C–O Bond Hydrogenolysis of Biomass–Derived Cyclic Ethers over Ni–Based Catalysts

Catalytic deoxygenation reactions play a crucial role for upgrading of biomass–derived oxygenates to high value chemicals. Among several deoxygenation processes, C–O hydrogenolysis has emerged as a viable technology to convert oxygenates such as sugar polyols and furanic derivates into target molecules. The key element to selectively cleave the C–O bond is the development of an efficient catalytic system, while minimizing the side reactions and carbon loss. Recent experimental studies suggested that rhodium and iridium catalysts modified by some oxophilic metals such as Re, Mo, W and V oxides display high activity and selectivity in the hydrogenolysis of glycerol^[1], tetrahydrofurfuryl alcohol (THFA)^[2] and tetrahydropyran–2–methanol (2–THPM)^[2-3] to their corresponding α,ω–diols. However, due to the high cost and depleting resources of noble metals, it is necessary to develop catalytic systems based on non–noble metals. Among non–noble metals, nickel–based catalysts are widely used in hydrogenation and hydrogenolysis reactions because they exhibit good catalytic performance and are inexpensive. It was reported that C–O bond cleavage can be occurred over Ni catalysts at temperatures above 473K for both furan and tetrahydrofuran rings^[4-5] . Therefore, in this contribution we focus on synthesis of Ni–based catalysts, suitable for ring opening of cyclic compounds derived from furanic conversions, particularly THFA. The effect of Ni and different support properties on their performance as THFA hydrogenolysis catalysts was examined under liquid phase reaction. The synergistic roles of the metal and acid sites of Ni/HZSM–5 and the reaction mechanism of THFA hydrogenolysis as well as their respective reaction intermediates and products are described and discussed. Ring opening of THFA into 1,5–PDO takes place over both nickel metallic sites and HZSM–5 acidic sites, followed by ring closure into tetrahydropyran (THP) product over acidic sites up to 70% yield.

[1] Y. Nakagawa, M. Tamura, K. Tomishige, J. Mater. Chem. A. 2014, 2, 6688-6702.

[2] Y. Nakagawa, M. Tamura, K. Tomishige, ACS Catal. 2013, 3, 2655-2668.

[3] T. Buntara, S. Noel, P. H. Phua, I. Melián‐Cabrera, J. G. de Vries, H. J. Heeres, Angew. Chem. Int. Ed. 2011, 50, 7083-7087.

[4] S. Sitthisa, D. E. Resasco, Catal. Lett. 2011, 141, 784-791.

[5] J. Lee, Y. Xu, G. W. Huber, Appl. Catal., B. 2013, 140, 98-107.