Influence of Ca/P ratio on the catalytic performance of Ni/hydroxyapatite samples in dry reforming of methane

A series of Ni/hydroxyapatite samples presenting different Ca/P molar ratios were synthesised to study the influence of the hydroxyapatite support composition on their catalytic properties in the dry reforming of methane. Our results reveal that a preparation starting from a sub-stoichiometric composition (Ca/P < 1.67) followed by the impregnation of Ni results in suitable properties which give the highest catalytic performance compared with stoichiometric (Ca/P = 1.67) and over-stoichiometric (Ca/P = 1.73) compositions, respectively. The characterisation of the investigated Ni/HAP materials shows that their texture, surface chemistry (acid/base) and the Ni species distribution are mainly derived from the structural properties of the used support. The activity of the Ni/HAP samples in DRM shows that their performances follow this trend: Ni/HAP-D2 (Ca/P = 1.62) > Ni/HAP-D1 (1.57) > Ni/HAP-S (1.67) > Ni/HAP-E (1.73). The superiority of the sample with a Ca/P molar ratio of 1.62 was explained by a suitable surface chemistry consisting of an abundance of strong acid sites and basic sites. While the former act as anchoring sites for Ni species the latter serve as CO2 chemisorption sites producing intermediate species which in turn react with deposited carbon to form CO. This distribution together with its improved textural properties lead to the deposition of highly dispersed, efficient and coke resistant Ni species.