Selective Catalytic Oxidation Research Articles

A DFT Study of Adsorption of Keto Alcohol Oil on a WO3 (001) Surface Modified with Silver Clusters of Specific Size

AbstractThe essential raw materials, cyclohexanol and cyclohexanone, are derived from the selective catalytic oxidation of cyclohexane. Due to their closely matched boiling points, the efficient separation among the components remains a significant challenge in industrial catalysis. In this work, we employed DFT calculations to explore the adsorption behavior of CyH, CyOH, and Cy═O, on both clean and Ag‐modified ɦ‐WO3 (001) surfaces. The calculation results reveal that Ag4 exhibits the highest stability on the ɦ‐WO3 (001) surface. The organic species adsorbed onto the Agn‐WO3 surfaces through distinct host‐guest interactions: CyH via CH···Ag, CyOH, and Cy═O via HO···Ag and C═O···Ag, respectively. The optimal separation efficacy of CyOH and Cy═O on the Ag2‐WO3 surface results in CyOH as the preferred product, while on the Ag4‐WO3 surface, Cy═O serves as the ultimate outcome. Our theoretical calculations provided in this study offer a valuable theoretical foundation for the separation of the KA oil mixture.

Improving H2S remediation efficiency through metal-free biochar modification: Nitrogen introduction and mesopore formation

Hydrogen sulfide (H₂S) poses substantial risks to human safety and infrastructure due to its toxicity and corrosive properties. In this study, we present a novel approach to enhance the selective catalytic oxidation of H₂S by synthesizing a nitrogen-doped mesoporous carbon catalyst (denoted as M/B-X-PZ-T) through pyrolysis at 600–800 °C. Our catalyst, derived from commercial biochar, incorporates melamine as a nitrogen source and employs KCl and ZnCl₂ as porogens via the salt-templating method. The resulting catalyst, M/B-1-PZ-700, exhibits an impressive specific surface area of up to 1269.77 m²/g and a high mesopore ratio, with effective nitrogen doping reaching up to 15.35 at%. Remarkably, M/B-1-PZ-700 demonstrated exceptional performance, achieving 100 % H₂S conversion and 94 % sulfur selectivity at 170 °C, surpassing previous nitrogen-doped carbon catalysts. Furthermore, our optimized catalyst maintained over 95 % H₂S conversion and superior sulfur yield for 36 h, indicating excellent long-term stability. This metal-free catalyst derived from biochar offers a promising, sustainable, and eco-friendly solution for effectively mitigating hazardous H₂S emissions.

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.

Promotion of Nb-Co3O4 chemical interfaces on N2 selectivity in selective catalytic oxidation of NH3 over cobalt-based catalysts

Co3O4 catalysts possess high activity in selective catalytic oxidation of NH3 (NH3-SCO), but the low N2 selectivity hinders their potential application. To enhance N2 selectivity, the chemical bonded Nb-O-Co catalyst by the deposition of Nb species onto Co3O4 (Nb/Co3O4-0.03) is constructed. It shows 100 % NH3 conversion and 82 % N2 selectivity at 180°C, and the N2 selectivity is 2.2-fold higher than that of Co3O4 (38 %). The failure of enhancement in N2 selectivity for physically mixed Co3O4 and NbOx (NbOx|Co3O4-0.03) further indicates the crucial role of chemical bonded Nb-O-Co in enhancing N2 selectivity. In situ diffuse reflectance infrared Fourier transform spectra and NH3 temperature-programmed desorption results show the formation of new NH3 adsorption sites. Importantly, intermediates NO- stabled on Nb/Co3O4-0.03 tends to react with -NH2 to produce N2 through internal selective catalytic reduction (iSCR). This work offers insights into enhancing the N2 selectivity in NH3-SCO and advances understanding of iSCR mechanism.

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

Extra trees regression assisted 1D monolith reactor simulations based on microkinetic analysis and rate transformation

The incorporation of microkinetic method for surface reaction calculation is a key development direction in monolith reactor simulations, albeit posing significant computational stability and efficiency challenges. A data-driven multi-scale simulation framework is proposed to bridge the gap between macroscopic numerical model and microscopic reaction solvers. After the generating of precomputed microkinetic dataset, we utilize a tailor-designed preprocessing transformation, AD_log10, to effectively manage the common challenges of large variances and reversed directions in microkinetic rate data. A suite of machine learning regression models is developed as reaction rate solver integrated into the 1D two-phase monolith model. We employ NH3 selective catalytic oxidation on Cu(100) and Cu(111) as probe systems to validate our framework’s efficacy. In the context of on-board simulations under operating conditions, the Extra Trees Regression (with best regression performance) based model exhibits commendable accuracy and efficiency, successfully addressing complex processes previously unmanageable with interpolation-based models. This innovative approach paves the way for advanced monolith reactor modeling and sheds light on multi-scale simulation methodologies in chemical reaction engineering.

CePO4 supported Cr catalyst with superior sulfur tolerance for selective catalytic oxidation of ammonia

CePO4 supported Cr catalyst with superior sulfur tolerance for selective catalytic oxidation of ammonia

Promoting effect of Cu as electron transfer medium on NH3-SCO reaction in asymmetric Ag-Ov-Ti-Sm-Cu ring active site

Selective catalytic oxidation of ammonia (NH3-SCO) has become an effective method to reduce ammonia (NH3) emissions, and is a key part to solve the problem of NH3 pollution. Nevertheless, the optimization of this technology’s performance relies heavily on innovation and the development of catalyst design. In this study, a SmCuAgTiOx catalyst with an asymmetric Ag-Ov-Ti-Sm-Cu ring active site was prepared and applied to the NH3-SCO reaction. The low conversion of Cu-based catalysts in NH3 at low temperature and the inherent low N₂ selectivity of Ag-based catalysts were solved. The successful creation of the asymmetric ring active site improved the catalyst’s reduction performance. Additionally, Cu, acting as an electron transfer medium, plays a crucial role in enhancing electron transfer within the asymmetric ring active site, thus increasing the redox cycle of the catalyst during the reaction. In addition, some lattice oxygen is lost in the catalyst, resulting in the formation of a large number of oxygen vacancies. This process stimulates the adsorption and activation of surface-adsorbed oxygen, facilitating the conversion of NH3 to an amide (NH2) intermediate during the reaction and reducing non-selective oxidation. The N2 selectivity was improved without significantly affecting the performance of Ag-based catalyst. In-situ diffuse reflectance fourier transform infrared spectroscopy (In-situ DRIFTS) analysis reveals that the SmCuAgTiOx catalyst primarily follows an “internal” selective catalytic reduction (iSCR) mechanism in the NH3-SCO reaction, complemented by the imide mechanism. The asymmetric Ag-Ov-Ti-Sm-Cu ring active site developed in this study provides a new perspective for efficiently solving NH3 pollution in the future.

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.

Fe2O3/γ-Al2O3 and NiO/γ-Al2O3 catalysts for the selective catalytic oxidation of ammonia

Ammonia, a significant atmospheric pollutant, requires effective emission control due to its inherent toxicity and the generation of secondary pollutants like particulate matter. This control can be achieved through various methods, including catalytic processes. Therefore, our study focuses on evaluating the potential of catalysts based on iron oxide and nickel oxide supported on γ–Al2O3 for the selective catalytic oxidation of NH3 to N2 (NH3-SCO). The γ–Al2O3 was obtained by thermal decomposition of aluminum hydroxide, and 5 or 10 wt% of Fe or Ni was added through wetness incipient impregnation. XRD diffractograms confirmed the formation of the γ–Al2O3 phase. XRD, H2-TPR, and UV–vis DRS data showed the presence of Fe2O3, NiO, and NiAl2O4 in the catalysts. Introducing metal oxides onto the support led to a drop in the specific area, pore size, pore volume, and NH3 desorption, which was higher for the catalysts containing Fe. The catalysts were active in NH3-SCO, and the insertion of Fe or Ni was essential because it promoted a significant increase in the NH3 conversion (∼75 % Fe and ∼55 % Ni), compared to pure support (∼8 %), mainly from 400 °C. However, doubling the metal content has not resulted in a considerable increase in NH3 conversion. The N2 selectivity was higher for the catalysts containing Ni (∼85 %) from 400 °C compared to catalysts containing Fe (∼76 %). Such behavior was due to the larger surface area of the Ni-containing catalysts. Despite that, the 5Fe/γ–Al2O3 catalyst emerged as the most effective option for NH3-SCO applications, combining higher NH3 conversion and good N2 selectivity.

Sub-nanometric ruthenium clusters prepared by solid-state dispersion for catalytic selective aerobic oxidation of aromatic alcohols

The selective aerobic oxidation of alcohols to corresponding aldehydes is one of the most important challenges in the green chemical industry. In this work, Ru/Al2O3-SSD catalyst with highly dispersed metallic ruthenium clusters (average particle size of 0.97 nm) was prepared by solid-state dispersion (SSD) for efficient selective aerobic oxidation of aromatic alcohols to aldehydes. Compared with the counterpart catalyst Ru/Al2O3-IM prepared by wet impregnation (IM), this catalyst has smaller metal particles (0.97 nm vs. 3.4 nm), resulting in a special electronic structure, and exhibits much higher TOF (234 h−1 vs. 98 h−1) in the aerobic oxidation reaction of benzyl alcohol at 80 °C. The catalyst also shows excellent catalytic activity in the preparation of vanillin by selective aerobic oxidation of vanillyl alcohol at 100 °C, delivering a vanillin yield of 99%. The solid-state dispersion strategy provides an efficient and facile way for the fabrication of high-performance sub-nanometric metal catalysts.

Design Strategies for High-Performance NH3-SCO Catalysts: Identifying and Modulating Direct Anchoring Sites for Ag on TiO2.

Ammonia (NH3) slip from diesel vehicle aftertreatment systems and internal combustion engines fueled by NH3 or NH3/H2 poses serious environmental problems. Ag-based catalysts are widely used for the selective catalytic oxidation of NH3 to N2 (NH3-SCO), and their performance is greatly dependent on the state of Ag, which is influenced by the anchoring sites on the support. Despite efforts to identify the direct anchoring sites of metal atoms on TiO2, conflicting views persist. Here, we compared the correlation between Ag dispersion and the content of hydroxyl (OH) groups or defects on TiO2 and conducted density functional theory (DFT) calculations, and the results confirmed that the surface OH groups of TiO2 serve as the direct anchoring sites for Ag. By modulating the OH group content through thermal induction, the optimal OH group content on TiO2-800 resulted in more metallic Ag nanoparticles (Ag0 NPs) in larger sizes, leading to the development of an excellent NH3-SCO catalyst. Moreover, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), kinetic studies, and DFT calculations suggested that more Ag0 NPs in larger sizes on 10Ag/TiO2-800 were conducive to O2 activation and NH3 dissociation. Our findings provide new insights for designing efficient NH3-SCO catalysts, and OH groups as direct anchoring sites could be extended to other metals and supports for the rational design of catalysts.

Pt nanoparticles in cooperation with Mn-P composite drive base-free selective oxidation of 5-hydroxymethylfurfural

Selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a key approach to sustainable upgrading of furfural based biomass resources. In this work, small Pt nanoparticles (about 2.1 nm) loaded on MnPnOx composite were shown to effectively drive the base-free aerobic oxidation of HMF to FDCA in water. Regulating the P content in carrier enabled to tune HMF conversion and product distribution. The optimal Pt/MnP0.5Ox catalyst can reach 98% yield of FDCA at 110 °C under 10 bar of O2 after 24 h. It also showed the highest initial conversion rate of HMF (13 mmol molPt−1 s−1) and productivity of FDCA (4.1 mmol molPt−1 h−1) among all the Pt/MnPnOx catalysts. The carrier effect of P addition on promoting Pt oxidation catalysis was elucidated by using rigorous kinetic investigations and comprehensive characterizations. The initial conversion rate, rate constant and apparent activation energy were independently measured on oxidation of HMF and its derived intermediates. ICP-MS, XRD, TEM, H2-TPR, O2-TPD and XPS were used to acquire catalytic properties. It was demonstrated that P addition led to changes in carrier structure and metal-support interaction, which eventually promoted the formation of highly active electron-rich Pt0 sites and mobile reactive defect oxygen species. These features allowed improving the selective oxidation catalysis of supported-Pt nanoparticles for the base-free conversion of HMF to FDCA.

Homogeneous Tungsten Catalysis for Controllable Selective Oxidation of Anilines via the W(O)(η2-O2)2 Intermediate

Homogeneous Tungsten Catalysis for Controllable Selective Oxidation of Anilines via the W(O)(η²-O₂)₂ Intermediate

A rational construction of FexOy-N-ZSM-5 catalyst with graphene structures and FeNx sites for the selective catalytic oxidation of triethylamine

Stabilizing metal species at the atomic level and tuning their catalytic properties is a significant challenge. Herein, an N-doped FexOy-N-ZSM-5 catalyst with layered and chain-like graphene structures is reported. The catalyst can selectively catalyze the oxidation of triethylamine (TEA) with an efficiency of 99.7 % at 240 °C, and maintain an N2 yield of 97.6 % over the reaction temperature range of 240–360 °C. The results indicate that the layered graphene in the catalyst provide anchor sites for active Fe, while the abundant chain-like graphene act as connectors between ZSM-5 and the layered graphene, offering ample opportunities for TEA and its intermediates to contact the catalyst surface. This increases the number of active sites on the catalyst, thereby enhancing the catalytic performance of FexOy-N-ZSM-5. Notably, due to the interaction between FeOx and FeNx species, FexOy-N-ZSM-5 exhibits excellent thermal stability and water resistance, demonstrating promising potential for practical.

The effect of SO2 on NH3-SCR reaction synergistic CO oxidation over a Mn-Co-Ti catalyst

Mn–Co–TiO2 prepared using an impregnation method was applied to synergistic NH3-based selective catalytic reduction (NH3-SCR) and CO oxidation in a simulated flue gas. The NO conversion, NO oxidation, and CO oxidation were substantially enhanced after adding 15% Co3O4 to the 20MnTi catalyst. In an NO or NO + NH3 atmosphere, CO oxidation over the Mn–Co–TiO2 catalyst was mainly restrained by the competitive adsorption and formation of sulfate species. In contrast, the NH3-SCR reaction progressed almost unimpeded in a CO atmosphere. A SO2 atmosphere drastically reduced the NO conversion of the catalyst at lower temperatures and almost completely suppressed the oxidation activities toward NO and CO. The amount of remaining NO oxidation (approximately 10%) was primarily contributed by gas-phase oxidation of NO by O2. Next, fresh and SO2-poisoned Mn–Co–TiO2 were characterized using various methods. Results indicated that no conspicuous change occurred in the crystal structure of the samples after SO2 poisoning, but numerous sulfate products were deposited on the catalyst surface. The deposition of sulfate-species byproducts decreased the specific surface area and pore volume of the catalyst and shifted the surface acid sites to a higher temperature range, further reducing the CO oxidation performance. Moreover, the catalytic reaction of CO and NO followed the Eley–Rideal mechanism. Furthermore, the mechanisms through which multicomponent flue gases influence the synergistic NH3-SCR and CO oxidation performance were proposed.

Thermally stable high-loading single Cu sites on ZSM-5 for selective catalytic oxidation of NH3

Rigorous comparisons between single site- and nanoparticle (NP)-dispersed catalysts featuring the same composition, in terms of activity, selectivity, and reaction mechanism, are limited. This limitation is partly due to the tendency of single metal atoms to sinter into aggregated NPs at high loadings and elevated temperatures, driven by a decrease in metal surface free energy. Here, we have developed a unique two-step method for the synthesis of single Cu sites on ZSM-5 (termed CuS/ZSM-5) with high thermal stability. The atomic-level dispersion of single Cu sites was confirmed through scanning transmission electron microscopy, X-ray absorption fine structure (XAFS), and electron paramagnetic resonance spectroscopy. The CuS/ZSM-5 catalyst was compared to a CuO NP-based catalyst (termed CuN/ZSM-5) in the oxidation of NH3 to N2, with the former exhibiting superior activity and selectivity. Furthermore, operando XAFS and diffuse reflectance infrared Fourier transform spectroscopy studies were conducted to simultaneously assess the fate of the Cu and the surface adsorbates, providing a comprehensive understanding of the mechanism of the two catalysts. The study shows that the facile redox behavior exhibited by single Cu sites correlates with the enhanced activity observed for the CuS/ZSM-5 catalyst.

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.

Elucidation of synergism in Ce-Zr/SBA-15 mesoporous catalysts and the effects on the activity in selective glycerol to lactic acid reaction

The continued conversion of glycerol to value-added chemicals is essential in ensuring the sustainable development of the biodiesel industry. Selective catalytic oxidation of glycerol to lactic acid provides an alternative approach to valorizing glycerol. A mesoporous SBA-15 supported mixed-metallic oxide catalyst is deemed essential to selectively produce lactic acid in this mixed parallel and multi-step reaction. SBA-15-supported bimetallic Ce and Zr oxides were proved to be highly efficient catalysts for the selective glycerol oxidation into lactic acid in base-free media. The synergism between Ce and Zr in the bimetallic oxide compounds could enhance the creation of oxygen vacancies in the catalyst via the reduction of Ce4+ to Ce3+. The 2:1CeZr/SBA-15 catalyst exhibited prominent catalytic activity in selectively oxidizing glycerol to lactic acid, with a glycerol conversion of 91.8% and a lactic acid yield of 35.1%. This work achieved superior catalytic performance compared to previously conducted studies, primarily due to the significantly higher initial glycerol concentration employed in this study. To ascertain the intrinsic active sites of the catalyst, the physicochemical properties of the catalyst were thoroughly examined using BET, FTIR, XRD, FESEM, TEM, CO2-TPD, O2-TPD, and H2-TPR analysis. This work concluded that the synergistic interaction of the active sites, which led to the formation of active oxygen species, facilitated primary dehydrogenation of the terminal -OH bond in glycerol. Hence, in this work, a plausible glycerol conversion mechanism over the 2:1CeZr/SBA-15 catalyst was also proposed.