چكيده به لاتين
This study conducted the CO2 methanation reaction over the nickel-based catalysts supported on CaO.Al2O3 with different CaO/Al2O3 molar ratios. The catalyst support was synthesized with the mechanochemical method, and the influence of nickel loading was investigated on the selected catalyst support with an appropriate CaO/Al2O3 molar ratio. According to the results, incorporating Al2O3 into the CaO increased the BET area from 5 to 196 m2.g-1. Also, the SBET of the calcined catalysts decreased with the augmentation of nickel oxide percentage from 5 to 15 wt.% due to the pore blocking of the support after metal addition. Moreover, the activity of catalysts enhanced with the increment of CaO/Al2O3 molar ratio and NiO percentage, ascribed to the improvement in the reducibility of the catalysts. However, the excessive addition of CaO and nickel oxide reduced the CO2 conversion because of a significant decrease in surface area. Therefore, 10wt.% NiO/CaO.2Al2O3 catalyst possessed superior CO2 conversion (79.1%) and CH4 selectivity (98.1%) in CO2 methanation reaction at 450 °C, H2/CO2 = 4 and GHSV = 18,000 ml.h-1.g-1cat. The selected sample illustrated great stability for 11 h without any remarkable change in its initial catalytic activity. The impact of GHSV on the catalytic performance of the selected catalyst was evaluated, and the outcomes exhibited that decrement in GHSV value enhanced CO2 conversion. With the increment of feed ratio (H2/CO2) from 2 to 5, CO2 conversion reached 93.3%, ascribed to the existence of adequate hydrogen to react with CO2. The optimum amount of NiO was selected at 10 wt.% along with CaO:Al2O3 as support with the molar ratio of 1:2. The Co-doped catalyst showed the lowest pore size (9.4 nm) and the highest surface area (106 m2.g-1) among the promoted catalysts. The results exhibited that the Co3O4(3)-NiO(10)/CaO.2Al2O3 catalyst possessed superior catalytic performance in the CO2 methanation reaction. The results illustrated that the increase in cobalt oxide percentage up to 3 wt.% improved catalytic performance. However, further augmentation in the Co3O4 from 3 to 7 wt.% diminished the specific surface area. According to the performance tests, carbon dioxide conversion and methane selectivity were 83.1% and 99.5% at 450 °C under operating conditions (GHSV = 18,000 ml.gcat-1.h-1 and H2:CO2 = 4:1) over this catalyst. The processing conditions including calcination temperature, reduction temperature, GHSV, feed ratio, and long-term stability test were also examined over the selected catalyst. Outcomes revealed that CO2 conversion increased with a decrement in calcination temperature from 650 to 450 °C. Also, chosen catalyst reduced at 650 °C showed the highest performance. Besides, catalytic performance enhanced by raising feed ratio (H2:CO2) from 2:1 to 5:1 and decreased with augmentation of GHSV from 12,000 to 30,000 ml.gcat-1.h-1. Moreover, Co3O4(3)-NiO(10)/CaO.2Al2O3 catalyst possessed high stability during 14 h time on stream.
