Abstract

Nickel modified strontium hydroxyapatite (Ni/Sr-HAP) supported catalysts are studied in selective methanation of CO/CO₂. In this work, a new type of nano rod-shaped strontium hydroxyapatite-based catalysts with two different sizes and aspect ratios were prepared by sol–gel method and in next step, Ni precursor was wet impregnated i.e., denoted as Ni/Sr-HAP and Ni/Sr-HAP(F127). The catalytic tests were performed in CO and CO2 methanation reactions and evaluated the light-off temperatures curves (225–450 °C) under ambient pressure in a fixed-bed flow reactor. The physicochemical properties of the prepared catalysts were characterized by XRD, N2 physisorption, TEM, SEM, TPR, CO₂/H₂-TPD and H₂-chemisorption techniques. From XRD analysis, both Ni/Sr-HAP and Ni/Sr-HAP(F127) were identified as the hydroxyapatite type structure with high crystallinity and very low intensity peaks corresponds to strontium phosphates as the main phase and structure. The TEM and SEM micrographs of Ni/Sr-HAP catalysts displayed a nano- rod shaped morphology with different dimensions and exhibited average Ni particle size of ~ 9.2 nm. While Ni/Sr-HAP(F127) shown the rod size in the length in the range of 100–250 nm and width in the range of 20–40 nm with average Ni particle size 5.7 nm. The F127 mediated support Sr-HAP synthesis i.e., Ni/Sr-HAP(F127) mesoporous catalyst possessed higher metal surface with smaller Ni particles size and possessed higher CO₂ adsorption capacity. The medium strength basic sites of Ni/Sr-HAP catalyst played an important role in methanation reactions. Based on the characterization and the catalysts activity results, small sized nanorods of Ni/Sr-HAP(F127) is the most active and selective catalyst due to the higher Ni dispersion, higher amounts of medium basic sites, and reducibility character than the bigger nanorods based Ni/Sr-HAP catalyst.