Luisa Ma. Gómez-Sainero

Hydrodechlorination of carbon tetrachloride to chloroform in the liquid phase with a Pd/carbon catalyst. Study of the mass transfer steps

The e7ect of the resistance to interface mass transfer on the overall rate of the hydrodechlorination of carbon tetrachloride has been analyzed with a 1% Pd=carbon catalyst, in a bubble column slurry reactor. The reaction was carried out at 393 K and 3 MPa. The e7ect of catalyst concentration on the external di7usion was analyzed for 7:96; 19:09; 39:77 and 63:64 g l −1 TTCM (0:5; 1:2; 2:5 and 4 wt%, respectively) with an H2 <ow F(H2 )=2 4× 10 3 Nc m 3 h −1 and an average particle size of the catalyst, dp =7 5� m. The importance of the gas–liquid resistance for F(H2 )=3 × 10 3 ,1 2× 10 3 ,1 8× 10 3 ,2 4× 10 3 and 30 × 10 3 Nc m 3 h −1 was investigated with a catalyst concentration of 1:2 wt%. The e7ect of dp for 25, 75 and 130 � m was similarlystudied for F(H2 )=2 4× 10 3 Nc m 3 h −1 and 1:2 wt% of catalyst. The

Carbon-supported palladium catalysts for liquid-phase hydrodechlorination of carbon tetrachloride to chloroform

Several catalysts containing 1 wt% Pd on carbon were prepared by incipient wetness impregnation of the support with H 2 PdCl 4 (CPd series) or Pd(NO 3 ) 2 (NPd series) aqueous solutions. Catalysts of the CPd series were reduced at 393, 523, 623 and 723 K, whereas two NPd samples (one calcined and the other uncalcined) were reduced at 523 K. The TPR results indicate that reduction of Pd precursor in CPd is more difficult than in NPd samples, which are reduced at sub-ambient temperature. As shown by CO chemisorption, metal dispersion in NPd is lower than in CPd catalysts, in which dispersion decreases as the reduction temperature increases. Analysis by XPS shows that Pd 0 and Pd n+ species are present on the catalysts surface and that their proportion depends on the reduction temperature and the nature of the palladium precursor. All the catalysts were active in the hydrodechlorination of carbon tetrachloride to chloroform, the CPd samples being more selective than the NPd ones. The activity is related to the Pd n+ /Pd 0 ratio, and a maximum was found for the value≊1. The results are explained assuming that the active site is dual in nature [Pd n+ -Pd 0 ]. Carbon tetrachloride is adsorbed and activated on Pd n+ and H 2 is adsorbed and dissociated on Pd 0 . Interaction between these two adsorbed species gives CHCl 3 and HCl.

Effect of barium and lanthanum oxides on the properties of Pt/KL catalysts in the n-heptane dehydrocyclization

Six fractions of zeolite KL were impregnated with 1, 3 and 5 wt% of Ba or La, respectively, with nitrate precursors aqueous solutions. After calcination at 873 K to form BaO or La 2 O 3 , 1 wt% of Pt was incorporated to the supports by the impregnation method. Metal dispersion decreases as the Ba concentration increases, but it is not substantially affected by the La addition. The CO/FTIR and the competitive hydrogenation of benzene + toluene, results indicate that an electron enrichment of the Pt particles occurs by effect of the additives. The increase of the electron density of the Pt in Ba-catalysts is higher than for the La-catalysts. Moreover, the Ba addition highly enhances the aromatization and terminal hydrogenolysis activities, without substantial modification of the yields to the other reaction products. The yield to toluene is also increased by effect of 1 wt% of La, but it does not increases with the La concentration. The TEMEDX studies indicate that the different distribution of the BaO and La 2 O 3 in the zeolite may be the origin of the different surface and catalytic effects of these oxides in the Pt/KL catalysts.