The Effect of Preparation Method on Pt/Nb2O5 Catalysts

The use of the ion-exchange method and the addition of lithium to Pt/Nb2O5 catalysts were investigated in this work, using techniques of temperature-programmed reduction, H2 and CO chemisorption, UV-Vis diffuse reflectance spectroscopy and the conversion of n-heptane as a catalytic test. The superficial precursor present after the calcination step is platinum oxide, as previously observed for Pt/Nb2O5 catalysts prepared by the incipient wetness method. For some of the samples, autoreduction was observed during the calcination step, with the formation of low dispersion metallic platinum. The Pt/Nb2O5 catalysts prepared by ion exchange showed a high yield of olefins, as compared to aromatics, in the conversion of n-heptane. However, a high yield of hydrogenolysis products was also observed. For some of the lithium-containing samples, there was a suppression of dehydrogenation and aromatization reactions, with an increase in central C-C bond hydrogenolysis

1,3-Butadiene hydrogenation on pd-supported systems: geometric effects

A strong metal support interaction (SMSI) effect was observed on Pd/Nb2O5 and Pd/TiO2 catalysts, and it produces small, exposed Pd ensembles. A decrease in the trans/cis 2-butene ratio was observed after reduction at 773 K. Selectivity changes were ascribed to the decoration model. Theoretical models were developed based on semi-empirical molecular-orbital calculations for 1,3-butadiene and Pd n clusters. Experimental results are in agreement with our theoretical model, which proposes a greater stabilization of the cisoid intermediate on small Pd ensembles