Developing catalytic routes for upgrading biomass–derived oils in aqueous media is feasible due to the ubiquitous presence of water and its abundance in the biomass feedstock. Zeolites are promising solid acid catalysts for these applications due to high microporosity and acidity. In this work we study the impact of liquid water on the mechanistic pathway of cyclohexanol dehydration, the rate–limiting step of phenol hydrodeoxygenation (HDO), as well as the modification of the catalyst in water during catalysis. We have chosen as catalyst HBEA zeolites with different Si/Al ratios because the strong Brønsted acid sites (BAS) of HBEA can efficiently catalyze the elimination of water from cycloalkanols. The large pore size of HBEA also allows the C–C and C–O alkylation reactions parallel to dehydration. The results indicate that there is little modification of the HBEA active sites in water prior to complete zeolite framework decomposition. While aging the zeolites in water prior to catalytic testing caused a decrease in the dehydration rate, the turnover frequency (TOF) normalized to the concentration of strong BAS, however, remained nearly identical to the TOF of the parent untreated zeolites. The deactivation of the catalyst proceeds predominantly <i>via</i> the degradation of the zeolite pore walls due to Si–O–Si cleavage that follows a crack–like pattern. We suggest that the removal of framework Si is accompanied by re–precipitation leading to partial pore blocking that decreases the transport of molecules through the pores and thus inhibits the conversion on a fraction of the active sites. <br/>

Catalysis by HBEA zeolite in aqueous media: The impact of water on reaction pathways and catalyst performance

249th National Meeting (2015)

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