Structural and mechanistic investigation of a phosphate-modified HZSM-5 catalyst for methanol conversion

Langmuir : the ACS Journal of Surfaces and Colloids
Saifudin M AbubakarJames F Haw

Abstract

Phosphorus modification of a HZSM-5 (MFI) zeolite by wet impregnation has long been known to decrease aromatic formation in methanol conversion chemistry. We prepared and studied a catalyst modified by introducing trimethylphosphine under reaction conditions followed by oxidation. Magic-angle spinning (MAS) NMR shows that extensive dealumination occurs, resulting in a catalyst with a much higher framework SiO2/Al2O3 ratio, as well as extraframework aluminum and approximately 1.4 equiv of entrained phosphoric acid (under working conditions) per aluminum. Upon dehydration or regeneration, the phosphoric acid is converted, reversibly, to entrained P4O10. The aromatic selectivity of the modified catalyst is significantly lower than that of an unmodified zeolite with a similar, increased framework SiO2/Al2O3 ratio. By comparing the rates of H/D exchange in propene under conditions similar to those in methanol conversion chemistry, we determined that the acid site strength is indistinguishable on modified and unmodified zeolites, and this is consistent with theoretical modeling. On the phosphorus-modified zeolite, the rate of propene oligomerization is greatly suppressed, suggesting that entrained phosphate is an impediment to steric...Continue Reading

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Citations

Jan 17, 2014·Physical Chemistry Chemical Physics : PCCP·Hendrik E van der Bij, Bert M Weckhuysen
Jan 10, 2014·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Hendrik E van der BijBert M Weckhuysen
Jun 9, 2015·Chemical Society Reviews·Hendrik E van der Bij, Bert M Weckhuysen
Nov 6, 2014·Chemistry : a European Journal·Hendrik E van der BijBert M Weckhuysen
Apr 24, 2018·Physical Chemistry Chemical Physics : PCCP·Yueying ChuAnmin Zheng
Jun 26, 2021·Chemical Science·Raquel SimancasTatsuya Okubo
Aug 30, 2019·Journal of the American Chemical Society·Simon BailleulVeronique Van Speybroeck

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