Kinetics and deactivation mechanisms of the thermal decomposition of methane in hydrogen and carbon nanofiber Co-production over Ni-supported Y zeolite-based catalysts

This paper reports the reaction rate and deactivation kinetics of methane decomposition by using zeolite Y as the support and Ni as the active phase in a fixed bed reactor at a temperature range of 500 °C to 650 °C and at partial pressures of methane/nitrogen mixture of 0.2, 0.35, and 0.5 atm. The reaction order and activation energy were 2.65 and 61.77 kJ/mol, respectively. To quantify catalytic activity, carbon deposition rate was taken into consideration, which showed that the actual and thermodynamically predicted accumulated carbons were in good balance. Deactivation order, methane concentration dependency, and activation energy were 1.2, −1.28, and 94.03 kJ/mol, respectively. The kinetic experiment indicates that the optimum temperature range should be maintained to achieve the highest performance from 30% Ni/Y zeolite in terms of hydrogen formation rate, average hydrogen formation rate, total hydrogen formation, average carbon formation, total carbon formation, and carbon formation rate. TEM and XRD analysis were performed to characterize the deactivated, fresh, and calcined catalysts, and the results indicated that the formed filamentous carbon has the same diameter as the metallic nickel itself. The influence of volume hourly space velocity (VHSV) on methane conversion and carbon nanofiber production was also discussed.