Transformation of propane, n-butane and n-hexane over H3PW12O40 and cesiumsalts. Comparison to sulfated zirconia and mordenite catalysts

Over H3PW12O40 and its acidic cesium salts at 250 degrees C, alkane transfo rmations occur through the mechanisms previously proposed for sulfated zirc onia and mordenite catalysts: propane is mainly transformed into butanes th rough a trimerization-isomerization-cracking process, n-butane into isobuta ne, propane and pentanes through a dimerization-isomerization-cracking proc ess, n-hexane into methylpentanes and 2,3-dimethylbutane through a monomole cular mechanism. With all the samples, n-butane transformation is initially much faster than propane transformation, the difference in rate increasing significantly with the Cs content: from 25 times with H3PW12O40 to 350 tim es with Cs2.4H0.6PW12O40. On the other hand, n-hexane transformation is 2.3 to 7 times faster than n-butane transformation. A decrease in acid strengt h and in acid site density with Cs introduction is proposed to explain the increase in the rate ratios. For all the reactions, sulfated zirconia pretr eated at 600 degrees C is 2-3 times more active than the heteropolycompound s. HMOR10 which is the most active catalyst for n-hexane transformation is the least active for n-butane and especially propane transformation. This v ery low activity of mordenite for these bimolecular processes can be relate d to particularities of its pore system: bimolecular reactions are strongly unfavoured in the narrow non-interconnected channels of this zeolite.