Experimental and kinetic study of methane combustion with water over copper catalyst at low-temperature

• Water has an inhibitory effect on methane combustion.
• Water adsorbed on chemisorbed oxygen, generating OH groups.
• Methane effect was weakened by increasing water pressure.
• Apparent activation energy increases from 81.4 kJ/mol to 153 kJ/mol due to water adsorption.

In this paper, the effect of water on methane combustion over a copper catalyst in a fixed-bed catalytic reactor was investigated. The activity for methane combustion gradually decreased in the presence of water, whereas when water was turned off, methane conversion recovered completely. The reaction between surface hydroxyls and gas-phase methane was investigated by DRIFTS; high hydroxyls peaks made low methane conversion. Under differential conditions, kinetic studies revealed that oxygen pressure almost had no relationship with the reaction rate (β = 0), while methane pressure obviously affected the reaction order (α = 1.07). As water was added into the feed, the reaction order with respect to methane decreased from 1.07 to 0.86. Water exhibited an inhibitory effect on methane oxidation, and the water poisoning effect was slowly reversible. When the water concentration increased, the reaction order with respect to water decreased from −0.72 to −0.95. At low temperature (<450 °C), water reacted with chemisorbed oxygen (O∗), which could form hydroxyl groups (OH∗) on the active sites. This interaction inhibited the oxydehydrogenation of methane. Hence, methane needed more energy to combine with oxygen, and the apparent activation energy increased from 81.4 kJ/mol to 153.0 kJ/mol.