Dehydroisomerisation of n-butrane over (Pt,Cu)/H-TON catalysts

Direct formation of isobutene from n-butane was investigated over zeolite T ON and gamma -Al2O3 supported platinum and platinum-copper catalysts. Addit ion of Cu decreases Pt dispersion, irrespective of preparation methods and nature of catalyst supports. The presence of potassium was found to reduce acidity and Pt dispersion. The experiments were performed in a fixed-bed mi croreactor system operating at 673 K and atmospheric pressure. Changing the support from gamma -Al2O3 to TON, shows that n-butane conversion is almost independent of acidity. However, significant changes in products selectivi ties are observed. The selectivities to isobutene, C-1-C-3 fractions, and a romatics increases drastically from 3.5 to 32.6%, 20.3 to 27.2%, and 3.0 to 20.6%, respectively, for the TON-supported catalyst whereas dehydrogenatio n is largely predominant when gamma -Al2O3 is used as support. Addition of Cu, as expected, has an adverse effect on n-butane conversion as less activ e sites are available due to the reduction in Pt dispersion. Though Cu addi tion has marginal effect on isobutene selectivity, it certainly suppresses hydrogenolysis which evidences a reduction in size of the Pt ensembles at t he surface of the Pt particles. (C) 2000 Published by Elsevier Science B.V.