ABSTRACT
Abstract Activated carbon cloths (ACC) were oxidized and loaded with platinum-group metals (Ru, Pd, Pt) by cationic exchange or anionic adsorption. The ACC present a very narrow distribution of micropores that were not enlarged by subsequent treatments. The metal particles were homogeneously distributed inside the carbon fibers in the form of 2-3 nm particles. Ru/ACC catalysts exhibited a fair activity in glucose hydrogenation and gave higher yields in sorbitol (>99.5%) than Ru/C catalysts prepared from carbon powder or extrudates. The catalysts were also active in glucosone hydrogenation to fructose. Introduction Metal catalysts supported on activated carbon cloths (ACC) have been little studied in the past, particularly in liquid phase reactions (1-3). These catalysts present potentially a number of significant advantages with respect to conventional activated carbons in powder or granular form, e.g., high rate of mass transfer from the liquid phase, no need of decantation or filtration, and high flexibility to fit into any reactor geometry. The present work was intended to prepare and characterize the texture of well-dispersed ruthenium, palladium and platinum catalysts supported on activated carbon cloths. Two reactions of industrial importance, the hydrogenation of glucose to sorbitol and of glucosone to fructose were conducted on Ru/ACC and Pd/ACC catalysts, respectively, in an autoclave equipped with a special device holding the activated carbon cloth. Results and Discussion
The BET surface of ACC, oxidized ACC and Pt/ACC were 1300, 680, and 580 m2g-1, respectively. Surprisingly, the distribution of pore radius in the three samples exhibited 4 sharp peaks centered at the same position at 0.37, 0.55, 0.75, 0.95 nm, respectively (Table 1). Therefore, neither the NaOCl oxidizing treatment, nor the metal loading modified the micropore size. However, the peak heights decreased in the series ACC >> ACC(oxidized) > Pt/ACC resulting in a decrease of the differential volumes dV/dr given in Table 1. Therefore, the
micropores were not enlarged but their access was restricted because of the formation of carboxylic groups and of pore blockage by metal particles. However, new micropores centered at 1.1 and 1.3 nm were formed by the oxidizing treatment. Table 1 Distribution of pore radius and pore volume.
