Activity of NiCuAl catalyst in methane decomposition studied using a thermobalance and the structural changes in the Ni and the deposited carbon

Activity measurements of a NiCuAl catalyst for the thermal decomposition of methane have been carried out in a thermobalance at different operating temperatures and partial pressures of methane and hydrogen. The thermobalance allows, by gravimetry, a continuous record of the evolution of the deposited carbon during and at the end of the test and the extraction of a sufficient amount of homogenous sample to study the involved structural changes in Ni and the structural properties of the deposited carbon by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of the operating temperature, mainly derived from thermal sintering, on Ni particles and on the deposited carbon is highly significant. The effect of methane as a reactant and hydrogen as a reaction product is mostly derived from its influence on the reaction rate. Additionally, methane and hydrogen reduce the effect of thermal sintering on Ni lowering the surface energy by chemisorption. The study also shows that the deposited carbon on the Ni leading face probably diffuses to the Ni trailing face superficially, and not through bulk Ni as assumed by the present kinetic models.