Hollow ZSM-5 Encapsulated with Single Ga-atoms for the Catalytic Fast Pyrolysis of Biomass Waste

The development of efficient metal-zeolite bifunctional catalysts for catalytic fast pyrolysis（CFP） of biomass waste is highly desirable for bioenergy and renewable biofuel production.However,conventional metal-loaded zeolites often suffer from metal sintering during pyrolysis and are thus inactivated.In this study,single-site Ga-functionalized hollow ZSM-5（GaO x @HS-Z5） was synthesized via an impregnationdissolution-recrystallization strategy without H 2 reduction.The Ga atom was coordinated to four oxygen atoms in HS-Z5 frameworks.Benefitting from the highly dispersed single-Ga atoms and hollow zeolite framework,3GaO x @HS-Z5 performed the best in producing hydrocarbon-rich bio-oil compared to impregnated 3GaO x /HS-Z5 and H 2 -reduced 3Ga@HS-Z5 in the maize straw CFP.In particular,3GaO x @HS-Z5 delivered the highest bio-oil yield（23.6 wt%） and hydrocarbon selectivity（49.4 area%）.3GaO x @HS-Z5 also retained its structural integrity and catalytic activity after five pyrolysis-regeneration cycles,demonstrating its advantage in practical biomass CFP.The elimination of H 2 reduction during the synthesis of catalyst provides an additional advantage for simplifying the CFP process and reducing operating costs.The retained Ga micro-environment and anti-sintering properties were unique for 3GaO x @HS-Z5,as severe metal sintering occurred during pyrolysis for other metals（e.g.,NiO x ,ZnO x ,FeO x ,and CoO x ） that encapsulated HS-Z5.