Properties of Carbon-supported Precious Metals Catalysts under Reductive Treatment and Their Influence in the Hydrodechlorination of Dichloromethane

Abstract

This study analyzes the effect of the reduction temperature on the properties of Rh, Pt and Pd catalysts supported on activated carbon and their performance in the hydrodechlorination (HDC) of dichloromethane (DCM). The reduction temperature plays an important role in the oxidation state, size and dispersion of the metallic phase. Pd is more prone to sintering, followed by Pt, while Rh is more resistant. The ratio of zero-valent to electro-deficient metal increases with the reduction temperature, with that effect being more remarkable for Pd and Pt. The higher resistance to sintering of Rh and the higher stability of electro-deficient species under thermal reductive treatment can be attributed to a stronger interaction with surface oxygen functionalities. Dechlorination activity and a TOF increase with reduction temperature (250–450 °C) occurred in the case of Pt/C catalyst, while a great decrease of both was observed for Pd/C, and no significant effect was found for Rh/C. Pt0 represents the main active species for HDC reaction in Pt/C. Therefore, increasing the relative amount of these species increased the TOF value, compensating for the loss of dispersion. In contrast, Pdn+ appears as the main active species in Pd/C and their relatively decreasing occurrence together with the significant decrease of metallic area reduces the HDC activity. Rh/C catalyst suffered only small changes in dispersion and metal oxidation state with the reduction temperature and thus this variable barely affected its HDC activity.

Mechanochemical Preparation of Pd(II) and Pt(II) Composites with Carbonaceous Materials and Their Application in the Suzuki-Miyaura Reaction at Several Energy Inputs

“…For comparative purposes, palladium composites with GO and MWCNT were similarly prepared by grinding in ball mill. As it was indicated above, the use of the carbon-based material aims to improve the catalyst activity and stability in the reaction medium, allowing its recovery and reuse [ 2 , 3 , 4 , 5 , 6 , 7 , 17 , 18 , 19 , 20 , 21 , 25 , 26 , 27 , 28 , 29 ].…”

“…For comparative purposes, palladium composites with GO and MWCNT were similarly prepared by grinding in ball mill. As it was indicated above, the use of the carbon-based material aims to improve the catalyst activity and stability in the reaction medium, allowing its recovery and reuse [2][3][4][5][6][7][17][18][19][20][21][25][26][27][28][29]. ICP-MS analysis of the supported Pd and Pt catalysts was carried out to evaluate the actual loading amounts of Pd and Pt on AC.…”

“…Moreover, the use of supported Pd may prevent its aggregation upon reduction with the respective drop in activity [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. Among different carbon materials, activated carbon (AC) is the most used and studied support for Pd catalysts and in the C-C coupling chemistry due to its low price and abundance, unique chemical and mechanical properties [ 20 , 21 , 25 , 26 , 27 , 28 , 29 ]. Thus, carbon is a high tensile material, able to sustain the amount of energy produced in ball milling, with the advantage of not inhibiting the SM reaction.…”

Two Scenarios of Dechlorination of the Chlorinated Hydrocarbons over Nickel-Alumina Catalyst

“…The supported noble metals (Pt, Pd, Rh, and Ru) and their alloys are recognized as the most effective catalysts for the hydrodechlorination due to their high reactivity in the target reaction and very high resistance to the deactivation caused by the chlorination [2,3,8,[10][11][12][13][14][15][16]. However, high prices and limited availability of the precious metals render their industrial applications unreasonable.…”

Editorial: Special Issue Catalysis by Precious Metals, Past and Future

“…On the other hand, A. Arevalo-Bastante et al [6] compared the activity of the carbon-supported Pd catalysts to their Pt and Rh homologues in the hydrodechlorination of dichloromethane. The Pd catalyst in this case was taken over by Pt and Rh catalysts due to their higher stability upon sintering and their ability to maintain the active site unaltered during the treatment prior reaction and therefore.…”