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).