The ethanol to jet pathway is a promising route to produce aviation fuel from renewable biomass-based feedstocks, where ethanol to butene-rich C3+ olefins is a critical step. A multifunctional catalyst consisting of Cu, Zn, and Y supported on dealuminated beta zeolite allows for high selectivity to butenes in one step through cascade reactions and by suppressing alcohol dehydration. Maintaining high yield requires high selectivity to ethanol dehydrogenation which is catalyzed by copper. However, the lifecycle of copper on these catalysts, and the effect its speciation has on the reaction network is poorly understood. This work focuses on understanding copper speciation in dealuminated beta zeolite, and the effect this speciation has on the product distributions in the ethanol upgrading reaction. Copper speciation was studied on trimetallic Cu-Zn-Y/Beta and a model monometallic copper catalyst Cu/BEA. The local structure of copper at various stages of the catalyst lifecycle was studied by in-situ and operando X-ray absorption spectroscopy (XAS) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). In the as-synthesized state XAS revealed that Cu is dispersed as Cu2+ single sites bonded to the framework. Treating at 270°C in hydrogen reduces the single sites to Cu+, while CuO clusters (present in aged catalysts) form metallic copper nanoparticles. This copper speciation persists under differential ethanol conversion as determined by in-situ XAS measurements. Catalyst aging occurs through the reduction of single sites to the metallic state, which then agglomerates to form copper nanoparticles. Reaction rates and product selectivity at different stages of the catalyst life were correlated with XAS results to understand the active Cu sites. Rate measurements as a function of copper loading showed that copper both adds a dehydrogenation functionality and suppresses ethanol dehydration inherent to the support.

Structural insight into deactivation and stability of multifunctional Cu-Zn-Y/Beta during ethanol conversion to butene-rich C3+ olefins

ACS Spring 2022

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