Effect of the Hydride and Carbide Phases of Palladium Nanoparticles on the Vibration Frequencies of Adsorbed Surface Molecules

Palladium-based materials, including nanoparticles, are widely used in the petrochemical, pharmaceutical, automotive, and other industries. The hydride, carbide, and oxide phases of palladium formed during the hydrogenation or oxidation reactions of hydrocarbons significantly affect the catalytic properties of the catalyst. Based on theoretical calculations performed by the density functional theory (DFT) method, the effect of Pd-Pd interatomic distances and the presence of carbon atoms occupying octahedral voids in the fcc lattice of palladium on the vibrational frequencies of adsorbed hydrocarbons represented by ethylidene is shown. Theoretical research is supported by experimental data of infrared (IR) diffuse reflectance Fourier-transform spectroscopy (DRIFTS) collected in situ during the formation of carbide and hydride phases of palladium in commercial Pd/Al2O3 nanocatalyst under the influence of ethylene and hydrogen. The proposed approach can be used to develop new methods for IR spectra analysis leading to the quantitative diagnostics of structural changes in palladium during various catalytic reactions in the in situ mode.