Preparation and characterization of bifunctional Pt-Sn/H[Al]ZSM5 catalysts

Bifunctional monometallic Pt/H[Al]ZSM5, Sn/H[Al]ZSM5, and bimetallic Pt-Sn/H[Al]ZSM5 (tin atomic fraction, X_Sn, of 0.46) catalysts were prepared and characterized by means of XPS, ESR, TEM, and toluene hydrogenation. The species on their surface and the presence of an effect of the electronic and/or geometric type between Pt and Sn in the bimetallic catalyst, which would lead to the existence of reduced tin species (Sn⁰ and/or Sn-Pt), were determined. These species explained the decrease in the hydrogenating activity in the toluene hydrogenation reaction. The ESR analysis was compatible with the results obtained by XPS, since by means of this technique the presence of PtO_ads, Pt⁰, Pt-Sn and Sn in the form of oxides (II and/or IV) was demonstrated. Since most of the platinum and tin species detected on the surface of the catalyst were diamagnetic, the paramagnetic signal generated by Pt⁰ would be hardly detectable due to the small fraction of this species in the bimetallic Pt-Sn/H[Al]ZSM5 catalyst.