Sintering is a common deactivation mechanism for metal-catalyzed reactions in heterogeneous catalysis. It is particularly pervasive in biomass-upgrading reactions, where severely reducing reaction conditions are commonplace. Recently, a Cu-Zn-Y/deAl-Beta catalyst comprising isolated Cu, Zn, and Y sites on dealuminated Beta was reported for direct ethanol conversion to C₃₊ olefins with a high yield of butene-rich olefins (88%, 300°C) which can be oligomerized to sustainable aviation fuel. Figure 1a shows ethanol conversion and product selectivity over Cu-Zn-Y/deAl-Beta. After regeneration, the initial activity and product selectivity is fully recovered. STEM images of the spent catalyst show large Cu nanoparticles; however, these nanoparticles are absent in regenerated catalysts. In-situ XAS experiments on fresh, simulated aged, and regenerated catalyst (Figure 1b) shows Cu⁰ agglomeration, which redisperse during regeneration back to Cu²⁺ single sites. The redispersion was confirmed by in-situ STEM imaging of the catalyst during regeneration, and in-situ aging and regeneration experiments monitored by DRUV-Vis. AIMD simulations were used to evaluate the thermodynamics of the redispersion process. A copper single site model was constructed based on the condensation of a CuO monomer with a silanol nest and was consistent with EXAFS modeling. It was found that the site can heterolytically dissociate H₂ to from a third silanol group and a bound CuH. Full protonation of the silanol nest ejects the CuH which quickly agglomerates to form a metal nanoparticle and H₂. During Calcination entrained water can aid in the solvation and detachment of CuO monomers from a CuO agglomerate, which can then react exergonically with a fully protonated silanol nest to regenerate the initial site.

<b>Figure 1.</b> a) EtOH conversion and product selectivity over Cu-Zn-Y/deAl-Beta (300°C, 7 kPa EtOH, 94 kPa H<sub>2</sub> 0.3 h<sup>-1</sup> WHSV). b) in-situ Cu K edge EXAFS spectra of fresh Cu-Zn-Y/deAl-Beta, after aging in H<sub>2</sub>, and after regeneration in air.

Figure 1. a) EtOH conversion and product selectivity over Cu-Zn-Y/deAl-Beta (300°C, 7 kPa EtOH, 94 kPa H₂ 0.3 h^-1 WHSV). b) in-situ Cu K edge EXAFS spectra of fresh Cu-Zn-Y/deAl-Beta, after aging in H₂, and after regeneration in air.

Dr. Qiyuan Wu

Postdoctoral Researcher, NREL

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