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A bimetallic Pd-Pt catalyst (0.5 and 0.9% w/w of Pd and Pt, respectively) supported on activated carbon has been prepared and tested for hydrodechlorination of dichloromethane (DCM). Different reduction temperatures were used during the catalyst synthesis, and the catalyst reduced at 250 °C was tested under varying reaction conditions, which included H/DCM molar ratio, inlet DCM concentration, reaction temperature and space-time, always at 1 atm pressure. Formation of bimetallic particles was evidenced by TEM. Complete dechlorination was achieved at 250 °C, 2.5 kg h mol space-time and H/DCM = 50. Graphical Abstract: [ABSTRACT FROM AUTHOR]

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, 77 K N 2 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 0.6 kg h mol −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 0.90 wt.% of Pt and 0.50 wt.% of Pd yielded the best results. Under intensified conditions, viz. 250 °C and 1.73 kg h mol −1 , 100% DCM conversion and 98.6% overall dechlorination were obtained. This catalyst had most of its metallic particles within the range of 0.5–1 nm. [ABSTRACT FROM AUTHOR]

Abstract: Monometallic (Pt or Pd) and bimetallic (Pt–Pd) catalysts supported on zirconia promoted with sulfate (SZ) or tungsten oxide (WZ) were prepared and tested in the gas-phase hydrodechlorination of dichloromethane. The catalysts showed a high selectivity to non-chlorinated products (between 80% and 90% at 250°C) being methane the main reaction product. As a general trend, the WZ catalysts yielded significantly higher dichloromethane conversion than the SZ ones, yielding all the catalysts initial conversions higher than 80% at a reaction temperature of 250°C. However, the former showed a very poor stability regardless of the metallic active phase. On the other hand, the presence of palladium in the sulfated zirconia catalyst avoids deactivation as proved in long-term experiments (80-h time on stream). XPS and elemental analyses of the used catalysts suggest that adsorption of organochlorinated species is a cause of deactivation by blocking the active sites. In the monometallic SZ Pt catalyst, deactivation occurs also by poisoning of the Pt sites by the H2S resulting from sulfate reduction under the hydrogen-rich gas atmosphere. The metal particle size appears to be a critical point with regard to stability of the catalysts. The one with the highest dispersion showed the highest stability with no signs of deactivation after more than 80h on stream. [Copyright &y& Elsevier]