Coke formation and its effects on shape selective adsorptive and catalytic properties of ferrierite

Channels or cavities of ferrierite are blocked by carbonaceous deposits (coke) which are formed during butene treatments. The pore blocking inside ferrierite/alumina catalysts affects the yield and selectivity to isobutylene in the catalytic reaction of butene isomerization. Pore size distribution experiments show that the blocking of 10-member ring channels (4.2 x 5.4 A) and 8-member ring channels (3.5 x 4.8 A) of ferrierite by coke reduces the channel size smaller than that of the nitrogen molecule (4.09 A). TPD data show that ammonia uptake for coked samples of different times on stream is decreased from about 62% to 35% of that for the fresh sample. Uptakes for more bulky molecules such as 1-butene (2.99 x 4.71 A) and isobutylene (3.28 x 4.14 A) are severely reduced by coke formation (< 9% of 1-butene and isobutylene uptakes for the fresh sample). About 76.9% of the coke formed after 18 h is deposited inside the micropores (< 10 A) of ferrierite/alumina. Modification of pore shapes through such coke deposition favors reactions involving small molecules, such as butene isomerization to isobutylene. 45 refs., 12 figs., 4 tabs.