Kinetic dependencies and reaction pathways in hydrocarbon and oxyhydrocarbon conversions catalyzed by ceria-based materials

Abstract

Hydrocarbons (i.e. CH4, C2H4, C2H6, and C3H8) and oxyhydrocarbon (i.e. CH3OH) conversions with and without co-reactants (H2O and CO2) were studied over ceria-based materials prepared by precipitation and cationic surfactant-assisted methods with/without Zr doping with an aim to understand their influences on material specific surface area, oxygen storage capacity (OSC), hydrocarbon reaction rate, resistance toward carbon deposition, and rigorous kinetic dependencies.High surface area CeO2 and Ce-ZrO2 from the cationic surfactant-assisted method provided a higher degree of oxygen storage capacity (OSC) and reaction rates with greater resistance toward carbon deposition than those from the precipitation method. The reaction rates (mol gcat−1 s−1) per degree of OSC (molOxygen gcat−1) were identical for all materials, indicating the linear influence of OSC on the rates. Nevertheless, the kinetic dependencies were unaffected by specific surface area, doping element, degree of OSC and reactions (i.e. H2O reforming, CO2 reforming and cracking). The rates were proportional to hydrocarbon partial pressures with positive fraction reaction orders; independent of co-reactant partial pressures; but inhibited by CO and H2. These kinetic dependencies were explained by a set of redox mechanistic proposal, in which the relevant elementary step is the reaction of intermediate surface hydrocarbon with lattice oxygen (OOx), and that lattice oxygen is efficiently replenished by rapid surface reactions with oxygen source from either CO2, H2O, or even CH3OH.