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Here, in this work, yttrium containing dealuminated Beta zeolites (Y/deAlBeta) were synthesized and characterized by various spectroscopic techniques to improve understanding of ethanol upgrading over these materials. Characterization results indicate yttrium atoms partially condense with framework silanol nests formed during dealumination of parent Al-Beta supports. Active sites for conversion of ethanol and acetaldehyde to butadiene were quantified on a series of Y/deAlBeta catalysts (0.1–10 wt% yttrium) via ex situ chemisorption and transmission Fourier transformed infrared (FTIR) spectroscopy measurements by first measuring the integrated molar extinction coefficient (IMEC) for pyridine bound to Lewis acidic yttrium sites. In situ titrations with pyridinemore » demonstrate that the number of sites quantified by ex situ chemisorption IR is quantitatively similar to the number of sites that catalyze butadiene formation, which varies (from 0.05 to 0.35) across the series of catalysts. In situ pyridine titrations impact butadiene site time yields (STY), but not crotonaldehyde STY, indicating that a distribution of yttrium sites is present, and that discrete yttrium site types participate in distinct steps in the pathway from ethanol to butadiene. Apparent kinetic parameters including activation energies and reaction orders were measured, these suggest differences in reactant (or reactant-derived intermediate) surface coverages result in higher STYs (per mol Y or per Lewis acidic Y site) for samples with low Y loadings relative to those with higher Y loadings. Isotopic labeling experiments evince the existence of other kinetically relevant steps in addition to the crotonaldehyde transformation to crotyl alcohol. Together, these findings provide further guidance into the heterogeneities in site structures in yttrium-containing zeolites and their relevance for the various steps in the pathway from ethanol to C₄ products useful for production of sustainable aviation fuel and renewable butadiene.« less

Single-site copper-based catalysts have shown remarkable activity and selectivity for a variety of reactions. However, deactivation by sintering in high-temperature reducing environments remains a challenge and often limits their use due to irreversible structural changes to the catalyst. Here, we report zeolite-based copper catalysts in which copper oxide agglomerates formed after reaction can be repeatedly redispersed back to single sites using an oxidative treatment in air at 550 °C. Under different environments, single-site copper in Cu–Zn–Y/deAlBeta undergoes dynamic changes in structure and oxidation state that can be tuned to promote the formation of key active sites while minimizing deactivation throughmore » Cu sintering. For example, single-site Cu²⁺ reduces to Cu¹⁺ after catalyst pretreatment (270 °C, 101 kPa H₂) and further to Cu0 nanoparticles under reaction conditions (270–350 °C, 7 kPa EtOH, 94 kPa H₂) or accelerated aging (400–450 °C, 101 kPa H₂). After regeneration at 550 °C in air, agglomerated CuO was dispersed back to single sites in the presence and absence of Zn and Y, which was verified by imaging, in situ spectroscopy, and catalytic rate measurements. Ab initio molecular dynamics simulations show that solvation of CuO monomers by water facilitates their transport through the zeolite pore, and condensation of the CuO monomer with a fully protonated silanol nest entraps copper and reforms the single-site structure. Importantly, the capability of silanol nests to trap and stabilize copper single sites under oxidizing conditions could extend the use of single-site copper catalysts to a wider variety of reactions and allows for a simple regeneration strategy for copper single-site catalysts.« less

We report ethanol conversion to C₄₊ olefins remains a critical yet nonselective process for producing renewable middle distillates. Here, Cu–La/Beta catalysts composed of copper and lanthanum incorporated onto a dealuminated Beta support are reported for ethanol conversion to C₄₊ olefins (73% selectivity, ~98% ethanol conversion, 623 K,<4% C₁–C₃ hydrocarbons) which particularly favors C₅₊ olefin formation (43% selectivity) as a distinction from the benchmarking Cu–Y/Beta catalyst. Monometallic Cu/Beta or La/Beta samples are insufficient to catalyze the C₄₊ olefin formation and primarily form dehydration products (e.g., ethylene and diethyl ether), indicating the necessity of both Cu and La species for butene andmore » C₅₊ olefin formation. Increasing the bulk La loading at a fixed Cu content yields higher C₅₊ olefins until the La/Cu molar ratio reaches 3.6. These findings indicate Cu–La/Beta as an effective ethanol conversion catalyst that facilitates multiple C–C bond formation events required for synthesizing C₅₊ olefins (i.e., hexenes and octenes).« less

Direct and selective production of C₃₊ olefins from bioethanol remains a critical challenge and important for the production of renewable transportation fuels such as aviation biofuels. In this study, we report a Cu–Zn–Y/Beta catalyst for selective ethanol conversion to butene-rich C₃₊ olefins (88% selectivity at 100% ethanol conversion, 623 K), where the Cu, Zn, and Y sites are all highly dispersed. The ethanol-to-butene reaction network includes ethanol dehydrogenation, aldol condensation to crotonaldehyde, and hydrogenation to butyraldehyde, followed by further hydrogenation and dehydration reactions to form butenes. Cu sites play a critical role in promoting hydrogenation of the crotonaldehyde C═C bondmore » to form butyraldehyde in the presence of hydrogen, making this a distinctive pathway from crotyl alcohol-based ethanol-to-butadiene reaction. Reaction rate measurements in the presence of ethanol and acetaldehyde (543 K, 12 kPa ethanol, 1.2 kPa acetaldehyde, 101.9 kPa H₂) over monometallic Zn/Beta and Y/Beta catalysts indicate that Y sites have higher C–C coupling rates than over Zn sites (initial C–C coupling rate, 6.1 × 10^–3 mol mol_Y^–1 s^–1 vs 1.2 × 10^–3 mol mol_Zn^–1 s^–1). Further, Lewis-acidic Y-site densities over Cu–Zn–Y/Beta with varied Y loadings are linearly correlated with the initial C–C coupling rates, suggesting that Lewis-acidic Y sites are the predominant sites that catalyze C–C coupling in Cu–Zn–Y/Beta catalysts. Control experiments show that the dealuminated Beta support is important to form higher density of Lewis-acidic Y sites in comparison with other supports such as silica, or deboronated MWW despite similar atomic dispersion of Y sites and Y–O coordination numbers over these supports, leading to more than 9 times higher C–C coupling rate per mole Y over dealuminated Beta relative to other supports. This study highlights the significance of unique combination of metal sites in contributing to the selective valorization of ethanol to C₃₊ olefins, motivating for exploring multifunctional zeolite catalysts, where the presence of multiple sites with varying reactivities and functions allows for controlling the predominant molecular fluxes toward the desired products in complex reactions.« less