Platinum clusters supported in zeolite LTL: Influence of catalyst morphology on performance in n-hexane reforming

摘要: Abstract KLTL zeolite-supported platinum catalysts were synthesized from aqueous tetraammineplatinum(II) nitrate solutions and nonacidic zeolite crystallites, including some with dimensions as little 300×500 A. The crystallites had various morphologies, being predominantly disk-shaped particles mosaics of rod-like domains a range c -dimension lengths. activity selectivity each catalyst evaluated for dehydrocyclization n -hexane in the presence H 2 to form benzene at conversions typically 45–90%. data presented here provide detailed characterization deactivation such absence sulfur. EXAFS show that was present clusters about 20 atoms each, on average. Electron micrographs nearly evenly dispersed surfaces intracrystalline extracrystalline surfaces. catalytic performance virtually independent channel length, but activity, selectivity, resistance found be correlated ratio surface area external crystallite within pores. is dependent this (which related morphology) follows: comparison others, relatively low fractions outside pores are more active, selective formation, resistant deactivation. One well-prepared catalyst, example, gave greater than 90% no measurable over 140 h operation flow reactor 420°C atmospheric pressure. These match those characterizing most reported. Consistent interpretation E. Iglesia J. Baumgartner ( “New Frontiers Catalysis” (L. Guczi, F. Solymosi, P. Tetenyi, Eds.), p. 993, Studies Surface Science Catalysis, Vol. 75. Elsevier, Amsterdam, 1993), associated pores; it hypothesized coke formation rapid distinguishing characteristic best pores, where may inhibited by constraints