Plasma Activation Enables Highly Dispersed Ag Species in ZSM-5 for Efficient Dehydrogenation-Cracking of n -Hexane to Light Olefins

Abstract

Bifunctional dehydrogenation-cracking metal/zeolite catalysts are promising for the production of light olefins from alkanes, but their activation commonly relies on high-temperature calcination. This conventional activation can induce metal migration and aggregation, damage the zeolite framework, reduce micropore accessibility, and alter the acid-site distribution, thereby compromising the dehydrogenation-cracking synergy. Herein, ion-exchanged Ag/ZSM-5 catalysts were activated by dielectric barrier discharge (DBD) plasma as a mild alternative to thermal calcination for nitrate removal and Ag-site reconstruction. Plasma activation could effectively remove nitrate precursors while better preserving the crystallinity, micropore accessibility, and acidity of ZSM-5. More importantly, it suppressed Ag migration and aggregation, increased the fraction of highly dispersed Ag+ species associated with exchange sites, and promoted a more favorable Brønsted/Lewis acid balance. As a result, the plasma-activated Ag/ZSM-5 catalysts exhibited enhanced catalytic performance in n-hexane cracking, with higher selectivity to light olefins. At a low Ag loading, the plasma-activated catalyst delivered a light-olefin selectivity of 50.7% after 6 h of reaction, higher than those of the calcined counterpart (46.8%) and parent ZSM-5 (34.7%). Meanwhile, it showed slower deactivation during the 6 h fixed-bed reaction, together with lower tendencies toward hydrogen transfer, aromatics formation, and coke deposition.