Structural and Mechanistic Investigation of a Phosphate-Modified HZSM-5 Catalyst for Methanol Conversion

摘要: 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 catalyst modified introducing trimethylphosphine under reaction conditions followed oxidation. Magic-angle spinning (MAS) NMR shows that extensive dealumination occurs, resulting with much higher framework SiO2/Al2O3 ratio, as well extraframework aluminum approximately 1.4 equiv entrained phosphoric acid (under working conditions) per aluminum. Upon dehydration or regeneration, the is converted, reversibly, P4O10. The selectivity significantly lower than an unmodified similar, increased ratio. By comparing rates H/D exchange propene similar those chemistry, we determined site strength indistinguishable on zeolites, this consistent theoretical modeling. On phosphorus-modified zeolite, rate oligomerization greatly suppressed, suggesting phosphate impediment sterically demanding reactions.