Solid-state solvent-free catalyzed hydrogenation: Enhancing reaction efficiency by spillover agents

The adsorption kinetics of hydrogen on solid support is accelerated by three orders of magnitude upon adding carbon nanotubes (CNT) to the support. The gas-solid catalytic hydrogenation is studied at ambient temperature and sub atmospheric pressure while the support consists of a mixture of nano Pd-on-carbon with unsaturated hydrocarbon H-acceptor. The addition of a small amount of pristine CNT minimizes the required Pd concentration. A similar effect is demonstrated by addition of different oxides to the composite, but at much higher additive concentrations. The addition of the spillover agent improves the transport of the hydrogen atoms in the composite to remote sites with low Pd concentration via a spillover mechanism. Therefore, it is possible to overcome the decelerating effect of inhomogeneity in the support. The irreversible gas-solid hydrogenation could serve as a simplified platform to study the slower step of hydrogen spillover, which operates also in hydrogen storage processes. (C) 2013 Elsevier B.V. All rights reserved.