Upgrading of bio-oil over metal/zeolite bi-functional catalysts, is of high necessity and popularity in converting biomass to high-quality hydrocarbons (transportation fuels and petrochemicals) to reduce the overall CO2 emissions of fossil based materials.

ZSM-5 zeolites, Ga modified via different methods (in situ hydrothermal synthesis, mechanical mixing, incipient wetness impregnation, solid-state ion exchange, and liquid phase ion exchange), were systematically investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), 29Si, 27Al, and 71Ga magic-angle spinning (MAS) NMR, and H2 temperature-programmed reduction (H2-TPR). It is important to prove that both impregnation and liquid phase ion exchange could facilitate the incorporation of Ga species into the framework in addition to in situ hydrothermal synthesis. The liquid phase ion exchange method drove part of the Ga species into the framework, and it was further migrated into the framework by drying, while the incipient wetness impregnation method promoted part of the Ga species into the framework only during the calcination process. In the n-heptane catalytic aromatization procedure on the fixed bed, Ga modified ZSM-5 by in situ hydrothermal synthesis showed the highest benzene, toluene, ethylbenzene and xylene (BTEX) selectivity, owing to the increased strong Lewis acidic sites and mesopore volumes induced by the framework Ga species.

It is challenging to selectively upgrade phenolic compounds to aromatics because of much weaker adsorption of hydroxyl compared to that of phenyl upon Ni catalysts. With 10% Ni loading in theory, three Ni catalysts with different Ni nanoparticle sizes were prepared with the wet impregnation method on SiO 2 and Silicalite-1 and with the in situ encapsulation method (Silicalite-1). On the basis of the results, we proposed a general rule concerning temperaturedependent selectivity control on phenol hydroconversion over Ni catalysts. As well as benzene saturation in consecutive mode, hydrogenation of phenyl ring was more dramatically inhibited at elevated temperature via decreased adsorption of benzene rings than that of hydroxyl to selectively favor hydrogenolysis over hydrogenation in parallel mode. Among three Ni catalysts, Ni@Silicalite-1 with 3−5 nm Ni nanoparticle sizes encapsulated imposed the restricted adsorption conformation of phenol via end-up mode within channels of Silicalite-1 zeolite to further improve benzene selectivity. Because of the restriction of channels and smaller Ni nanoparticle sizes, better activity and stability were simultaneously achieved over Ni@Silicalite-1 catalyst, as well as superior benzene selectivity at higher temperature via thermodynamic hindrance on phenyl adsorption to facilitate benzene formation in kinetics rather than hydrogenation of phenyl without further saturation of benzene via hindrance on benzene adsorption.

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