EFFECT OF THE SI AL RATIO AND OF THE ZEOLITE STRUCTURE ON THE PERFORMANCE OF DEALUMINATED ZEOLITES FOR THE REFORMING OF HYDROCARBON MIXTURES/

Various 12-membered ring pore zeolites were employed for the reforming of ''synthetic'' hydrocarbon mixtures which simulate industrial napht has. All the zeolites were dealuminated to various extents. It was fou nd that, under the present conditions over the samples which are sligh tly dealuminated, bimolecular-condensation reactions followed by recra cking are responsible for the relatively large selectivities of C-4 pa raffins. The monomolecular cracking (via pentacoordinated carbonium io ns) of the latter hydrocarbons is responsible for the large generation of CH4 from the cracking of C-4 paraffins. When the Si/Al ratio incre ases, the selectivity of methane passes through a steep minimum, while those of C-3, C-4, and C-5 pass through a maximum. It was also found that the zeolite pore structure is a very important factor for the tim e on stream activity of zeolite-based catalysts. Zeolites with reduced aluminum content and pore structures, which do not favor the formatio n of coke precursors in their cavities, can lead to very promising cat alysts for acid-catalyzed reactions. From our study a 12-membered ring pore zeolite, which demonstrates minimal coke deactivation, was ident ified.