The need for sustainable production of everyday materials in addition to market volatility of petroleum-based feedstocks has motivated research into the production of renewable aromatic chemicals from biomass. Specific chemicals of interest include p-xylene, the feedstock for polyethylene terephthalate (PET). We have proposed a renewable method of producing renewable p-xylene by cycloaddition of biomass-derived dimethylfuran (DMF) and ethylene, which serves as the last step in a complete process for producing p-xylene from cellulose.1 The reaction occurs by symmetry-allowed [4 + 2] Diels-Alder cycloaddition of ethylene and DMF and subsequent aromatization by acid-catalyzed dehydration in multiple elementary steps to p-xylene.2
In our previous study, we have reported that Brønsted acid zeolite catalysts, in particular H-BEA zeolite, exhibited outstadning catalytic activity for the reaction with a selectivity of 90% to p-xylene.3 However, the lack of catalytic site for Diels-Alder cycloaddition and fast catalyst deactivation of Brønsted acid zeolite catalysts require further catalsyt development. It has been known that Lewis acid can coordinate with dienes to catalyze the Diels-Alder reaction. Previous DFT study also suggested that solid Lewis acids can catalyze the dehydration of cycloadduct intermediate to form p-xylene.4 Aiming for enhancing the production rate of p-xylene and reducing catalyst deactivation, several Lewis acid zeolites including Sn-, Zr-, and Ti-BEA and bifuncational zeolite catalysts were prepared and employed in the reaction. The results suggested that, different from metal oxides (SnO2, ZrO2, TiO2), Lewis acid zeolites (Sn-, Zr-, Ti-BEA) are active for catalyzing the reaction and yield p-xylene with a selectivity of 90%. In particular, Zr-BEA exhibited a higher reaction rate than other Lewis zeolite catalysts and Brønsted acid zeolite catalysts. The superior catalytic performance of Zr-BEA might be due to their catalytic activities for both the Diels-Alder reaction for the formation of cycloadduct and the following dehydration reaction for the formation of p-xylene. Zr-BEA also deactivates slower than other Lewis and Brønsted acid zeolite catalysts, which is partialy becasue the acid strength of Lewis acid zeolites is weaker than Brønsted acid zeolite catalysts. The hydrophobic feature of the Lewis acid zeolites developed in the study may also contribute to the slow deactivation.
(1) Williams, C. L.; Chang, C.-C.; Do, P.; Nikbin, N.; Caratzoulas, S.; Vlachos, D. G.; Lobo, R. F.; Fan, W.; Dauenhauer, P. J., ACS Catal. 2012, 2 (6), 935-939.
(2) Do, P. T. M.; McAtee, J. R.; Watson, D. A.; Lobo, R. F., ACS Catal. 2013, 3 (1), 41-46.
(3) Chang, C.-C.; Green, S. K.; Williams, C. L.; Dauenhauer, P. J.; Fan, W., Green Chem. 2014, 16 (2), 585-588.
(4) (a) Nikbin, N.; Feng, S.; Caratzoulas, S.; Vlachos, D. G., J. Phys. Chem. C 2014, 118 (42), 24415-24424; (b) Nikbin, N.; Do, P. T.; Caratzoulas, S.; Lobo, R. F.; Dauenhauer, P. J.; Vlachos, D. G., J. Catal. 2013, 297 (0), 35-43.
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