Selective Butene Formation in Direct Ethanol-to-C₃₊-Olefin Valorization over Zn-Y/Beta and Single-Atom Alloy Composite Catalysts Using in Situ-Generated Hydrogen

The selective production of C₃₊olefins from renewable feedstocks, especially via C₁and C₂platform chemicals, is a critical challenge for obtaining economically viable low-carbon middle-distillate transportation fuels (i.e., jet and diesel). Here, we report a multifunctional catalyst system composed of Zn-Y/Beta and “single-atom” alloy (SAA) Pt-Cu/Al₂O₃, which selectively catalyzes ethanol-to-olefin (C₃₊, ETO) valorization in the absence of cofed hydrogen, forming butenes as the primary olefin products. Beta zeolites containing predominately isolated Zn and Y metal sites catalyze ethanol upgrading steps (588 K, 3.1 kPa ethanol, ambient pressure) regardless of cofed hydrogen partial pressure (0-98.3 kPa H₂), forming butadiene as the primary product (60% selectivity at an 87% conversion). The Zn-Y/Beta catalyst possesses site-isolated Zn and Y Lewis acid sites (at ∼7 wt % Y) and Brønsted acidic Y sites, the latter of which have been previously uncharacterized. A secondary bed of SAA Pt-Cu/Al₂O₃selectively hydrogenates butadiene to butene isomers at a consistent reaction temperature using hydrogen generatedin situfrom ethanol to butadiene (ETB) conversion. This unique hydrogenation reactivity at near-stoichiometric hydrogen and butadiene partial pressures is not observed over monometallic Pt or Cu catalysts, highlighting these operating conditions as a critical SAA catalyst application area for conjugated diene selective hydrogenation at high reaction temperatures (>573 K) and low H₂/diene ratios (e.g., 1:1). Single-bed steady-state selective hydrogenation rates, associated apparent hydrogen and butadiene reaction orders, and density functional theory (DFT) calculations of the Horiuti-Polanyi reaction mechanisms indicate that the unique butadiene selective hydrogenation reactivity over SAA Pt-Cu/Al₂O₃reflects lower hydrogen scission barriers relative to monometallic Cu surfaces and limited butene binding energies relative to monometallic Pt surfaces. DFT calculations further indicate the preferential desorption of butene isomers over SAA Pt-Cu(111) and Cu(111) surfaces, while Pt(111) surfaces favor subsequent butene hydrogenation reactions to form butane over butene desorption events. Under operating conditions without hydrogen cofeeding, this combination of Zn-Y/Beta and SAA Pt-Cu catalysts can selectively form butenes (65% butenes, 78% C₃₊selectivity at 94% conversion) and avoid butane formation using onlyin situ-generated hydrogen, avoiding costly hydrogen cofeeding requirements that hinder many renewable energy processes.