Tuning of Ni Metallic Sites over Strontium Hydroxyapatite Nanorods for Syngas Methanation

We investigate CO methanation over nickel-decorated strontium hydroxyapatite (NiSH) nanorods based catalysts by varying Ni loadings, prepared by the impregnation method. The catalytic experiments were conducted at light-off temperatures ranging from 225°C to 400 °C, under ambient pressure. The key properties of prepared catalysts were characterized by XRD, N2 physisorption, TEM, SEM, TPR and H2-TPD and H2-chemisorption. The basicity of the catalysts was measured by CO2-TPD analysis. A 10NiSH catalyst is optimal for CO methanation, with over 90% CH4 selectivity at 300 °C and 0.1 MPa, with complete CO conversion. The synergistic interaction between highly dispersed Ni species and the basic Sr-modified hydroxyapatite support significantly enhances catalytic activity and CH4 selectivity. Unlike conventional Ni-supported catalysts, the present 10NiSH system provides improved Ni dispersion, optimized reducibility, enhanced CO adsorption/activation, and superior hydrogenation ability, resulting in high yield of CH4 at relatively low temperature. In-situ DRIFT spectroscopy evidenced reaction intermediates, and a reaction mechanism is proposed. The basicity of SH role is CO2 adsorption in conjunction with Ni metal in hydrogenation activity are key roles. The optimal loading exhibited better properties in terms of Ni particle size, narrowly distributed histograms, and better reducibility. Based on the catalyst performance results, overall, the 10NiSH is the most active and selective catalyst due to its high Ni dispersion.