Role of Ca and Pt-Ga in the conversion of propane over Ga/HZSM-5 and Pt-Ga/Hzsm-5

摘要

The conversion of light alkanes to aromatics, chiefly benzene, toluene and xylene (BTX), could be accomplished by using zeolites of ZSM- 5 type. Over HZSM-5, the propane conversion and the selectivity to aromatics are lower, but over ZSM-5 modified with Ga or Pt-Ga (bimetal), both the total conversion and the selectivity to aromatics are increased. It is found that the number of Bronsted acid sites decreases on the Ga/HZSM-5 catalyst pretreated with hydrogen. The addition of Pt promotes the reduction of Ga species on Pt-Ga/HZSM-5, and the reduced Ga species may neutralize a part of acid sites on Ga/HZSM-5, resulting in highly unsaturated sites. These sites may act as Lewis acidic sites which are able to abstract hydride Ions from propane and intermediate oligomers, and then propane forms Aromatics selectively.