Selectivity to Olefins in the Hydrodechlorination of Chloroform with Activated Carbon-Supported Palladium Catalysts

Abstract

This study analyzes the selectivity of Pd (1 wt%) catalysts supported on different activated carbons to produce olefins from hydrodechlorination of chloroform. It was found that selectivity to olefins was favoured by a higher zero-valent to electrodeficient Pd ratio (Pd 0 /Pd n+) and by a lower amount of oxygen-containing surface functional groups on the activated carbon supports. Thus, the highest selectivity to olefins was obtained by catalysts supported on FeCl 3 and ZnCl 2-activated carbons. Conversely, the catalysts supported on KOH-, NaOH-, and H 3 PO 4-activated carbons gave the lowest selectivity to olefins. These catalysts showed higher surface concentrations of electro-deficient Pd as well as high concentrations of oxygen functional groups that enhance the adsorption of reactants and intermediates. This leads to complete hydrogenation of reaction intermediates and poisoning of active sites by the adsorption of chlorocarbon compounds. ZnCl 2-derived catalysts with the highest selectivity to olefins also showed an outstanding

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

“…Comparing the results of both studies (this work with zeolites and the previous one with activated carbons), the highest selectivities to ethane and propane were very similar at 300 °C. Hydrogen concentration has been reported to have a substantial impact on the selectivity of the HDC reaction [30]. Decreasing the H2:CM ratio generally increases the selectivity to olefins, although it can also reduce the chloromethanes conversion and even reduce the stability of the catalyst.…”

“…The conversion values decreased slightly when reducing the H2/DCM molar ratio from 100 to 10. Regarding the effect of the H2/CM Hydrogen concentration has been reported to have a substantial impact on the selectivity of the HDC reaction [30]. Decreasing the H 2 :CM ratio generally increases the selectivity to olefins, although it can also reduce the chloromethanes conversion and even reduce the stability of the catalyst.…”

“…So, the probability of hydrogen insertion into the same carbon tetrachloride fragment is higher when using Pd than with Pt, resulting in more methane with Pt, and more ethane with Pd [26]. We have previously reported two studies about trichloromethane (TCM) conversion into C2-C3 hydrocarbons by catalytic hydrodechlorination with Pd supported on activated carbons obtained by the chemical activation of lignin [29,30]. These works concluded that the KOH-derived carbon catalyst achieved the best results in terms of selectivity to ethane and propane, with a selectivity to those compounds higher than 80% and a high dechlorination degree at 300 • C. However, Pd containing ZnCl 2 -and FeCl 3 -derived carbon catalysts yielded the best selectivity to olefins.…”

The Effect of Shape-Controlled Pt and Pd Nanoparticles on Selective Catalytic Hydrodechlorination of Trichloroethylene

“…Chlorine containing organic molecules have been widely used in industry as dry cleaning solvents for degreasing, as intermediates for the production of refrigerants [1,2] or for micro structured silicon carbide films in semiconductor production [3]. However, the contamination by chlorinated organic compounds is very hazardous for the environment and causes pollution of underground water, depletion of the ozone layer and threats the human health because of toxicity and carcinogenic effects [3][4][5][6][7][8][9][10]. Trichloroethylene (TCE), being a chlorinated organic solvent, is a volatile molecule and exposure to TCE causes liver and lung tumor in mice, kidney and cervix cancer, serious central nervous problems and is potentially carcinogen for humans [3,10].…”

“…However, the contamination by chlorinated organic compounds is very hazardous for the environment and causes pollution of underground water, depletion of the ozone layer and threats the human health because of toxicity and carcinogenic effects [3][4][5][6][7][8][9][10]. Trichloroethylene (TCE), being a chlorinated organic solvent, is a volatile molecule and exposure to TCE causes liver and lung tumor in mice, kidney and cervix cancer, serious central nervous problems and is potentially carcinogen for humans [3,10]. Recycling and recovery are recommended instead of disposal [11][12][13], because thermal treatments such as incineration or catalytic combustion produce dioxine, chloro-furan and phosgene as byproducts [14][15][16][17][18][19][20].…”