Deactivation behavior of Pd/C and Pt/C catalysts in the gas-phase hydrodechlorination of chloromethanes : structure-reactivity relationship

Abstract

This study analyzes the influence of chemical and physical properties of Pd/C and Pt/C hydrodechlorination (HDC) catalysts in the different evolution of their activity during time on stream. Pt/C showed stable activity in the HDC of dichloromethane (DCM) and chloroform (TCM), while Pd/C was deactivated after 90h of operation, particularly during HDC of DCM. The deactivation of Pd/C catalyst can be attributed to the lower proportion of zero-valent species and larger metal particle size. This appears to hinder the H dissociation, enhance the irreversible chemisorption of reactants and reaction products, and favor coupling reactions (leading to the formation of carbonaceous deposits) and/or metal phase change reactions. The more extensive deactivation of Pd/C in the HDC of DCM is attributed to the stronger chemisorption of the reactant on the catalyst, which leads to the formation of a new PdC phase by the incorporation of carbon atoms into the metal lattice.