Oxide Catalysts Research Articles

Effect of carbon-supported rare earth oxide catalysts on the microstructure, hydrogen storage kinetics, and thermodynamics of Mg-La-Ni alloys

In this study, using an improved chemical vapor deposition carbonization method, Eu2O3@C, PrO1.83@C, and La2O3@C composite catalysts were successfully synthesized and incorporated into Mg96La3Ni alloys via ball milling. These catalysts significantly enhanced the hydrogen storage properties of the alloys, particularly in terms of hydrogenation kinetics. Among the catalysts, PrO1.83@C demonstrated the most significant improvement. At 360 °C, the Mg96La3Ni alloy containing 3 wt% PrO1.83@C achieved a 75.1 % hydrogenation saturation ratio within 2 min and released 3 wt% H2 in 3.1 min. While the catalysts did not significantly alter the alloy's thermodynamics, they substantially reduced the dehydrogenation activation energy. The addition of 3 wt% Eu2O3@C, PrO1.83@C, and La2O3@C lowered the activation energy barriers to 116.6, 101.4, and 114.8 kJ/mol H2, respectively, compared to 121.67 kJ/mol H2 for the pristine Mg96La3Ni alloy. This enhancement is attributed to the synergistic effects of the "hydrogen pump" mechanism of rare earth hydrides and the abundant active sites provided by the carbon component, which collectively promote faster hydrogen diffusion and nucleation reactions.

Mechanism study on the influence of surface properties on the synthesis of dimethyl carbonate from CO2 and methanol over ceria catalysts

The direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol has attracted much attention as an environmentally benign and alternative route for conventional routes. Herein, a series of cerium oxide catalysts with various textural features and surface properties were prepared by the one-pot synthesis method for the direct DMC synthesis from CO2 and methanol, and the structure-performance relationship was investigated in detail. Characterization results revealed that both of surface acid-base properties and the oxygen vacancies contents decreased with the rising crystallinity at increasingly higher calcination temperature accompanied by an unexpectedly volcano-shaped trend of DMC yield observed on the catalysts. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies indicated that the adsorption rate of methanol is slower than that of CO2 and the methanol activation state largely influences the formation of key intermediate. Although the enhanced surface acidity-basicity and oxygen vacancies brought by low-temperature calcination could facilitate the activation of CO2, the presence of excess strongly basic sites on low-crystallinity sample was detrimental to DMC synthesis due to the preferred formation of unreactive mono/polydentate carbonates as well as the further impediment of methanol activation. Moreover, with the use of 2-cyanopyridine as a dehydration reagent, the DMC synthesis was found to be both influenced by the promotion from the rapid in situ removal of water and the inhibition from the competitive adsorption of hydration products on the same active sites.

Efficient photoreforming of plastic waste using a high-entropy oxide catalyst

Simultaneous catalytic hydrogen (H2) production and plastic waste degradation under light, known as photoreforming, is a novel approach to green fuel production and efficient waste management. Here, we use a high-entropy oxide (HEO), a new family of catalysts with five or more principal cations in their structure, for plastic degradation and simultaneous H2 production. The HEO shows higher activity than that of P25 TiO2, a benchmark photocatalyst, for the degradation of polyethylene terephthalate (PET) plastics in water. Several valuable products are produced by photoreforming of PET bottles and microplastics including H2, terephthalate, ethylene glycol and formic acid. The high activity is attributed to the diverse existence of several cations in the HEO lattice, lattice defects, and appropriate charge carrier lifetime. These findings suggest that HEOs possess high potential as new catalysts for concurrent plastic waste conversion and clean H2 production.

Exploring the atomic-scale dynamics of Fe3O4(001) at catalytically relevant temperatures using FastSTM

Surfaces and interfaces of functional nanoscale materials are typically highly dynamic when employed at elevated temperatures. Both, lateral surface and vertical bulk exchange diffusion processes set in, which can be relevant for applications such as heterogeneous catalysis. Time-resolved scanning tunneling microscopy (STM) is being pushed to ever faster measurement modes to follow such dynamic phenomena in situ. Here, we present FastSTM movies monitoring a range of atomic-scale dynamics of a prototypical reducible oxide catalyst support, Fe3O4(001), at elevated temperatures. Antiphase domain boundaries between two domains of the reconstructed surface exhibit local mobility from around 350 K, while Fe-rich point defects, in a stable equilibrium with the bulk, appear to diffuse in a peculiar zigzag pattern above 500 K. Finally, exploiting the diffusivity of Fe interstitials, we follow the propagation of step edges in the topmost atomic layer of the Fe3O4(001) surface in an oxygen atmosphere.

Improved Catalytic Partial Oxidation of Methane via Lattice Oxygen Modification on Supported Copper Oxide Catalyst System

AbstractThirteen kinds of supported copper oxide catalysts (Cu/MOx, MOx: La2O3, Al2O3, SiO2, TiO2, CeO2, ZrO2, SnO2, SrCO3, BaCO3, Ta2O5, Nb2O5, WO3, and MoO3), which form Cu−O−M sites at the interface between CuOx and MOx or within the complex oxides (CuMOx), were tested for CH4 partial oxidation to find out catalytically active Cu−O−M combinations for production of CH3OH and HCHO. Among the thirteen Cu/MOx tested, Cu/WO3 exhibited the highest total yield of CH3OH and HCHO in a CH4‐O2‐H2O flow reaction at 400 °C. The structural and property analysis of Cu/WO3 revealed the formation of CuWO4, of which the lattice oxygen is active for the partial oxidation of CH4.

Unveiling the Synthesis of a Zirconium-Substituted Copper Bismuth Oxide Catalyst for Visible Light-Responsive Photocatalytic Degradation of Persistent Organic Dye

Unveiling the Synthesis of a Zirconium-Substituted Copper Bismuth Oxide Catalyst for Visible Light-Responsive Photocatalytic Degradation of Persistent Organic Dye

Engineering Active Sites of Metal/Metal Oxide Catalysts by Oxide Ligand Overlayers.

Engineering sites of supported metal catalysts is essential to enhancing activity and selectivity. Such enhancement is typically achieved by particle size modification, surface alloying, or attaching molecular ligands. Yet, control strategies for complex, multifunctional molecules and catalysts, where selectivity is crucial, are lacking. Here, we demonstrate that submonolayer WOx with tunable coverage preferentially decorates well-coordinated Pt terrace sites as a stable ligand. By combining experimental kinetics with probe molecules, in situ spectroscopies, and first-principles modeling, we show that the WOx coverage on Pt modifies the metal-to-acid site balance while retaining the acid strength intact and results in optimal reactivity for metal-acid catalyzed reactions at a specific metal, size, and support-dependent WOx coverage. The oxide can also alter the reactant adsorption mode, reversing selectivity and pathways from terrace- to step-dominated, as evidenced in furfural decarbonylation and hydrogenation. The insights open avenues for improving metal/metal oxide catalysts beyond the specific system.

Engineering Active Sites of Metal/Metal Oxide Catalysts by Oxide Ligand Overlayers

Engineering sites of supported metal catalysts is essential to enhancing activity and selectivity. Such enhancement is typically achieved by particle size modification, surface alloying, or attaching molecular ligands. Yet, control strategies for complex, multifunctional molecules and catalysts, where selectivity is crucial, are lacking. Here, we demonstrate that submonolayer WOx with tunable coverage preferentially decorates well‐coordinated Pt terrace sites as a stable ligand. By combining experimental kinetics with probe molecules, in situ spectroscopies, and first‐principles modeling, we show that the WOx coverage on Pt modifies the metal‐to‐acid site balance while retaining the acid strength intact and results in optimal reactivity for metal‐acid catalyzed reactions at a specific metal, size, and support‐dependent WOx coverage. The oxide can also alter the reactant adsorption mode, reversing selectivity and pathways from terrace‐ to step‐dominated, as evidenced in furfural decarbonylation and hydrogenation. The insights open avenues for improving metal/metal oxide catalysts beyond the specific system.

Open frame-like Co-Fe oxides superstructures for highly efficient cross-dehydrogenative coupling reaction of N-phenyltetrahydroisoquinoline under mild conditions

An open frame-like Co-Fe oxides catalyst has been successfully prepared using a time-controlled strategy. Benefiting from the unique open frame-like superstructure and synergistic bimetallic composition, this novel catalyst exhibits excellent catalytic activity (up to 91 % isolated yield) and substrate suitability for Cross-Dehydrogenative Coupling reaction (CDC) of N-phenyltetrahydroisoquinolines and nitroalkanes using oxygen as the oxidant under mild reaction conditions. And after several runs, the reused catalyst still maintains great stability. This may attributed to the interaction between Fe and Co. In addition, through the radical trapping experiments, we found that O2·− species play an important role in the cross-dehydrogenative coupling reaction.

Effective periodate activation by the ball-milled bimetallic zero-valent iron/manganese oxides catalyst for sulfamethoxazole degradation

Developing a green and efficient catalyst for oxidant activation to tackle refractory organics pollution is challenging for water purification. In this study, we prepared a zero-valent iron-based bimetallic catalyst (ZVI/Mn3O4) for periodate (PI) activation using a simple and convenient ball-milling method. Electrochemical characterization and theoretical calculations confirm that the synergy between Fe and Mn enables the ZVI/Mn3O4 system to exhibit higher electron transfer efficiency compared to its individual components. Consequently, the ZVI/Mn3O4/PI system demonstrated enhanced PI activation and significantly improved removal of sulfamethoxazole (SMX), with reaction rates being 18.61 to 57.01 times higher than the comparison systems. The influence of various physicochemical parameters on SMX removal was investigated, confirming the wide tolerance ZVI/Mn3O4/PI system towards multiple aqueous matrices. Furthermore, the scalability of this system for industrial applications was validated through the preparation of larger batches of catalysts (4.21 g per batch) and testing in a custom-designed magnetic plate continuous-flow reactor. Quenching experiments and electron spin resonance tests confirmed that •O2– and 1O2 were the primary reactive species responsible for SMX degradation, with no toxic iodine byproducts detected, attributed to the carefully designed catalyst, which optimized the interaction between PI and the catalyst. Based on these findings, a potential catalytic mechanism and degradation pathway were proposed, highlighting ZVI's role as an electron pump to enhance Mn3O4's activation of PI. Additionally, toxicity assessments via prediction, zebrafish cultivation, wheat germination, and E. coli culture confirmed the excellent detoxification capability of ZVI/Mn3O4/PI system for SMX degradation. Overall, this work provides a new research paradigm for the convenient manufacture of ZVI-based catalysts and the development of advanced techniques for PI activation in water purification.

Trimetallic MOF–derived Fe–Mn–Sn oxide heterostructure enabling exceptional catalytic degradation of organic pollutants

Developing efficient and environmentally benign heterogeneous catalysts that activate peroxymonosulfate (PMS) for the degradation of persistent organic contaminants remains a challenge. Metal–organic frameworks (MOFs)–derived metal oxide catalysts in advanced oxidation processes (AOPs) have received considerable attention research fraternity. Herein, we report an innovative magnetic trimetallic MOF-derived Fe-Mn-Sn oxide heterostructure (FeMnO@Sn) with adjustable morphology, size and Sn content, prepared through an impregnation–calcination strategy. The formation of a novel magnetic Fe2O3/Fe3O4/Mn3O4 heterostructure induces the generation of abundant Fe2+ and Mn2+ sites on the FeMnO@Sn surface. Meanwhile, the introduction of SnO2 into the Fe2O3/Fe3O4/Mn3O4 heterostructure facilitates the cleavage of the OO bond in adsorbed PMS. The synergy among the different functionalities of each metal oxide plays a vital role in the swift and effective degradation of pollutants. In addition, the uniquely designed catalyst exhibits magnetic properties that facilitate easy recycling and repeated use, thereby meeting environmental protection requirements. Overall, this research highlights the design of heterogeneous catalysts for the effective activation of PMS and provides valuable insights for the advancement of future environmental catalysts.

Uncovering the synthesis of a visible light-driven manganese-doped copper bismuth oxide catalyst for enhanced degradation of dye: Insights into the factors affecting the degradation

In recent times, effluent pollution has had an exceptionally detrimental effect on aquatic life as well as human beings. The management of wastewater has emerged as a formidable undertaking for scientists owing to the existence of organic contaminants. Herein, we synthesized the manganese-doped copper bismuth oxide (Mn0.15Cu0.85Bi2O4) through hydrothermal method and employed them for successfully eliminating complex pollutants. The assessment of the visible light-induced photocatalytic efficacy of the catalyst was performed for the degradation of methyl violet (MV). MV had a degradation of 89.68% when CuBi2O4 was used. However, the degrading rate of the Mn0.15Cu0.85Bi2O4 escalated to 99.18% in 36 min. The rate constant exhibited a rise between 0.0627 and 0.1134 min−1, confirming the effectiveness of the Mn0.15Cu0.85Bi2O4. The effectiveness of the Mn0.15Cu0.85Bi2O4 is due to its superior surface area (51.97 m2/g), which arises from the integration of Mn-ions. Additionally, examining the impact of different reaction variables revealed a substantial correlation with the elimination of MV dye. The potential reason for the deterioration of MV could be attributed to the generation of •OH and O2•− radicals, which was confirmed by radical trapping experiments. The photostability of the generated Mn0.15Cu0.85Bi2O4 catalyst exhibited remarkable characteristics. Ultimately, this study presents a technique for creating effective catalysts for treating wastewater that is both economical and practical.

Mesostructured manganese oxides for efficient catalytic oxidation of CO, ethylene, and propylene at mild temperatures: Insight into the role of crystalline phases and physico-chemical properties

Removing pollutants for indoor air purification is a key point to ensure the health and well-being of people in confined environments. This work aims to provide new insight into the development of promising manganese oxide catalysts. The effects of different crystalline phases (MnO2 and Mn2O3) and the role of redox properties and structural defects were investigated to abate indoor pollutants at mild temperatures. These materials were extensively characterized through complementary techniques and catalytic tests were performed to oxidize 100 ppm of CO, ethylene, or propylene. The most promising catalyst was obtained through solution combustion synthesis, achieving total removal at 118, 222, and 172 °C, respectively, with the highest oxidation rate (2.41, 0.88, and 2.47 μmolg−1s−1) and lowest activation energy (50, 32, and 45 kJmol−1) for the three molecules. The synergy between crystalline phases enhanced the catalytic performance and their distribution in the structure was a crucial parameter affecting the number of structural defects.

Coupled Lattice‐Expanded Ni and MoO2 Array for Efficient Alkaline Hydrogen Evolution

AbstractTransition metal oxides have attracted much attention due to their good electrical conductivity, high chemical stability, and easy electronic structure modulation. However, it is still a great challenge to solve the problems of sluggish reaction kinetics and high overpotential in the alkaline hydrogen evolution reaction (HER) due to their poor intrinsic activity. Herein, a lattice‐expanded Ni‐decorated MoO2 array (Ni‐MoO2‐700) catalyst is prepared for the alkaline HER. Unlike most of the reported literature, the decoration of metal heteroatoms may lead to lattice expansion of the carrier catalyst. In contrast, lattice expansion of Ni is also achieved by adjusting the annealing temperature in this work. The Ni‐induced lattice‐expanding effect can not only modulate the electronic structure of the catalyst but also accelerate electron transfer during the reaction, thus increasing its intrinsic activity for the HER. As a result, Ni‐MoO2‐700 exhibits significantly enhanced catalytic activity with an overpotential of 74.9 mV at 10 mA cm−2 in 1.0 m KOH, which is far superior to that of most of the reported advanced Ni‐ and Mo‐based materials. This work provides deep intrinsic insight and a great opportunity to design efficient transition metal oxide catalysts for the alkaline HER.

Processes of Metal Oxides Catalyst on Conversion of Spent Coffee Grounds into Rich-Synthesis Gas by Gasification

Spent coffee grounds (SCGs), a waste product of the coffee industry, present a significant untapped resource for fuel production. This study aims to optimize the gasification of SCG using various metal catalysts (NiO, MnO2, Al2O3, and Fe2O3) to maximize syngas yield. SCG samples were gasified at different temperatures (800 °C, 900 °C, 1000 °C) and analyzed using Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TG-DTA), and Fourier Transform Infrared (FTIR) spectroscopy to evaluate catalyst performance and reaction mechanisms. The findings indicated that utilizing mixing techniques for physical contact to introduce catalysts led to a uniform distribution of catalyst particles throughout the sample. The decomposition rate of the gasification experiment after adding the catalyst was 24% faster than that of the pure SCGs. In the gasification experiment, the MnO2 catalyst showed the highest CO production, which was 71% higher than that of NiO under the same conditions. At this temperature, MnO2 generated around 171% more CO than at 800 °C, surpassing the yields observed with other catalysts. The study concludes that Mn emerged as the most promising catalyst, significantly improving both CO and CH4 yields. Selecting the appropriate metal catalyst and optimizing operational temperatures are crucial for enhancing the efficiency of SCG gasification.

Ruthenium catalyst processing and oxidation for scalable complementary metal-oxide-semiconductor-compatible metal-assisted chemical etch

Ruthenium catalyst processing and oxidation for scalable complementary metal-oxide-semiconductor-compatible metal-assisted chemical etch

Reducing noble metal content in water electrolysis catalysts: A study on high-entropy oxides

This study presents the development of high-entropy oxide (HEO) catalysts based on Iridium-Ruthenium oxides (IrRuOx) for the oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWEs). By incorporating 3d transition metals such as Fe, Co, and Ni, we achieved catalysts with enhanced performance and stability. Using density functional theory (DFT) calculations, we predicted that HEOs possess a more favorable electronic structure for catalytic reactions. The synthesized rutile-type HEO catalyst (RuIrFeCoNi)O2, created via a molten salt oxidation method, exhibited a low overpotential of 261 mV and excellent cycling stability, maintaining a stable voltage of 1.73 V at 1 A cm−2 over 100 hours of electrolysis. This innovative approach not only reduces noble metal content but also leverages multimetallic synergistic effects to optimize the catalytic performance and stability, offering a promising avenue for the industrial application of acidic water electrolysis in PEMWEs.

Viability of strontium carbonate-modified Co3O4 catalysts for chlorinated VOCs oxidation

A series of cobalt oxide catalysts modified with strontium carbonate (Sr:Co molar ratios 0.1–0.4) were prepared, characterised using various techniques (N2 physisorption, XRD, SEM, SEM-EDX, H2-TPR, O2-TPD, XPS) and kinetically evaluated in the gas-phase oxidation of vinyl chloride and 1,2-dichloroethane. Initially, the incorporation of strontium enhanced several physico-chemical properties, including increased surface area, reduced crystal size, and a higher amount of surface oxygen species, suggesting improved catalytic performance. However, the Sr-Co catalysts showed relatively poor catalytic stability, with an increase in chlorinated organic species as catalytic activity decreased. The used catalysts exhibited high concentrations of chlorine, particularly on the surface, along with a decrease in surface area and an increase in crystallite size. Additionally, a reduction in surface oxygen species, crucial for pollutant oxidation, was observed. Therefore, this catalytic chlorination, combined with the loss of textural and structural properties, were inferred to be closely related to catalysts deactivation.

Reduction and structural modification of MoOx/γ-Al2O3 catalysts through acetic acid treatment for green diesel production from corn distiller’s oil

Enabling new environmentally-friendly resources for fuels and platform chemicals is crucial to fulfill our future energy demands while enhancing circularity. Corn distiller’s Oil (CDO) − as a coproduct of the ethanol industry, serves as a sustainable supply of carbon that may be converted into energy, fuels and specialty chemicals. A current challenge in using renewable oxygenated feedstocks is the high amount of coking and catalyst fouling that occurs. This study examined the hydrothermal deoxygenation of CDO into green diesel using molybdenum oxide (MoOx) catalysts in a continuous process without using any external hydrogen. The possibility of reduction and developing oxygen-deficient surfaces on molybdenum oxide (MoOx) catalysts through acetic acid treatment or adding ceria (CeO2) was investigated in order to enhance the acidity of catalysts as well as catalytic activity and stability required for the production of green diesel from CDO. Results showed that the acidity of these catalysts as measured by NH3 temperature programmed desorption (NH3-TPD) had a strong correlation between the degree of deoxygenation and catalyst stability. Acetic acid treatment of the 7.5 wt% MoO3/γ-Al2O3 catalyst reduced MoO3 to MoO3-x, increased the Mo5+ species from 8.7 % to 22 %, created Mo4+ species and increased the catalyst surface acidity in the range of low to moderate strength by approximately 17 %. The use of acetic acid-treated molybdenum oxide (Hac-7.5 wt% MoO3/γ-Al2O3) catalyst enabled nearly complete (99.9 %) deoxygenation of CDO and heavy hydrocarbons cracking to produce diesel-like fuels. A moderate increase in catalyst surface acidity by acetic acid treatment also increased the selectivity of diesel-like fuel through hydrocracking of long-chain hydrocarbons. This low-cost modification step of catalyst improvement is promising for industrial application. However, cracking of hydrocarbons generated amorphous coke (no graphitic coke was observed) on the catalyst surface, which required periodic removal by controlled calcination of the catalyst in presence of air for further use.

Effective Screening of Metal Dopants for In2O3 Catalyst to Tune Catalytic Performance of CO2 Hydrogenation to Formic Acid

The metal doping is an effective strategy to adjust catalytic performance for indium oxide catalyst in CO2 hydrogenation. In current work, a series dopant, Co, Fe, Ni, Pd, Pt, Rh and Ru, are selected and examined in CO2 hydrogenation to formic acid by DFT based microkinetic simulation. It is found that substitutional doping is local effect which mainly promotes the reactivity of adjacent oxygen atoms. The calculations of both CO2 adsorption and hydrogen molecule dissociation certify the positive effects induced by doping, and the adsorption energy of CO2 has a linear relation with the transferred charges for all investigated catalysts which helps to explain the C‐O bond activation mechanism. Two pathways, Formate and Carboxyl, are investigated under same footing. It is noted that doping significantly reduces the hydrogenation barriers on two pathways compared with undoped surfaces. Moreover, the calculated TOF of formic acid formation is greatly increased on doped surfaces and Pt, Pd, Ru are identified as the most active dopants. In the end, it is concluded that reaction obeys Carboxyl mechanism and a valid descriptor of trans‐HCOOH* and H* formation energy is proposed for the screening of effective dopants.