Effects of O2/CH4 ratio on methane catalytic combustion over Cu/γ-Al2O3 particles

Rate measurements of methane catalytic combustion over copper catalyst were investigated in a fixed bed differential reactor with different pressure ratios of O2/CH4. Three kinetic regions were defined by the influence of pressure ratios of O2/CH4 on methane catalytic combustion. And surface reaction mechanism, as well as kinetic characteristics, was also discussed. It was found that, when O2/CH4 > 2, methane reaction rate had a positive relationship with methane pressure, and the reaction parameters were: α = 0.9, β = 0, Ea = 146.3 kJ/mol (α and β are reaction orders with respect to methane and oxygen, Ea is apparent activation energy). Coverage ratio of chemisorbed oxygen on catalyst surface approached a saturated state. When 0.1 < O2/CH4 < 2, both methane and oxygen could affect reaction rate (α = 0.43, β = 0.68 and Ea = 99.8 kJ/mol), and chemisorbed oxygen was unable to occupy active sites completely. When 0 < O2/CH4 < 0.1, reaction rate only depended on oxygen pressure (α = 0, β = 1.0, Ea = 60.8 kJ/mol). Chemisorbed oxygen was depleted, and unoccupied copper sites became the most abundant surface intermediates. Transition of rate-determining step was from the reaction between methane and oxygen to oxygen adsorption on catalyst surface with decreasing pressure ratio of O2/CH4.