A series of ZSM-22 molecular sieves were synthesized by adjusting the time of adding aluminum source by two-step crystallization method,and the distribution of acid sites was regulated.XRD,SEM,N2adsorption/desorption,NH3-TPD,FTIR,Py-IR,ICP,TEM-EDS and other characterization methods were used to characterize the phase,morphology,texture properties,acidity and element.The results show that ZSM-22 molecular sieve is synthesized in situ from amorphous silicate which is not crystallized on the surface of high silicon ZSM-22 after the first step of crystallization with the addition of aluminum source under the induction of template agent,and a layer of ZSM-22 molecular sieve with low Si/Al ratio is grown on the surface of high silicon ZSM-22,thus changing the acid site of the molecular sieve.The Pt-supported bifunctional catalyst was prepared and its hydroisomerization performance of n-dodecane was studied.The results show that the two-step crystallization of ZSM-22 can inhibit the cracking reaction in micropores and obtain higher isomerization selectivity.The conversion of S6-C at 330℃ is 89.3％,the selectivity is 89.4％,and the yield is 79.8％.ZSM-22 molecular sieve synthesized by two-step crystallization had more active sites located on the outer surface and near the pore mouth of the molecular sieve,thus changing the distribution of its isomers,reducing the proportion of isomers with branch chains at the end of the carbon chain,and preferring to generate isomers with branch chains at the middle of the carbon chain.The distribution ratio of 2-methylundecane in S12-C is about 10％lower than that of conventional ZSM-22.
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