Oxygen availability and catalytic performance of NaWMn/SiO2 mixed oxide and its components in oxidative coupling of methane

The catalytic performance in oxidative coupling of methane and the surface basicity of La 2O 3, Nd 2O 3, ZrO 2 and Nb 2O 5☆

Further evidence of responsibility of impurities in MgO for variability in its basicity and catalytic performance in oxidative coupling of methane

Atomically dispersed SrOx species on exposed {2 2 2} facets of pyrochlore La2Zr2O7 nanocrystals for boosting low-temperature oxidative coupling of methane

The paper presents the research results obtained in the process of oxidative coupling of methane, in which unpurified biogas was used as the feedstock. Biogas obtained from two kinds of biomass materials, i.e., plant materials (potato and beet pulp, Corn-Cob-Mix—biogas 1) and animal waste (waste from fish filleting—biogas 2) was considered. The influence of temperature, the ratio of methane/oxygen and total flows of feedstock on the catalytic performance in oxidative coupling of methane process was investigated. Comparative tests were carried out using pure methane and a mixture of methane-carbon dioxide to simulate the composition of biogas 2. The process was carried out in the presence of an Mn-Na2WO4/SiO2 catalyst. Fresh and used catalysts were characterised by means of powder X-ray diffraction, X-ray photoelectron spectroscopy, and low-temperature nitrogen adsorption techniques. In oxidative coupling of methane, the type of raw material used as the source of methane has a small effect on methane conversion (the differences in methane conversion are below 3%), but a significant effect on the selectivity to C2. Depending on the type of raw material, the differences in selectivity to C2 reach as high as 9%. However, the Mn-Na2WO4/SiO2 catalyst operated steadily in the tested period of time at any feedstock composition. Moreover, it was found that CO2, which is the second main component of biogas in addition to methane, has an effect on catalytic performance. Comparative results of catalytic tests indicate that the CO2 effect varies with temperature. Below 1073 K, CO2 exerts a small poisoning effect on methane conversion, while above this temperature the negative effect of CO2 disappears. In the case of selectivity to C2+, the negative effect of CO2 was observed only at 1023 K. At higher temperatures, CO2 enhances selectivity to C2+. The effect of CO2 was established by correlating the catalytic results with the temperature programmed desorption of CO2 investigation. The poisoning effect of CO2 was connected with the formation of surface Na2CO3, whose concentration depends on temperature.

A novel particle/monolithic two-stage catalyst bed reactor and their catalytic performance for oxidative coupling of methane

Atomic-level control in catalyst synthesis is critical for optimizing the catalytic performance. Here, we have developed a generalizable and scalable liquid atomic layer deposition (L-ALD) technique using stoichiometric injections of metal alkoxide precursors to deposit lanthanum on Al2O3 nanoparticles, with precise control over surface chemistry and catalyst properties. Quantitative gas chromatography revealed distinct stoichiometric reaction stages during lanthanum deposition, showing initial ligand exchange with surface hydroxyl groups and transition to sterically hindered saturation due to limited hydroxyl utilization. Optimized acidic hydrolysis conditions (1 mM HNO3, 40 °C) ensured a nearly complete counter-reaction with unreacted ligands, regenerating hydroxyl sites effectively and promoting consistent deposition cycles. Cyclic L-ALD systematically modulated the surface acidic and basic sites, influencing the catalytic behavior. As a model reaction, an La thin-film coating of Al2O3 was demonstrated for enhanced and selective catalytic performance in oxidative coupling of methane (OCM), with a C2+ hydrocarbon selectivity of 32% with a stable (90 h) CH4 conversion (∼35 to 40%) after five deposition cycles. Structural and spectroscopic characterizations (X-ray diffraction (XRD), TEM, X-ray photoelectron spectroscopy (XPS), and CO2/NH3TPD) confirmed the formation of uniform, conformal lanthanum aluminate layers, controlled lanthanum dispersion, and optimized electronic interactions at the catalyst surface. This work demonstrates how atomic-scale deposition techniques can precisely tune surface and electronic properties, enabling enhanced catalytic selectivity and stability for complex environmentally and energy-related reactions such as OCM.

The effect of gas atmosphere used in the calcination of MgO on its basicity and catalytic performance in oxidative coupling of methane

Oxidative coupling of methane over calcium chloride-promoted calcium chlorophosphate

The effect of some impurities on the basicity of MgO tested by the transformation of 2-butanol and on its catalytic performance in oxidative coupling of methane

Investigations of the selective partial oxidation of methanol and the oxidative coupling of methane over copper catalysts

Al- and Mg-doped SrTiO3 perovskite steps: The catalytic performance for oxidative coupling of methane

Effect of Metallo-organic Precursors on the Synthesis of Sm–Sn Pyrochlore Catalysts: Application to the Oxidative Coupling of Methane

A reactor with dual catalyst beds was proposed for the direct improvement of methane productivity to C2 hydrocarbons. In this bed configuration, methane was converted to ethane and ethylene over lithium supported magnesium oxide as a primary catalytic bed. The reaction tests were performed in the presence of CaO–ZnO catalysts as the secondary bed to convert the methane residue into ethane and ethylene. Both Li/MgO and CaO–ZnO catalysts were prepared by the wet impregnation method, tested in the dual fixed bed quartz reactor and characterized by BET, XRD, scanning electron microscopy and temperature programmed desorption of carbon dioxide. Catalytic activity tests were carried out at different temperatures ranging from 675 to 825 °C. The influence of CaO–ZnO supplementation as a secondary bed and its composition on total catalytic performance for oxidative coupling of methane was studied by changing Zn/Ca ratio. The effects of secondary bed dilution with quartz and mixed bed configuration on reaction productivity were also investigated. The experimental results showed that this supplementation could improve total yield toward C2 production.

Na-Mn-W/SiO2 catalysts were prepared and their catalytic performance for oxidative coupling of methane (OCM) was evaluated in a stainless-steel microreactor at elevated pressure. The results show that a CH4 conversion of 15.1% with a C2+ selectivity of 71.8% was obtained under 750oC, 1.0×105h-1 GHSV, CH4/O2 ratio of 8 and 1.0 MPa. Moreover, 17.3% CH4 conversion with 51.6% C2 selectivity and 23.6% C3-C4 selectivity was obtained under 750oC, 2.0×105h-1 GHSV, CH4/O2 ratio of 8 and 1.0 MPa.

Oxidative coupling of methane has been studied over (Mn+A+W)/SiO2 catalysts in a continuous–flow micro reactor, where A represents an alkali ion of Li, Na, K or Cs having different weight percents. The main aim of this study is to find the role of alkali ions in interaction between Mn and W species with SiO2 to make a proper structure for catalyzing oxidative coupling of methane (OCM) reaction. The catalysts were characterized by XRD, SEM, FTIR, TPR and also the electrical conductivity was measured in air and under OCM reaction. It was found that for the formation of crystallized catalyst, the amount of alkali ion should be such that the catalyst containing tungsten transforms into A2WO4. Using a smaller amount of alkali ions does not result in crystalline catalyst by calcination under the same condition of temperature and atmosphere. However, under the OCM reaction condition the catalyst gradually turns into a crystalline structure and its catalytic performance, i.e. conversion and selectivity, for the OCM reaction is almost similar to the (Mn+A2WO4)/SiO2 catalyst. The transformation of the catalyst containing alkali ions from amorphous to crystalline one indicates a kind of structural flexibility of the catalyst under OCM atmosphere. The structural flexibility of the catalyst under the OCM reaction is considered to be the main chemical role of the alkali ions.