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

• CO2 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 CO2 methanation.
• Water vapor suppressed carbonyl species on the surface of Ni/MSN.
• 85% conversion of CO2 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 CO2 methanation were studied. X-ray diffraction, N2 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 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 623 K for more than 100 h. 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 6 h, reaction temperature of 614 K, gas hourly space velocity (GHSV) of 69105 mL gcat−1 h−1, and H2/CO2 ratio of 3.68.

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