Impact of pore structure on hydroxyapatite supported nickel catalysts (Ni/HAP) for dry reforming of methane

The hierarchical supports have motivated intensive research interests of chemists in the catalytic field because of the rational combination of mass transport property and large surface area. In this work, hydroxyapatite (HAP) supported nickel catalysts were prepared and employed to promote the dry reforming of methane (DRM). The proportion of mesopore/macropore in HAP was adjusted by the heating temperature (20, 50, 80, 120 degrees C) during the preparation process. The pore structure played an important role in regulating the physiochemical properties and thus affecting the catalytic performance in DRM. With increasing the proportion of mesopore on HAP, Ni preferentially dispersed on mesopore channel to form small-size particles. All catalysts possessed weak interaction between Ni nanoparticles and HAP; however, the interaction enhanced gradually with decreasing the Ni particles diameter. High proportion of macropore led to large-size Ni nanoparticle, while high proportion of small-size mesopore at 2-5 nm resulted in the complete blockage of these pore structures. These two boundary situations led to relatively weak interaction between nickel particles and the support, low metal dispersion and hence low activity as well as rapid deactivation in the DRM evaluation. Ni nanoparticles on HAP-80 and HAP-120 supports possessed relatively higher dispersion, which imparted these two catalysts with the function of strong anti-sintering ability and carbon resistance, thereby exhibiting better catalytic activity and stability in DRM evaluation. The deactivation of all catalysts during the reforming reaction was mainly ascribed to the sintering as well as encapsulation of Ni nanoparticles by graphitic carbon.