Interactionof Isophorone with Pd(111): A Combinationof Infrared Reflection–Absorption Spectroscopy Near-Edge X-rayAbsorption Fine Structure and Density Functional Theory Studies

摘要

Atomistic level understanding of interaction of α,β-unsaturated carbonyls with late transition metals is a key prerequisite for rational design of new catalytic materials with the desired selectivity toward C=C or C=O bond hydrogenation. The interaction of this class of compounds with transition metals was investigated on α,β-unsaturated ketone isophorone on Pd(111) as a prototypical system. In this study, infrared reflection–absorption spectroscopy (IRAS), near-edge X-ray absorption fine structure (NEXAFS) experiments, and density functional theory calculations including van der Waals interactions (DFT+vdW) were combined to obtain detailed information on the binding of isophorone to palladium at different coverages and on the effect of preadsorbed hydrogen on the binding and adsorption geometry. According to these experimental observations and the results of theoretical calculations, isophorone adsorbs on Pd(111) in a flat-lying geometry at low coverages. With increasing coverage, both C=C and C=O bonds of isophorone tilt with respect to the surface plane. The tiltingis considerably more pronounced for the C=C bond on the pristinePd(111) surface, indicating a prominent perturbation and structuraldistortion of the conjugated π system upon interaction withPd. Preadsorbed hydrogen leads to higher tilting angles of both πbonds, which points to much weaker interaction of isophorone withhydrogen-precovered Pd and suggests the conservation of the in-planegeometry of the conjugated π system. The results of the DFT+vdWcalculations provide further insights into the perturbation of themolecular structure of isophorone on Pd(111).