A Kinetic Study of Methane Pyrolysis over Ni–Zn/USY Catalysts

A comprehensive kinetic model for methane pyrolysis over a 50Ni–5Zn/USY catalyst has been developed. The experimental investigation was conducted in a packed-bed reactor under atmospheric pressure, with temperatures ranging from 500 to 650 °C and methane partial pressures varying between 0.225 and 0.8 bar. Various reaction mechanisms were considered, and multiple kinetic models were formulated based on the Langmuir–Hinshelwood framework, exploring several choices for the rate-determining step. Equilibrium conversion was explicitly accounted for by incorporating constraints that enforce a zero net reaction rate at equilibrium conditions, ensuring consistency with thermodynamic principles. Statistical methods were employed for model discrimination, while a packed-bed reactor model provided additional validation of the proposed conclusions. The preferred kinetic model suggests that the reaction is governed by a dissociative adsorption mechanism, with the rate-determining step being the first hydrogen abstraction from the methane molecule. The calculated activation energy of 80.9 kJ/mol aligns closely with previously reported values in the literature, confirming the validity of the proposed model.