Gas phase dehydrocyclization of diphenylamine(DPA)to carbazole over monometallic and bimetallic 0.4 wt%Pt-based catalysts in a fixed bed reactor was studied in the presence of hydrogen at a temperature of 550℃.Alumina and carbon supported Pt catalysts showed very high initial activity(＞95%).The selectivity for carbazole over carbon supported Pt catalysts was slightly lower.Doping of the catalyst with potassium led to an increase in the selectivity for carbazole by 15%.Bimetallic Pt-Sn catalysts prepared by co-impregnation were less selective than catalysts prepared by successive impregnation.The selectivity for carbazole Over bimetallic Pt-Sn catalysts prepared by suc cessive impregnation Was 75%,but their activity decreased with increased Sn loading.Highly active and reasonably selective catalysts were Ir-doped bimetallic Pt-based catalysts.The conversion of diphenylamine over Pt-IX catalysts was above 98%and the selectivity for carbazole was nearly 55%,while the lifetime Was much longer.