Bimetallic Oxide Catalysts Research Articles

Highly active Mn-Cu bimetallic oxide catalyst assembled as 3D-printed monolithic agitating paddles for advanced oxidation process

Catalytically agitating paddles are essential to perform liquid-solid heterogeneous catalytic reactions on an industrial scale due to the improved mass transfer and easy catalyst recovery. Herein, bimetallic oxides were formed after the calcination of nanomaterials derived from metal-organic frameworks (MOFs). Particularly, Mn(M)-BTC nanomaterials were synthesized by self-assembly of Mn2+ ions (mixed with various dopants such as Cu2+, Ce3+, or Fe2+) and H3BTC ligands in a mixed solvent of ethanol and water. It was found that in the powdery form, the Mn-Cu oxide derivate exhibited the highest degradation rate in the catalytic wet peroxide oxidation process (CWPO process), which was significantly higher than that of single metal oxide as well as Mn-Fe and Mn-Ce oxide derivates. The reason was caused by the synergistic effect between Mn-Cu promoted the formation of Mn3+ and Cu+ species to boost the CWPO reaction. Furthermore, the obtained Mn-Cu powdery catalysts were 3D-printed to obtain monolithic agitating paddles with different geometries, which were then mounted on a central shaft in the stirred reactor. An advanced oxidation process was used to investigate the effect of 3D patterns on the degradation efficiency of various organic dyes. It was discovered that the 3D-printed grid with higher cell density (484 cpsi) had better liquid mixing efficiency and thus better catalytic performance, which could be repeatedly used more than seven times. Additionally, the numerical simulation analysis (computational fluid dynamics) revealed a good mixing efficiency and improved mass transfer in the entire reactor equipped with the designed monolithic agitating impellers.

Improved performance of bimetallic oxides CuO–Y2O3 synthesized by sol–gel for methanol steam reforming

AbstractA series of bimetallic oxide catalysts CuO–Y2O3 were synthesized by different sol–gel methods for methanol steam reforming (MSR). The performance of the synthesized catalyst was investigated by characterization of X‐ray diffraction, Brunauer–Emmett–Teller, scanning electron microscopy, transmission electron microscope, and X‐ray photoelectron spectrometer techniques. The effects of different complexing agents on the property of the CuO–Y2O3 were identified. The results showed that CuO–Y2O3 synthesized by citric acid‐EDTA as a complexing agent showed the best performance, which has the largest specific surface area and shows the highest dispersion of particles and lowest average size than others. The relatively large specific surface area could increase the contact area between the catalyst and the feed, thereby improving the catalytic performance of the catalyst. Moreover, without hydrogen reduction treatment, the selectivity of hydrogen to CuO–Y2O3 can reach more than 99%, whereas the selectivity of CO is only 0.3% (under the reaction conditions: temperature of 300°C, the ratio of water to methanol of 4:1, feed flow rate of 4 ml/h). The addition of yttrium enhances the interaction of the two active components, copper and yttrium, thereby preventing the migration of the active components. This work provides a potential and economical Cu–Y oxide catalyst for onboard in situ hydrogen production from MSR, because it can reduce the hydrogen reduction process time.

Hydrocracking of Crude Palm Oil over Bimetallic Oxide NiO-CdO/biochar Catalyst

The bimetallic oxide NiO-CdO/biochar catalyst was prepared by coprecipitation and calcination methods. Characterizations of catalyst were carried out using Fourier Transform Infra Red (FTIR), Surface Area Analyzer (SAA), X-ray Diffraction (XRD), and Scanning Electron Microscope-Energy Dispersive X-ray (SEM-EDX) mapping methods. The catalyst showed a good average crystalized size of 12.30 nm related to the nanoparticles and high dispersion of Ni and Cd metals on the biochar surface. Analysis of liquid fuel products was observed using Gas Chromatography - Mass Spectrometry (GC-MS) which was separated to the main product of gasoline fraction (C6–C10), and the second product of kerosene fraction (C11–C16), and diesel fraction (C17–C23). The presence of the catalyst in the hydrocracking resulted in more liquid product of 56.55 wt% than the thermal cracking with a liquid product of 20.55 wt%. The best performance activity of catalyst was found at a temperature of 150 °C with high selectivity to hydrocarbon fuel with 12 types of gasoline fractions (39.24 wt%) compared to gasoline fractions obtained at higher hydrocracking temperatures of 250 °C and 350 °C. The results of this study showed that the bimetallic oxide catalyst supported with biochar from palm kernel shell plays an important role in the hydrocracking process to increase the selectivity of the gasoline fraction. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Synergistic degradation of sulfamethoxazole using peroxymonosulfate activated by Fe-Mn-Cu hollow spheres: Kinetics and mechanism studies

The synergistic effect of bimetallic or trimetallic oxide catalysts plays a vital role in sulfate radical-based advanced oxidation processes (SR-AOPs). Herein, a composite catalyst of iron-manganese-copper hollow spheres (FCMHS) was synthesized by hard template method and used for peroxymonosulfate (PMS) activation to degrade sulfamethoxazole (SMX). The catalytic activity of FCMHS was comprehensively evaluated under different conditions (including catalyst loading, PMS dosage, pH etc.). A removal efficiency of 99.1% and a mineralization efficiency of 39.7% for SMX were achieved under the optimal conditions. The kinetic studies demonstrated that the reaction rate for SMX removal by using FCMHS was about 3.5 times faster than that for using copper-manganese hollow spheres (CMHS). The enhanced catalytic performance mainly stemmed from the confined high instantaneous concentration of SMX in the local void space and the synergistic effects of Mn2+/Mn3+/Mn4+, Cu+/Cu2+/Cu3+ and Fe2+/Fe3+ redox cycles to generate radicals and non-radicals. More importantly, the introduction of iron oxide into CMHS substantially facilitated charge transfer at the interface between FCMHS and reaction solution, leading to a high rate and good product selectivity. Furthermore, SMX degradation pathways were proposed by LCMS-IT-TOF assisted with density functional theory (DFT) calculations, and the mechanism was proposed comprehensively. This study opens a reliable and promising avenue for the efficient treatment of antibiotics-polluted water based on trimetallic oxide catalysts.

Karanja oil transesterification using green synthesized bimetallic oxide catalyst, gCaO-CeO2: Comparative investigations with the monometallic oxide catalysts on the catalytic efficacy and stability

In the present study, a novel plant-mediated approach was reported to synthesize a bimetallic oxide (BMO, gCaO-CeO2) catalyst from waste egg shells. Previously, an equi-molar mixture of cerium nitrate and shell recovered calcium nitrate was considered as precursor for Prosopis juliflora mediated green synthesis. The prepared gCaO-CeO2 was characterized by means of FT-IR, TG/DTA, XRD and surface area analyzer. X-ray diffraction results showed that the gCaO-CeO2 is thermally stable even after the calcination process at 800 °C as the peaks for the cubic fluorite of cerium oxide (CEO) and cubic nature of calcium oxide (CO) were observed intact. Batch transesterification of karanja oil showed an improved catalytic activity for gCaO-CeO2 than monometallic oxides due to the increased basicity of the catalysts with the reduced temperature maxima. The highest fatty acid ethyl ester (FAEE) content of 96.17 % was attained for 6:1 mol ratio of ethanol-karanja oil over 4% (weight basis) of gCaO-CeO2 catalyst at 65 °C in 5 h. Further, the physico-chemical parameters of the transesterified products were found consistent with ASTM D6751 biodiesel standards. The study also reported the potential reuse of gCaO-CeO2 catalyst upto 6 operations with no appreciable loss in catalytic activity during transesterification.

Boosting peroxymonosulfate activation to mineralize organic pollutant by 2D defected CoMn bimetallic oxide catalyst through the enhanced non-radical pathway

Here, we present a Co-Mn mixed oxide (Co4Mn1) with abundant defects to improve peroxymonosulfate (PMS) activation efficiency in catalytic bisphenol A (BPA) degradation. The degradation efficiency of BPA reached ∼100% within 3 min by the catalysis of Co4Mn1, and the catalyst showed superior catalytic activities over a broad pH range of 4.0 ∼ 11.0. Free radical scavenger experiment and electron spin resonance (ESR) analysis showed that singlet oxygen (1O2) acted as the dominant reactive oxygen species (ROS) for BPA degradation, while •SO4- and •OH radicals played an auxiliary role. Due to the construction of Co-O-Mn mixed bond and the defect structure, the Co4Mn1 catalyst possessed more oxygen vacancy and surface Mn4+ species, and therefore accelerated the BPA degradation by nonradical pathway significantly. This work highlights the important role of catalyst structure in ROS production during PMS activation and reaction pathway of BAP degradation, and furnishes theoretical support for the treatment of real wastewater by PMS oxidation.

Bimetallic Oxide Catalyst for the Dehydrogenative Oxidation Reaction of Alcohols: Practical Application in the Synthesis of Value-Added Chemicals

This work demonstrates the preparation of zinc cobalt oxide materials (ZCO-1, ZCO-2, and ZCO-3) via thermal annealing of novel zinc cobalt acetate hydroxide precursors prepared in three different Co/Zn molar ratios (2:1, 1:1, and 1:2). Among these, the ZCO-1 sample displayed superior catalytic activity for the dehydrogenative oxidation of alcohols to carboxylic acids, exhibiting wide substrate applicability and high yield output with concomitant evolution of hydrogen gas (latent fuel) under oxidant-free conditions. The high catalytic activity of ZCO-1 can be accredited to synergistic effects arising from a balanced molar ratio of Co/Zn (2:1), which led to the formation of pure spinel-structured zinc cobalt oxide and a sufficiently high surface area capable of furnishing copious active sites, resulting in faster reaction kinetics and higher productivity. Moreover, the practical utility of the current protocol was displayed via ZCO-1-catalyzed gram-scale synthesis of value-added chemicals like nicotinic acid, terephthalic acid, and succinic acid.

Ce-Fe Bimetallic Oxide Catalysts for Co Catalytic Oxidation: Promoted Activity and So2 Resistance

Ce-Fe Bimetallic Oxide Catalysts for Co Catalytic Oxidation: Promoted Activity and So2 Resistance

ReaxFF Force Field Development and Application for Toluene Adsorption on MnMOx (M = Cu, Fe, Ni) Catalysts.

In numerous studies, the application of the molecular dynamics scheme based on the reactive force field (ReaxFF) method has been proven effective in modeling the catalytic behavior of metal–organic compounds. Recently, this method has been successfully applied for MxOy (M = Cu, Fe, Mn, Ni) transition-metal oxides. Yet, bimetallic metal oxides of the type MnMOx (M = Cu, Fe, Ni) were also present in the experimental system but could not be modeled since not all of the force field parameters were available at the time. To bridge this gap, the force field for modeling bimetallic metal oxides had to be developed. Here, we establish the needed force field parameter sets (namely, Cu/Mn/O, Fe/Mn/O, and Ni/Mn/O) and apply them to the problem of toluene adsorption on bimetallic oxide catalyst surfaces to verify their validity. Each training set consisted of at least 10 crystal structures containing at least Cu–Mn–O, Fe–Mn–O, or Ni–Mn–O atoms in contact obtained from the available structure databases. The parameter training has been done using the in-home-compiled version of the ReaxFF code. After training the force fields for geometry reproduction, the parameters were refined using the optimization by atom charges, comparing the ReaxFF values to those obtained for the respective structures using periodic crystal density functional theory (DFT) codes. The as-developed force fields were then applied to the process of toluene adsorption/degradation on MnMOx catalysts. Results obtained show agreement with previous experimental expectations, although some remarks are given since the initially presumed crystal structure of bimetallic oxide Mn1–xMxOy crystallites may still have an impact on theoretical predictions. The presented are, to the best of the authors’ knowledge, the first applications of the ReaxFF approach to the Mn–(Cu|Fe|Ni)–O–C–H interaction.

CuFe2O4 supported on montmorillonite to activate peroxymonosulfate for efficient ofloxacin degradation

Copper ferrite embedded in montmorillonite (CuFe2O4-montmorillonite, CF-Mt) was designed and employed as a composite catalyst for peroxymonosulfate (PMS) activation to degrade ofloxacin (OFL). CuFe2O4 characterization confirmed that this compound successfully dispersed on the surface of the montmorillonite. CF-Mt loaded with 40% CuFe2O4 (0.4CF-Mt) possessed favorable magnetic properties, excellent pore structure, and abundant catalytic sites, obtaining the highest OFL degradation efficiency (85.2%) in the presence of PMS compared to other CF-Mt composites with different CuFe2O4 loads. Influencing parameters including catalyst dosage, PMS concentration, initial pH, and co-existing anions were also investigated. High catalyst dosage and PMS concentrations were found to favor OFL degradation. The optimum pH in the 0.4CF-Mt/PMS system for OFL removal was 6.8 (neutral pH). Additionally, Cl− promoted OFL degradation performance, whereas H2PO4− and HCO3− had the opposite effect. Radical quenching experiments and electron paramagnetic resonance demonstrated that the OFL degradation in the 0.4CF-Mt/PMS system was largely attributed to free radical pathways dominated by SO4·- and ·OH. OFL mineralization increased with reaction time, finally reaching a mineralization rate of 54.8%. Furthermore, 0.4CF-Mt maintained excellent catalytic activity after repeated use. Taken together, this study provides a basis for the development of strategies to design bimetallic oxide catalysts for the efficient treatment of antibiotic-contaminated wastewater with PMS.

Syngas production employing nickel on alumina‐magnesia supported catalyst via dry methane reforming

AbstractNickel supported on alumina‐magnesia bimetallic oxide support (Ni/Al2O3‐MgO) nano‐catalysts were prepared by the co‐precipitation followed by impregnation (two steps) method separately and tested for the dry methane reforming. The optimum bimetallic oxide catalyst support ratio (i. e., alumina: magnesia) is tested and it has been found that alumina:magnesia ratio of 1 : 2 showed the most stable results. The effect of nickel loading has been studied by impregnating the bimetallic oxide support with nickel as 10 wt.%, 12 wt.%, 14 wt.%, and 16 wt.%. It has been found that the catalyst containing 12 wt.% nickel showed the best activity in terms of methane (CH4) and carbon dioxide (CO2) percentage conversions, syngas (H2:CO) ratio, lowest coke formation and stability for dry methane reforming at 800 °C, 1 atm and methane: carbon dioxide ratio of unity. The Brunauer‐Emmett‐Teller surface area and pore size analysis of fresh catalyst has been carried out. The x‐ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive x‐ray and elemental mapping analysis for fresh and spent catalysts has been obtained confirming the coke formation during the reaction.

Intensification of the steam stimulation process using bimetallic oxide catalysts of MFe2O4 (M\u2009=\u2009Cu, Co, Ni) for in-situ upgrading and recovery of heavy oil

In this study, bimetallic catalysts based on transition metals CuFe2O4, CoFe2O4 and NiFe2O4 are proposed for catalyzing aquathermolysis reaction during steam-based EOR method to improve in-situ heavy oil upgrading. All upgrading experiments were carried out under a nitrogen atmosphere for 24 h in a 300-ml batch Parr reactor at 250 and 300 °C under high pressure 35 and 75 bar, respectively. To evaluate the catalytic performance of the bimetallic catalysts used, comprehensive studies of changes in the physical and chemical properties of the improved oils, including the viscosity, elemental composition and SARA fractions of oils before and after upgrading processes were used. Furthermore, individual SARA fractions were characterized in detail by Gas Chromatography (GC), High-Performance Liquid Chromatography (HPLC) and Carbon-13 Nuclear Magnetic Resonance (13C NMR), respectively. The results showed that bimetallic catalysts have high catalytic performance at 300 °C for the upgrading of heavy crude oil in viscosity reduction, increasing the amount of saturates (especially alkanes with low carbon number) as a result of thermal decompositions of high molecular weight compounds like resin and asphaltenes leading to their increasing. Furthermore, the upgrading performance is reflected in the improvement of the H/C ratio, the removal of sulfur and nitrogen through desulfurization and denitrogenation procedures, and the reduction in polyaromatic content, etc. CoFe2O4 gives the best performance. Generally, it can be concluded that, used bimetallic based catalysts can be considered as promising and potential additives improving in-situ upgrading and thermal conversion the heavy oils.

Focused Plasma- and Pure Water-Enabled, Electrode-Emerged Nanointerfaced NiCo Hydroxide-Oxide for Robust Overall Water Splitting.

Bimetallic, bifunctional electrocatalysts capable of driving both oxygen (OER) and hydrogen (HER) evolution half-reactions on both electrodes in commercial water electrolysis cells are among the most promising materials systems for clean hydrogen energy generation. However, insufficient hydrogen and oxygen production activity at industry-relevant current densities and long-term catalyst stability on the electrode surface prevent this approach from industrial translation. This work resolves these challenges by advancing the promising, yet far-from-successful attempts to sprout bimetallic electrocatalytic nanostructures directly from electrode frames. For the first time, we utilize magnetic-field-focused, atmospheric-pressure plasma jets in oxygen-argon gas mixtures to successfully induce the nanointerfaced bimetallic NiCo hydroxide and oxide catalyst phases. After a simple hydrothermal treatment in pure water, NiCo bimetallic hydroxide nanosheets are densely covered with strongly bonded bimetallic NiCo oxide nanoparticles which ensure high catalytic activity evidenced by the low overpotentials for both HER and OER for delivering a current density of 100 mA cm-2 (j100) of only 306 and 484 mV, respectively. The electrode-emerged nanointerfaced NiCo hydroxide-oxide bimetallic system (NiCo2O4-NiCo(OH)x) shows an ultrastable electrocatalytic performance under a high current density of j200, which only decays 5.8% and 6.3% for HER and OER processes within 100 h. The competitive H2 and O2 production rates are about 1.27 and 0.69 mmol h-1 cm-2 (near to 2:1, under j10 conditions), meeting a nearly 100% Faradaic efficiency. Furthermore, the theory calculation indicates that the Ni and Co sites of NiCo2O4-NiCo(OH)x are the catalytic centers for the HER process. Our new plasma-enabled approach for the controlled production of bimetallic hydroxide-oxide active nanointerfaced systems is generic and is potentially suitable for diverse materials systems and applications well beyond electrocatalysis.

Rational design of oligomeric MoO3 in SnO2 lattices for selective hydrodeoxygenation of lignin derivatives into monophenols

Novel Mo-Sn bimetallic oxide catalysts with highly dispersed oligomeric MoO3 in SnO2 lattices, which were synthesized by the co-precipitation method and pretreated by anhydrous ethanol, were first employed in the hydrodeoxygenation of various lignin derivatives to produce monophenols with high activity and selectivity. In comparison with the pure α-MoO3 and the previous reported catalysts, the α-2Mo1Sn exhibited superior activity in the hydrodeoxygenation of guaiacol, with full conversion and 92.5% phenol yield at 300 °C under 4 MPa initial H2 pressure in n-hexane for 4 h. According to comprehensive characterizations and catalytic measurements, the excellent performance of α-2Mo1Sn was ascribed to the formation of abundant Sn-O-Mo-OV interfacial sites, which possessed strong Mo-Sn interaction with enhanced surface area, electron-donating group binding ability, Lewis acidity, and redox ability. It was demonstrated that over the present α-2Mo1Sn catalyst system, the Sn-O-Mo-OV interfacial sites could greatly facilitate the adsorption and activation of Caromatic-OCH3 and Caromatic-CH3 bonds, and thus significantly promote the demethoxylation and demethylation reaction to produce phenol. This work figures out the rational design of MoO3-based catalyst and displays a clear potential for the selective hydrodeoxygenation of lignin derivatives into monophenols.

Selective Oxidation of Methane to Methanol over Ceria‐Zirconia Supported Mono and Bimetallic Transition Metal Oxide Catalysts

AbstractSeveral ceria‐zirconia supported mono and bi‐metallic transition metal oxide clusters containing Fe, Cu, and Ni are synthesized by dry impregnation. Through XRD, H2‐TPR, NH3‐TPD, pyridine adsorption followed by FTIR spectroscopy and XAS, the well‐dispersed nature of the transition metal oxide clusters is revealed, and the Lewis acidity of the catalysts is assessed. In‐situ FTIR spectroscopy is used to monitor the methane activation on catalyst surfaces. All catalysts activate methane at 250 °C forming methyl, alkyl, and methoxy species on the catalyst surface. By co‐feeding steam and oxygen together with methane, continuous direct oxidation of methane to methanol can be achieved, with the complete oxidation to CO2 as the other reaction path. Methoxy species are found to be a key intermediate for methanol production. Lowering the methane conversion improves the methanol selectivity. By extrapolation, it is estimated that methanol selectivity close to unity can be achieved below a threshold of methane conversion at about 0.002 %. The formation of CuO and NiO mixed metal oxides produces stronger Lewis acid sites and yields higher methanol selectivity.

ZSM-5-supported V-Cu bimetallic oxide catalyst for remarkable catalytic oxidation of toluene in coal-fired flue gas

A close-coupled catalytic oxidation module after the NH3-SCR section has been constructed that employs catalytic materials to achieve high-efficiency oxidation of toluene (a surrogate for VOCs stemming from coal combustion) during flue gas purification. The V-Cu bimetallic bifunctional catalyst supported on ZSM-5 zeolite (V-Cu/ZSM-5) not only efficiently removed VOCs but also tolerated to complex flue gas. The catalytic material that removed the toluene was easily fabricated via the impregnation method. Results showed that, compared with single metal-supported catalysts, the V-Cu/ZSM-5 catalyst exhibited enhanced performance. This superior performance was attributed to improved reducibility at lower temperatures, higher electron transfer efficiency, more abundant Oα species and lower C7H8 activation temperature. The material also exhibited excellent flue gas tolerance and COx selectivity. The suppression mechanism of VOCs oxidation under complex coal-fired flue gas has been elucidated for the first time. There was competitive adsorption between the toluene and NH3 and/or NO. SO2 in the flue gas would cause chemical poisoning of the catalyst. Finally, in-situ DRITFS studies gave insights on the reaction mechanism. In short, this work provides new ideas and strategies for removing VOCs from complex coal-fired flue gas.

Cobalt oxide promoted tin oxide catalysts for highly selective glycerol acetalization reaction

The excessive production of glycerol as a by-product in the biodiesel industry increased environmental problems due to issues related to storage and waste management. Therefore, the catalytic conversion of glycerol into value-added chemicals is of great interest. Using heterogeneous catalysis, we investigated the selective acetalization of glycerol to solketal (C6H12O3), an additive used in fuel production, using acetone in the presence of bimetallic oxide catalysts (Co3O4/SnO2). The catalytic materials were fully characterized using physical and chemical techniques such as nitrogen sorption (BET), power X-ray diffraction, (p-XRD), temperature-programmed desorption, (TPD-CO2 and TPD-NH3), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). An attempt to correlate the acidic sites to the catalyst activity was not successful. However, it is important to note that, the reaction gave conversions greater than 90% and maximum selectivity to the formation of the solketal. Optimum conditions were investigated and showed the most active catalyst to be Co3O4/SnO2 (75:25) with conversion above 90%. Catalyst stability evaluations showed that Co3O4/SnO2 (50:50) is very stable and can be recycled up to 6 catalytic cycles with minor catalyst loss.

Effects of Hydrothermal Aging on CO and NO Oxidation Activity over Monometallic and Bimetallic Pt-Pd Catalysts

By combining scanning transmission electron microscopy, CO chemisorption, and energy dispersive X-ray spectroscopy with CO and NO oxidation light-off measurements we investigated deactivation phenomena of Pt/Al2O3, Pd/Al2O3, and Pt-Pd/Al2O3 model diesel oxidation catalysts during stepwise hydrothermal aging. Aging induces significant particle sintering that results in a decline of the catalytic activity for all catalyst formulations. While the initial aging step caused the most pronounced deactivation and sintering due to Ostwald ripening, the deactivation rates decline during further aging and the catalyst stabilizes at a low level of activity. Most importantly, we observed pronounced morphological changes for the bimetallic catalyst sample: hydrothermal aging at 750 °C causes a stepwise transformation of the Pt-Pd alloy via core-shell structures into inhomogeneous agglomerates of palladium and platinum. Our study shines a light on the aging behavior of noble metal catalysts under industrially relevant conditions and particularly underscores the highly complex transformation of bimetallic Pt-Pd diesel oxidation catalysts during hydrothermal treatment.

Evolution mechanism of transition metal in NH3-SCR reaction over Mn-based bimetallic oxide catalysts: Structure-activity relationships

The unexpected phenomenon in which different transition metals (Co, Ni and Cu) presented significant variation of participation levels as the auxiliaries in Mn-based bimetallic oxide catalysts were reported here. It is found that the Co element more easily to form Mn enriched surface bimetallic oxides with Mn than Ni and Cu, resulting in Co-MnOx exhibited the best deNOx activity and SO2 tolerance, followed by Ni-MnOx and Cu-MnOx. The role of different transition metal and structure-activity relationships were systematically investigated by advanced techniques including Synchrotron XAFS and in situ DRIFTs analysis. The excellent activity of Co-MnOx was related to its unique Mn-enriched surface (Co2+)tet(Mn3+ Co3+)octO4 structure with Mn cations occupying the octahedral sites, which is superior to the Ni-MnOx and Cu-MnOx with Mn-lean surface. In addition, the reaction energy barrier of Co-MnOx is weakened due to the lower electron cloud density around the Mn atom as compared to Ni-MnOx and Cu-MnOx. Moreover, Co-MnOx benefiting from the rapid electron migration between Mn and Co, more active bidentate/bridged nitrates could react with adsorbed NH3 in faster reaction rates following the L-H mechanism.

Insight into the catalytic performance and reaction routes for toluene total oxidation over facilely prepared Mn-Cu bimetallic oxide catalysts

Developing facile preparation method to obtain the satisfied low-temperature catalytic performance of transitional metal oxide-based materials is still a challenge in deep degradation of VOCs. Here, a series of Mn-Cu bimetallic oxide catalysts were prepared by one-step hydrothermal-redox method for catalytic total oxidation of toluene. The CH3COOH concentration, Cu/Mn molar ratio and calcination temperature greatly affected the crystal structure, micromorphology and catalytic performance. Amongst, MnCu spinel structured catalyst exhibited excellent low-temperature catalytic activity, superior durability and water resistance in toluene total oxidation owing to its abundant surface adsorbed oxygen species, higher amount of Cu+ and Mn3+ and excellent low-temperature reducibility. The reaction rate of MnCu was 7.0 times higher than that of MnCu0.5 at 210 °C. The cyclic redox process with enough oxygen vacancy played a vital role in toluene oxidation. The deep oxidation of benzene was the key step in the toluene oxidation. Proton transfer reaction-mass spectrometry (PTR-MS) results revealed the reaction intermediates including benzaldehyde, benzene and phenol, which further decomposed to acetone, ethanol, acetic acid, ketone and acetaldehyde by ring opening before total mineralization. Therefore, PTR-MS provided a facile method to investigate the reaction mechanism of toluene oxidation.