(513d) Effect of Water Concentrations on the Cyclohexanol Dehydration in Zeolites - a First Principles Density Functional Theory Study

The Catalytic conversion of lignocellulosic biomass resources to transportation fuels and value-added chemicals has been attracted enormous interests due to the decreasing fossil fuel supplies and environmental concerns. Aqueous phase hydrodeoxygenation (HDO) of lignin-derived model linkages via direct hydrogenolytic C−O bond cleavage over supported metal catalysts and sequential hydrogenation-dehydration reactions catalyzed by solid acid catalysts is one of most promising routes. In this regard, phenol HDO generally proceeds over a dual functional catalyst. The hydrogenation of phenol leads to the formation of cyclohexanol, which is dehydrated using zeolite catalysts.In the present study, the dehydration mechanism of cyclohexanol and the possible ether formation via the C-C coupling in the presence of hydronium water clusters (e.g., (H₂O)_n·H₃O⁺) (n=1~24) were studied using periodic density functional theory (DFT) calculations. The catalytically active hydronium water clusters affect both the protonation equilibrium of cyclohexanol and the rate-limiting C−O bond cleavage. Our DFT results not only illustrate recent experimental observations, but also provide fundamental insights into Aqueous-phase alcohol dehydration using zeolite catalysts.