exposed facets for maximizing the active sites and regulating the reaction route towards a specific channel for achieving high selectivity. Moreover, the shape and crystal phase of TiO₂ nanoparticles alter their interactions with metal species, which are commonly termed as strong metal-support interactions involving interfacial strain and charge transfer. On the other hand, metal particles, clusters and single atoms interact differently with TiO₂, because of the variation of the electronic structure, while the surface of TiO₂ determines the interfacial bonding via a geometric effect. The dynamic behavior of the metal-titania interfaces, driven by the chemisorption of the reactive molecules at elevated temperatures, also plays a decisive role in elaborating the structure-reactivity relationship.

Construction and evolution of active palladium species on phase-regulated reducible TiO2 for methane combustion

Non-traditional amorphous Pd²⁺ species on the surface of Pd/TiO₂ catalysts facilitate CH₄ combustion, while formed Pd_xTi_1−xO₂ would be detrimental.

Highly efficient Ru/CeO2 catalysts for formaldehyde oxidation at low temperature and the mechanistic study

Ru species have a high redox capacity on a CeO₂ support, and the metallic Ru species could be easily oxidized back to RuO_x species.

Facet- and defect-engineered Pt/Fe2O3 nanocomposite catalyst for catalytic oxidation of airborne formaldehyde under ambient conditions

Formaldehyde (HCHO) is one of the most infamous indoor pollutants that imposes a great threat to human health. Herein, we report the development of a high-performance Pt/Fe₂O₃ catalyst for HCHO oxidation employing a facet- and defect-engineering strategy, with special focus on the surface structure effect of α-Fe₂O₃ on the catalytic properties. A supported Pt nanocatalyst on hollow octadecahedral α-Fe₂O₃ with exclusively exposed {113} and {104} facets was prepared using a hydrothermal method followed by impregnation-reduction treatment. The high-index facets of α-Fe₂O₃ render the formation of abundant oxygen vacancies and an improved dispersion of Pt nanoparticles. This led to an increased Pt/O-vacancy coexistence in close proximity, which collaboratively promote the generation of active oxygen and surface OH species. As a consequence, the Pt/Fe₂O₃-HO catalyst exhibited impressively high and stable activity towards HCHO oxidation at room temperature, which was five-fold higher than that of the supported Pt catalyst on commercial α-Fe₂O₃.

Liberating Active Metals from Reducible Oxide Encapsulation for Superior Hydrogenation Catalysis

The strong metal-support interaction (SMSI) is of significant importance to heterogeneous catalysis. The electronic modification and encapsulation of active metals by reducible supports are the intrinsic properties of the SMSI, where the latter would decrease or even cease the catalytic activity of transition metals. Here, we demonstrate for the first time that alkalies are the functional additives that can effectively manipulate the SMSI for better hydrogenation catalysis. Specifically, both thermodynamic analyses and experimental results show that the addition of alkalies to the Ru/TiO₂ catalyst could form a titanate top layer that effectively hampers the migration of TiO_2-x to the surface of Ru nanoparticles. In the meantime, a substantially enhanced reduction of the support is achieved, leading to an even stronger electron donation from the support to Ru. The alkali-modified Ru/TiO₂ exhibits superior low-temperature catalytic activity in the hydrogenation of aromatics, which is ca. an order of magnitude higher than that of the commercial Ru/Al₂O₃ catalyst and is in clear contrast to that of the neat Ru/TiO₂ catalyst that shows negligible activity due to the severe encapsulation of Ru by TiO_2-x.

Pd/meso-CoO derived from in situ reduction of the one-step synthesized Pd/meso-Co3O4: high-performance catalysts for benzene combustion

The 0.93Pd/meso-CoO is prepared via in situ reduction of 0.85Pd/meso-Co₃O₄ derived from KIT-6-templating method. The excellent catalytic activity of 0.93Pd/meso-CoO is related to the formed Pd⁰ species and good oxygen activation ability.