Effect of the basicity created by La2O3 addition on the catalytic properties of Co(O)/SiO2 in CH4 + CO2 reaction

A series of Co(O)/SiO2 catalysts modified by various amounts of La2O3 (5, 10 or 50 wt.%) were synthesized and studied in the reaction of reforming of methane by carbon dioxide to syngas at the temperature of 873 K. The catalysts were prepared by successive incipient wetness impregnation: La2O3–SiO2 supports were first prepared by impregnating silica with La(NO3)3 solutions. After drying and calcining under airflow, samples were then submitted to a second impregnation with Co(NO3)2. The purpose of this work is to study the acid–base property of these catalysts by CO2 adsorption calorimetry at 353 K and to look at their impact on the catalytic property. The amounts of chemisorbed CO2 and the site strength distribution of the basic sites, i.e., the basicity, were shown to be strongly dependent on La2O3 content. The following order of basicity was observed: Co(O)/5 wt.%La2O3–SiO2 < Co(O)/10 wt.%La2O3–SiO2 ≪ Co(O)/50 wt.%La2O3–SiO2. The addition of La2O3 to the Co(O)/SiO2 reference sample revealed a very positive effect on the catalytic stability of catalysts. La2O3 prevented cobalt phase sintering by avoiding particle coalescence.