Niobium Phosphate-Modified HY Zeolite with Enhanced Acidity and Hydroxyl Density for Efficient Alkylation of Bio-Oil Phenolics

The diversity of phenolics in bio-oil with large differences in polarity and the low reactivity of methoxyphenols poses a challenge for conventional catalysts. This paper attempts to intensify the acid strength of HY zeolite by doping niobium phosphate (NbP@HY) so as to promote the alkylation of phenolics in bio-oil. NH₃-TPD and Py-IR confirmed that the strong/Lewis acid content in NbP@HY was significantly increased, and the alkylation yields of phenol, methylphenol, and diphenol were >92%. Furthermore, XPS and FTIR characterization confirmed that the increased hydroxyl density on the surface of NbP@HY facilitates the adsorption of guaiacol, thereby boosting the alkylation yield to 94.96%. XAFS proved a pivotal role of the Nb-O-P bond for enhancing both Lewis acidity and hydroxyl density of NbP@HY. Moreover, NbP@HY still maintained high activity in real lignin-derived bio-oil with a total alkylation yield of 90.11%. In addition, NbP@HY exhibited good stability and coking was the main factor causing deactivation.