Studying the adsorption and activation of benzene and chlorobenzene on Ni(12%)/Al2O3 by means of gas chromatography and quantum chemistry

In studying the surface and adsorption properties of Al₂O₃ and Ni(12%)/Al₂O₃ with respect to C₆H₆ and C₆H₅Cl, it is found that adsorbate-adsorbent interaction is stronger than adsorbate-adsorbate interaction. It is shown that the calculated isosteric heats of adsorption vary in a range of 61 to 45 kJ/mol depending on adsorption magnitude; for Ni(12%)/γ-Al₂O₃, as in the case of γ-Al₂O₃, the heat of adsorption of chlorobenzene is higher at low degrees of filling than that of benzene. According to density functional theory quantum-chemical calculations of the structures of complexes (NinC₆H₅Cl) ^z and (Ni _n C₆H₆) ^z (n = 1, 4; z = −1, 0, +1), a nickel atom can penetrate into C₆H₅Cl along the C-Cl bond. It is concluded that a negative charge on nickel contributes to the efficient activation of the C-Cl bond and to an increase in the rate of desorption of benzene, a key step in the hydrodechlorination of chlorobenzene.