Skeletal isomerization of 1-butene on synthetic clinoptilolite zeolite

A pure, highly crystalline clinoptilolite (CLI) zeolite with a Si/Al ratio of 5.8 has been synthesized using a small amount (1%) of seed crystals and tested as a catalyst for the skeletal isomerization of I-butene at 623-723 K at atmospheric pressure. The catalytic results are compared to those obtained from a ferrierite (FER) zeolite with a Si/Al ratio of 7.6. It is found that selectivity for isobutene is very high on CLI zeolite, but conversion was lower than for FER zeolite. The simulated distribution and calculated potential profile of I-butene molecules in CLI zeolite pore 10-ring channels show that the spatial constraints imposed by the pores are very severe. The exceptional selectivity and the low conversion of CLI zeolite results from the strict restriction of adsorption to very specific sites, inhibiting dimerization, as well as from the high potential barrier which reduces mass transfer.