The gas phase hydrogenation of 2-butanone over supported nickel catalysts:introduction of enantioselectivity

The gas phase hydrogenation of 2-butanone to 2-butanol at 343 K promoted us ing a Y zeolite-supported nickel catalyst (2.2% w/w Ni) prepared by ion exc hange and a range of Ni/SiO2 catalysts (1.5-20.3% w/w Ni) prepared by preci pitation/deposition and impregnation has been studied. The freshly activate d catalysts generated racemic products and enantioselectivity was introduce d to a negligible degree by in situ and to an appreciable degree by ex situ treatment with a methanolic solution of L-tartaric acid. The effectiveness of the latter modification was strongly dependent on modifier concentratio n and an optimum enantiomeric excess (ee) of 31% was achieved at an interme diate tartaric acid concentration (8 x 10(-3) mol dm(-3)) where the latter also served to raise the fractional conversion of the 2-butanone feedstock when compared with the unmodified catalyst under the same reaction conditio ns, Treatment with L-valine or L-glutamic acid did not result in the introd uction of any appreciable level of product optical activity. Conversion of 2-butanone over Ni/SiO2 was subject to a short term loss of catalytic activ ity which was however readily restored by heating in flowing hydrogen at 67 3 K. Deactivation of the Ni/Na-Y catalyst was more severe and was not rever sed by such a heat treatment; loss of activity in this case is attributed t o an irreversible pore blocking. Non-selective hydrogenation is approximate d by pseudo-first-order kinetics, the possibility of thermodynamic limitati ons is considered and the effects of varying the hydrogen partial pressure and gas space velocity are addressed. The reaction exhibits a high degree o f structure sensitivity and the relationship between specific rate constant acid nickel particle diameter is presented wherein an optimum particle siz e of ca. 3 nm is identified. (C) 2000 Elsevier Science B.V. All rights rese rved.