Basic surface sites of various Ni-supported catalysts for methanation of CO2

Abstract

Carbon dioxide (CO2) is considered to be a major factor in the greenhouse effect and its concentration in the atmosphere is increasing. Thus, decrease of CO2 in the atmosphere is very important. Many techniques for CO2 reduction and fixation have been developed and studied over the last decade. In these techniques, the process of CO2 methanation is a practical approach to effectively decrease CO2, because CO2 is converted into reusable chemicals and an appropriate catalyst can promote the reaction under relatively moderate conditions at ambient pressure. Extensive studies have been carried out on the methanation reaction under various catalytic systems1-3. In this study, the catalysts containing 0.5 wt% Ni supported on Mesostructured silica nanoparticles (MSN), Silica, MCM-41 (Mobile Crystalline Material), HY (protonated Y zeolite) and ?-Al2O3 were prepared by impregnation method for the methanation of CO2. Catalytic testing was conducted in the temperature range of 423-723 K under atmospheric pressure in the presence of H2. The activity of CO2 methanation followed the order: Ni/MSN > Ni/MCM-41 > Ni/HY > Ni/SiO2 > Ni/?-Al2O3. The high activity of Ni/MSN is due to the presence of both intra- and interparticle porosity which led to the high concentration of basic sites evidenced by N2 isotherm and pyrrole adsorbed IR spectroscopy results. The methanation activities were found to be correlated to the concentration of basic sites as the basic sites were determined from the IR peak intensity of FTIR pyrrole adsoprtion (Figure 1). Therefore, high basic sites is essential for high carbon dioxide adsorption on the catalyst to form carbon species, while Ni sites dissociated hydrogen to form atomic hydrogen. The surface carbon species then interacted with atomic hydrogen to form methane.