Impact of Pd:Pt ratio of Pd/Pt bimetallic catalyst on CH4 oxidation

Abstract

Bimetallic Pd/Pt catalysts have recently attracted considerable attention in controlling emission control of methane. Here, we show the impact of Pd/Pt ratio (1:0, 9:1, 3:1, 1:1, 1:3, 1:9, 0:1) on the catalytic methane oxidation under simulated exhaust environments from the CH4-rich to-lean feed. Under dry feed conditions, the CH4 oxidation activity was linear to the Pd:Pt ratio, where the Pd-only (1:0) exhibited the best performance. However, under wet feed conditions containing 5% of water vapor, bimetallic Pd/Pt catalysts having a small fraction of Pt showed superior overall activities in a wide range of reaction environments. The interaction of Pd-Pt, forming active PdO-Pt pair sites, was confirmed by a series of analysis such as STEM-EDS, XPS and H2-TPR. The evidence by DFT calculations relates the distinct properties of bimetallic Pd/Pt sites to (i) stable CH4 adsorption, (ii) facile C-H bond cleavage and (iii) weaker adsorption of water on Pt site.