Effect of Preparation Method of Co-Ce Catalysts on CH4 Combustion

Effect of Potassium Doping on the Structural and Catalytic Properties of Co/MnOx Catalyst in the Steam Reforming of Ethanol

The promotional effect of potassium (~1.25 wt%) on a Co/MnOx catalyst was studied for samples prepared by the impregnation method in the steam reforming of ethanol (SRE) process at 420 °C for a H2O/EtOH molar ratio of 12/1. The catalysts were characterized using physicochemical methods to study their textural, structural, and redox properties. The XRD studies revealed that, during the treatment of both cobalt-based catalysts under a hydrogen atmosphere at 500 °C, Co0 and MnO phases were formed by the reduction in Co3O4 and Mn2O3/Mn3O4 phases, respectively. Potassium doping significantly improved stability and ability for the C-C bond cleavage of the Co/MnOx catalyst. The enhancement of activity (at ~25%) and selectivity to hydrogen (at ca. 10%) and the C1 product, mainly carbon dioxide (at ~20%), of the Co/MnOx catalyst upon potassium doping was clarified by the alkali promoter's impact on the reducibility of the cobalt and manganese oxides. The microscopic observations revealed that fibrous carbon deposits are present on the surface of Co/MnOx and KCo/MnOx catalysts after the SRE reaction and their formation is the main reason these catalysts deactivate under SRE conditions. However, carbon accumulation on the surface of the potassium-promoted catalyst was ca. 12% lower after 18 h of SRE reaction compared to the unpromoted sample.

Recent Advances in Co3O4-Based Composites: Synthesis and Application in Combustion of Methane

In recent years, it has been found that adjusting the organizational structure of Co₃O₄ through solid solution and other methods can effectively improve its catalytic performance for the oxidation of low concentration methane. Its catalytic activity is close to that of metal Pd, which is expected to replace costly noble metal catalysts. Therefore, the in-depth research on the mechanism and methods of Co₃O₄ microstructure regulation has very important academic value and economic benefits. In this paper, we reviewed the catalytic oxidation mechanism, microstructure regulation mechanism, and methods of nano-Co₃O₄ on methane gas, which provides reference for the development of high-activity Co₃O₄-based methane combustion catalysts. Through literature investigation, it is found that the surface energy state of nano-Co₃O₄ can be adjusted by loading of noble metals, resulting in the reduction of Co-O bond strength, thus accelerating the formation of reactive oxygen species chemical bonds, and improving its catalytic effect. Secondly, the use of metal oxides and non-metallic oxide carriers helps to disperse and stabilize cobalt ions, improve the structural elasticity of Co₃O₄, and ultimately improve its catalytic performance. In addition, the performance of the catalyst can be improved by adjusting the microstructure of the composite catalyst and optimizing the preparation process. In this review, we summarize the catalytic mechanism and microstructure regulation of nano-Co₃O₄ and its composite catalysts (embedded with noble metals or combined with metallic and nonmetallic oxides) for methane combustion. Notably, this review delves into the substance of measures that can be used to improve the catalytic performance of Co₃O₄, highlighting the constructive role of components in composite catalysts that can improve the catalytic capacity of Co₃O₄. Firstly, the research status of Co₃O₄ composite catalyst is reviewed in this paper. It is hoped that relevant researchers can get inspiration from this paper and develop high-activity Co₃O₄-based methane combustion catalyst.

Metal-organic frameworks-derived hierarchical Co3O4/CoNi-layered double oxides nanocages with the enhanced catalytic activity for toluene oxidation

The development of active transition-metal oxide (TMO) catalysts for the abatement of volatile organic compounds (VOCs) remains a great challenge. Controllable synthesis of TMOs with specific morphology and suitable composition is a promising way for acquiring efficient oxidation catalysts. Herein, a series of hierarchical Co₃O₄/CoNi-layered double oxides (CoNi-LDO) nanocages covered by interlaced nanosheets were synthesized using a cobalt metal-organic framework (Co-MOF)-based strategy. The textural properties, morphology, surface chemical state, and reducibility of the CoNi-LDO catalysts were systematically characterized by various techniques. The catalytic activity toward toluene oxidation and the stability performance was investigated. Results demonstrated that the morphology, composition, and textual properties can be controlled by tuning the post-synthetic etching reaction conditions. Benefiting from the structural and compositional merits, as well as the superior low-temperature reducibility, the CoNi-LDO-1 catalyst (Ni/Co molar ratio was 0.39) with core-shell structure exhibited excellent activity toward toluene oxidation. Our work offers a new strategy for the design of high-performance oxidation catalysts for the abatement of VOCs.

Total Oxidation of Methane on Oxide and Mixed Oxide Ceria-Containing Catalysts

Methane, discovered in 1766 by Alessandro Volta, is an attractive energy source because of its high heat of combustion per mole of carbon dioxide. However, methane is the most abundant hydrocarbon in the atmosphere and is an important greenhouse gas, with a 21-fold greater relative radiative effectiveness than CO2 on a per-molecule basis. To avoid or limit the formation of pollutants that are dangerous for both human health and the atmospheric environment, the catalytic combustion of methane appears to be one of the most promising alternatives to thermal combustion. Total oxidation of methane, which is environmentally friendly at much lower temperatures, is believed to be an efficient and economically feasible way to eliminate pollutants. This work presents a literature review, a statu quo, on catalytic methane oxidation on transition metal oxide-modified ceria catalysts (MOx/CeO2). Methane was used for this study since it is of great interest as a model compound for understanding the mechanisms of oxidation and catalytic combustion on metal oxides. The objective was to evaluate the conceptual ideas of oxygen vacancy formation through doping to increase the catalytic activity for methane oxidation over CeO2. Oxygen vacancies were created through the formation of solid solutions, and their catalytic activities were compared to the catalytic activity of an undoped CeO2 sample. The reaction conditions, the type of catalysts, the morphology and crystallographic facets exposing the role of oxygen vacancies, the deactivation mechanism, the stability of the catalysts, the reaction mechanism and kinetic characteristics are summarized.

Investigation of Co3O4 and LaCoO3 Interaction by Performing N2O Decomposition Tests under Co3O4-CoO Transition Temperature

The research presented in this paper addresses the question: How does the addition of a small amount of LaCoO3 impact the activity of a Co3O4 catalyst? By testing such a catalyst in N2O decomposition under conditions at which the thermal decomposition of Co3O4 to CoO is possible, one gains unique insight into how the two phases interact. The activity of such a catalyst increases in the entire studied temperature range, unlike the activity of the undoped cobalt catalyst which is lower at 850 °C than at 800 °C due to the reduction of Co3O4 to CoO. XRD measurements showed that CoO was also the main cobalt oxide present in the Co3.5La catalyst after operating at 850 °C, as did the XPS measurements, but there was no drop of activity associated with this change. The influence of NO, O2 and H2O on the activity of the new catalyst, Co3.5La, was determined. Lack of positive effect of NO, a known oxygen scavenger, on the activity was noticed at all temperatures, showing that the effect of LaCoO3 is probably due to increased oxygen desorption. Temperature programed oxidation (TPO) tests showed that the beneficial effects of the presence of LaCoO3 on the activity of cobalt oxide at 850 °C were probably caused by enhanced diffusion of O2− anions through the entire catalyst, which facilitates desorption of oxygen molecules from the surface.

Catalytic conversion of high-GWP gases N2O and CH4 to syngas (H2 + CO) on SiO2@Ni-Cr layered nano-oxide-coated monolithic catalyst

Layered double hydroxides (LDHs) are 2D nano-sheets where different M²⁺ and M³⁺ metal cations are uniformly distributed in Mg(OH)₂ brucite-like sheets and various charge-compensating anions (A^n-) are present in their interlayer spaces. This work includes preparation of different SiO₂@Ni/Cr mixed-metal layered nano-oxide-type catalysts by the calcination of SiO₂@Ni-Cr LDH nano-composite-based alcogel coated over a honeycomb monolithic substrate and their use as a catalytic device for the study of catalytic partial oxidation (CPO) of CH₄ both in the presence of O₂ and in the presence of N₂O under atmospheric pressure at different temperatures not exceeding 500 °C to study the effect of N₂O on the CPO of CH₄. It was observed that in the presence of O₂ the yield of syngas (H₂ + CO) did not exceed 90% whereas in the presence of N₂O about 99.9% syngas (H₂ + CO) was observed. The selectivity towards syngas production reached a maximum value when an optimal reaction condition was maintained at 1:1 CH₄:N₂O mol ratio with a temperature of 500 °C. XPS analysis showed that a NiO-type compound formed on the decomposition of the LDH component after H₂ treatment was reduced to disperse Ni⁰_, which acted as an active catalytic species. Graphical abstract Schematic representation of catalytic partial oxidation of CH₄ in the presence of N₂O by SiO₂@Ni-Cr-LDH-based mixed-metal nano-oxide.

Emissions Control Catalysis

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Synthesis, Characterization and Kinetic Behavior of Supported Cobalt Catalysts for Oxidative after-Treatment of Methane Lean Mixtures

The present work addresses the influence of the support on the catalytic behavior of Co₃O₄-based catalysts in the combustion of lean methane present in the exhaust gases from natural gas vehicular engines. Three different supports were selected, namely γ-alumina, magnesia and ceria and the corresponding catalysts were loaded with a nominal cobalt content of 30 wt. %. The samples were characterized by N₂ physisorption, wavelength dispersive X-ray fluorescence (WDXRF), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction with hydrogen and methane. The performance was negatively influenced by a strong cobalt-support interaction, which in turn reduced the amount of active cobalt species as Co₃O₄. Hence, when alumina or magnesia supports were employed, the formation of CoAl₂O₄ or Co-Mg mixed oxides, respectively, with a low reducibility was evident, while ceria showed a lower affinity for deposited cobalt and this remained essentially as Co₃O₄. Furthermore, the observed partial insertion of Ce into the Co₃O₄ lattice played a beneficial role in promoting the oxygen mobility at low temperatures and consequently the catalytic activity. This catalyst also exhibited a good thermal stability while the presence of water vapor in the feedstream induced a partial inhibition, which was found to be completely reversible.