CO2 methanation over Ni-promoted mesostructured silica nanoparticles: influence of Ni loading and water vapor on activity and response surface methodology studies

Abstract

The effects of Ni loading and water vapor on the properties of Ni/mesoporous silica nanoparticles (MSN) and CO2 methanation were studied. X-ray diffraction, N2 adsorption-desorption, and pyrrole-adsorbed infrared (IR) spectroscopy results indicated that the increasing Ni loading (1-10wt.%) decreased the crystallinity, surface area, and basic sites of the catalysts. The activity of CO2 methanation followed the order of 10Ni/MSN˜5Ni/MSN>3Ni/MSN>1Ni/MSN. These results showed that the balance between Ni and the basic-site concentration is vital for the high activity of CO2 methanation. All Ni/MSN catalysts exhibited a high stability at 623K for more than 100h. The presence of water vapor in the feed stream induced a negative effect on the activity of CO2 methanation. The water vapor decreased the carbonyl species concentration on the surface of Ni/MSN, as evidenced by CO+H2O-adsorbed IR spectroscopy. The response surface methodology experiments were designed with face-centered central composite design (FCCCD) by applying 24 factorial points, 8 axial points, and 2 replicates, with one response variable (CO2 conversion). The Pareto chart indicated that the reaction temperature had the largest effect for all responses. The optimum CO2 conversion was predicted from the response surface analysis as 85% at an operating treatment time of 6h, reaction temperature of 614K, gas hourly space velocity (GHSV) of 69105mLgcat -1h-1, and H2/CO2 ratio of 3.68.