Single-event microkinetics of hydrocarbon cracking on zeotype catalysts: effect of acidity and shape selectivity

This work fits in the research on the design and optimization of the catalytic cracking of hydrocarbons. Because increasingly heavier petroleum fractions are fed industrially, it is important to rationally design new catalysts with larger pores than the current zeolites. In this respect, it is essential to develop fundamental kinetic models, that can account for the effect of catalyst properties such as acidity and shape selectivity on the catalytic behavior. In this work, the effect of these catalyst properties on the activity and selectivity is studied experimentally on a series of commercial zeolites and on two newly developed zeotype materials with bimodal pore network. Based on these results, accurate and flexible kinetic models are developed that explicitly describe these effects

Catalytic cracking of methylcyclohexane on FAU, MFI, and bimodal porous materials: influence of acid properties and pore topology

Catalytic cracking of methylcyclohexane has been studied on eight commercially available zeolites, five FAUs and three MFIs, and on two newly developed zeotype materials with bimodal porous structure, BIPOMs. Both BIPOMs are composed of an MFI ultramicropore (<1 nm) network and a different supermicropore (1.5-2.0 nm) network. Site time yields obtained on FAU and MFI zeolites with varying acid properties are in the same range, showing that mass transfer limitations inside the pores of both zeolite frameworks are absent. Site time yields obtained on BIPOM3 are comparable to those on commercial MFI with similar Si/Al ratio, while BIPOM1 is significantly less active. Within a given framework type, the zeolite acid properties determine its activity in methylcyclohexane cracking, while the pore topology controls its selectivity. On FAU, methylcyclohexane isomerization, followed by ring opening and subsequent cracking, is the main reaction pathway, while on MFI, protolytic scission, followed by cracking, is predominant. This is explained by the occurrence of transition state shape selectivity in MFI, hampering the bimolecular hydride transfer reaction. These typical features allow one to distinguish between FAU- and MFI-type catalytic behavior and to locate the active sites of BIPOM1 mainly in the supermicropores and those of BIPOM3 in both micropore networks but to a greater extent in the ultramicropores

Catalytic cracking of 2,2,4-trimethylpentane on FAU, MFI, and bimodal porous materials: influence of acid properties and pore topology

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