Preparation of Pd/Cu MCM-41 catalysts for hydrodechlorination: Influence of the synthesis procedure

Abstract

A series of bimetallic mesostructured Pd/Cu MCM-41 catalysts were obtained by incipient wetness impregnation and direct hydrothermal synthesis using two different silica sources (silicates and Teos) and replacing the conventional hydrothermal treatment by the microwave hydrothermal one. Catalysts were tested in the hydrogen assisted dechlorination of CF3OCFClCF2Cl to CF3OCFCF2. The influence of the synthesis procedure on the supports and catalysts chemico-physical properties was investigated by XRD, N2 adsorption/desorption, HRTEM/EDS, and TPR. The incorporation of Pd and Cu in the course of MCM-41 synthesis, regardless of the hydrothermal treatment, did not destroy the typical hexagonal channel array and ordered pore system of MCM-41. However, the calcination for the removal of the template provoked the segregation of oxides, and thus large PdCu bimetallic particles are obtained after reduction. The impregnation leads to pore-occlusion, more remarkable for the sample obtained from silicates as silica source, and after reduction, both isolated monometallic Cu particles and large bimetallic PdCu particles coexist on the external surface of the support. The larger the metallic particles, the lower the conversion of CF3OCFClCF2Cl; while the presence of monometallic particles may decrease the selectivity in CF3OCFCF2, fostering the formation of CF3OCHCF2 by dehalogenation.