Chemical and kinetic study of acetophenone hydrogenation over Pt/Al2O3: Application of BTEM and other multivariate techniques to quantitative on-line FTIR measurements

The heterogeneous catalytic hydrogenation of acetophenone (Aceph) over Pt/Al2O3 in d8d8-toluene/h8h8-toluene at 273 K was performed in semibatch mode, using a recycle configuration and on-line quantitative Fourier transform infrared (FTIR) spectroscopy measurements. Based on the d8d8-toluene solvent used and the multivariate analysis applied, further details of the reaction chemistry were elucidated, including the following: (i) Solvent activation occurred during reaction, leading to observable hydrogenation and H–D exchange, and (ii) 1-phenylethanol (Phel), cyclohexyl methyl ketone (CMK), and cyclohexylethanol (Che) were observable products, and little H–D exchange occurred. The on-line FTIR measurements, with sensitivity on the order of 10−5 mol/L10−5 mol/L, also lead to the following kinetic observations: (i) Water had a strong inhibiting effect on the hydrogenation rates, and (ii) very interesting short time-scale kinetic behavior occurred after some perturbations. The latter included rapid initial hydrogenations on fresh catalyst (due to the presence of spillover hydrogen) and observable adsorption–desorption of other reactants. The reaction rates obtained from the well-defined experiments in h8h8-toluene were fit to a number of Langmuir–Hinshelwood–Hougen–Watson (LHHW) models, in which the effects of solvent and water were included. A model involving a pairwise addition of adsorbed dissociated hydrogen to the adsorbed substrate provided the best fit of the data. The regression of the kinetic data suggested that water made a statistically significant contribution to the competitive adsorption on the catalyst surface. In more general terms, the present contribution suggests the utility of detailed on-line liquid-phase spectroscopy together with multivariate techniques for exploratory studies of heterogeneous catalytic systems.