Fixed bed enantioselective heterogeneous catalysis and on-line spectroscopic study of liquid phase heterogeneous catalysis

Abstract

Multiple syntheses including modification, de-modification, and re-modification, were successfully used for alternating enantiomer syntheses on one-and-the-same chiral fixed bed reactor. Residual chiral induction and enantiomeric excess reversal were observed during piece-wise continuous multiple syntheses. An irreversible modification of the surface was suggested during the 50A?C cleaning step. This would constitute a 2nd and previously unknown origin for the stereo-differentiation in the Orito reaction. Two models, involving modification of the support surface and morphological changes in the platinum crystallites were proposed. A versatile and compact experimental apparatus for the on-line spectroscopic study of liquid- phase catalytic systems was designed and characterized. The utility of the system was demonstrated by two semi-batch differential heterogeneous catalytic reactions, the racemic hydrogenation of acetophenone and 2-butanone over Pt/Al2O3, where band-target entropy minimization (BTEM) and multivariate analytical techniques were used for the signal processing. New aspects for hydrogenation of simple ketones with toluene as solvent over Pt/Al2O3 catalyst are elucidated, which includes: (i) the coexistence of competitive hydrogenation of solvent; and (ii) the significance of the trace amount of water in the reaction system, which may account for the low reaction rates as shown in hydrogenation of 2-butanone in d8-toluene. Langmuir-Hinshelwood (L-H) model was used to fit the kinetic data of acetophenone hydrogenation to 1-phenylethanol in toluene at 0 oC with the effects of water and solvent included.