Alumina and zirconia supported Pt and Pt–Sn catalysts have been tested in the dehydrocyclization (DHC) of n-octane at 823 K to alkylaromatics as desired products using pure hydrogen (H2) and water vapour containing hydrogen (WVH2) atmospheres. The materials were characterized by nitrogen adsorption, NH3-TPD, TPR, XRD, XPS, TEM and EDX. The characterization results reveal the formation of PtSn alloys on alumina support after a catalyst precursor reduction in H2 at 873 K. This observation enables an interpretation of the higher on-stream stability of Pt–Sn/Al2O3 catalyst in H2 as well as in WVH2 compared to the monometallic sample, using the well-known concept of the ensemble effect of Sn by alloying to Pt. The alumina supported Pt and Pt–Sn catalysts act bifunctionally in H2 atmosphere, producing a mixture of benzene, mono- and dialkylaromatics, near the chemical equilibrium. In WVH2