Metal Oxide Catalysts Research Articles

Enhancing SO2 Resistance of Mn−Ce−Co Loaded Activated Carbon Catalysts for Low‐Temperature NH3‐SCR: Insight into the Effect of Citrate Addition

AbstractThe low‐temperature performance and ability to withstand SO2 poisoning of catalyst are crucial factors in evaluating the NH3‐SCR technology. In this study, honeycomb activated carbon loaded with Mn−Ce−Co catalysts was prepared using the citric acid complex impregnation method, simple impregnation and citric acid pre‐oxidation methods for low‐temperature NH3‐SCR. The synergistic effect of citric acid and ternary metals results in catalysts prepared by the citric acid complex impregnation method exhibiting excellent redox properties and a high abundance of acidic sites. By increasing catalyst acidity and introducing CeO2 sacrificial sites, the catalytic performance was improved, resulting in weaker adsorption capacity of the catalysts for SO2, enhancing SO2 tolerance. The catalyst demonstrated 100 % NOx removal at 160 °C which remained stable even after a 100 ppm SO2 pass for four hours. In addition, the catalyst showed good CO oxidation performance, with 78 % CO removal at 170 °C, which broadened the application scenario of the catalyst. This study highlights the denitrification effect of activated carbon supported Mn−Ce−Co ternary metal oxide catalysts and reveals the potential of multiple coupled approaches in improving the sulfur resistance of the catalysts.

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.

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.

Research Progress in Structure Evolution and Durability Modulation of Ir- and Ru-Based OER Catalysts under Acidic Conditions.

Green hydrogen energy, as one of the most promising energy carriers, plays a crucial role in addressing energy and environmental issues. Oxygen evolution reaction catalysts, as the key to water electrolysis hydrogen production technology, have been subject to durability constraints, preventing large-scale commercial development. Under the high current density and harsh acid-base electrolyte conditions of the water electrolysis reaction, the active metals in the catalysts are easily converted into high-valent soluble species to dissolve, leading to poor structural durability of the catalysts. There is an urgent need to overcome the durability challenges under acidic conditions and develop electrocatalysts with both high catalytic activity and high durability. In this review, the latest research results are analyzed in depth from both thermodynamic and kinetic perspectives. First, a comprehensive summary of the structural deactivation state process of noble metal oxide catalysts is presented. Second, the evolution of the structure of catalysts possessing high durability is discussed. Finally, four new strategies for the preparation of stable catalysts, "electron buffer (ECB) strategy", combination strength control, strain control, and surface coating, are summarized. The challenges and prospects are also elaborated for the future synthesis of more effective Ru/Ir-based catalysts and boost their future application.

NiMo-MMO catalyst derived from LDHs precursors toward the deep hydrogenation of pyrene

A series of Ni-based catalysts were prepared via structural topological transformation from the Ni@Al2O3 layered double hydroxides (LDHs) precursors, and applied for the deep catalytic hydrogenation saturation of pyrene in a high-pressure reactor. The pore structures, active species dispersion, surface morphology, amount and type of acid of the prepared catalysts were characterized by BET, XRD, SEM, TEM, XPS, SEM, NH3-TPD and Py-IR. We studied the influence of physicochemical properties of Ni-based catalysts on the regularity and mechanism of deep hydrogenation of pyrene. Meanwhile, the synergy between Ni and Mo, and the interaction between active metals and support were discussed to further reveal the constitutive relationship during the hydrogenation reaction of pyrene. The results of the evaluation of the catalytic hydrogenation of pyrene show that the as-prepared NiMo mixed metal oxide (MMO) catalyst showed excellent catalytic activity: ∼95% pyrene conversion, 90.12% for the selectivity of deep hydrogenation products (hexahydropyrene, decahydropyrene and hexadecahydropyrene). It was expected that the successfully preparation and utilization of NiMo-MMO catalyst could provide a theoretical basis for the design of this kind of catalysts for deep catalytic hydrogenation of polycyclic aromatic hydrocarbons (PAHs).

MnO2 as efficient and robust catalyst for halogen-free synthesis of cyclic carbonate from CO2 and epoxides

Cyclic carbonate is an important fine chemical/intermediate and their synthesis from CO2 and epoxides is economical and green pathway, however, it is still a challenge to develop a efficient and robust catalyst for halogen-free synthesis of cyclic carbonate. Herein, we successfully prepared large-scale MnO2 catalysts by microfluidics method, and the MnO2 especially δ-MnO2 showed >99.9 % propylene carbonate yield under 393 K, 3 MPa CO2 and DMF solvent. Moreover, the initial TOF value over δ-MnO2 on the basis of total catalyst amount was 5.80 h−1, which was the maximum among all the reported heterogeneous metallic oxide catalysts for halogen-free synthesis of propylene carbonate from CO2 and epoxides, and the superior catalytic performance can be ascribed to the abundant moderate acidic–basic active sites on the δ-MnO2 surface and the synergistic effect of δ-MnO2 and DMF. Furthermore, the δ-MnO2 can be reused at least 4 times and exhibited wide substrate applicability.

Heteropolyacid and Lithium Infused Calcium Oxide Catalyst for Biodiesel Production from Food Waste

The advancement of mixed metal oxide catalysts has attracted considerable attention among various workers. Supported MoOx catalyst materials possess more Lewis and Brønsted acid functionalities which assist in the efficient biodiesel production. In this study, ammonium molybdate and Li+ were loaded over eggshells-derived calcium oxide to transesterify the frying oil/waste cooking oil (WCO) to produce biodiesel/fatty acid methyl ester (FAME). Characterization techniques i.e., X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analysis were employed to confirm the material. The surface modelling predicted the transesterification reaction parameters. The optimal condition to transesterify WCO with synthesized Mo/Li/CaO catalyst was 6 wt.% catalyst dose, 13.70:1 ratio of methanol:oil (m/o), time of 1 h and 60 ºC temperature. The optimum FAME yield of 97% was observed. The gas chromatography-mass spectroscopy (GC-MS) and other spectroscopic techniques were used to analyze produced FAME. The reusability of catalyst was good and the catalyst can be reutilized effectively up to a limit of 5 runs. By leveraging this innovative catalyst derived from eggshells, this study contribute to a more sustainable and cost-effective biodiesel production process.

High-throughput dataset of impurity adsorption on common catalysts in biomass upgrading applications

An extensive dataset consisting of adsorption energies of pernicious impurities present in biomass upgrading processes on common catalysts and support materials has been generated. This work aims to inform catalyst and process development for the conversion of biomass-derived feedstocks to fuels and chemicals. A high-throughput workflow was developed to execute density functional theory calculations for a diverse set of atomic (Al, B, Ca, Cl, Fe, K, Mg, Mn, N, Na, P, S, Si, Zn) and molecular (COS, H2S, HCl, HCN, K2O, KCl, NH3) species on 35 unique surfaces for transition-metal (Ag, Au, Co, Cu, Fe, Ir, Ni, Pd, Pt, Re, Rh, Ru) and metal-oxide (Al2O3, MgO, anatase-TiO2, rutile-TiO2, ZnO, ZrO2) catalysts and supports. Approximately 3,000 unique adsorption geometries and corresponding adsorption energies were obtained.

Imidacloprid degradation activated by peroxydisulfate with NiCoAl layered metal oxide catalysts: The unique role of Al

Improper use of neonicotinoid insecticides (NNIs) can cause serious harm to aquatic ecosystems and human health. Despite the demonstrated excellent reactivity of nonradical persulfate activation in complex aquatic environments, the relationship between defect engineering and catalytic activity, as well as the construction of nonradical directed activation systems, remains uncertain. In this study, we synthesized and characterized Al-doped NiCoAl-LDO layered metal oxide catalysts for the first time. These catalysts were then used to activate peroxydisulfate (PDS) for degrading imidacloprid (IMI) in wastewater. Through degradation experiments and characterization analysis, singlet oxygen (1O2) and electron transfer were identified as the primary mechanisms responsible for IMI removal. Under optimized conditions (0.5 g/L catalyst loading, 1 mM PDS dosage, pH = 7.0), the degradation rate of IMI reached 0.06 min−1. The NiCo2Al1-LDO/PDS system exhibited efficient IMI degradation over a wide pH range (pH = 4–10) (> 73.6 %) and demonstrated excellent resistance against interference from anions such as Cl−, SO42−, HCO3−, CO32−, as well as Humic acid (HA). Our findings confirm that Al doping induces lattice distortion and enhances interfacial electron transfer processes in the catalyst structure, thereby facilitating the transformation from radical to nonradical pathway during the degradation process. This study not only advances our fundamental understanding of metal oxide active site doping regulation, but also presents a novel defect engineering strategy for nonradical oxidation of IMI, offering valuable insights for future research and practical applications of persulfate.

Elusive supported surface M2Ox dimer active site (M = Re, W, Mo, Cr, V, Nb, and Ta)

Supported transition metal oxide catalysts are extensively used as heterogeneous catalysts for various energy, chemical, and environmental applications. The molecular structures of dehydrated surface metal oxide phases are crucial for understanding structure-activity/selectivity relationships that guide the design of enhanced catalysts. Some early studies suggested that dimeric (aka binuclear) surface metal oxide sites were more active/selective than monomeric (aka mononuclear) sites, prompting interest in synthesizing catalysts with supported dimeric metal oxide structures. This review examines the literature on dehydrated silica-based supported group 7-5 MOx catalysts (ReOx, WOx, MoOx, CrOx, VOx, NbOx, and TaOx on SiO2, MCM-41, AlOx/SiO2, and H-ZSM-5) for their surface metal oxide structures. In situ Raman, extended x-ray absorption fine structure, and ultraviolet-visible spectroscopy indicate that monomeric surface MOx structures predominate in all such catalysts. Therefore, the cursory use of dimeric surface M2Ox sites in catalytic mechanisms and reaction models in heterogeneous catalysis by supported metal oxides is questionable, and moving forward, the invoking of supporting dimeric surface M2Ox sites should be critically examined and backed up with direct spectroscopic methods.

Prediction of catalytic performance of metal oxide catalysts for alkyne hydrogenation reaction based on machine learning

In the field of catalyst design, machine learning is gaining significant attention, especially in situations where data is limited. Facing this challenge, we have developed a neural network model that enhances predictive accuracy through the careful selection of catalyst descriptors and feature engineering, aiming to predict the conversion rate and selectivity of the acetylene semi-hydrogenation reaction. Our model has identified promising metal oxide catalysts, such as CuO, ZnO, and V2O5, for the acetylene semi-hydrogenation reaction, and these predictions have been experimentally validated. Among them, CuO achieved an acetylene conversion of 99.6 % and an ethylene selectivity of 90 % at 50–100°C, which is unprecedented at the reaction space velocity we tested. This high activity at relatively low temperatures indicates a more promising industrial application. Looking ahead, machine learning will play a pivotal role in catalyst design, accelerating the discovery and industrial application of new materials.

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.

Catalytic Decontamination of Carbon Monoxide Using Strong Metal–Support Interactions on TiO2 Microparticles

The traditional catalytic oxidation of carbon monoxide (CO) using metal oxide catalysts often requires either high temperatures (thermocatalysis) or ultraviolet light (UV) excitation (photocatalysis), limiting practical applications under ambient conditions. Our research aimed to develop a catalytic system capable of oxidizing CO to CO2 at room temperature and in the dark. Using the Strong Metal–Support Interaction (SMSI) methodology, several titanium oxide (TiO2)-complexed metals were prepared (Ag, Au, Pd, and Pt). The highest catalytic efficiency of CO oxidation at room temperature was demonstrated for the TiO2-Pt complex. Therefore, this complex was further examined structurally and functionally. Two modes of operation were addressed. The first involved applying the catalytic system to remove CO from an individual’s environment (environmental system), while the second involved the installation of the catalysis chamber as a part of a personal protection unit (e.g., a mask). The catalytic activity exhibited a significant reduction in CO levels in both the environmental and personal protection scenarios. The practical application of the system was demonstrated through efficient CO oxidation in air emitted from a controlled fire experiment conducted in collaboration with the Israel Fire and Rescue Authority.

Zn0.5Ni0.5MnxFe2-xO4 magnetically separable nano ferrite: A highly efficient photocatalyst for environmental remediation

The escalating pollution from industries poses a severe threat to water resources, necessitating efficient photocatalysts for environmental remediation. In this study, we introduce a novel Zn0.5Ni0.5MnxFe2-xO4 nano ferrite, synthesized via sol–gel auto-combustion method. The phase purity of Zn0.5Ni0.5MnxFe2-xO4 nano ferrites was confirmed from X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy. The microstructural investigation of nano ferrites was investigated using Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). The catalyst’s magnetic properties allow easy separation, addressing the challenge of catalyst retrieval in photocatalysis. Incorporating Zn, Ni, and Mn at tetrahedral and octahedral sites enhances crystallinity, crucial for catalytic efficiency. This mixed metal oxide catalyst demonstrates superior photocatalytic activity, with Zn0.5Ni0.5MnFeO4 exhibiting a remarkable 97% degradation of Reactive Orange (RO) dye under sunlight. Notably, the photocatalyst displays stability and reusability over multiple cycles. The study provides valuable insights into the potential of Zn0.5Ni0.5MnxFe2-xO4 ferrite as a magnetically separable, efficient photocatalyst for environmental remediation.

Actual reliance of catalytic activities tuned oxygen vacancies on VOx/Ce1-xZrxO2 catalyst for selective oxydehydrogenation of methanol to dimethoxymethane

Metal oxide catalysts like ceria-supported vanadia (VOx/Ce1-xZrxO2) with different Zr contents were prepared by coupling ceria-zirconia solid solution and vanadia. Characterization revealed that the insertion of zirconia into ceria significantly improved catalytic activity due to the generation of more oxygen vacancies and distortion of the composite structure. The oxygen vacancy concentration initially increased with the increase of Zr (x= wt%) and peaked at x=0.7 and then decreased. The reliance of oxygen vacancy concentration in VOx/Ce1-xZrxO2 catalyst on their catalytic activity in methanol oxydehydrogenation was further investigated. Results indicated that oxygen vacancies not only activated oxygen species but also cleaved C–H bonds alongside V5+ active site contained terminal oxygen atoms for cleaving O–H and C–H bonds within the adsorbed methanol. The VOx/Ce0.3Zr0.7O2 exhibited the best catalytic activity with the methanol conversion of 76 % and the dimethoxymethane selectivity of 96 % at 200 ℃ and atmospheric pressure in a fixed-bed reactor.

Manipulation of Mn/Ce ratio for deep chlorobenzene oxidation: Catalytic mechanisms and byproducts analysis

In this research, a sequence of spatial porous MnCeOx catalysts with varying Mn/Ce from 3:1 to 1:7 were synthesized using the sol–gel method for chlorobenzene (CB) oxidation. Mn1Ce1 exhibited the best performance due to its high lattice oxygen content and the strong interaction between Ce and Mn. The increase in Mn content in CeO2 catalysts resulted in enhanced redox properties and acidity, which was beneficial for the adsorption and activation of CB, thus enhancing the selectivity and the desorption of HCl on the catalyst surface. Carbon deposition and the formation of metal chloride were the main reasons for catalyst deactivation. At low temperature regions (150 ∼ 300 °C), insufficient oxidation capability and the chlorine deposition on the catalyst surface resulted in the formation of various chlorinated compounds. As the temperature increases (300 ∼ 450 °C), the release of HCl and more reactive oxygen species is available on the catalytic interface, generating various oxygen-containing degradation intermediates. This work proposed a fine-designed, low-cost mixed metal oxide catalysts for low temperature CB oxidation, and provided novel in-depth understandings of degradation intermediate formation thermodynamics. Our findings would be helpful for deep purification of chlorinated VOCs polluted industrial tail gas.

Conversion of 5‐Hydroxymethylfurfural and Carbohydrates to 2,5‐Diformylfuran Over MoOx/Biochar Catalysts

AbstractHere, a series of nitrogen‐doped carbon (NC) supported transition metal oxide catalysts were prepared by pyrolysis of chitosan‐metal salt mixtures for the efficient synthesis 2,5‐diformylfuran (DFF) from 5‐hydroxymethylfurfural (HMF) and fructose. Among them, supported molybdenum‐based species on nitrogen‐doped carbon (Mo/NC) exhibited excellent activity and selectivity for selective oxidation of HMF to DFF. The presence of nitrogen species reduces the electron cloud density around the Mo species, thereby improving the catalytic activity. Moreover, the interaction between active MoO2 species on the catalyst surface and NC ensured the stability of the catalyst, resulting in no significant loss of activity after four catalytic cycles. 99.5 % and 55.1 % yields of DFF with full conversion were obtained from HMF and fructose respectively over Mo/NC‐chitosan‐600 in DMSO under ambient air. In order to enhance DFF yield from fructose, sulfonate groups were introduced into Mo/NC‐chitosan‐600 catalyst, leading to the highest DFF yield of 70.2 %. In addition, this catalyst also allowed 10.0%, 22.9% and 33.3% DFF yields from glucose, sucrose and inulin, respectively.

Effect of mixed metal oxide‐based catalysts for the removal of hydrophobic phthalates from water

AbstractContaminants of emerging concern (CECs) such as phthalic acid esters (PAEs) are ubiquitous, toxic and persistent in aquatic environments. Current study explored mixed metal oxide catalysts derived from magnesium aluminium (MAH), magnesium aluminium ruthenium (MAR‐H), magnesium aluminium nickel (MANH) hydroxides and copper aluminium hydroxides of ammonium (CAM‐Am) and sodium molybdate (CAM‐Na) to remove dibutyl phthalate (DBP) and di‐2‐ethyl hexyl phthalate (DEHP) from water. Powder X‐ray diffraction (XRD) studies of the catalysts before and after the treatment showed that their structures were stable and robust. During Fourier Transform Infrared (FTIR) studies, vibrational bands or peaks of ester and alkane functional groups of DBP and DEHP were observed at all the catalysts after treatment. Thermogravimetric analysis (TGA) confirmed phthalate adsorption at the five catalysts. Hydrolysis of DBP and DEHP was observed during treatment using CAM‐Am and CAM‐Na that was analysed and quantified using total organic carbon (TOC), high performance liquid chromatography (HPLC) and high‐resolution mass spectrometry (HRMS). From TOC analyses, optimal conditions of 500 mg L−1 catalyst dosage and 30 h treatment time were deduced for catalytic hydrolysis of DBP and DEHP. Present study illustrated that the catalysts MAH and MANH can adsorb PAEs while CAM‐Na can adsorb and hydrolyse them.

Defect engineering for surface reconstruction of metal oxide catalysts during OER

Defect engineering for surface reconstruction of metal oxide catalysts during OER