Identification and quantification of Sn-based species in trimetallic Pt-Sn-In/Al2O3-Cl naphtha-reforming catalysts

Trimetallic Pt/Al2O3SnIn-Cl naphtha-reforming catalysts were prepared via co-precipitation route. Platinum and chlorine were introduced by the incipient wetness technique on the alumina support already doped with about 0.3 %wt of Sn to obtain about 0.3 %wt of Pt and 1.5 %wt of Cl. For the same Pt, Sn and Cl composition, indium loading ranged from 0.06 to 0.6 wt.%. The obtained catalysts were investigated by Sn-119 Mossbauer spectroscopy between 95 and 300 K. Two Sn(IV), Sn(II) and Sn(0) environments have been identified and well characterized by their hyperfine parameters. The Lamb-Mossbauer factors have been determined for each environment and found to be 0.53, 0.27 and 0.31 for Sn(IV), Sn(II) and Sn(0) respectively. The addition of indium has been found to favour the formation of PtxSn alloys. Sn-119 Mossbauer spectroscopy results show that addition of even small amount of In (0.06 wt.%) leads to the formation of a Pt3Sn alloy. At higher indium loadings, higher amounts of PtxSn alloys of almost equal Pt and Sn atomic concentrations were detected. The increasing formation of PtxSn alloys with higher indium loading is in good correlation with a decrease of catalyst's overall conversion and selectivity to C1 and C3-C4 paraffins and increase of isomerization selectivity.