P promotion on the performance of Pd-based catalyst for emission control of natural gas driven vehicles

A model catalyst for natural gas vehicles (NGVs), Ce-Pd/Al2O3 (Pd-C/A), was modified with P. The chemical properties of the catalyst were affected significantly by P modification. The P-modified catalyst (Pd-CP/A) showed better reducibility, more Pd step sites and surface PdO species. The catalysts were tested for the removal of CH4, CO and NO under simulated stoichiometric NGVs exhaust conditions. Compared to Pd-C/A, Pd-CP/A showed enhanced activity for the removal. The time on stream (TOS) results further demonstrated that the P additive was capable to stabilize Pd species in the form of active PdO, resulting in significantly improved durability for Pd-CP/A. The electronic interaction of Pd with P was found to contribute to the stabilization. The P additive could also considerably suppress the formation of PdO2 which is much less active for the reactions. Our work may provide a general approach to design highly efficient catalysts for NGVs emission control. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.