SHAPE-SELECTIVE CRACKING OF N-OCTANE AND 2,2,4-TRIMETHYLPENTANE OVER AN ALUMINA-PILLARED CLAY

A mixture of n-octane (nC-8) and 2,2,4-trimethylpentane (224-TMP) was cracked over an alumina-pillared montmorillonite (Al-PILC) acid cataly st as a means of characterising its pore structure and shape selectivi ty. The shape selectivity of the catalyst was quantified by a time dep endent parameter analogous to the constraint index, called the selecti vity ratio (SR), and defined as log(fraction of nC-8 remaining)/log(fr action of 224-TMP remaining). The SR was measured over Al-PILC, a 0.16 wt% Pt loaded Al-PILC, a Y zeolite, and an amorphous silica-alumina. The SR was greater over Al-PILC compared with Y-zeolite even though th e pore openings of the Al-PILC were of similar or larger size than tho se in the Y-zeolite. Doping Al-PILC with Pt caused a large increase in the SR. As found with constraint index measurements, internal pore di mensions and reaction mechanisms appear to be the determinants of SR. However, SR is better capable of discriminating larger pore microporou s materials.