Conversion of n-pentane and of n-butane catalyzed by platinum-containing WOx/TiO2

Abstract

Tungstated titania, with and without platinum, was used to catalyze the conversion of n-butane and of n-pentane at atmospheric pressure and temperatures in the range of 423–573 K, both in the presence and in the absence of H₂ in the feed stream to a flow reactor. The catalysts were active for isomerization and cracking, and the products included alkenes, in contrast to those observed in catalysis by tungstated zirconia. The catalytic activity of tungstated titania is much less than that of sulfated zirconia and similar to that of tungstated zirconia. The results characterizing tungstated titania indicate a bifunctional reaction network involving metal and acidic sites responsible for hydrogenation/dehydrogenation and carbenium ion reactions, respectively. Platinum in the catalyst and H₂ in the feed strongly suppress the otherwise rapid catalyst deactivation associated with coke deposition. The catalyst was found to be stable after a period of initial deactivation, and kinetics data are reported for partially deactivated catalysts. High platinum contents lead to high selectivities for cracking in the presence of H₂ and high selectivities for unsaturated products in the absence of H₂. Increasing tungsten loadings raise catalyst acidity and favor isomerization. The performance of tungstated titania containing platinum resembles that of the zirconia-based catalysts less than it resembles the performance of platinum supported on (chlorided) alumina, a well-known naphtha reforming catalyst.