Oxidative coupling of methane over SrO deposited on different commercial supports precoated with La₂O₃

Abstract

The influence of catalyst carrier or support (with different chemical compositions and surface properties), catalyst deposition method (viz., impregnation and coating), precursor for strontium oxide (SrO; Sr-nitrate, acetate, hydroxide, and carbonate), and loading of SrO and lanthanum oxide (La₂O₃; 0-25 wt %) on the surface properties and performance of catalyst in oxidative coupling of methane (OCM; at 850 ° C, gas hourly space velocity = 1.02 × 10⁵ cm³.g^-1.h^-1 and CH₄/O₂ = 4 or 16) was thoroughly investigated. The basicity, acidity, and O₂ chemisorption of the catalysts were studied by the temperature programmed desorption (TPD) of CO₂, NH₃, and O₂, respectively, from 50 to 950 ° C. The total and strong basic sites, acidity, and OCM activity of the supported catalyst were strongly influenced by the support used and also by the La2O3 loading on the support. The catalyst with a sintered low surface area porous silica-alumina support and high (20 wt %) La₂O₃ and SrO loadings showed the best performance in the OCM process. The OCM activity was influenced by SrO loading, but to a smaller extent, and also by the method of SrO deposition. The OCM activity of the supported catalysts could be related to their strong basic sites (measured in terms of the CO₂ desorbed between 500 and 950 ° C).