IMPROVING THE STABILITY OF H-MORDENITE FOR N-BUTANE ISOMERIZATION

The conversion of n-butane over mordenite-based catalysts in the prese nce of hydrogen and water was investigated for reaction temperatures b etween 523 and 623 K. Special attention was given to the influence of Pt upon catalytic activity, selectivity, and stability. With parent mo rdenite the catalytic activity for n-butane conversion decreased marke dly after a short time on stream. Deactivation can be minimized by hyd rogen (in the presence of Pt) and water addition. Both measures are th ought to reduce the concentration of intermediate olefins in the zeoli te pores. The best results with respect to selective conversion of n-b utane to isobutane were obtained for 0.25 wt% Pt on mordenite in the p resence of hydrogen. Higher concentrations of Pt in the catalyst are s hown to be detrimental for n-butane isomerization, because of increasi ng selectivity to hydrogenolysis. A detailed mechanistic scheme for n- butane conversion over Pt-containing mordenites is presented. n-Butane conversion is concluded to occur via a bimolecular mechanism involvin g a complex network of hydrogen transfer, oligomerization/cracking, is omerization, hydrogenation/dehydrogenation, and hydrogenolysis. (C) 19 97 Academic Press.