Transport and reactivity of hydrocarbon molecules in a shape-selective zeolite

摘要: For the catalytic cracking of C6 to C9 hydrocarbons on ZSM-5, we demonstrate quantitatively contributions each two mechanisms for molecular shape selectivity. Using crystallites different sizes and activities, classical methods evaluating diffusion inhibition reaction rate, separate effects mass-transport-induced selectivity from that created by steric size a complex. The selective n-paraffins compared monomethyl paraffins (from C9) is due higher intrinsic rate constant n-paraffin, with diffusional mass transport playing no appreciable role. In contrast, dimethyl paraffin strongly diffusion-inhibited. methyl paraffin/n-paraffin discrimination result constraint sizeable paraffin/carbonium ion This structural shown be absent corresponding olefins where such complexes do not arise. diffusivities at conditions have been determined. linear hydrocarbon, diffusivity notably exceeds expected Knudsen model. reminds us review assumptions conventional concepts transport. availability zeolites now allows probe many basic phenomena in catalysis, configuration dynamics, including