QUANTUM-CHEMICAL MODELING OF ADSORPTION OF CARBON TETRACHLORIDE AND ITS HYDRODECHLORINATION PRODUCTS ON SURFACE OF PALLADIUM CLUSTERS

Liquid-phase hydrodechlorination of carbon tetrachloride in the presence of palladium-containing catalysts based on nanodiamonds (1 wt. % Pd/ND) and activated carbon (1 wt. % Pd/C) was carried out under mild conditions (solvent – ethanol, T = 318 K, Pн2 = 0.1 MPa). Catalyst 1 wt. % Pd/ND turned out to be more active (TOF = 3.5 min–1) compared to the catalyst based on activated carbon (TOF = 2.5 min–1). According to gas-liquid chromatography data, the process of hydrodechlorination proceeds stepwise with the formation of trichloromethane and dichloromethane, however, hydrodechlorination products do not immediately enter the reaction mass, but remain on the surface of the catalyst and undergo further transformations. The degree of conversion of carbon tetrachloride increases nonlinearly and reaches about 70-80%, depending on the nature of the catalyst after five hours of reaction. The simulation of adsorption of carbon tetrachloride molecules and reaction products (mono-, di-, trichloromethanes and methane) on the surface of the active centers of a catalyst – Pd13 cluster was carried out by the quantum-chemical method (DFT/PBE/LANL2DZ). In the Pd13+complexes, the substrate geometry of the Pd13 cluster changes slightly: the Pd–Pd bonds lengths involved in the interaction with the chlorine atoms of the substrates have increased. The geometry of the substrates changes more significantly: the C–Cl(H) bonds involved in the interaction with the palladium atoms lengthened from 0.010 to 0.136 Å. Based on the results of quantum chemical calculations, it can be assumed that on the Pd13 cluster possible formation of Pd13+substrate complexes with different adsorption energies. Moreover, the more chlorine atoms in chloromethane molecules form a bond with the atoms of the cluster, the higher the value of the adsorption energy.