Phosphoric Acid Zeolites for Production of p-Xylene from 2,5-Dimethylfuran and Ethylene: Homogeneous or Heterogeneous?
Jason Gulbinski,a,b Limin Ren,b,c Vivek Vattipalli,a,b Paul Dauenhauer,b,c Michael Tsapatsis,b,c Huiyong Chend, and Wei Fan*a,b
a Department of Chemical Engineering, University of Massachusetts Amherst, 686 N. Pleasant Street, Amherst, MA 01002, USA. E-mail: email@example.com;
b Catalysis Center for Energy Innovation, a U.S. Department of Energy – Energy Frontier Research Center, University of Delaware, 150 Academy Street, Newark, Delaware 19716, USA
c Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Ave. SE, Minneapolis, MN 55455, USA
d School of Chemical Engineering, Northwest University, 229 North Taibai Road, Xian, Shaanxi Province, China 710069
The renewable production of p-xylene is of high industrial importance to reduce dependence on crude oil and fossil fuels. Phosphorus containing zeolites (P-BEA) have shown very high selectivity towards p-xylene (>97%) from the reaction between 2,5-dimethylfuran and ethylene1, but the reasons for their high selectivity have not been addressed. To deduce the nature of their activity, p-xylene reactions were performed with phosphoric acid catalysts in different local environments within the reactor: 1) adsorbed on the zeolite through ex-situ impregnation of phosphoric acid as with P-BEA, 2) free phosphoric acid in the absence of solid support, and 3) free phosphoric acid in the presence of solid support, but not impregnated ex-situ. Free phosphoric acid is active in catalyzing the reaction in the absence of solid support, but the reaction selectivity is highly dependent on phosphoric acid concentration. The presence of solid support increases the selectivity to p-xylene even at high concentration of phosphoric acid; however, the physical properties of the support can greatly influence the activity phosphoric acid. Stability of the phosphoric acid on solid support under reaction conditions are also studied; while phosphorus in P-BEA shows high stability under reaction conditions and likely catalyzes the reaction heterogeneously, free phosphoric acid with solid support may have both heterogenous and homogenous reaction occurring in tandem. 31P NMR is used to observe the various phosphorus species on the surface of P-BEA, and humidity treatment reveals how the phosphorus species change upon exposure to water. Temperature-programmed desorption (TPD) of a probe amine molecule on P-BEA reveals how the Bronsted acid character of the zeolite changes with calcination temperature.
 Cho, H.J., et al., Renewable p-Xylene from 2,5-Dimethylfuran and Ethylene Using Phosphorus Containing Zeolite Catalysts. ChemCatChem, 2017. 9(3): p. 398-402.