Kinetic Study of the Hydrodechlorination of Chloromethanes with Activated-Carbon-Supported Metallic Catalysts

The kinetics of the hydrodechlorination (HDC) of dichloromethane (DCM) and chloroform (TCM) with Pd, Pt, Rh, and Ru on activated carbon catalysts has been studied at temperatures between 100 and 250 degrees C. Different kinetic models have been checked, namely, pseudo-first-order and Langmuir-Hinshelwood-Hougen-Watson (LHHW) with adsorption, chemical reaction, or desorption control. The HDC of DCM and TCM with the Pd and Pt catalysts was well-described by the LHHW model with reactant adsorption as the rate-controlling step. However, with Rh and Ru catalysts, chemical reaction and desorption of the reaction products appear to be the rate-controlling steps in the HDC of DCM and TCM, respectively. In this last case, different sets of complex reactions seem to occur on the surface of the catalyst depending on the temperature, preventing determination of a confident value of the activation energy, because of the formation of oligomeric coke-like deposits and the subsequent severe deactivation of these catalysts. The corresponding kinetic parameters for the proposed models have been calculated.