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, 77 K 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 ºC, 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 ºC 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 to 1 nm.

Promoting Light Hydrocarbons Yield by Catalytic Hydrodechlorination of Residual Chloromethanes Using Palladium Supported on Zeolite Catalysts

“…Catalysts 2020, 10,199 6 of 17 The different values of mean particle size can be explained by the surface acidity of the zeolites, which was analyzed by temperature programmed desorption of ammonia (NH3-TPD). Figure 4 depicts the NH3-TPD profiles of the five different catalysts.…”

“…Catalysts 2020, 10,199 7 of 17 around five times the mean particle size of HL catalyst (1.4 nm). NaY and HY followed the same tendency, showing a higher particle size than non-exchanged zeolite (4.2 nm), although the difference between these two catalysts was lower.…”

“…Catalysts 2020, 10,199 3 of 17 Figure 1 represents the nitrogen adsorption-desorption isotherms of the different catalysts at −196 °C. According to IUPAC classification, HMOR and KL isotherms are of type I, with most of the N2 uptake at low relative pressure and negligible hysteresis cycles, characteristics of microporous materials.…”

“…HDC has been extensively studied for the removal of chloromethanes due to the mild required conditions of pressure and temperature [7]. However, only a few works have reported high selectivity to olefins in the HDC reaction, using different types of supports and metallic active phases [8][9][10][11][12]. In most of those studies, deactivation and low concentration of chloromethane reactant considerably limited the possible application of the results.…”

Deactivation of a Pd/Pt Bimetallic Oxidation Catalyst Used in a Biogas-Powered Euro VI Heavy-Duty Engine Installation

“…From the X-ray diffractograms shown in Figure 3, it is evident that the peak around 40 degrees (2Θ) is shifted towards higher angles for the aged samples, in particular for the inlet sample of the engine bench aged oxidation catalyst. This indicates that the bimetallic catalyst has more mono-metallic sites, and in combination with the increased intensity of that peak, it is clear that there are larger mono-metallic particles present after aging of the catalyst [32][33][34][35]. The increased intensity is also seen for the Pd peak around 46.5 degrees, which is in agreement with the TEM analysis and activity tests, also showing that the particle size is increased and that more mono-metallic particles are present after exposure to biogas exhaust.…”