Abstract
In this study, chitosan was employed as a biopolymer template for the preparation of alumina supports via a sol-gel method for nickel-based catalysts in CO(2) methanation. The effects of ammonium hydroxide (NH(4)OH) and sodium hydroxide (NaOH) coagulation agents on the structural formation of alumina were investigated using TGA, FTIR, CHN analysis, FESEM, XRD, N(2) adsorption-desorption isotherms, CO(2)-TPD, NH(3)-TPD, H(2)-TPR, and XRF. The C-Al-NH(4)OH support exhibited superior textural properties and enhanced reducibility of nickel species. However, it was observed that increasing the NH(4)OH concentration accelerated chitosan adsorption onto aluminum species but hindered the formation of the alumina network, leading to reduced BET surface area and pore volume. Furthermore, TGA results indicated substantial aluminum loss during preparation in a NaOH coagulation bath due to the formation of water-soluble sodium aluminate species. The catalytic activity of Ni/C-Al catalysts for CO(2) methanation was evaluated in terms of CO(2) conversion and CH(4) selectivity. Process optimization was carried out using a face-centered central composite design response surface methodology (FCCCD-RSM) with reaction temperature, H(2)/CO(2) ratio, and gas hourly space velocity (GHSV) as the primary variables. The optimized 30Ni/C-Al-3NH(4)OH catalyst achieved a maximum CO(2) conversion of 93.2% and CH(4) selectivity of 97.1% under the optimal conditions at 386 °C, a H(2)/CO(2) ratio of 6, and a GHSV of 7851 h(-1). In addition, the catalyst demonstrated excellent stability over a 48-h continuous operation.