Factors controlling the activity and selectivity of conversion of cyclohexane in the presence of hydrogen over ruthenium supported on alumina

Abstract

The effects of Ru dispersion (or particle size) and residual Cl of Ru/Al₂O₃ on the catalytic activity and the selectivity for the cyclohexane conversion in the presence of hydrogen were investigated. In the case of Cl-free Ru/Al₂O₃ prepared from Ru₃(CO)₁₂, the turnover frequency (TOF) of hydrogenolysis was greater for higher Ru dispersion, and that of dehydrogenation was nearly independent of the dispersion, where TOF was calculated on the basis of H₂ adsorption, i.e. the selectivity depends on the Ru dispersion. For Cl-containing Ru/Al₂O₃ catalysts, which were obtained from RuCl₃ or by the addition of Cl to the Cl-free Ru/Al₂O₃, the dispersion–TOF correlations were different from those of the Cl-free Ru/Al₂O₃. Consequently, the selectivity oppositely depended on the Ru dispersion for the Cl-free and the Cl-containing Ru/Al₂O₃. The dispersion and the residual Cl were the crucial factors controlling the activity and selectivity, and these effects were differentiated.