Influence of the Calcination Technique of Silica on the Properties and Performance of Ni/SiO2 Catalysts for Synthesis of Hydrogen via Methane Cracking Reaction.

Abstract

Deactivation of catalysts due to rapid blocking of active surfaces and pores is a major problem for methane cracking. The removal of the template using different calcination methods contributes to the different characteristics of catalyst support. Therefore, silica supports were prepared with the sol–gel method, where sodium silicate and chitosan are a silica source and a template, respectively. Calcination using a microwave muffle furnace (MWF) was preferred over the conventional electric muffle furnace at the heating rates of 2 and 17 °C/min (CEF2 and CEF17, respectively) in order to remove the chitosan template. A nickel nitrate precursor was loaded onto the obtained silica supports by the incipient wetness impregnation method. The properties of the silica support and the Ni/SiO2 catalysts were characterized by means of N2-sorption, X-ray diffraction, scanning electron microscopy–energy-dispersive X-ray, field emission transmission electron microscopy, and H2 temperature-programmed reduction. The catalytic activity was evaluated using a fixed-bed reactor at 550 °C with a CH4/N2 ratio of 1:4 in the feed. The amount and the allotropes of carbon deposited on the spent catalysts were investigated using thermogravimetric/differential thermal analysis. The results showed that the SiO2-MWF support had a higher surface area and a larger pore volume of a mesoporous structure with larger interparticle channels than that of the SiO2-CEF supports. This leads to the higher dispersion of Ni metal particles over and inside the interparticle channels of the SiO2-MWF support. This provided a higher metal–support interaction, resulting in lower rates of methane conversion and carbon deposition on the catalyst surface than those of Ni/SiO2-CEF catalysts. However, it displayed a lower bed pressure. It was found that the carbon fibers deposited on all the catalysts were multiwalled carbon nanotubes (MWCNTs). Additionally, the base-growth mechanism of MWCNTs was only exhibited by the Ni/SiO2-MWF catalyst.