Composite Oxide Catalysts Research Articles

Enhancing hydrogen storage properties of MgH2 via reaction-induced construction of Ti/Co/Mn-based multiphase catalytic system

The inherent kinetic limitations and high operating temperatures of magnesium hydride (MgH2) hinder its practical applications. Herein, we report the successful synthesis of a TiO2@MnCo2O4.5 composite transition metal oxide catalyst and investigate its effect on the hydrogen storage performance of MgH2. TiO2@MnCo2O4.5 exhibits exceptional catalytic activity in the hydrogen dissociation and recombination reactions of during absorption and desorption processes, reducing the dehydrogenation activation energy of MgH2 to 75.54 kJ/mol. Notably, the MgH2-6 wt% TiO2@MnCo2O4.5 system releases 6.04 wt% H2 within 30 min at 250 °C, and 4.98 wt% H2 within 120 min at 225 °C. Furthermore, it can absorb 5.08 wt% H2 within 3 min at 150 °C and achieve a hydrogen absorption capacity of 2.02 wt% within 30 min even at 30 °C. The reaction-induced decomposition and phase transformation of TiO2@MnCo2O4.5 create a multiphase, multi-site catalytic environment. The hydrogen storage system based on the coexistence of Mg6MnO8, Mn, Ti2O3, and CoO features abundant diffusion pathways and nucleation sites, playing a critical role in suppressing the energy barriers for MgH2 hydrogen absorption and desorption reactions. These findings provide a meaningful theoretical foundation for the microstructural optimization and performance regulation of Mg-based hydrogen storage materials.

Hydrogen Production from Ammonia Decomposition: A Mini-Review of Metal Oxide-Based Catalysts.

Efficient hydrogen storage and transportation are crucial for the sustainable development of human society. Ammonia, with a hydrogen storage density of up to 17.6 wt%, is considered an ideal energy carrier for large-scale hydrogen storage and has great potential for development and application in the "hydrogen economy". However, achieving ammonia decomposition to hydrogen under mild conditions is challenging, and therefore, the development of suitable catalysts is essential. Metal oxide-based catalysts are commonly used in the industry. This paper presents a comprehensive review of single and composite metal oxide catalysts for ammonia decomposition catalysis. The focus is on analyzing the conformational relationships and interactions between metal oxide carriers and active metal sites. The aim is to develop new and efficient metal oxide-based catalysts for large-scale green ammonia decomposition.

Enhanced catalytic transfer hydrogenation of biomass-based furfural into furfuryl alcohol over Co3O4-based mixed oxide catalysts from hydrotalcite

Catalytic furfural (FF) into high value-added furfuryl alcohol (FOL) is a very important biomass improvement process and remains a challenging task. Herein, a series of Co-based composite oxide (CoMgAl-LDO) catalysts with highly dispersed Co3O4-based spinel oxide nanoparticles were synthesized by the topological transformation of Co-based ternary layered hydroxides (CoMgAl-LDH) under calcination conditions and tested for catalytic transfer hydrogenation of FF to FOL using isopropanol (2-PrOH) as hydrogen donor. The CoMgAl-LDO, especially Co1.5Mg1.5Al1-LDO calcinated at 500 °C (Co1.5Mg1.5Al1-LDO-500) offered the outstanding catalytic performance for the catalytic transfer hydrogenation of FF to FOL (99.7 % FF conversion and 95.9 % FOL selectivity), which was attributed to effectively dispersed active sites, abundant acid-base sites and mesoporous structure. Additionally, the Co1.5Mg1.5Al1-LDO-500 catalyst manifested good stability with wider universality to other carbonyl compounds, making the catalytic system extremely economical and practical in various biomass hydrogenation processes.

Preparation of Nanosized Copper–Manganese Composite Oxides and Their Catalytic Performance in the Oxidation of Toluene

Nanosized Cu–Mn composite oxide catalysts were prepared from potassium permanganate, copper nitrate, n-butanol, and cetyltrimethylammonium bromide as a manganese source, copper source, reducing agent, and surfactant, respectively. The Cu[Formula: see text]–Mn sample possessed a small particle size (10–40[Formula: see text]nm) and a relatively high specific surface area ([Formula: see text]); its main components were Cu[Formula: see text]Mn[Formula: see text]O4 and Mn3O4. As a consequence, the Cu[Formula: see text]–Mn catalyst exhibited good catalytic activity in the oxidation of toluene. At a toluene concentration of 1000[Formula: see text]ppm and a space velocity of [Formula: see text], the [Formula: see text] and [Formula: see text] of the Cu[Formula: see text]–Mn catalyst toward toluene were 239[Formula: see text]C and 250[Formula: see text]C, respectively. Furthermore, even after 30[Formula: see text]h of operation at 275[Formula: see text]C, the conversion of toluene was 99% (at the space velocity of [Formula: see text]).

Solvent‐Free Efficient Hydrogenation of Levulinic Acid over Silicotungstic Acid Promoting the Activity of CuNiAl Catalysts: A Synergistic Effect

AbstractMulti‐metallic catalysts rely on the synergistic effect between metals to perform better catalytic effect in biomass hydrogenation experiments compared with mono‐metallic catalysts. A series of CuNiAl composite metal oxide catalysts promoted by silicotungstic acid (HSiW), which were prepared by co‐precipitation and impregnation methods, were characterized by powder X‐ray diffraction (XRD), N2‐physisorption, scanning electron microscope (SEM) and NH3 program temperature desorption (NH3‐TPD) and pyridine infrared adsorption (Py‐FTIR). Their catalytic performance was evaluated in the hydrogenation of levulinic acid (LA) to prepare γ‐valerolactone (GVL). The results showed that the addition of Cu could improve the hydrogenation activity of Ni, and the addition of HSiW could further increase the amount of acid sites in the catalysts. Both of them could enhance the conversion of LA to some extent. CuNiAl‐5SiW, the par excellence catalyst, relied on the synergistic interactions between metals as well as the Brønsted and Lewis acid active sites to show efficient hydrogenation performance. The CuNiAl‐5SiW catalyst demonstrated 96.9 % conversion of LA and more than 99 % selectivity to GVL under 2 hours of reaction time, 180 °C of reaction temperature, 3.0 MPa of initial hydrogen pressure and solvent‐free conditions.

Base-Free Oxidation of HMF to FDCA over Ru/Cu-Co-O·MgO under Aqueous Conditions.

The copper-cobalt metal oxide composite magnesium oxide catalyst loaded with Ru has achieved the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to the bio-based polyester monomer 2,5-furandicarboxylic acid (FDCA) under base-free conditions. Several Ru/Cu-Co-O·MgO catalysts were prepared, with Cu-Co-O being a combination of CuO and Co3O4. The catalyst's activity was boosted by the synergistic interaction between copper and cobalt, as well as an optimal copper-to-cobalt molar ratio. Optimal catalytic activity was observed in the Ru4/Cu1-Co1-O·MgO catalyst, loaded with 4 wt% Ru when copper-to-cobalt molar ratio of 1:1 and magnesium oxide compounding amount of 6 mmol were employed. The inclusion of MgO and the load of Ru not only expanded the specific surface area of the catalyst but also heightened its basicity. Additionally, the presence of loaded Ru improved the catalyst's reducibility at low temperatures. In aqueous solution under oxygen pressure, the conversion rate of HMF achieved 100%, and the yield of FDCA was 86.1%. After five reaction cycles, examining the catalyst and solution revealed that Ru nanoparticles resisted leaching or oxidation, and MgO exhibited only slight dissolution. The green separation of the product was achieved using semi-preparative liquid chromatography, selectively collecting the FDCA-containing solution by exploiting variations in interactions between solutes and the stationary/mobile phases. The subsequent steps involved rotary evaporation and drying, resulting in FDCA powder with a purity exceeding 99%. Notably, this approach eliminated the need to introduce concentrated hydrochloric acid into the system for FDCA separation, providing a novel method for synthesising powdered FDCA.

Constructing dual sulfite-mediated processes via inner-sphere complexation and photogenerated carrier modulation with Hematite/Fe2TiO5 heterojunction for ofloxacin degradation

Hitherto, various sulfite-based advanced oxidation processes have emerged with particular vantages of low cost and potential for efficient contaminant degradation, which still requires increasing strategies for addressing its drawback. To achieve system-neutral feasibility and overcome the limitations, a metal oxide composite catalyst Hematite/Fe2TiO5 integrated with S-scheme heterojunction was constructed for ofloxacin degradation under S(IV)-visible light conditions. Impressively, the as-built system manifested significant promotion on substrate removal (more than four times the original Fe2TiO5), which indicated the accelerated inner-sphere interactions between catalyst and S(IV) with beneficial Vis contributed primarily to the degradation, demonstrating the dual sulfite-mediated effective pathway through modulated photogenerated carriers and oxy-sulfur radical chain reactions. Additionally, the interfacial enhancement by the heterojunction structure was further investigated by First-principles computation, which confirmed the mechanism of facilitated electron-hole pair separation. Overall, this work reveals the critical mechanism of Vis-induced S(IV)-AOP and provides constructive perspectives to address the limitations of conventional processes.

Laser-Induced Pd-PdO/rGO Catalysts for Enhanced Electrocatalytic Conversion of Nitrate into Ammonia.

Electrochemical reduction of nitrate to ammonia (eNO3RR) is proposed as a sustainable solution for high-rate ammonia synthesis under ambient conditions. The complex, multistep eNO3RR mechanism necessitates the use of a catalyst for the complete conversion of nitrate to ammonia. Our research focuses on developing a novel Pd-PdO doped in a reduced graphene oxide (rGO) composite catalyst synthesized via a laser-assisted one-step technique. This catalyst demonstrates dual functionality: palladium (Pd) boosts hydrogen adsorption, while its oxide (PdO) demonstrates considerable nitrogen adsorption affinity and exhibits a maximum ammonia yield of 5456.4 ± 453.4 μg/h/cm2 at -0.6 V vs reversible hydrogen electrode (RHE), with significant yields for nitrite and hydroxylamine under ambient conditions in a nitrate-containing alkaline electrolyte. At a lower potential of -0.1 V, the catalyst exhibited a minimal hydrogen evolution reaction of 3.1 ± 2.2% while achieving high ammonia selectivity (74.9 ± 4.4%), with the balance for nitrite and hydroxylamine. Additionally, the catalyst's stability and activity can be regenerated through the electrooxidation of Pd.

Resourcification of CO2 to high-value-added glycerol carbonate by ZnAlCe composite oxides with frustrated Lewis pairs

Zinc-aluminum-cerium composite oxide (ZnAlCe) catalysts were prepared by co-precipitation to catalyze the direct synthesis of glycerol carbonate (GC) from carbon dioxide (CO2) and glycerol. The characterization results showed that the lattice oxygen served as Lewis basic centers and Ce4+ served as Lewis acidic centers on Zn4AlCe catalyst, and frustrated Lewis pairs (FLPs) were formed due to the steric hindrance in the catalyst structure. CO2 was easily activated by FLPs because the acidic and basic centers of FLPs bound to the oxygen and carbon atoms of CO2, respectively. The experimental results indicated that Zn4AlCe catalyst presented excellent catalytic performance with good thermal stability and strong regeneration ability. Under the reaction conditions of 0.115 g catalyst, 12 h, 170 °C, 4.5 MPaCO2 and 5 mL acetonitrile dosage, the GC yield and selectivity were 28.9 % and 51.0 %, respectively. The GC yield is relatively high among similar catalysts reported so far, which lays the foundation for future industrial considerations.

Study on the Catalytic Activity Modification of Pr and Nd Doped Ce0.7Zr0.3O2 Catalysts for Simultaneous Removal of PM and NOX

Cerium-zirconium composite oxides (Ce0.7Zr0.3O2) have a remarkable effect on catalytic removal of carbon particles (PM) and nitrogen oxides (NOX) emitted from diesel engine, in order to further improve the thermal stability, oxygen storage capacity and low temperature catalytic REDOX performance of cerium zirconium composite oxides (Ce0.7Zr0.3O2), a small amount of Pr and Nd rare earth elements are doped to improve the catalytic activity of cerium zirconium composite oxides. In this paper, the composite oxide of Pr6O11–Nd2O3–CeO2–ZrO2 is prepared by unsteady co-precipitation method, and the physicochemical properties of the composite oxide catalyst are analyzed by BET, SEM, XRD and ICP. The gas adsorption capacity and catalytic activity of composite oxide catalysts are measured by temperature programmed reaction technology (TPR). The results show that the composite oxide of Pr0.05Nd0.05Ce0.6Zr0.3O2 prepared by using rare earth elements Pr and Nd inhibits the growth process of grain, refining the grain, and improving the sintering phenomenon at high temperature. The addition of Pr and Nd causes lattice defects, increases the number of oxygen vacancies, and improves the mobility of lattice oxygen, namely promotes oxide oxygen storage property, gas adsorption and catalytic oxidation reduction ability. After modification, Pr0.05Nd0.05Ce0.6Zr0.3O2 has good resistance to high temperature aging performance, prolongs the service life, reduces the PM lowest ignition temperature and minimum catalytic activity temperature of nitrogen oxide, and promotes the NOX reduction rate. For Pr0.05Nd0.05Ce0.6Zr0.3O2, the lowest ignition temperature of PM is about 150 °C, and the lowest catalytic activity temperature of NO is about 130 °C. The maximum CO2 production rate is 68.3%, and the maximum NO reduction rate is 45%.

Advances in CO-tolerant anode catalysts for proton exchange membrane fuel cells

Pt-based catalysts are often used in a proton exchange membrane fuel cell due to their high activities to oxygen reduction and hydrogen oxidation reaction. However, these catalysts are easily poisoned by CO, resulting in a significant reduction of fuel cell performance. The use of CO-tolerant catalysts can effectively solve this problem. The CO poisoning mechanism and anti-poisoning strategies were briefly discussed in this article. It mainly focused on the research progress on CO-tolerant catalysts in three aspects: Pt alloy catalysts, metal oxide composite catalysts, and blocking layer covered catalysts. The advantages and limitations of various catalysts in recent years were also discussed. Creating a porous blocking layer covered on the surface of the catalyst can effectively enhance the CO-tolerance of the catalysts which could be a promising approach for developing anti-poison catalysts other than CO-tolerance. Finally, the prospects for future development of CO-tolerant fuel cell catalysts were described.

Low temperature activation of methane to hydrogen depending on tailored electron transfer over Ni–Cr composite oxide

Current industrial use of methane depends mainly on high-temperature conversion, resulting in high energy consumption and catalyst sintering inactivation. In this paper, metal oxide catalysts with different Ni/Cr ratios were obtained by the sol-gel method for the methane activation reaction. The structure-property relationships of the catalysts were investigated by XRD, XPS, H2-TPR, TG, N2 adsorption-desorption, and CV, focusing on the interaction between Ni–Cr in the composite oxide catalysts. The results showed that Ni0–NiCrO3/Cr2O3 structure was formed after the Ni–Cr oxides underwent the reduction and calcination process, which provided a structural support for electron transfer between the two metals. The least prone to sintering nickel metal particles and the highest content of high-valent chromium ions were present in Ni1Cr2. XPS confirmed that this counterpart acts as the donor and acceptor for electron transfer in the catalysts, accelerating oxidation-reduction reaction over the catalyst. The catalyst exhibited the most excellent conversion and product selectivity in the methane activation reaction.

New method for the preparation of hierarchical nanotube K0.3xMnxCe1-xOδ catalysts and their excellent catalytic performance for soot combustion

A series of nanofibrous K-Mn-Ce composite oxide catalysts were prepared via a centrifugal spinning method for the first time, and their physicochemical properties were studied. The prepared K0.3xMnxCe1-xOδ metal oxide catalyst, which is a composite of CeO2 and cryptopotassium manganese-type K2-xMn8O16, exhibits a hierarchical nanotube structure with uniform nanoneedles on its surface. During the process of soot oxidation, CeO2 utilizes its unique oxygen storage and release capacity to supply oxygen species. Simultaneously, the excellent redox properties of K2-xMn8O16 effectively promote valence cycling of the active components and produce more active oxygen species. This synergistic effect effectively enhances the intrinsic activity of the catalysts. Among the prepared catalysts, K0.15Mn0.5Ce0.5Oδ exhibits the highest catalytic performance, with 10% (T10), 50% (T50), and 90% (T90) soot conversion temperatures of 267 °C, 309 °C, and 338 °C, respectively, and shows good stability and water and sulfur resistance. Based on their simple preparation, low cost, and good catalytic performance, K0.3xMnxCe1-xOδ composite metal oxide catalysts have good potential in catalytic soot combustion applications.

Investigation of Co–Mn–Ce Ternary Composite Oxide Catalyst for Low-Temperature Selective Catalytic Reduction of NOx with NH3

Investigation of Co–Mn–Ce Ternary Composite Oxide Catalyst for Low-Temperature Selective Catalytic Reduction of NOx with NH3

Effect of sulfation on the catalytic performance of Mn-Co composite oxide catalyst for the selective catalytic reduction of NOx by NH3

The effect of sulfation on the catalytic performance of Mn-Co composite oxide catalyst for the selective catalytic reduction of NOx by NH3 (NH3-SCR) has been investigated. Different concentrations of SO2 have been used to sulfate Mn-Co composite oxide catalyst. The catalyst sulfated with 30 ppm SO2 showed the widest activity temperature window, over which 80% NOx conversion was obtained in the temperature range of 80–350 °C. The sulfation leads to the appropriate redox property of Mn-Co composite oxide, thus improving the N2 selectivity. Meanwhile, the sulfation contributes to the generation of more Brønsted acid sites, which is crucial for the enhanced activity. In situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS) demonstrated that the adsorbed NH3 species on both Lewis acid and Brønsted acid sites, monodentate nitrite, bidentate nitrate and cis-nitrite species are the reactive intermediates in the NH3-SCR reaction. This study provides an idea for the regulating the activity temperature window of NH3-SCR catalyst to adapt to its practical application.

Catalytic oxidation of dichloromethane over W-Nb composite oxide catalysts modified by Co: The influence of redox ability and acidity

Catalytic oxidation of highly toxic chlorinated volatile organic compounds often places high demands on the anti-poisoning ability of the catalysts. Here, Co/WNb catalysts with different Co loadings were prepared for the catalytic oxidation of dichloromethane (DCM). Notably, the interaction between the active components and the carriers resulted in a high Co2+/Co3+ ratio on the catalyst surface, which facilitated the generation of oxygen vacancies (Ov) and enhanced the redox properties of the catalyst. Furthermore, the WNb carrier offered ample surface acidic sites, bolstering the catalyst's resilience against chlorine poisoning. The study revealed that achieving a more balanced combination of redox properties and acidity was beneficial for enhancing the catalytic degradation efficiency of DCM. 3% Co/WNb exhibited the best catalytic activity (T90 = 269 °C). The catalyst also exhibited excellent stability and outstanding water resistance. Potential reaction routes for the catalytic oxidation of DCM were explored using in-situ IR spectra analysis. This study offers novel insights for the development of efficient, stable, and environmentally friendly catalysts for DCM degradation.

Research on Alternative Pt-based or Non-Pt catalysts for Solid Oxide Fuel Cells

Nowadays, heavy environmental and economic pressure from energy consumption is increasingly evident, and the research and application of new batteries is an effective strategy to solve above problems. Fuel cell is a chemical device that produces electricity directly from chemical energy. It has attracted much attention due to its lightweight device, simple mechanism, and clean energy. In the operation of fuel cells, the efficiency and stability of cells are determined by the ability of catalyst in redox reactions. However, pure platinum or platinum-based catalysts commonly applicated in solid oxide fuel cells are normally expensive and not renewable. Therefore, it is particularly important to develop alternative Pt-based catalysts or non-Pt catalysts. In this paper, several alternative low-platinum or non-platinum catalysts are systematically investigated, and novel platinum-based and non-platinum multi-metal composite oxide catalysts are found to have higher catalytic activity and economic feasibility compared with pure platinum catalysts. The popularity of these new catalysts can effectively address the scarcity of resources and energy.

A Unique Amorphous Porous BiSbOx Nanotube with Abundant Unsaturated Sb‐Stabilized BiO8−x Sites for Efficient CO2 Electroreduction in a Wide Potential Window

AbstractThe CO2 electroreduction reaction using sustainable electricity emerges as a viable strategy to produce high‐value‐added and profitable chemicals. The achievement of superior activity at a lower overpotential and higher selectivity in a wide potential window is vitally important for large‐scale industrial applications. Herein, a carbon‐composite amorphous porous BiSbOx nanotube with abundant unsaturated sites is reported to boost the conversion of CO2 to formate, exhibiting a formate selectivity of >90% in an extremely broad range of potentials from −0.5 to −1.4 V versus reversible hydrogen electrode (RHE) and a maximal energy conversion efficiency of 77.1%. Importantly, pure formic acid solution is directly obtained in a solid‐electrolyte cell for industrial‐scale applications. The porous tubular structure can expose more catalytic active sites, accelerate the mass transfer, and show fast surface charge transfer. Moreover, the unique coordination‐unsaturated Sb‐stabilized BiO8−x site can not only enhance the adsorption and activation of CO2 but also reasonably balance the stabilization and hydrogenation of *OCHO intermediate, thus leading to its obviously higher catalytic performance. As a result, a novel amorphous porous BiSbOx nanotube is successfully designed for efficient CO2 electroreduction, which may shed new light on developing many more amorphous composite metal oxide catalysts for conversion of inert small molecules.

Promoted O2 resistant performance of CO selective catalytic reduction via carbon-coated CuCoAl mixed metal oxides

Selective removal of nitrogen oxides (CO-SCR) by CO as a reducing agent has attracted wide attention. However, it has been found that the presence of O2 in the CO+NO system can poison the catalyst, which affected the application of CO-SCR technology. In this paper, CuCoAl composite metal oxide catalysts without carbon source and carbon coating were prepared by coprecipitation method, and the denitrification activity and oxidation resistance of CO-SCR catalyst were studied. It was found that CuCoAlOx@C catalyst prepared by glucose doping had excellent antioxidant properties. When 5 vol% O2 was introduced into the reaction system, the NO conversion rate of CuCoAlOx catalyst dropped sharply, while the NO conversion rate of CuCoAlOx@C catalyst remained above 85%. First of all, glucose can not only provide carbon coating, bringing a high specific surface area (121.8 m2/g), which in turn allows the exposure of active sites and enhances the catalytic activity of the catalyst. Secondly, carbon cladding can activate O2 to O* (Oxygen Free Radical), followed by partial oxidation of CO to CO2 through the MvK mechanism, thus avoiding the direct reaction of CO with O2 to form CO2 in the presence of catalyst, and to a certain extent promoting the regeneration of oxygen vacancies and the reaction of NO+CO to enhance the antioxidant performance. Thirdly, this study found that carbon-coated composite metal oxides provide a new way to improve the anti-O2 poisoning performance of CO-SCR catalysts.

Screening Spinel Oxide Supports for RuO2 to Boost Bifunctional Electrocatalysts for Advanced Zn–Air Batteries

AbstractThe compositing strategy offers great potential in designing bifunctional oxygen electrocatalysts for Zn–air batteries. Recent reports reveal that the couple of RuO2, serving as a benchmark oxygen evolution reaction (OER) catalyst, with other oxygen reduction reaction (ORR) catalysts is a wise choice to build highly efficient bifunctional electrocatalysts. However, the design criteria for ORR and OER activities of RuO2‐based composite catalysts are still unclear. Herein, a series of transition metal (Fe, Co, Mn, and Ni)‐doped spinel oxides are designed to support RuO2 nanorods for exploring the reaction mechanism. Through advanced technology, it is considered that increasing the content and binding energy of Co3+ and enhancing the oxidation state of Ru4+ is an efficient strategy to promote ORR and OER activities for RuO2/Co‐based spinel oxide composite catalysts. It is found that coupling Mn‐doping Co3O4 (CMO) supports with RuO2 can induce the highest catalytic activities in ORR/OER and excellent performance in rechargeable Zn–air batteries. Operando electrochemical impedance spectroscopy and theoretical calculation further prove the synergistic effect between RuO2 and CMO supports originated from the oxygen overflow to overcome the large barrier for oxygen desorption on RuO2 during OER and oxygen adsorption on CMO supports during ORR.