Core-shell and Egg-shell Zeolite Catalysts for Enhanced Hydrocarbon Processing
Thuy Tran Le, Kumari Shilpa, Choongsze Lee, Sungmin Han, Conan Weiland, Simon Bare, Paul Dauenhauer, Jeffrey Rimer
Developing structure-performance relationships with the underlying goal of optimizing known zeolite catalysts involves the manipulation of their physicochemical properties. Here, we systematically assessed the impact of mesoscopic gradients in acid site concentration, which has received little attention in the design of zeolite catalysts for hydrocarbon upgrading. A series of core-shell MEL-type zeolites were synthesized with catalytically active ZSM-11 cores and passivated silicalite-2 shells of varying thickness. Our findings revealed that ZSM-11@silicalite-2 particles with ultrathin shells (< 10 nm) have enhanced mass transport, characteristic of relatively smaller particles, compared to the corresponding ZSM-11 core. Catalytic testing using the methanol-to-hydrocarbon (MTH) reaction showed that core-shell zeolites exhibit longer lifetimes, higher total turnovers, and an unexpected promotion of the aromatic cycle in the hydrocarbon pool mechanism. Time-resolved acid titration of core and core-shell catalysts confirmed that the siliceous shell introduces a hydrophobic exterior that impacts molecular diffusion. In comparison, prepared MFI core-shells (ZSM-5@silicalite-1) showed similar enhancement in catalyst performance. Moreover, we prepared egg-shell configurations of each zeolite, silicalite-2@ZSM-11 and silicalite-1@ZSM-5, comprised of an inert core and catalytically active shell. This inverse design of the egg-shell created pseudo nanosheets with total turnovers that were markedly higher than their homogeneous counterparts. Collectively, this study demonstrated that mesoscopic gradients in acid concentration via the design of core-shell and egg-shell zeolites markedly improve catalyst performance over conventional analogues for hydrocarbon upgrading.
, Shilpa, K.
, Lee, C.
, Han, S.
, Weiland, C.
, Bare, S.
, Dauenhauer, P.
and Rimer, J.
Core-shell and Egg-shell Zeolite Catalysts for Enhanced Hydrocarbon Processing, Journal of Catalysis, [online], https://doi.org/10.1016/j.jcat.2021.11.004
(Accessed September 28, 2023)