SYNTHESIS OF PROPYLENE-OXIDE FROM PROPYLENE, OXYGEN, AND HYDROGEN CATALYZED BY PALLADIUM-PLATINUM-CONTAINING TITANIUM SILICALITE

Pt promoted and unpromoted Pd/TS-1 catalysts were prepared by impregna tion with [Pd(NH3)(4)](NO3)(2) and [Pt(NH3)(4)]Cl-2, characterized by TPR, TEM, and ESCA and tested as catalysts for the synthesis of propyl ene oxide (PO) from propylene, oxygen, and hydrogen. The effect of var ious reduction methods and Pt loading on the catalytic performance and physical characteristics of the catalysts have been studied. The auto reduction by the amine ligands under a flow of N-2 at 150 degrees C le ads to maximum PO selectivities and yields, whereas catalysts that wer e hydrogen reduced or calcined prior to reduction were less effective. Results obtained by ESCA and TEM show that PO formation was favoured by small Pd clusters and a high fraction of Pd(II) species. Pd agglome ration was detected on the outer surface of TS-1 crystals and was espe cially pronounced for calcined and reduced catalysts with cluster size s up to 70 mm. Maximum PO yield (11.7%) with a selectivity of 46% were obtained over a TS-1 catalysts loaded with 1 wt% Pd and 0.02 wt% Pt a nd autoreduced under N-2 at 150 degrees C. The increase in PO yield by adding minor amounts of Pt to a Pd/TS-1 catalyst correlates with a sh arp increase in the fraction of Pd(II) species. Further addition of Pt changed the form and size of Pd clusters without further increasing t he fraction of Pd(II) species, thus leading to decreasing PO yields an d selectivities. (C) 1998 Academic Press.