Peculiar Formation of CO₂ in C₂H₄ Combustion by Addition of H₂

Abstract

The effect of H₂ addition on hydrocarbon oxidation over Al₂O₃-supported noble metal catalysts was investigated. CO₂ was formed below the light off temperature of olefin combustion by the addition of H₂ over Pt and Ir catalysts. Particularly for C₂H₄ combustion, Pt catalysts exhibited significant CO₂ formation at 70 °C. CO₂ formation at low temperature increased with increasing Pt particle size. CO₂ formation in the C₂H₄ + O₂ + H₂ reaction at 70 °C over Pt/Al₂O₃ decreased with increasing contact time. Pt/Al₂O₃ showed very high activity for hydrogenation of C₂H₄ even at room temperature. DRIFTS measurement revealed that ethylidene was formed as an intermediate of the C₂H₄ + H₂ reaction, and then consumed by the addition of O₂. We conclude that ethylidene intermediates of C₂H₄ hydrogenation are involved in the low-temperature CO₂ formation.