Guaiacol Hydrodeoxygenation over Pd Catalyst with Mesoporous ZSM-5 Support Synthesized by Solid-State Crystallization

ABSTRACT Mesoporous structure is important to promote mass transport and active site utilization of zeolites when used in reactions involving bulky molecules. However, their conventional hydrothermal synthesis is energy and labor intensive, requiring high-pressure operation, and lengthy heating a huge amount of alkaline liquid. We successfully synthesized new mesoporous zeolites, Meso-ZSM-5, via solid-state crystallization of dry aluminosilicate nanogels. Neighbor developing nanocrystals further joint at edges, creating connected, inter-lattice mesoscale pathway in the finished single crystalline zeolites. Palladium was further loaded on these zeolites to form a bi-functional catalyst (Pd/Meso-ZSM-5). When used in the hydrodeoxygenation (HDO) of guaiacol, a major bio-oil compound with disappointing conversion and severe coking issue over many HDO catalysts, Pd/Meso-ZSM-5 exhibits superior guaiacol conversion and product distribution when compared with those supported on conventional microporous ZSM-5 counterparts. This is attributed to the improved diffusion and accessibility of active sites inside Meso-ZSM-5 with its unique hierarchically porous structure. Ring saturated hydrocarbons are largely produced at 200 °C when hydrogenation dominates while alkaylated aromatics become major HDO products as deoxygenation becomes favorable at 250 °C. These encouraging results may ignite the wide use of these mesoporous zeolites in many other reactions in both traditional fossil fuel and emerging renewable energy fields.