(53b) Structural Insight into Deactivation and Stability of Metal-Loaded Dealuminated Beta Zeolites during Ethanol Conversion to Butene-Rich C3+ Olefins

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. Multifunctional copper-containing catalysts supported on dealuminated beta zeolite allow 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 distribution in the ethanol upgrading reaction.

Copper speciation was studied on a trimetallic catalyst 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). In the as-synthesized state XAS revealed that Cu is dispersed as Cu²⁺ single sites bonded to the framework. This is in contrast to most copper-exchanged zeolite catalysts which typically contain [Cu·(H₂O)₆]⁺². Treating at 270°C in hydrogen reduces the single sites to Cu⁺, while CuO clusters (present in aged catalysts) form copper nanoparticles. This copper speciation persists under differential ethanol conversion as determined by operando XAS measurements. Catalyst aging occurs through the reduction of single sites to the metallic state, which then agglomerate 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.