(304d) Improving Ethyl Acetate Selectivity in Ethanol Dehydrogenation through Proximity Effects in Supported Cu Catalysts

Ethanol has been proposed as a liquid organic hydrogen carrier (LOHC) that could potentially displace compressed or liquified H₂. Ethyl acetate is a much more viable dehydrogenation product compared to acetaldehyde, being highly volatile and carcinogen. In this study, we exploit interfacial effects in Cu catalysts to maximize ethyl acetate selectivity during ethanol dehydrogenation.

The synthesis involved the preparation of copper dispersed over tetragonal Zirconia (Cu/t-ZrO₂), along with control samples: Copper dispersed over Silica (Cu/SiO₂) and bare t-ZrO₂. A mixed-metal oxide sample, CuZrO_x, was synthesized. Characterizations were conducted using BET, X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR), N₂O selective-chemisorption, and Fourier transform infrared (FTIR) spectroscopy. Results revealed CuO–ZrO₂ interfaces proposed being essential for esterification chemistry. Catalytic ethanol dehydrogenation performed over these pre-reduced samples under atmospheric pressure showed that Cu/SiO₂ exhibited more than 95% acetaldehyde selectivity at 35% ethanol conversion at 200°C, while t-ZrO₂ alone showed negligible activity, indicating ethanol dehydrogenation occurred on copper sites (Figure 1). Additionally, a double-bed consisting of Cu/SiO₂ followed by t-ZrO₂ improved acetaldehyde reactivity without affecting ethyl acetate selectivity (4%). To capture proximity effects in the chemistry, physically-mixed and thoroughly-grounded beds were tested, results compared with Cu/t-ZrO₂ revealed significantly higher ethyl acetate selectivity (20%) than former. The CuZrO_x sample achieved even better selectivity of (38%). A clear increasing trend in ethyl acetate selectivity was observed in subsequent runs where Cu and the ZrO₂ moieties were brought near through their synthesis. We also evidence the effectuation of ethyl acetate formation through hemiacetal-mediated steps and elucidate the participation of Cu, ZrO₂, and Cu-Zr interfacial domains in different steps within the overall reaction network. This work highlights the critical role of metal-support interfaces, and the use of synthetic and reaction engineering variables to amplify proximity effects in improving selectivity for LOHC applications specifically, and dehydrogenation reactions more generally.