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

• The higher Mn+/M0 ratio and larger metal particle size intensify deactivation of Pd/C.
• Metal sintering and blockage by reactants and/or reaction products take place in Pd/C.
• Pd/C shows greater deactivation when dichloromethane (DCM) is used as the reactant.
• A PdCx phase is formed by the incorporation of carbon atoms from the DCM in the Pd lattice.
• DCM chemisorption on Pdn+ and formation of PdCx promotes deactivation of Pd/C under DCM.

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 90 h 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 H2 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 PdCx phase by the incorporation of carbon atoms into the metal lattice.

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