Selective C=O hydrogenation of cinnamaldehyde over Ir-based catalysts and the comparison with C-O hydrogenolysis of polyols

Abstract

Ir-based bimetallic catalysts supported on rutile TiO2 with low surface area were applied to selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. Ir-FeOx/rutile (Ir: 3 wt%, Fe/Ir = 0.1 (molar basis)) was particularly effective. The Ir-FeOx/rutile catalyst can be applied to selective hydrogenation of various unsaturated aldehydes (crotonaldehyde, furfural, 2-hexenal and citral) to unsaturated alcohols (≥ 95% selectivity, ≥ 81% yield). Since Ir-FeOx/rutile catalysts have been reported to be also effective in C-O hydrogenolysis of 1,2-diols to 2-monoalcohols, the structure-performance relationship was closely compared between hydrogenation and C-O hydrogenolysis. The optimum catalyst for hydrogenation had lower Ir loading and lower Fe/Ir ratio than that for C-O hydrogenolysis. In addition, high-temperature reduction of catalyst decreased the activity in cinnamaldehyde hydrogenation, while the effect of reduction temperature was reported to be small in C-O hydrogenolysis. Characterization with transmission electron microscope (TEM), CO adsorption, XPS and FT-IR suggested similar structure of the optimized catalysts in the two reactions: Ir-Fe alloy and Fem+ species modifying the alloy surface; however, higher Fem+/Fe0 ratio was observed for the optimized catalyst in cinnamaldehyde hydrogenation. From the kinetic studies (first order towards H2 pressure and zero order towards cinnamaldehyde concentration, which are similar to C-O hydrogenolysis), the nucleophilic attack of the hydride species to the adsorbed cinnamaldehyde was considered as the rate-determining step. The Ir-Fe alloy can give the hydride nature to the adsorbed hydrogen species, and the Fem+ modifier can be the adsorption site. In cinnamaldehyde hydrogenation, supplying adsorption site of cinnamaldehyde is more effective.

Supplementary files

Article information

Article type
Paper
Submitted
23 Jan 2025
Accepted
20 Feb 2025
First published
21 Feb 2025
This article is Open Access
Creative Commons BY license

Catal. Sci. Technol., 2025, Accepted Manuscript

Selective C=O hydrogenation of cinnamaldehyde over Ir-based catalysts and the comparison with C-O hydrogenolysis of polyols

Z. Dong, Y. Nakagawa, B. Liu, S. Mihara, M. Yabushita and K. Tomishige, Catal. Sci. Technol., 2025, Accepted Manuscript , DOI: 10.1039/D5CY00087D

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