(337e) Mesoporous Catalysts for Conversion of 2,3-Butanediol to Butene

2,3-butanediol has significant potential as a platform chemical for production of renewable fuels and chemicals since it can be produced with high productivity via fermentation and provides a C4 building block for further synthesis. Previous work has shown that Cu/ZSM-5 can convert 2,3-butanediol to butene with high selecitivty (~70%) [1]. This study expands on these results by investigating the role of pore size in 2,3-butanediol conversion to butene. Three different types of mesoporous materials (Al-MCM-48, Al-SBA-15 and meso-ZSM-5) were loaded with ~20wt% CuO and tested in the conversion of 2,3-butanediol to butene. Mesoporous aluminosilicate molecular sieves Al-MCM-48 with different SiO₂/Al₂O₃ ratios of 23, 50, 100 and 200 were synthesized at room temperature by using N-Hexadecyltrimethylammonium bromide (CTAB) as the surfactant, tetraethyl orthosilicate (TEOS) and aluminum isopropoxide (Al(ⁱProx)₃) as Si and Al source [2]. Mesoporous aluminosilicate Al-SBA-15 with different SiO₂/Al₂O₃ ratios of 23, 50, 100 and 200 were prepared by the â??pH-adjustingâ? method [3], using triblock copolymer Pluronic 123 surfactant (EO₂₀PO₇₀EO₂₀) as the structure-directing agent in a strong acidic HCl solution (2M), TEOS and Al(ⁱProx)₃ as Si and Al source. Meso-ZSM-5 was prepared by using a simple NaOH treatment of parent HZSM-5 zeolite [4]. Al-MCM-48 and Al-SBA-15 materials were characterized by small-angle X-ray scattering (SAXS), nitrogen adsorption and transmission electron microscopy (TEM), which clearly showed that the obtained Al-MCM-48 and Al-SBA-15 materials have highly ordered three-dimensional (3D) Ia3d cubic and two-dimensional (2D) p6mm hexagonal mesostructure, respectively. The pore (mesopore) size of Al-MCM-48, Al-SBA-15 and meso-ZSM-5 are about 2 nm, 10 nm and 20 nm, respectively, which is determined by the pore size distributions derived from the N₂adsorption-desorption isotherms using BJH method. It should be noted that, apart from the mesopores, micropores with diameter of 0.5 nm were observed on meso-ZSM-5 zeolite, which is typical for the conventional ZSM-5.

Reactions were performed over reduced catalysts at the same reaction conditions (feed rate of 2,3-butanediol of 3.0 mL/h, hydrogen to 2,3-butanediol molar ratio of 5, reaction temperature 250 ^oC). The catalytic results demonstrated that 20%CuO/Al-SBA-15(50) exhibited the highest initial selectivity of butenes, which is 76.6% at 10 min of reaction. In addition, the results showed that the existence of mesopores on the catalysts (Al-MCM-48 and Al-SBA-15 types) could decrease the selectivities of products from cracking reactions, especially C₃⁼ and C₅⁼- C₇⁼, by comparison with the previous report on the catalyst 20%CuO/ZSM-5(280) [1]; meanwhile, the selectivity of C₈⁼ was found to increase with increasing pore size of the catalyst. However, the activities of the catalysts with MCM-48 and SBA-15 types were decreased dramatically over time. With respect to CuO/meso-ZSM-5(280) catalyst, it can be seen that the catalyst has the composited performance of both CuO/ZSM-5(280) catalyst and mesoporous copper catalysts (CuO/Al-MCM-48 and CuO/Al-SBA-15). Cu/meso-ZSM-5(280) is displayed high activity on the cracking reaction (C₃⁼, C₅⁼~C₇⁼), and the oligomerization (C₈⁼) as well. Interestingly, Cu/meso-ZSM-5(280) showed an excellent catalytic stability; the selectivity of butenes dropped from 71% to 61% in 670 min of reaction, which is much better than the catalyst with Cu loaded on the conventional ZSM-5(280), the selectivity of butenes dropped from 71% to 50% in 550 min.

[1] Q. Zheng, M.D. Wales, M.G. Heidlage, M. Rezac, H. Wang, S.H. Bossmann, et al., Conversion of 2,3-butanediol to butenes over bifunctional catalysts in a single reactor, J. Catal. 330 (2015) 222â??237. doi:10.1016/j.jcat.2015.07.004.

[2] K. Schumacher, C.D.F. Von Hohenesche, K.K. Unger, R. Ulrich, a. Du Chesne, U. Wiesner, et al., The Synthesis of Spherical Mesoporous Molecular Sieves MCM-48 with Heteroatoms Incorporated into the Silica Framework, Adv. Mater. 11 (1999) 1194â??1198.

[3] S. Wu, Y. Han, Y.C. Zou, J.W. Song, L. Zhao, Y. Di, et al., Synthesis of Heteroatom Substituted SBA-15 by the â??pH-Adjustingâ? Method, Chem. Mater. 16 (2004) 486â??492. doi:10.1021/cm0343857.

[4] J.C. Groen, J. a. Moulijn, J. Perez-Ramirez, Desilication: on the controlled generation of mesoporosity in MFI zeolites, J. Mater. Chem. 16 (2006) 2121. doi:10.1039/b517510k.