(406g) Oxidant-Free Dehydrogenation of 2,3-Butanediol to 3-Hydroxy Butanone on Metal Catalysts: A Combined Experimental and Computational Study

Upgrading biomass derivatives to fuels and chemicals are believed to be sustainable alternative to petrochemical processes. 2,3-butanediol (2,3BDO) is a common biomass derived product that still lacks a sizeable derivative process. Valorisation of such di-alcohols would incentivise the biochemical routes for its production to replace the current petrochemical routes. One such derivative, acetoin (3-hydroxy butanone), is widely used in industries such as food and beverage, cosmetics, pharmaceuticals as well as chemical synthesis. Here, we report the non-oxidative catalytic dehydrogenation of 2,3-BDO over various silica-supported metal (Co, Ni, Cu, Pd, Ag, Pt) catalysts prepared by incipient wetness impregnation method. Detailed characterization of the catalysts was done using XRD, TPR, XRF and TEM analyses. The catalytic activity in dehydrogenation of 2,3BDO was evaluated in a plug flow reactor at temperatures ranging from 250 °C to 400 °C. The highest acetoin yield of around 85% was obtained on Cu catalyst, followed by Ag, Pt, Ni, Co and Pd, in that sequence. To understand the high efficiency of Cu catalyst in forming acetoin, compared to metals like Pt, and to elucidate the pathways for the formation of the different observed products, density functional theory (DFT) based calculations were performed. The two-step dehydrogenation of 2,3BDO to acetoin on Cu catalyst has relatively high activation barriers and these steps are energetically uphill. The comparatively weak interaction of acetoin with the Cu catalyst combined with the fact that the subsequent dehydrogenation steps to form diacetyl are also energetically uphill explains the formation of acetoin as the predominant product on the Cu catalyst. Acetoin may also undergo hydrodeoxygenation to form 2-butanone. The successive dehydrogenation of 2,3BDO on Pt catalyst leads to formation of diacetyl with much lower activation barriers than on Cu catalyst and these steps are energetically downhill. Diacetyl undergoes facile C-C cleavage to form C₂ species, explaining the significantly lower yield of C₄ products on Pt catalyst compared to Cu catalyst. This is likely to be the case for other active metals like Pd. This study highlights the potential for development of non-oxidative dehydrogenation processes at moderate conditions on cheap copper based catalysts for upgradation of biomass derived diols.

References

[1] K.M. Kwok, C.K.S. Choong, D.S.W. Ong, J.C.Q. Ng, C.G. Gwie, L. Chen, A. Borgna, Hydrogen‐Free Gas‐Phase Deoxydehydration of 2, 3‐Butanediol to Butene on Silica‐Supported Vanadium Catalysts, ChemCatChem 2017, 9, 2443-2447.