Adsorption of Multiple H2 Molecules on Pd3 and Pd4 Clusters. A Density Functional Study

A quantum chemical study of hydrogen adsorption on carbon-supported palladium clusters

A key step for achieving better insight into catalytic hydrogenation reactions is to understand in detail the process of hydrogen adsorption on the catalyst. The present article focuses on hydrogen adsorption on carbon-supported palladium clusters, which are nowadays one of the most common catalysts in industrial applications. Density functional theory is applied to study Pd₆ and Pd₂₁ clusters to reveal the influence of the carbon support material on the properties of the catalyst as well as on the mechanisms and energetics of the hydrogen adsorption. In general, a stepwise hydrogen adsorption process is observed consisting of molecular adsorption followed by dissociative chemisorption. The carbon support material does not noticeably affect the reaction mechanisms, but has a large influence on energy barriers and preferential adsorption sites. Our comparison of Pd₆ and Pd₂₁ systems reveals that small clusters, such as Pd₆, are able to model some but not all important properties of palladium nanoparticles and, therefore, it is essential to also study larger cluster sizes.

Versatile reactivity of Pd-catalysts: mechanistic features of the mono-N-protected amino acid ligand and cesium-halide base in Pd-catalyzed C–H bond functionalization

The C–H functionalization strategies, complexity in Pd-catalyzed chemical transformations, unprecedented Pd-clustering, base (Cs-halide) and weakly coordinated amino acid ligand effects.

H-Spillover through the Catalyst Saturation: An Ab Initio Thermodynamics Study

The spillover phenomenon, which essentially involves transfer of H from a metal catalyst to a graphitic receptor, has been considered promising for efficient hydrogen storage. An open question about the spillover mechanism is how a H atom binds to graphene instead of forming the thermodynamically preferred H(2). Using ab initio calculations, we show that the catalyst saturation provides a way to the adsorption of hydrogen on the receptor by increasing the H chemical potential to a spillover favorable range. Although it is energetically unfavorable for the spillover to occur on a pristine graphene surface, presence of a phase of hydrogenated graphene facilitates the spillover by significantly improving the C-H binding. We show that thermodynamic spillover can occur, both from the free-standing and from the receptor-supported clusters. Further, the computed energy barrier of the motion of a H from the catalyst to the hydrogenated graphene is small (0.7 eV) and can be overcome at operational temperatures.

Theoretical study of the H2 reaction with a Pt4 (111) cluster

The C(s) symmetry reaction of the H(2) molecule on a Pt(4) (111) clusters, has been studied using ab initio multiconfiguration self-consistent field plus extensive multireference configuration interaction variational and perturbative calculations. The H(2) interaction by the vertex and by the base of a tetrahedral Pt(4) cluster were studied in ground and excited triplet and singlet states (closed and open shells), where the reaction curves are obtained through many avoided crossings. The Pt(4) cluster captures and activates the hydrogen molecule; it shows a similar behavior compared with other Pt(n) (n=1,2,3) systems. The Pt(4) cluster in their lowest five open and closed shell electronic states: (3)B(2), (1)B(2), (1)A(1) (3)A(1), (1)A(1), respectively, may capture and dissociate the H(2) molecule without activation barriers for the hydrogen molecule vertex approach. For the threefolded site reaction, i.e., by the base, the situation is different, the hydrogen adsorption presents some barriers. The potential energy minima occur outside and inside the cluster, with strong activation of the H-H bond. In all cases studied, the Pt(4) cluster does not absorb the hydrogen molecule.