Deactivation mechanism of PdCl2-CuCl2/Al2O3 catalysts for CO oxidation at low temperatures

Abstract

Supported Wacker catalysts exhibited high activity for low temperature CO oxidation, but high concentrations of water in the reaction gas could lead to the deactivation of the catalyst. The PdCl 2 -CuCl 2 /Al 2 O 3 catalysts were prepared, and a high relative humidity deactivation mechanism was suggested after characterizing the fresh and spent catalyst by X-ray diffraction, N 2 absorption-desorption, X-ray photoelectron spectroscopy, H 2 -temperature programmed reduction and in situ diffuse reflectance infrared Fourier transform spectroscopy. The results showed that the water could adsorb and condense on the surface of the catalyst, which arouses the aggregation and transfer of Cu species into the internal pores of the catalyst. This weakens the interactions between the Pd and Cu species and reduces the re-oxidation ability of Pd 0 to Pd 2+ , which blocks redox cycling and results in the decrease of CO oxidation activity. 采用X射线衍射、N 2 吸-脱附、X射线光电子能谱分析、氢气-程序升温还原和原位红外漫反射等方法对新鲜和失活的PdCl 2 -CuCl 2 /Al 2 O 3 低温催化CO氧化催化剂进行表征, 研究了高相对湿度(100%)下催化剂的失活机理. 结果表明, 催化剂表面沉积的水使得活性铜物种容易从催化剂表面向载体孔道内部迁移, 由于Pd、Cu相互作用弱化从而减弱了Pd与Cu物种间的相互作用, 使得催化剂的氧化还原性能受到影响, 抑制了Pd 0 再氧化为Pd 2+ 的过程, 从而因CO氧化反应中催化剂氧化还原循环受阻而导致失活. The transfer of Cu species to the internal pores of the support in the presence of water weakens the Pd and Cu species interactions, which causes catalyst deactivation.