Mechanistic insights into selective hydrodeoxygenation of lignin-derived beta-O-4 linkage to aromatic hydrocarbons in water

Luo Zhicheng; Zhao Chen

摘要

The route for selective hydrodeoxygenation of phenethoxybenzene (PEB, which represents the dominant beta-O-4 linkage in lignin) to produce benzene and ethylbenzene is realized by employing a multi-functional Ru/sulfate zirconium (Ru/SZ) catalyst in the aqueous phase. One-pot hydrodeoxygenation of PEB is initially cleaved, forming C-6 phenol and C-8 ethylbenzene via the selective cleavage route of the C-aliphatic-O bond (k(1)). While the C-8 ethylbenzene is stable against further hydrogenation under the selected conditions, the C-6 phenol intermediate is hydrogenated to cyclohexanol with a rapid rate (k(2)), and the sequential steps of cyclohexanol dehydration (k(3)) as well as cyclohexene dehydrogenation (k(4)) lead to the target benzene formation. A high temperature (240 degrees C) together with a low hydrogen pressure (8 bar) is essential for achieving such a specific route, suppressing the side-reactions of aromatic hydrogenation. Compared to Ru/SZ, Pd/SZ catalyzes the high rate for cleavage of ether (k(1)), but fails in sequential C-6 phenol hydrogenation (k(2)) and cyclohexanol dehydration (k(3)), and thus is not able to accomplish the complex cascade reaction. Pt/SZ performs poorly in the primary step of ether cleavage (k(1)), and therefore, blocks the following sequential steps. The separate kinetics tests on phenol and cyclohexanol hydrodeoxygenation reveal that benzene is not produced by direct hydrogenolysis, but by the dehydration-dehydrogenation route. The high benzene yield from phenol is probably attributed to few surface adsorbed H-center dot species retained on Ru/SZ during phenol hydrodeoxygenation, as evidenced by the model reaction of cyclooctene hydrogenation with the used Ru/SZ in the presence of N-2.

机译：的选择性hydrodeoxygenation的路线phenethoxybenzene (PEB,这代表了主导beta-O-4连杆生产木质素)苯、乙苯是用人而实现的一个多功能俄文/硫酸锆(俄文/深圳)催化剂在水相。hydrodeoxygenation PEB最初裂解,形成其他酚和8乙苯通过选择性乳沟C-aliphatic-O的路线债券(k(1))。反对进一步加氢下选中其他条件下,苯酚中间氢化和快速环己醇(k(2))和环己醇的顺序步骤脱水(k(3))和环己烯脱氢(k)(4)导致目标苯形成。与低氢压力(8条)基本实现这样一个特定的路线,抑制芳香的副反应加氢。劈理的高速率醚(k(1)),但是未在其他顺序苯酚加氢(k(2))和环己醇脱水(k (3))因此不能完成的复杂级联反应。醚裂解的主要步骤(k (1))因此,块下面的顺序步骤。苯酚和单独的动力学测试环己醇hydrodeoxygenation显示,苯并不是直接产生的氢解作用,但在dehydration-dehydrogenation路线。从酚可能是高苯产量归因于一些表面吸附H-center点在苯酚物种保留俄文/深圳模型hydrodeoxygenation,就是明证环辛烯加氢的反应使用俄文/深圳的n - 2。

Mechanistic insights into selective hydrodeoxygenation of lignin-derived beta-O-4 linkage to aromatic hydrocarbons in water

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