Enhanced activity of carbon-supported Pd–Pt catalysts in the hydrodechlorination of dichloromethane

Abstract

Monometallic and bimetallic catalysts with different proportions of Pd and Pt prepared by co-impregnation on activated carbon have been deeply characterized by inductively coupled plasma-mass spectroscopy, temperature-programmed reduction, 77K N2 adsorption-desorption, CO chemisorption, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. They have been tested in the gas-phase hydrodechlorination of dichloromethane (DCM) at atmospheric pressure, reaction temperatures of 150-200°C, and a space-time of 0.6kghmol-1. The presence of Pd and Pt in the catalysts produces a synergistic effect observed in terms of dichloromethane conversion and overall dechlorination, especially when both metals are in similar proportions. The results from catalysts characterization suggest that the enhanced activity is due to a significant decrease of the metallic particles size and an optimum ratio of electro-deficient to zero-valent species in the bimetallic catalysts. The catalyst with 0.90wt.% of Pt and 0.50wt.% of Pd yielded the best results. Under intensified conditions, viz. 250°C and 1.73kghmol-1, 100% DCM conversion and 98.6% overall dechlorination were obtained. This catalyst had most of its metallic particles within the range of 0.5-1nm