Dehydrogenation of propane over Pt-SBA-15 and Pt-Sn-SBA-15: Effect of Sn on the dispersion of Pt and catalytic behavior

The objective of this work was to gain a better understanding of the influence of Sn on the dispersion of Pt in platinum supported SBA-15 catalysts and thereby on the dehydrogenation of propane (DHP) activity, selectivity to propylene, coking and catalyst stability. To this end, DHP over Pt-SBA-15 and Pt-Sn-SBA-15, prepared by incipient wetness impregnation (IW), was studied at 793 K by means of tapered element oscillating microbalance (TEOM) coupled with on-line gas-chromatography. This allowed us to determine simultaneously the comprehensive information from a single catalysis experiment. The catalysts were characterised by N2-physisorption, transmission electron microscopy (TEM-EDXS), X-ray diffraction (XRD) and H2-chemisorption, which revealed that the presence of Sn results in higher Pt dispersion by the formation of Pt–Sn alloy. It is evident from TEOM studies that after 220 min on stream the amount of coke formed is almost three times higher over Pt-Sn-SBA-15-IW than on its counterpart Pt-SBA-15-IW, albeit the former exhibits considerably higher propane conversion, superior selectivity to propylene and stability than the latter. It is demonstrated that propane conversion and coke formation on the catalysts can be correlated with Pt particle size. A modified drain-off effect is proposed to explain the superior selectivity and stability of the bimetallic than the monometallic catalyst.