''Hydrogen-free'' hydrogenation of nitrobenzene over Cu/SiO₂ via coupling with 2-butanol dehydrogenation

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 H-2 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 N-2 physisorption, temperature programmed reduction (TPR), H-2 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 H-2 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 H-2. Our results establish in situ hydrogen generation via catalytic dehydrogenation as a viable hydrogenation route to commercially important products.