L.M. Gómez-Sainero

Platinum Nanoparticles Supported on Activated Carbon Catalysts for the Gas-Phase Hydrodechlorination of Dichloromethane: Influence of Catalyst Composition and Operating Conditions

DCM is classified among the most hazardous atmospheric pollutants and therefore, the development of safe methods for the disposal of residual DCM is of great importance. Activated carbon- supported catalysts containing platinum nanoparticles as the active phase, with a high proportion of metal in the zero-valent state, were prepared in order to obtain catalysts of high performance in the gas-phase hydrodechlorination (HDC) of dichloromethane (DCM). Catalysts with Pt particles of sizes as low as 1.6 nm per average metal particle were obtained, leading to a high effectiveness in the dechlorination of effluent. All catalysts showed high initial dechlorination activity; however, a lower surface acidity in the support led to a higher stability of the conversion during the operation, as it avoids coke formation. When increasing metal load up to 2% (w/w), platinum nanoparticles of similar sizes originated, while a greater amount of Pt0 was obtained; this process therefore improved dechlorination activity to a significant extent. DCM conversion up to 90% and selectivity for non-chlorinated products higher than 90% were achieved. The influence of DCM concentration in the feed and the H2/DCM molar ratio was also investigated.

Chloroform conversion into ethane and propane by catalytic hydrodechlorination with Pd supported on activated carbons from lignin

Conversion of chloroform (TCM) by gas-phase catalytic hydrodechlorination (HDC) has been addressed to maximize the selectivity to ethane and propane. Several own-made Pd (1 wt%) catalysts have been tested. The catalysts were prepared by incipient wetness impregnation of five different activated carbons. These carbons were obtained by chemical activation of lignin with different activating agents, namely, H3PO4, ZnCl2, FeCl3, NaOH and KOH. The catalysts were fully characterized by N2 adsorption–desorption at −196 °C, CO2 adsorption at 0 °C, TPR, NH3-TPD, XRD, XPS and TEM. The activating agents provided important differences in the characteristics of activated carbon supports, and hence in the resulting catalysts, in terms of their porous texture, surface acidity, Pd oxidation state and Pd particle size distribution. NaOH and KOH activation led to carbons with the highest surface areas (2158 and 2991 m2 g−1, respectively) and low Pd0/Pdn+ ratios, while ZnCl2- and H3PO4-activated carbons yielded the highest surface acidity and mean Pd particle sizes. The analysis of the TOF values revealed that the HDC of TCM on these catalysts is a structure-sensitive reaction, increasing TOF values with Pd particle size. The best results, in terms of selectivity to ethane and propane, were obtained with the catalysts supported on KOH- and NaOH-activated carbons. The former allowed 80% selectivity to the target compounds at almost complete dechlorination (>99%) at 300 °C. The KOH-based catalyst showed fairly good stability at a reaction temperature of 200 °C.