Core-shell and egg-shell zeolite catalysts for enhanced hydrocarbon processing

Hydrocarbon Products Occluded within Zeolite Micropores Impose Transport Barriers that Regulate Brønsted Acid-Catalyzed Propene Oligomerization

“…The sizes and shapes of these voids influence the intrinsic kinetic behavior of H + sites , and also regulate the diffusion of reactant and product molecules, as well established in concepts of shape selectivity. ,, The coupled effects of H + -site reactivity and diffusional constraints imposed by the inorganic zeolitic framework are well documented to influence rates, selectivity, and catalyst lifetime for various zeolite-catalyzed reactions including toluene disproportionation, n -heptane isomerization, n -paraffin cracking, methanol to olefins and hydrocarbons, − and cumene synthesis . This recognition has spurred advances in the synthesis and modification of zeolite crystallites with altered diffusion properties, including engineering changes in crystal size and habit, mesoporosity, and crystallite-scale H + -site distributions. − Here, we provide evidence that additional transport barriers are imposed by an organic phase composed of hydrocarbon products that accumulate within the micropores of medium-pore (e.g., 10-membered ring, 10-MR) zeolites during alkene oligomerization reactions.…”

Coke Formation over Zeolite Catalysts in Light Alkanes Aromatization and Anti-Carbon-Deposition Strategies and Perspectives: A Review

“…A solid core–shell structure (core@shell) is an assembly form which has at least two types of catalytic materials, so that the reactions could take place in a pre-designed order in a hierarchical structure (Figure A). Meanwhile, the shape of the core–shell structure can be controlled, thus providing more choices for the design of diffusion paths and acid sites …”

Molecular transport in zeolite catalysts: depicting an integrated picture from macroscopic to microscopic scales

“…Recently, Rimer and co-workers successfully synthesized a series of core–shell zeolites with various shell thicknesses (ZSM-5@silicalite-1 and ZSM-11@silicalite-2) by secondary growth of a purely-siliceous shell on the zeolite surface. 25 In that work, the sample C-30 represents the seed ZSM-11 crystal, and the samples CS- x represent the core–shell zeolites where x is the Si/Al ratio of the shell. The performance of the seed zeolite and core–shell zeolite catalysts was further assessed over the methanol-to-hydrocarbon (MTH) reaction.…”

“…Introducing an inert siliceous or aluminous exterior rim to form a core–shell configuration in zeolite catalysts would also markedly reduce their mass transport resistance, prolong the catalyst lifetime, and increase their activities. 25 The nature of these effects remains unclear, but it would be likely ascribed to the modifications of surface diffusion properties. First, introducing such a core–shell configuration in zeolite catalysts can selectively passivate the defective sites on surfaces during the external growth of the inert shells.…”