Effect of preparation method on the properties of Nb2O5 promoted platinum catalysts

Pt/Nb2O5 catalysts were prepared on a reducible support by ion exchange and incipient wetness of different platinum salts. The Pt/Nb2O5/Al2O3 catalysts were prepared with several loading of niobium oxide over alumina, aiming different surface coverages and platinum dispersions. These catalysts were characterized by using different techniques: TPR, DRS, chemisorption of H-2, CO, CO2 and pyridine. The catalytic activity was evaluated in the n-heptane conversion. Platinum oxide was the main surface, precursor on the Nb2O5 supported catalysts, while a oxychloroplatinum surface complex was the precursor for Pt/Nb2O5/Al2O3 catalysts. These different precursors promote the formation of different platinum particle sizes, being the Pt/Nb2O5/Al2O3 samples more disperse. After high temperature of reduction, the platinum adsorption capacity decrease on all the samples, due to the reduction of Nb2O5, and subsequent blocking of surface platinum atoms. Nb2O5 and Nb2O5/Al2O3 supported catalysts are very selective to olefins in the n-heptane conversion. Furthermore, Bronsted acidic sites an formed on Pt/Nb2O5/Al2O3 catalysts with higher Nb2O5 loading, leading to a better stability of the catalysts. (C) 1998 Elsevier Science B.V. All rights reserved.