‘‘Hydrogen-Free’’ Hydrogenation of Nitrobenzene Over Cu/SiO2 Via Coupling with 2-Butanol Dehydrogenation

Abstract

The feasibility of a coupled reaction system for the simultaneous production of 2-butanone (from 2-butanol dehydrogenation) and aniline (from nitrobenzene hydrogenation) over Cu/SiO2 in continuous gas phase operation without an external H2 supply has been established. Two (15.9 and 1.8 % w/w) Cu/SiO2 catalysts were prepared by deposition–precipitation and characterised in terms of N2 physisorption, temperature programmed reduction (TPR), H2 chemisorption, powder XRD, STEM and XPS analysis. Following TPR, the higher Cu loading showed a wider particle size distribution (1–15 nm, mean 7.8 nm) than 1.8 % w/w Cu/SiO2 (1–6 nm, mean 3.1 nm), where the latter exhibited a modified electronic character based on XPS measurements and a (fourfold) higher H2 uptake capacity. The reactions showed antipathetic (dehydrogenation) and sympathetic (hydrogenation) structure sensitivity in terms of turnover frequency (TOF) dependence on Cu size. We have achieved, for the first time, 100 % yield to both target products (2-butanone and aniline) with appreciably (by a factor of 50) enhanced hydrogen utilisation in the coupled system relative to conventional nitrobenzene reduction using pressurised H2. Our results establish in situ hydrogen generation via catalytic dehydrogenation as a viable hydrogenation route to commercially important products.