Biomass Processing via Base Catalysis

Resolving Transformative Reactions in Zeolites under Catalytic Hydrothermal Conditions

“…In the context of biomass catalysis, FAU-type zeolites facilitate chemical conversions through a combination of Brønsted acid sites (BASs) and Lewis acid sites (LASs) or incorporated active species, such as metal centers, and basicity arising from framework oxygen. ,− In addition, acido-basicity of the FAU framework could be tailored by appropriate strategies to catalyze a large number of reactions including conversion of glucose to 5-hydroxymethylfurfural, conversion of γ-valerolactone and triglycerides for biofuel production, and transesterification of vegetable oils. ,− However, FAU benefits from large pores, whereby the active sites located in the supercages account to one-third of the total catalytic active species, and a minor fraction of active sites in sodalite cages are accessible to reactants. , Thus, postsynthesis modifications such as steaming in case of Y zeolites to induce dealumination are commonly performed, resulting in mesoporous frameworks often referred to as “ultra-stabilized Y” (USY) with increased accessibility and crystallinity . Another simple strategy is the reduction of particle size down to the nanoscale in order to augment the overall accessibility of active sites. − Consequently, postsynthesis surface modification strongly influences the accessibility of different sites, reactivity, and zeolite stability in hot liquid water under relevant biomass reaction conditions, in conjunction with external factors such as pressure and temperature during the catalytic process. ,,− Despite the tremendous interest and potential of zeolites in biomass conversion, the underlying mechanistic details of how topological/morphological transformations occur in the presence of catalytically relevant hydrothermal reaction conditions have been seldom investigated at the atomic level, particularly for the zeolitic surfaces lacking long-range structural order.…”