Impact of catalyst reduction mode on selective hydrogenation of cinnamaldehyde over Ru-Sn sol-gel catalysts

This work is focused on the investigation and chemical reduction improvement of sol-gel Ru-Sn/SiO₂ catalysts. To clarify the reduction effect, the catalysts were characterized by a range of techniques [e.g., X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller analysis, pore size distribution, X-ray fluorescence, elementary analysis]. Liquid-phase hydrogenation of cinnamaldehyde (433 K, 70 bar, 2-propanol) was performed in order to evaluate the catalytic properties of synthesized materials. Conventional ruthenium- and sodium-modified catalysts yielded mainly saturated aldehyde, while reduced and nonreduced sol-gel catalysts afforded the formation of unsaturated alcohol with high selectivity. Chemical reduction was essential to increase the catalyst activity. A higher Sn/Ru ratio improved the selectivity to unsaturated alcohol in the cases of reduced and sodium-modified catalysts. Catalyst reduction is essential for the removal of chlorine and carbon residues. The novel coulometric method showed an increase of ruthenium surfaces in reduced catalysts. According to XPS data, Sn improves the ruthenium catalysts' selectivity performance through an electronic effect.