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

Abstract

• CO 2 methanation is dependence to the Ni loading (1–10 wt.%) on MSN. • The order of reaction activity was 10Ni/MSN ≈ 5Ni/MSN > 3Ni/MSN > 1Ni/MSN. • 0.5 vol% water vapor in the feed gave a negative effect on the CO 2 methanation. • Water vapor suppressed carbonyl species on the surface of Ni/MSN. • 85% conversion of CO 2 was achieved over 5Ni/MSN under the optimum condition by RSM. The effects of Ni loading and water vapor on the properties of Ni/mesoporous silica nanoparticles (MSN) and CO 2 methanation were studied. X-ray diffraction, N 2 adsorption–desorption, and pyrrole-adsorbed infrared (IR) spectroscopy results indicated that the increasing Ni loading (1–10 wt.%) decreased the crystallinity, surface area, and basic sites of the catalysts. The activity of CO 2 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 CO 2 methanation. All Ni/MSN catalysts exhibited a high stability at 623 K for more than 100 h. The presence of water vapor in the feed stream induced a negative effect on the activity of CO 2 methanation. The water vapor decreased the carbonyl species concentration on the surface of Ni/MSN, as evidenced by CO + H 2 O-adsorbed IR spectroscopy. The response surface methodology experiments were designed with face-centered central composite design (FCCCD) by applying 2 4 factorial points, 8 axial points, and 2 replicates, with one response variable (CO 2 conversion). The Pareto chart indicated that the reaction temperature had the largest effect for all responses. The optimum CO 2 conversion was predicted from the response surface analysis as 85% at an operating treatment time of 6 h, reaction temperature of 614 K, gas hourly space velocity (GHSV) of 69105 mL g cat −1 h −1 , and H 2 /CO 2 ratio of 3.68.