CO₂ coverage on Pd catalysts accelerates oxygen removal in oxy-combustion systems

Oxy-combustion systems result in enriched CO₂ in exhaust gases; however, the utilization of the concentrated CO₂ stream from oxy-combustion is limited by remnant O₂. CH₄ oxidation using Pd catalysts has been found to have high O₂-removal efficiency. Here, the effect of excess CO₂ in the feed stream on O₂ removal with CH₄ oxidation is investigated by combining experimental and theoretical approaches. Experimental results reveal complete CH₄ oxidation without any side-products, and a monotonic increase in the rate of CO₂ generation with an increase in CO₂ concentration in the feed stream. Density-functional theory calculations show that high surface coverage of CO₂ on Pd leads to a reduction in the activation energy for the initial dissociation of CH₄ into CH₃ and H, and also the subsequent oxidation reactions. A CO₂-rich environment in oxy-combustion systems is therefore beneficial for the reduction of oxygen in exhaust gases.