Insights into the Hydrothermal Stability of ZSM-5 Under Relevant Biomass Conversion Reaction Conditions

Zeolite catalysts used for the conversion of carbohydrates to renewable platform chemicals (e.g., glucose to HMF) in the condensed phase are shown to be sensitive to the presence of inorganic salts which alter the zeolite surface chemistry.  Although zeolites such as ZSM-5 have been shown to be stable in de-ionized water, the presence of NaCl in the reaction mixture at dilute and saturated levels enhances the hydrolysis of the Si-O-Al bridges and the release of Al3+ species.  These dissolved Al3+ species catalyze the conversion of glucose through homogeneous catalytic processes and obscure the apparent reactivity of the zeolite catalyst.  Comparative XRD, solution-state NMR, and ICP-MS show that the reactive aluminum species in solution are leeched in a time-limited process from Si-O-Al bonds involved in extra-framework species and/or at defect sites without affecting the zeolite lattice