Catalysts For Oxidation Research Articles

A Recyclable Inorganic Lanthanide Cluster Catalyst for Chemoselective Aerobic Oxidation of Thiols

A Recyclable Inorganic Lanthanide Cluster Catalyst for Chemoselective Aerobic Oxidation of Thiols

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.

Accelerating alcohol oxidation kinetics for electrochemical biomass upgrading via photoinduced active CuIII-O generation

Copper-based compounds exhibit broad prospects in the electrocatalytic oxidation of biomass for sustainable production of high-value-added chemicals due to their passivated oxygen evolution reaction (OER) competitiveness. However, the sluggish reaction kinetics remain the main challenge in constraining their scalable application. Herein, a highly selective electrooxidation of 5-hydroxymethylfurfural (HMF) to 2, 5-furandicarboxylic acid (FDCA) on CuO is achieved via photoinduced surface reconstruction. The experimental results confirmed that the photogenerated hole accumulation on the surface of CuO with matched valence band position can promote the CuOOH active phase generation. Density functional theory (DFT) calculations and the overall relationship between structure and selectivity indicate the CuOOH species can accelerate the spontaneous dehydrogenation process of hydroxyl group. Therefore, the activated CuO electrode under illumination can effectively regulate the conversion of 5-Hydroxymethyl-2-furancarboxylic acid (HMFCA) key intermediates and exhibits accelerated reaction kinetics, FDCA yield increased by 17.79 % compared to dark condition. Additionally, a general enhancement effect on the oxidation of benzyl alcohol and furfuryl alcohol was also revealed. This work introduces photoassistance effect for the first time in HMF oxidation, opening up prospects for the application of photoelectric synergy in biomass value-added conversion and providing insights into the activity mechanism of Cu-based catalysts in organic oxidation.

Photoredox Cascade Catalysts for Solar Hydrogen Production from Sustainable Hydrogen Sources.

Visible-light-driven photocatalytic hydrogen (H2) production has been extensively studied as a clean and sustainable energy resource. Although sacrificial electron donors (SEDs) are commonly used to evaluate photocatalytic activity, their irreversible decomposition forces charge separation, which disrupts the inherent dual productivity of photocatalysis, that is, the formation of both the reduction and oxidation products. To achieve highly efficient photoinduced charge separation without SED decomposition, the layer-by-layer assembly of redox-active photosensitizing dyes and electron mediators through Zr4+-phosphonate bonds has been extensively studied as an artificial mimic of the electron transport chain in natural photosynthesis. This concept paper presents an overview of photoredox cascade catalytic (PRCC) systems comprising multiple Ru(II)-trisbipyridine-type dyes and mediator layers on Pt-loaded TiO2 nanoparticles for H2 production from redox reversible electron donors (RREDs). The PRCC structure-activity relationship for photocatalytic H2 production is briefly discussed in terms of layer thickness, surface structure and modification, and cooperativity with molecular oxidation catalysts. Finally, new insights into the design of efficient dual-production photocatalysts based on the PRCC structure are presented.

Highly Active Oxidation Catalysts through Confining Pd Clusters on CeO2 Nano‐Islands

AbstractCeO2‐supported noble metal clusters are attractive catalytic materials for several applications. However, their atomic dispersion under oxidizing reaction conditions often leads to catalyst deactivation. In this study, the noble metal cluster formation threshold is rationally adjusted by using a mixed CeO2‐Al2O3 support. The preferential location of Pd on CeO2 islands leads to a high local surface noble metal concentration and promotes the in situ formation of small Pd clusters at a rather low noble metal loading (0.5 wt %), which are shown to be the active species for CO conversion at low temperatures. As elucidated by complementary in situ/operando techniques, the spatial separation of CeO2 islands on Al2O3 confines the mobility of Pd, preventing the full redispersion or the formation of larger noble metal particles and maintaining a high CO oxidation activity at low temperatures. In a broader perspective, this approach to more efficiently use the noble metal can be transferred to further systems and reactions in heterogeneous catalysis.

Highly efficient Ag/Ce–Zr catalyst for catalytic oxidation of NVOCs: balance of redox ability and acidity

Highly efficient Ag/Ce–Zr catalyst for catalytic oxidation of NVOCs: balance of redox ability and acidity

Kinetic Study and Catalytic Activity of Cr3+ Catalyst Supported on Calcium Silicate Hydrates for VOC Oxidation

Volatile organic compounds (VOCs) are pollutants that pose significant health and environmental risks, necessitating effective mitigation strategies. Catalytic oxidation emerges as a viable method for converting VOCs into non-toxic end products. This study focuses on synthesizing a catalyst based on calcium silicate hydrates with chromium ions in the CaO-SiO2-Cr(NO3)3-H2O system under hydrothermal conditions and evaluating its thermal stability and catalytic performance. A catalyst with varying concentrations of chromium ions (10, 25, 50, 100 mg/g Cr3+) was synthesized in unstirred suspensions under saturated steam pressure at a temperature of 220 °C. Isothermal curing durations were 8 h, 16 h, and 48 h. Results of X-ray diffraction and atomic absorption spectroscopy showed that hydrothermal synthesis is effective for incorporating up to 100 mg/g Cr3+ into calcium silicate hydrates. The catalyst with Cr3+ ions (50 mg/g) remained stable up to 550 °C, beyond which chromatite was formed. Catalytic oxidation experiments with propanol and propyl acetate revealed that the Cr3+ catalyst supported on calcium silicate hydrates enhances oxygen exchange during the heterogeneous oxidation process. Kinetic calculations indicated that the synthesized catalyst is active, with an activation energy lower than 65 kJ/mol. This study highlights the potential of Cr3+-intercalated calcium silicate hydrates as efficient catalysts for VOC oxidation.

3-(Sulfamic acid)-propyltriethoxysilane on biochar nanoparticles as a practical, biocompatible, recyclable and chemoselective nanocatalyst in organic reactions.

Recyclable and inexpensive catalysts, waste regeneration, use of available and safe solvents are important principles of green chemistry. Therefore, in this project, biochar nanoparticles (BNPs) were synthesized by the pyrolysis method from chicken manure. Then, 3-(sulfamic acid)-propyltriethoxysilane (SAPES) was immobilized on the surface of BNPs (SAPES@BNPs). The prepared catalyst (SAPES@BNPs) was used as a commercial, practical, biocompatible and reusable catalyst in the selective oxidation of sulfides to sulfoxides. Further, the catalytic application of SAPES@BNPs was explored in the multicomponent synthesis of tetrahydrobenzo[b]pyrans under mild and green conditions. BNPs were characterized using SEM, TGA and XRD techniques. SAPES@BNPs were characterized using SEM, FT-IR spectroscopy, WDX, EDS, TGA, and XRD techniques. Particle size distribution was obtained by histogram graph. SAPES@BNPs can be recovered and reused several times. The purity of the products was studied using NMR spectroscopy.

Rutile TiO2-Supported Pt Nanoparticle Catalysts for the Low-Temperature Oxidation of Ethane to Ethanol.

Structure-function relationships of supported metal nanoparticle catalysts in the CO-assisted oxidation of ethane to ethanol were investigated. A rutile TiO2-supported Pt nanoparticle catalyst exhibited the highest ethanol production rate and selectivity. During the reaction, sequential changes in the geometric/electronic states and the particle size of the Pt nanoparticles were observed. The comparison of the catalytic performances of model catalysts with controlled metal-support interactions revealed that Pt0 nanoparticles of 2-3 nm with a high fraction of the surface Ptδ+ species are highly active for the oxidation of ethane to ethanol. The coadded CO plays a pivotal role not only in tuning the oxidation state of the surface Pt but also in producing H2O2, which is the true oxidant for the reaction. The supported Pt nanoparticle uses in situ-generated H2O2 to activate ethane, where the C2H5OOH intermediate is formed through a nonradical mechanism and subsequently converted to C2H5OH. This reaction occurs even at 50 °C with an apparent activation energy of 32 kJ mol-1. The present study sheds light on the usefulness of surface-engineered Pt nanoparticles for the low-temperature oxidation of ethane to ethanol.

Rutile TiO2-Supported Pt Nanoparticle Catalysts for the Low-Temperature Oxidation of Ethane to Ethanol.

Structure-function relationships of supported metal nanoparticle catalysts in the CO-assisted oxidation of ethane to ethanol were investigated. A rutile TiO2-supported Pt nanoparticle catalyst exhibited the highest ethanol production rate and selectivity. During the reaction, sequential changes in the geometric/electronic states and the particle size of the Pt nanoparticles were observed. The comparison of the catalytic performances of model catalysts with controlled metal-support interactions revealed that Pt0 nanoparticles of 2-3 nm with a high fraction of the surface Ptδ+ species are highly active for the oxidation of ethane to ethanol. The coadded CO plays a pivotal role not only in tuning the oxidation state of the surface Pt but also in producing H2O2, which is the true oxidant for the reaction. The supported Pt nanoparticle uses in situ-generated H2O2 to activate ethane, where the C2H5OOH intermediate is formed through a nonradical mechanism and subsequently converted to C2H5OH. This reaction occurs even at 50 °C with an apparent activation energy of 32 kJ mol-1. The present study sheds light on the usefulness of surface-engineered Pt nanoparticles for the low-temperature oxidation of ethane to ethanol.

The Surface/Interface Modulation of Platinum Group Metal (PGM)-Free Catalysts for VOCs and CO Catalytic Oxidation.

Effective management of volatile organic compounds (VOCs) and carbon monoxide (CO) is critical to human health and the ecological environment. Catalytic oxidation is one of the most promising technologies for achieving efficient VOCs and CO emission control. Platinum group metal (PGM)-free catalysts are recently receiving sustainable attention in catalyzing VOCs and CO removal due to their low cost, superior catalytic activity, and excellent stability, but PGM-free catalysts face challenges in low-temperature catalytic efficiency. In this mini-review, starting with discussing the catalytic mechanism of VOCs and CO oxidation, we summarize the surface/interface modulation strategies of PGM-free catalysts to promote oxygen and VOCs/CO molecule activation for enhanced low-temperature oxidation activity, including oxygen vacancy engineering, heteroatom doping, surface acidity modification, and active interface construction. We highlight the currently remaining challenges and prospects of advanced PGM-free catalyst development for highly efficient VOCs and CO emission control in practical applications.

Rb‐Promoted Au/CeO2 Nanocatalyst for Remarkably‐Enhanced Aniline Conversion to Azoxybenzene with Ultrahigh Selectivity

AbstractAromatic azo compounds have proven to be a relevant class of building blocks in chemical synthesis. However, uncontrollable selectivity towards azo compounds and low reactant conversion in traditional synthetic methods seriously impede their applications. Herein, Rb‐doped Au/CeO2 nanocatalyst (Rb−Au/CeO2) was prepared and utilized as a highly efficient supported metal catalyst for the selective oxidation of anilines to azocompounds using hydrogen peroxide as an oxidant, which reached ultrahigh selectivity (92 %) towards azoxybenzene and complete aniline conversion (100 %). The addition of Rb+ accelerates the electron transformation of Au to produce Au+, which is ready for catalysis. This research presents a promising Rb‐doped strategy for achieving complete aniline conversion and high selectivity towards azoxybenzene, opening up new possibilities for the application of aromatic azo compounds in chemical synthesis.

Synthetic Pt-Fe(OH)x catalysts by one-pot method for CO catalytic oxidation

Catalytic oxidation is used to control carbon monoxide (CO) emissions from industrial exhaust. In this work, The prepared Pta-Fe(OH)x catalysts (x represents the mass fraction of Pt loading (%), a = 0.5, 1 and 2) by the one-pot reduction method exhibited excellent CO catalytic activity, with the Pt2-Fe(OH)x catalyst, 70% and ∼100% CO conversion was achieved at 30°C and 60°C, respectively. In addition, the Pt2-Fe(OH)x catalyst also showed excellent H2O resistance and hydrothermal stability in comparison to the Pt2/Fe(OH)x catalyst prepared by impregnation method. Characterization results showed that the excellent catalytic performance of the catalysts was mainly attributed to the abundant surface oxygen species and Pt0 the presence of H2O, which promoted the catalytic reaction of CO, and Density functional theory (DFT) calculation showed that this was mainly attributed to the catalytic activity of the hydroxyl (-OH) species on Pt2-Fe(OH)x surface, which could easily oxidize CO to -COOH, which could be further decomposed into CO2 and H atoms. This study provides valuable insights into the design of high-efficiency non-precious metal catalysts for CO catalytic oxidation catalysts with high efficiency.

Synthetic Pt-Fe(OH)x catalysts by one-pot method for CO catalytic oxidation

Catalytic oxidation is used to control carbon monoxide (CO) emissions from industrial exhaust. In this work, The prepared Pta-Fe(OH)x catalysts (x represents the mass fraction of Pt loading (%), a = 0.5, 1 and 2) by the one-pot reduction method exhibited excellent CO catalytic activity, with the Pt2-Fe(OH)x catalyst, 70% and ∼100% CO conversion was achieved at 30°C and 60°C, respectively. In addition, the Pt2-Fe(OH)x catalyst also showed excellent H2O resistance and hydrothermal stability in comparison to the Pt2/Fe(OH)x catalyst prepared by impregnation method. Characterization results showed that the excellent catalytic performance of the catalysts was mainly attributed to the abundant surface oxygen species and Pt0 the presence of H2O, which promoted the catalytic reaction of CO, and Density functional theory (DFT) calculation showed that this was mainly attributed to the catalytic activity of the hydroxyl (-OH) species on Pt2-Fe(OH)x surface, which could easily oxidize CO to -COOH, which could be further decomposed into CO2 and H atoms. This study provides valuable insights into the design of high-efficiency non-precious metal catalysts for CO catalytic oxidation catalysts with high efficiency.

Fe-doped BN monolayer: A single-atom catalyst for efficient formaldehyde oxidation

Formaldehyde (HCHO) is a ubiquitous air pollutant, and the prolonged inhalation poses a serious threat to human health, thus it is imperative to develop HCHO oxidation catalysts with high activity. FeNx-based catalysts have shown brilliant catalytic performance due to their unique electronic structures. In this work, the active FeN3 site is designed by doping Fe atom at the B-vacancy in BN monolayer without introducing additional N atoms. Our first principles calculation results show that the Fe atom has good dispersibility, dynamical stability and thermal stability on the BN monolayer. Two oxidation mechanisms (Langmuir-Hinshelwood and Eley-Rideal) of HCHO on Fe-doped BN monolayer are investigated to explore the possible reaction pathways. The dissociation of O2 molecule is identified as the rate-limiting step, and the lowest energy barrier is 0.99 eV. Moreover, the excellent desorption behaviors of the produced CO2 and H2O molecules on substrate (small desorption energy of 0.20 and 0.75 eV, and short desorption time of 2.39 × 10−9 and 4.64 s) enable this catalyst to maintain high activity during the reaction cycle. Our results suggest the feasibility of Fe-doped BN monolayer for the catalytic oxidation of HCHO and broaden the application of BN-based single-atom catalysts.

Optimized preparation of La3Mn2O7 with superior lattice oxygen mobility and adsorbed oxygen utilization for catalytic removal of toluene

The R-P type layered perovskite La3Mn2O7 (LLM) is considered a more promising toluene oxidation catalyst than perovskite LaMnO3 (LMO) due to the versatile environment it provides for oxygen atoms, yet the challenge of realizing an optimal synthesis route remains. Herein, we revealed how calcination temperature influenced the structure–activity relationship and the mechanism by which the layered structure enhanced oxygen species reactivity. LLM700 possesses optimal toluene adsorption performance, oxygen species activation capability and low-temperature reducibility, thus exhibiting the highest catalytic activity (T90 = 283 °C) among single layered perovskite catalysts. The large interlayer gaps in the layered structure, combined with the weaker Mn-O bond strength near the layered structure, facilitate the easy removal of oxygen atoms, creating oxygen vacancies that act as pathways for oxygen ions to migrate within the lattice. Together, these factors enable the layered structure to enhance the mobility of lattice oxygen and the utilization of adsorbed oxygen, making LLM an ideal model for catalyzing the oxidation of toluene. Furthermore, the possible reaction pathway for the oxidation of toluene on LLM700 was inferred using GC–MS. This work paves the way for the catalytic applications of layered perovskites.

Synthesis and characterization of bagasse cellulose-based quaternary ammonium peroxyphosphotungstate and their catalytic properties for cyclohexene oxidation in the absence of any solvent

Bagasse cellulose, an industrial waste byproduct of sugar production, was demonstrated to be a viable solid support for a solid-phase ionic oxidation catalyst enabling organic solvent-free aqueous reaction conditions and facile catalyst recovery. Bagasse cellulose-supported quaternary ammonium peroxyphosphotungstate was synthesized from bagasse cellulose-supported quaternary ammonium chloride, phosphotungstic acid, and hydrogen peroxide. The chemical structure of this material was characterized by SEM, XRD, FT-IR, XPS, and 13C NMR, revealing stability of the cellulose matrix to the catalyst loading conditions and effective dispersion of the acicular catalyst crystals throughout the matrix. High catalytic activity of this synthetic complex was demonstrated in the oxidation of cyclohexene to 1,2-cyclohexanediol with hydrogen peroxide in the absence of solvent. Optimized conditions providing trans-1,2-cyclohexanediol with 86.2 % selectivity were 12 wt% catalyst and 4 mL/g 30 % H2O2 (vs. cyclohexene) at 50 °C for 10 h.

Optimizing the Catalytic Performance of Ba1-xCexMnO3 and Ba1-xLaxCu0.3Mn0.7O3 Perovskites for Soot Oxidation in Simulated GDI Exhaust Conditions.

Ba1-xCexMnO3 (BM-Cex) and Ba1-xLaxMn0.7Cu0.3O3 (BMC-Lax) perovskite-type mixed oxides were synthesized using the sol-gel method adapted for aqueous media with different values of x (0, 0.1, 0.3, 0.6) to estimate the effect of the degree of the partial substitution of Ba by Ce or La on the structure and properties that are relevant for their use as catalysts for gasoline direct injection (GDI) soot oxidation. The samples were deeply characterized by ICP-OES, XRD, XPS, N2 adsorption, H2-TPR, and O2-TPD, and their potential as catalysts for soot oxidation has been analyzed in various scenarios that replicate the exhaust conditions of a GDI engine. By comparing the catalytic performance for soot oxidation of the two tested series (BM-Cex and BMC-Lax) and in the two conditions used (100% He and 1% O2 in He), it could be concluded that (i) in the absence of oxygen in the reaction atmosphere (100% He), BMC-La0.1 is the best catalyst, as copper is also able to catalyze the soot oxidation; and (ii) if oxygen is present in the reaction atmosphere (1% O2/He), BM-Ce0.1 is the most-active catalyst as it presents a higher proportion of Mn(IV) than BMC-La0.1. Thus, it seems that the addition of an amount of Ce or La higher than that corresponding to x = 0.1 in Ba1-xCexMnO3 and Ba1-xLaxCu0.3Mn0.7O3 does not allow us to improve the catalytic performance of BM-Ce0.1 and BMC-La0.1 for soot oxidation in the tested conditions.

Role of regulating synthetic solvents in enhancing the catalytic performance of VPO catalysts for n-butane oxidation to maleic anhydride

Vanadium phosphorus oxide (VPO) catalysts have been successfully applied in the selective oxidation of n-butane to maleic anhydride (MA). However, there is still much work to be done to enhance the n-butane conversion while maintaining a relatively high MA selectivity. Regulating the solvents in preparing VPO catalysts is an effective way to improve the catalytic performance. In this work, the correlation between the physicochemical properties of VPO catalysts and the composition of solvents was investigated by combining various characterization techniques to reveal the role of regulating synthetic solvents in enhancing the catalytic performance. Varying synthetic solvents could regulate both the synthetic mechanism and crystal growth of VOHPO4·0.5H2O. The VOHPO4·0.5H2O tended to form a nice plate-like structure in isobutanol but possessed large crystallite sizes and a low specific surface area. The introduction of n-butanol prevented the continuous growth of VOHPO4·0.5H2O, reducing the crystallite sizes and thus increasing the specific surface area. Introducing the n-butanol also optimized the catalyst surface chemical properties. The best catalyst synthesized in a solvent containing 80 % n-butanol and 20 % isobutanol enhanced the n-butane conversion from 71 % to 87 % while maintaining the MA selectivity (64 %) almost unchanged compared to the catalyst synthesized in a conventional solvent.

Integration of Facet‐Dependent, Adsorbate‐Driven Surface Reconstruction into Multiscale Models for the Design of Ni‐Based Bimetallic Catalysts for Hydrogen Oxidation

Integration of Facet‐Dependent, Adsorbate‐Driven Surface Reconstruction into Multiscale Models for the Design of Ni‐Based Bimetallic Catalysts for Hydrogen Oxidation