Catalysts For Selective Oxidation Research Articles

Noble Metal-Based Catalysts for Selective Oxidation of HMF to FDCA: Progress in Reaction Mechanism and Active Sites

5-hydroxymethylfurfural (HMF) is oxidized to 2,5-furandicarboxylic acid (FDCA), which serves as a sustainable alternative to the petrochemical derivative terephthalic acid as a polyester monomer. Currently, noble metal catalysts that combine high HMF conversion rates with FDCA selectivity have become one of the mainstream catalytic systems for HMF oxidation. This paper summarizes and discusses the research progress on HMF oxidation to FDCA over different noble metal-based catalysts by combining DFT theoretical calculations, introducing various reaction pathways and mechanisms of HMF oxidation. It also analyzes the characteristics and electronic properties of metal active sites, geometric effects, metal–support interactions, and confinement effects, discussing and revealing the roles and activation mechanisms of different metal active sites, the structure of catalysts, active substances, metal valence states, activity, and the relationship between metal and the oxidation of C=O and OH groups. Finally, it presents views on the challenges and future development in the design of noble metal-based catalysts.

Insights into Contribution of Active Ceria Supports to Pt-Based Catalysts: Doping Effect (Zr; Pr; Tb) on Catalytic Properties for Glycerol Selective Oxidation

How important is the support during the rational design of a catalyst? Herein, doped ceria (Zr; Pr and Tb) was used as an active support to prepare Pt catalysts (0.5 wt%) for glycerol selective oxidation. A thorough characterization of achieved catalytic systems showed that the nature of doping elements led to different physicochemical properties. The presence of surface Pr3+ and Tb3+ not only increased oxygen vacancies but also electron mobility, modifying the oxidation state of platinum particles. The redox properties of the catalyst were also affected, achieving a close interaction between the support and metal particles even in the form of Pt-O-Pr(Tb) solid solutions. Furthermore, the combination of medium-sized metal particle dispersion, strong metal–support interaction and a synergy between the amount of oxygen vacancies and Pt0, observed in the Pt/CeTb catalyst, led to a high turnover frequency (TOF) and increased selectivity to glyceric acid. Thus, the present study reveals how a simple structural modification of active supports, such as cerium oxide, by means of doping elements is capable of improving the catalytic performance during glycerol selective oxidation, avoiding the cumbersome methods of synthesis and activation treatments.

Polyethylene Glycol–Bridged Diimidazolium Polyoxometalates: Thermoregulated Reusable Catalysts for Selective Oxidation of Toluene to Benzaldehyde

ABSTRACTThe oxidation of toluene to benzaldehyde holds great industrial significance, and it typically involves toxic reagents and/or affords difficult‐to‐separate product mixtures. Herein, polyethylene glycol (PEG)–bridged diimidazolium polyoxometalates (POMs) with a Keggin‐type tungstovanadophosphoric heteropolyacid anion and various PEG‐functionalized diimidazolium cations were prepared and evaluated as catalysts for the eco‐friendly oxidation of toluene using aqueous tert‐butyl hydroperoxide in acetonitrile. The bridging of diimidazolium cations by PEG enabled the fine‐tuning of heteropolyanion redox properties and increased catalyst reactivity and solubility in the reaction system. The best‐performing POM exhibited thermoregulated phase‐separation behavior, that is, it was fully soluble in the reaction medium at elevated temperatures and hardly soluble at room temperature. Further, it showed almost no performance deterioration after sevenfold reuse and achieved an acceptable toluene conversion (82%) and benzaldehyde selectivity (68%). Thus, our work enables the development of eco‐friendly processes for the catalytic oxidation of industrially relevant hydrocarbon and thus facilitates the establishment of a more sustainable society.

Tailored pore-confined single-site iron(III) catalyst for selective CH4 oxidation to CH3OH or CH3CO2H using O2

Direct oxidation of methane to valuable oxygenates like alcohols and acetic acid under mild conditions poses a significant challenge due to high C‒H bond dissociation energy, facile overoxidation to CO and CO2 and the intricacy of C−H activation/C−C coupling. In this work, we develop a multifunctional iron(III) dihydroxyl catalytic species immobilized within a metal-organic framework (MOF) for selective methane oxidation into methanol or acetic acid at different reaction conditions using O2. The active-site isolation of monomeric FeIII(OH)2 species at the MOF nodes, their confinement within the porous framework, and their electron-deficient nature facilitate chemoselective C‒H oxidation, yielding methanol or acetic acid with high productivities of 38,592μmolCH3OHgFe−1h−1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$38,592\\,\\upmu {{{\\rm{mol}}}}_{{{{\\rm{CH}}}}_{3}{{\\rm{OH}}}}{{{{\\rm{g}}}}_{{{\\rm{Fe}}}}}^{-1}{{{\\rm{h}}}}^{-1}$$\\end{document} and 81,043μmolCH3CO2HgFe−1h−1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$81,043\\,\\upmu {{{\\rm{mol}}}}_{{{{\\rm{CH}}}}_{3}{{{\\rm{CO}}}}_{2}{{\\rm{H}}}}{{{{\\rm{g}}}}_{{{\\rm{Fe}}}}}^{-1}{{{\\rm{h}}}}^{-1}$$\\end{document}, respectively. Experiments and theoretical calculations suggest that methanol formation occurs via a FeIII-FeI-FeIII catalytic cycle, whereas CH3CO2H is produced via hydrocarboxylation of in-situ generated CH3OH with CO2 and H2, and direct CH4 carboxylation with CO2.

Study on Effect of Calcination and Ag Loading on Ag/TiO2 Catalyst for Low-Temperature Selective Catalytic Oxidation of Ammonia

Study on Effect of Calcination and Ag Loading on Ag/TiO2 Catalyst for Low-Temperature Selective Catalytic Oxidation of Ammonia

Facet-dependent effect of α-MnO2 on Ag atoms anchoring and low-temperature selective catalytic oxidation of ammonia

Ammonia (NH3) contributes greatly to haze formation, posing significant risks to ecology and health. As a typical NH3 selective catalytic oxidation (NH3-SCO) catalyst, Ag supported catalysts can balance activity and selectivity. In this research, Ag atoms were anchored on the various crystal facets ({310}, {110} and {100}) of α-MnO2 and were studied for the NH3-SCO. The facet-dependence on Ag atoms anchoring mechanism, as well as the anchored Ag structure, have all been revealed in detail. It was found that the capturing of Ag on the facets of α-MnO2 followed the terminal hydroxyl anchoring mechanism, and further confirmed the linear relationship between Ag capturing quantity and the amount of terminal hydroxyl groups. The {310} facet has a strong ability to activate water molecules to produce surface hydroxyl groups, thereby exhibiting a heightened capability to capture Ag atoms; Ag atoms are loaded in the form of fine nanoparticles on the {310} facet, while anchored in a highly dispersed form on the {110} and {100} facets. The anchoring of Ag significantly improves the NH3-SCO performance of α-MnO2, especially, the Ag/α-MnO2 catalyst with Ag anchoring on the {310} facets exhibited the best activity, achieving 100 % conversion and greater than 80 % N2 selectivity at as low temperature as 100 °C. Finally, the adsorption and possible NH3-SCO mechanism of Ag/α-MnO2 catalysts were also explored by in-situ DRIFTS. The aim of this research is to reveal the facet-dependence of α-MnO2on Ag atoms anchoring,and its effect on low-temperature NH3-SCO activity.

One-Pot Synthesis of Mixed-Phase MoVTeNbOx Catalysts for Selective Oxidation of Propane to Acrylic Acid.

One-pot hydrothermal synthesis assisted by sodium citrate and citric acid is developed to fabricate mixed-phased MoVTeNbOx catalysts with different phase compositions for selective oxidation of propane to acrylic acid. Structures of various catalysts are comprehensively characterized. Interfacial interactions occur among the M1 and M2 phases of mixed-phase MoVTeNbOx catalysts to exert synergistic effects on the selective production of acrylic acid. Various mixed-phase MoVTeNbOx catalysts exhibit the same type of active site on the M1-phase component, with a significantly enhanced ability to adsorb and activate propane. The propane conversion increases linearly with the density of surface site for propane adsorption, while the propene selectivity increases linearly with the density of surface site for propene adsorption. Among the synthesized catalysts, a MoVTeNbOx catalyst composed of 35.3 wt % M1 phase, 19.2 wt % M2 phase, and 45.7 wt % amorphous phase exhibits the largest density of active site and consequently the best catalytic performance with 38.9% propane conversion and 71.2% acrylic acid selectivity at 380 °C.

Cerium(III) phosphate as a promising support for gold catalysts addressed to selective oxidation of glucose under base-free conditions

Supported gold nanoparticles are widely used active oxidation catalysts, however, their efficiency and stability vastly depend on the type of supports utilized. This study aims to unravel the potential application of cerium(III) phosphate as a new support for gold catalysts for selective oxidation of glucose under base-free conditions. Particular interest was directed to: i) the identification of the key factors that promote high activity of supported gold species, ii) the optimization of reaction conditions to assess the impact of catalyst loading and reaction time/temperature on the efficiency of glucose oxidation, and iii) the elucidation of the stability of Au/CePO4 catalyst in several reaction cycles. The results show that Au/CePO4 exhibits unique surface properties that enable obtaining of much higher activity of gold species in glucose oxidation compared to other well-known metal oxide-based systems. Precisely, it was found that the TOF value calculated for Au/CePO4 was ca. 2.5 times higher than in the case of Au/CeO2 (TOF = 5846 vs. 2309 h−1, respectively), and ca. 1.5 times higher than that observed for Au/TiO2 (Mintek, TOF = 3839 h−1). The presented results facilitate the development of more active and highly selective supported gold catalysts for oxidation of biomass-derived platform molecules (e.g., glucose).

Study on the effect and mechanism of support structure and characteristic on Ag-based catalysts for low-temperature selective catalytic oxidation of ammonia

Herein, the influence of support type and properties on the catalytic activity and selectivity of Ag-based NH3-SCO catalyst was studied through the evaluation of NH3-SCO performance, the physicochemical characterization of H2-TPR, NH3-TPD, N2 isothermal adsorption–desorption, XPR and XPS, and the mechanism study of 1H MAS NMR, In-situ DRIFTS and DFT calculations. Ag/nano-TiO2, Ag/Al2O3, and Ag/MnO2 all showed better NH3-SCO activity because of more abundant Brønsted and Lewis acid sites of Al2O3 and TiO2 and more actual Ag loading amount due to the larger specific surface area and suitable surface chemistry. The N2 selectivity of Ag/nano-TiO2 is significantly better, which may be due to the highly dispersed Ag species and the abundant Brønsted acid sites with higher N2 selectivity. The mechanism study showed that the terminal hydroxyl was the preferred consumption target of Ag species, and this consumption promoted the effective dispersion and stable anchoring of Ag on the TiO2 surface.

Ru/MgO-catalysed selective aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

Biomass valorisation through the selective oxidation of carbohydrate and lipid derivatives offers access to an array of platform chemicals through energy- and atom-efficient catalytic processes. Supported metal nanoparticles are promising catalysts for the aerobic selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), but typically require strong liquid base to achieve high selectivity. Here, we explore the utility of MgO as a solid base support for the Ru-catalysed aerobic oxidation of HMF, obtaining 68% FDCA yield at 160°C and 1.5 MPa of O2 using <1 mol-% metal.

Atomically Permeated MoP‐WOx Core‐Shell Catalysts for Efficient and Selective Oxidation of Thiophenic Sulfides in Fuels via Direct Electron Transfer Mechanism

AbstractHeterogeneous interfaces designed rationally in catalysts can induce geometrical, compositional, and electronic effects that can be applied to modulate catalytically active sites and consequently accelerate reaction kinetics. Here, a core‐shell heterostructure catalyst consisting of crystalline molybdenum phosphide (MoP) cores and amorphous tungsten oxide (WOx) shells on porous carbon nanosheets (PCN) is developed for oxidative desulfurization (ODS) of fuels. The strongly coupled core‐shell heterogeneous interface triggers a distinctive atomic permeation effect that induces substantial electron transfer from MoP to WOx and subsequent generation of electron‐rich W sites, consequently optimizing the adsorption of intermediates and substrates. The resulting catalyst (WOx@MoP/PCN) demonstrates a turnover frequency as high as 768.1 h−1 for ODS at 60 °C, exceeding that of almost all the state‐of‐the‐art ODS catalysts by 1–2 orders of magnitude. Moreover, a novel surface oxidation pathway based on direct electron transfer is identified in the WOx@MoP/PCN‐H2O2 system, which bypasses the formation of reactive oxygen species, consequently endowing the system with a moderate redox potential. Thus, WOx@MoP/PCN exhibits unprecedented selectivity, achieving 100% removal of thiophenic sulfides from real diesel with minimal consumption of oxidant.

Impact of M (M = Co, Cu, Fe, Zr) Doping on CeO2-Based Catalysts for Ammonia Selective Catalytic Oxidation at Low Temperatures

Impact of M (M = Co, Cu, Fe, Zr) Doping on CeO2-Based Catalysts for Ammonia Selective Catalytic Oxidation at Low Temperatures

Enhancing acidity of Ru/Ce/ZrO2 bifunctional catalysts for promoting N2 selectivity in selective catalytic oxidation of NH3

To solve the problem of low N2 selectivity of Ru/Ce/ZrO2 (R/C/Z) catalysts in NH3 selective catalytic oxidation (NH3-SCO) reaction, herein ZrO2 supports were treated with sulfuric acid and its effects on NH3-SCO performance were investigated systematically. The results showed that Ru/Ce/ZrO2-10S (R/C/Z-10S) catalyst, in which the mass ratio of sulfuric acid to ZrO2 was 10 %, exhibited N2 selectivity of 95.7 % at 350 °C, that was significantly higher than R/C/Z catalyst (57.8 %). NH3-TPD tests indicated that sulfate treatment of ZrO2 supports in R/C/Z catalysts led to more abundant acidic sites on catalyst surface, which was in favor of enhancing NH3 adsorption capacity remarkably. But when mass ratio of sulfuric acid to ZrO2 increased up to 20 %, an aggregation of metal oxides on the surface of R/C/Z-20S catalyst could be observed clearly, which might impose an adverse impact on NH3-SCO performance. In-situ DRIFTS results revealed that, compared to R/C/Z catalyst, there were much more Brönsted acid sites on the surface of R/C/Z-10S catalyst, and the corresponding NH3 species on acidic sites could be consumed quickly in intermediate reactions. More importantly, amide (-NH2) species rather than imide (-NH) and nitrosyl (-HNO) species, were the majority on the surface of R/C/Z-10S catalyst, implying that there might be a suppressing effect on further dehydrogenation of -NH2 species into -NH species owning to sulfate treatment of ZrO2 supports in R/C/Z catalysts. Therefore, internal selective catalytic reduction (i-SCR) mechanism rather than -NH mechanism played a vital role in NH3-SCO reaction over R/C/Z-10S catalyst.

Comprehensive mechanism and microkinetic model-driven rational screening of 4N-modulated single-atom catalysts for selective oxidation of benzene to phenol

Comprehensive mechanism and microkinetic model-driven rational screening of 4N-modulated single-atom catalysts for selective oxidation of benzene to phenol

Surface chlorination of IrO2(110) by HCl.

The ability to controllably chlorinate metal-oxide surfaces can provide opportunities for designing selective oxidation catalysts. In the present study, we investigated the surface chlorination of IrO2(110) by HCl using temperature programmed reaction spectroscopy (TPRS), x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. We find that exposing IrO2(110) to HCl, followed by heating to 650K in ultrahigh vacuum, produces nearly equal quantities of on-top and bridging Cl atoms on the surface, Clt and Clbr, where the Clbr atoms replace O-atoms that are removed from the surface by H2O formation. After HCl adsorption at 85K, only H2O desorbs at low Cl coverages during TPRS, but HCl begins to desorb in increasing yields as the Cl coverage is increased above about 0.5 monolayer (ML). The desorption of Cl2 was not observed under any conditions, in good agreement with the high barrier for this reaction predicted by DFT. A maximum Cl coverage of 1 ML, with nearly equal coverages of Clt and Clbr atoms, could be generated by reacting HCl with IrO2(110) in UHV. Our results suggest that a kinetic competition between recombinative HCl and H2O desorption under the conditions studied limits the saturation Cl coverage to a value less than the 2 ML maximum predicted by thermodynamics. XPS further shows that the partitioning of Cl between the Clt and Clbr states can be altered by subjecting partially chlorinated IrO2(110) to reductive or oxidative treatments, demonstrating that the Cl site population can change dynamically in response to the gas environment. Our results provide insights for understanding the chlorination of IrO2(110) by HCl and can enable future experimental studies to determine how Cl-modification alters the surface chemical reactivity of IrO2(110) and potentially enhances selectivity toward partial oxidation chemistry.

Nitrogen-Tungsten Oxide Nanostructures on Nickel Foam as High Efficient Electrocatalysts for Benzyl Alcohol Oxidation.

Electrocatalytic alcohol oxidation (EAO) is an attractive alternative to the sluggish oxygen evolution reaction in electrochemical hydrogen evolution cells. However, the development of high-performance bifunctional electrocatalysts is a major challenge. Herein, we developed a nitrogen-doped bimetallic oxide electrocatalyst (WO-N/NF) by a one-step hydrothermal method for the selective electrooxidation of benzyl alcohol to benzoic acid in alkaline electrolytes. The WO-N/NF electrode features block-shaped particles on a rough, inhomogeneous surface with cracks and lumpy nodules, increasing active sites and enhancing electrolyte diffusion. The electrode demonstrates exceptional activity, stability, and selectivity, achieving efficient benzoic acid production while reducing the electrolysis voltage. A low onset potential of 1.38 V (vs. RHE) is achieved to reach a current density of 100 mA cm-2 in 1.0 M KOH electrolyte with only 0.2 mmol of metal precursors, which is 396 mV lower than that of water oxidation. The analysis reveals a yield, conversion, and selectivity of 98.41%, 99.66%, and 99.74%, respectively, with a Faradaic efficiency of 98.77%. This work provides insight into the rational design of a highly active and selective catalyst for electrocatalytic alcohol oxidation.

Electrons redistribution of palladium-copper nanoclusters boosting the direct oxidation of methane to methanol

The direct oxidation of methane to methanol (DOMM) at mild conditions is an enormous attractive yet highly challenging, which is known as the “Holy Grail” reaction. In this work, we prepare the PdxCuy NCs supported on mesoporous sulfur-carbon materials and investigate their catalytic DOMM performance. The Pd14Cu1 NCs exhibits the excellent DOMM performance with the productivity of 34.3 mmol g−1 h−1 and the selectivity of 92.3 % at 150 °C when H2/O2 as active oxygen species, which was obviously superior to other PdCu catalysts. The enhanced performance of Pd14Cu1 NCs in DOMM is attributed to the non-crystalline atomic arrangement of tiny cluster structures and the synergistic electronic effect between Pd and Cu atoms, which can reduce the desorption temperature for methane, improve the in-situ generation of H2O2, and provide more active oxygen. The time-resolved in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) demonstrated that a radical-involved reaction pathway on Pd14Cu1 NC. This work provides the understanding for synergistic effect dual metallic and helps to design highly efficient and selective catalysts for the direct oxidation of CH4.

S-scheme TiO2/Bi2WO6 heterojunction for enhanced photocatalytic selective oxidation of toluene

Selective activation of saturated C–H bonds in hydrocarbons, such as the activation of the C–H bond in toluene, is an effective method for the production of high value-added chemicals. However, improving the C–H bond activation of toluene remains a challenge. In this study, S-scheme TiO2/Bi2WO6 composites were synthesized by loading TiO2 nanoparticles on Bi2WO6 flakes using a simple hydrothermal method. The physical and chemical properties of the prepared materials were characterized using X-Ray Diffraction (XRD), Fourier Transform Infrared Spectoscopy (FT-IR), Scanning Electronic Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and other characterization methods. Selective oxidation of toluene to benzaldehyde under visible light irradiation using air as an oxidizing agent. When the molar ratio of TiO2 and Bi2WO6 was 0.20, the composites exhibited excellent photocatalytic performance with a benzaldehyde production rate of 1725.41 μmol g−1 h−1, which was 2.31 and 1.91 times higher than that of TiO2 and Bi2WO6, respectively. This excellent performance is attributed to the formation of heterojunction structure by the loaded TiO2 nanoparticles, which improves the separation efficiency of photogenerated carriers and thus enhances its photocatalytic performance. In addition, the active substances involved in the photocatalytic reaction were identified by free radical trapping experiments as ·O2− and h+. Finally, the photocatalytic mechanism of S-scheme TiO2/Bi2WO6 composites was proposed by energy band structure analysis and radical trapping experiments. This study provides a simple design pathway for the construction of visible-light responsive bismuth tungstate-based heterojunction photocatalysts and some ideas for the development of new and efficient photocatalytic toluene selective oxidation catalysts.

Synergistic catalytic effect of titanium and iron incorporated to spherical MCM-41 in selective catalytic oxidation of diphenyl sulphide with H2O2

Spherical mesoporous silicas of MCM-41 type modified with titanium, iron or both these metals were prepared by co-condensation method and tested in the role of catalysts for selective oxidation of diphenyl sulphide with H2O2 to diphenyl sulphoxide and diphenyl sulphone. The monometallic catalysts containing titanium or iron were found to be active catalysts of diphenyl sulphide mainly to diphenyl sulphoxide. A very significant increase in catalytic activity was observed for the bimetallic samples, containing both titanium and iron. Moreover, in the case of bimetallic catalysts with higher titanium loading, diphenyl sulphone is a dominating reaction product. The increased activity of the bimetallic catalysts has been related to the synergistic operation of titanium and iron in conversion of hydrogen peroxide into reactive species, which in the next step oxidise diphenyl sulphoxide.

A broad-spectrum oxidation capability Ru-CeO2 catalyst for efficient synergistic selective oxidation of benzyl alcohol

Selective oxidation of alcohols to aldehydes by molecular oxygen is one of the most important transformations in multiphase catalysis. In this paper, a catalyst with selective oxidation ability was designed and synthesized for the selective catalytic oxidation of benzyl alcohol. N-doped carbon materials were prepared by high-temperature calcination using hydrothermal reaction products of citric acid and melamine as a carbon source, and a bimetallic catalyst supported by Ru-CeO2 was constructed using the mixture as the carrier for the selective oxidation of benzyl alcohol to benzaldehyde. The results showed that the introduction of CeO2 could effectively improve the oxidizing ability and catalytic activity of the catalyst. The Ru-Ce0.05/NC170–600 catalyst was able to convert 85.5 % benzyl alcohol into benzaldehyde at 140 °C, 6 h, and 2 MPa, and the selectivity for benzaldehyde was 100 %. It was demonstrated by DFT that it was theoretically feasible to generate benzaldehyde by extracting hydrogen atoms from benzyl alcohol molecules. Further, the selective oxidation experiments on other alcohols showed that the catalyst has high activity for the oxidation of various alcohols to generate the corresponding carbonyl products, and it is a catalyst with broad-spectrum selective oxidation ability. In this study, a green synthesis route of benzaldehyde was proposed to solve the problems in the traditional process. Meanwhile, it provides a new idea for the synthesis of carbonyl products by selective oxidation of alcohols.