Industrial & engineering chemistry research vol:49 issue:15 pages:6815-6823
Cracking experiments using 2,2,4-trimethylpentane as a model component have been performed on five FAU and three MFI zeolites. In addition to these eight commercially available catalysts, two newly developed zeotype materials with bimodal pore structure, BIPOMs, have been investigated. Both BIPOMs possess an MR ultramicropore (<1 nm) network but a different ordered supermicropore (1.5-2.0 nm) network. Site time yields are lower on MA than on FAU because of the slower diffusion of the reactant inside the pores. The site time yield obtained on the BIPOMs is comparable to commercial MFI with similar Al content. Within one framework type, the zeolite acid properties determine its activity in catalytic cracking of 2,2,4-trimethylpentane, while the framework topology controls its selectivity. The main reaction route on FAU is hydride transfer followed by beta-scission leading to mainly C-4 species, while on MFI protolytic scission is responsible for the formation of high amounts of C-1-C-3 species. This points to the presence of transition state shape selectivity in MFI. These features allow to distinguish between FAU and MFI type catalytic behavior and to locate the active sites of BIPOM1 in the supermicropores and those of BIPOM3 in both micropore networks.