Hydrodechlorination of Carbon Tetrachloride to Chloroform in the Liquid Phase with Metal-Supported Catalysts. Effect of the Catalyst Components

Abstract

The effect of the nature of catalyst components has been analyzed in the hydrodechlorination of carbon tetrachloride to chloroform. Active carbon, alumina, silica, and sepiolite were used as supports and Ru, Rh, Pd, Pt, and Ni as the metallic phase. The catalysts were characterized by CO chemisorption, TPR, and XPS. Reaction was carried out at 373 and 413 K in a slurry semibatch reactor. Dispersion of the catalysts containing different metals are very similar, while the values corresponding to Pd supported on different carriers follow the trend Pd/Al2O3 > Pd/carbon > Pd/SiO2 ≈ Pd/sepiolite. The XPS analysis showed that Pd, Ru, and Rh are homogeneously distributed on the carbon, Pt is preferentially deposited on the external surface, and Ni is inside the pores. On the other hand, Pd on silica or alumina is mainly located on the external surface of the support. Pd/C is highly active and selective to chloroform, but Pd supported on the other carriers is less active and leads the reaction toward hexachloroethane. Hydrodechlorination activity of carbon-supported catalysts are in the order Pd/C ≫ Pt/C > Rh/C > Ru/C > Ni/C, all of them being very selective toward chloroform. The results of the reaction are interpreted in terms of the spillover of hydrogen on carbon, the distribution of the metal on the support, and the density of states of the metals.

Reduction of chloroacetone over silica-supported noble metal catalysts

“…This means that the hydrodechlorination activity is in the order of Pd > Pt Rh > Ru, Ni, Co. The order is in agreement with that observed for the hydrodechlorination of CCl 4 [27], CCl 3 -CH 3 [28], CCl 2 F-CClF 2 (CFC-113) [29], and CCl 3 -CF 3 (CFC-113a) [30], but disagrees with that observed for the hydrodechlorination of chloroaromatics [7,16], CCl 2 F 2 (CFC-12) [31], and CF 3 -CCl 2 F (CFC-114a) [32]. The order seems to depend on the reactivity of reactant, the reaction system (liquid phase or gas phase), and the reaction conditions such as H 2 /reactant ratio and reaction temperature.…”

Hydrodehalogenation of haloarenes over Silica supported Pd and Ni

“…There is an apparent discrepancy in the literature concerning the TPR response of supported Pd that is compounded by incomplete procedural descriptions and a mismatch in terms of sample pretreatment prior to TPR. While it has been reported that PdO reduction on SiO 2 and Al 2 O 3 supports takes place at room temperature [84][85][86], H 2 consumption peaks up to 523 K have also been reported [80,87,88]. The appearance of a positive TPR peak in the Pd/SiO 2 profile shown in Fig.…”

Palladium supported on structured and nonstructured carbon: A consideration of Pd particle size and the nature of reactive hydrogen

“…Pd catalysts have been established as effective in promoting hydrodehalogenation [4,[6][7][8][9][10][11][12][13][14] (hydrogenolytic C-X bond scission), which is used as a model reaction system in this study. The hydrodechlorination (HDC) of chlorobenzene over supported Pd has been shown to be influenced by such parameters as catalyst synthesis [7], nature of the support [4,7,15,16], Pd loading [7], Pd particle size/dispersion [4,7,8,12,16], actiMetal dispersion is commonly obtained from gas chemisorption analysis where a unique uptake stoichiometry is assumed; H 2 [6][7][8][9][10][11]24,[27][28][29][30][31][32][33][34], CO [4,[24][25][26][27][28][29][35][36][37][38], and O 2 …”

“…The hydrodechlorination (HDC) of chlorobenzene over supported Pd has been shown to be influenced by such parameters as catalyst synthesis [7], nature of the support [4,7,15,16], Pd loading [7], Pd particle size/dispersion [4,7,8,12,16], actiMetal dispersion is commonly obtained from gas chemisorption analysis where a unique uptake stoichiometry is assumed; H 2 [6][7][8][9][10][11]24,[27][28][29][30][31][32][33][34], CO [4,[24][25][26][27][28][29][35][36][37][38], and O 2 [1,23,24,28] are the most widely employed adsorbates. Carbon monoxide can adsorb on metals in linear and bridged forms [24] and an assessment of the literature has revealed an inconsistency in terms of the Pd/CO adsorption stoichiometry that has been employed with values of 1 [4,[25][26][27]…”