The relation between surface composition of Pd-Cu/ACC catalysts prepared by selective deposition and their denitrification behavior

Pd-Cu catalysts supported on activated carbon cloth (Pd-Cu/ACC), prepared by selective catalytic deposition, showed a high activity (92% conversion) and selectivity (ca 93%) in the liquid phase hydrogenation of nitrates to nitrogen. From this study, first knowledge on the surface composition of a family of Cu-2 wt% Pd/AC bimetallic catalysts and their remarkable influence on the catalytic behavior in nitrate hydrogenation could be obtained. The results of the surface composition determination by the combination of CO chemisorption and HRSEM reveal a specific orientation for the Cu metal deposition on the core Pd crystallites, probably of Pd-Cu bimetallic islets and free Pd atoms. The main differences between samples with different Cu loadings are attributed to changes in these two metallic phases over the surface of metallic particles and they are reflected in the activity and selectivity of nitrate hydrogenation. The results reveal that TOFCu, i.e., the number of nitrate ions consumed per second per active surface Cu seems to be independent of surface composition, while TOFPd was found to increase with surface Cu, indicating the bifunctional nature of the Cu-Pd sites responsible for the nitrate reduction by red-ox reaction. Also, the surface ratio of Pd-Cu sites that catalyze nitrate-to-nitrite hydrogenation, to Pd sites, which catalyze the hydrogenation of nitrite to nitrogen, should be optimal. This might offer novel possibilities for the design of fibrous catalyst showing better performance. (C) 2008 Elsevier B.V. All rights reserved.