| The effects of modifying nano-HZSM-5 zeolite with different transitional metal ions and different steamed vapor temperatures and the effect of alkali metal ion and transional metal ion joint modification on its catalytic performance in mixed C4 liquid petrol gas cracking were studied in a small fixed bed reactor. By using catalyst characterization means such as, XRF, NH3-TPD, the following results are obtained:(1) Compared with HZSM-5, ethylene-propylene selectivity was improved obviously by modifying the H-type zeolite with steame, aromatics selectivity went down. Considering both high ethylene-propylene selectivity and aromatics selectivity, 540℃is the best steaming temperature. Aromatics selectivity obviously increased and ethylene-propylene selectivity little decreased over the transitional metal modification catalyst, the highest aromatics selectivity could come to 60%; the conversion rate of butane and butene decreased with the grow of steaming temperature; butane conversion rate decreased and butene conversion rate increased over Fe3+ modification catalyst; butane conversion rate and butene conversion rate increased over Zn2+ modification catalyst. The transformation of butene isomers was seen becoming more and more difficult at the sequence of butene-1, trans-butene-2, cis-butene-2, iso-butene and i-butane is more active than n-butane..(2) The effects of reaction conditions on the cracking of C4 hydrocarbons were studied with BP-01 catalyst. Results show that, low pressure, suitable butane consistency, and high temperature were beneficial for improving ethylene-propylene selectivity and aromatics selectivity. The suitable conditions were featured by 1 atm, 500～530℃, none carrier gas, and the consistency of butane higher than 70%.(3) Compared with transitional metal modification, alkali metal ion and transional metal ion joint modification lowing down the selectivity of dry gas and propane, increased the overall selectivity of ethylene-propylene and aromatics selectivity.
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