Selective hydrogenation of unsaturated carboxylic acids

Abstract

The production of valuable unsaturated compounds, e.g. aromatic alcohols and unsaturated acids, is one of the most important processes in industry, some of which can be achieved by selective hydrogenation of the widely available unsaturated carboxylic acids. Mild reaction conditions are preferred with the consideration of economy and sustainability. Herein, the liquid phase hydrogenation of unsaturated acids, benzoic acid, its derivatives and sorbic acid is investigated over Pt and Pd based catalysts, using tin dioxide, alumina and titania as the support. The addition of Sn and Re shows a promotional effect in the selectivity to the desired products. The interaction between metal(s) and metal oxide has been found to be the key of the high selectivity, which can also be influenced by the support via metal-support interaction. Pt/SnO2 and Pt-Sn/Al2O3 have been tested and shown to be highly selective and active in production of benzyl alcohol from benzoic acid, where the Pt-SnOx interaction with oxygen vacancies created during reduction has been found to be key for activation of the COOH group. Density functional theory (DFT) also suggests that the partially reduced tin oxide alters the adsorption mode of the reagent on the catalyst surface. Pt-Sn/Al2O3 has also displayed a high selectivity to hydrogenation of the carboxylic acid group of various benzoic acid derivatives, indicating the versatility of the catalyst. Pd-Re/TiO2 has been developed to selectively hydrogenate sorbic acid to 2-hexenoic acid. The oxophilicity of Re species and its dilution of Pd hinders the further hydrogenation of 2-hexenoic acid, improving the yield. Preliminary experiments in the continuous flow reactor with the selectivity to 2-hexenoic acid maintained indicates the feasibility in applying the catalyst for the continuous process.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Arthur Garforth (Supervisor) & Chris Hardacre (Supervisor)