The effects of Pt precursors on the performance of Pt/ZSM-22 catalysts for n-hexadecane hydroconversion were investigated with 0.5%platinum loading,which were prepared by the wetness impregnation technique using three platinum precursors respectively: platinum nitrate(Pt(NO3)2),hexachloroplatinic acid(H2PtCl6)and tetraamminplatinum chloride(Pt(NH3)4Cl2).The results indicated that the catalyst derived from H2PtCl6 exhibited the highest platinum dispersion and nPt/nA value,therefore displayed the highest isomerization selectivity.Three effects can be traced back to the precursors: valence state of Pt,its site(in cationic or anionic group),and the existence of chloride.The predominant effect is valence state of Pt in precursors.Different crystal orientation of Pt(0)on ZSM-22 surface was found by HRTEM in the reduced samples of Pt(Ⅳ)precursors with a direction growth along [011] crystallographic axis,while those of Pt(Ⅱ)precursors showed a crystal orientation of [001].The former may have more active(111)corner platinum sites,revealed by combination HRTEM with CO-IR studies.The catalyst with Pt sited at anionic precursor(H2PtCl6)performed a better isomerization reactivity than that with Pt sited at cationic precursor(Pt(NH3)4Cl2),ascribing to the fact that Pt with anionic precursor exhibited smaller particle size and higher platinum dispersion of Pt on the catalyst surface.Moreover,the samples containing chloride ions without amine groups in precursors were found to have better dispersion of Pt due to avoiding reduction of Pt precursors by NH3 in calcination stage.After all,the catalytic activity highly depends on the structure and Pt particle size,that is also surface/site effect.In addition,it was found that Pt(Ⅳ)and Pt(Ⅱ)tended to expose {111} and {100} planes,respectively.Moreover,Pt(111)/ZSM-22 showed higher selectivities to n-hexadecane hydroconversion than Pt(100)/ZSM-22.