Density Functional Theory Study of the Adsorption of Formaldehyde on Pd4 and on Pd4/γ-Al2O3 Clusters

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 112; no. 38; pp. 8929 - 8937
• Main Authors: Carneiro, José Walkimar de M, Cruz, Maurício T. de M
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 25.09.2008
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp801591z

B3LYP/LANL2DZ and B3LYP/6-31G(d)-restricted and -unrestricted calculations are employed to calculate energies and adsorption forms of formaldehyde adsorbed on planar and on tetrahedral Pd4 clusters and on a Pd4 cluster supported on Al10O15. Formaldehyde adsorbs on planar Pd4 in the η2(C,O)−di-σ adsorption mode, while on tetrahedral Pd4, it adsorbs in the η2(C,O)−π adsorption mode. The adsorption energy on planar Pd4 is −21.4 kcal·mol−1, whereas for the tetrahedral Pd4 cluster, the adsorption energy is −13.2 kcal·mol−1. The latter value is close to experimental findings (−12 to −14 kcal·mol−1). Adsorption of formaldehyde on Pd4 supported on an Al10O15 cluster leads essentially to the same result as that found for adsorption on the tetrahedral Pd4 cluster. Charge density analysis for the interaction between formaldehyde and the Pd4 clusters indicates strong backdonation in the η2 adsorption mode, leading to positive charge on the Pd4 cluster. NBO analysis shows that the highly coordinated octahedral aluminum atoms of Al10O15 donate electron density to the supported Pd4 cluster, while tetrahedral aluminum atoms with lower coordination number have acidic nature and therefore act as electron acceptors.