Ester Reduction with H2 on Bifunctional Metal‐Acid Catalysts: Implications of Metal Identity on Rates and Selectivities

• Published in: Angewandte Chemie International Edition Vol. 62; no. 14; pp. e202216165 - n/a
• Main Authors: Berdugo‐Díaz, Claudia E., Manetsch, Melissa T., Sik Yun, Yang, Lee, Jieun, Luo, Jing, Chen, Xue, Flaherty, David W.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 27.03.2023
• Edition: International ed. in English
• Subjects: Acetic acid; Alcohols; Aldehydes; Bifunctional Catalysis; Carbonyl compounds; Carbonyls; Catalysts; Copper; Dehydration; Esters; Ethers; Hydrogenation; Hydrogenolysis; Metals; Nanoparticles; Palladium; Platinum; Propyl acetate; Selectivity; Transition Metals; Zeolites
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202216165

Esters reduce to form ethers and alcohols on contact with metal nanoparticles supported on Brønsted acidic faujasite (M‐FAU) that cleave C−O bonds by hydrogenation and hydrogenolysis pathways. Rates and selectivities for each pathway depend on the metal identity (M=Co, Ni, Cu, Ru, Rh, Pd, and Pt). Pt‐FAU gives propyl acetate consumption rates up to 100 times greater than other M‐FAU catalysts and provides an ethyl propyl ether selectivity of 34 %. Measured formation rates, kinetic isotope effects, and site titrations suggest that ester reduction involves a bifunctional mechanism that implicates the stepwise addition of H* atoms to the carbonyl to form hemiacetals on the metal sites, followed by hemiacetal diffusion to a nearby Brønsted acid site to dehydrate to ethers or decompose to alcohol and aldehyde. The rates of reduction of propyl acetate appear to be determined by the H* addition to the carbonyl and by the C−O cleavage of hemiacetal. Enabling sustainable and continuous processes for ether production from bioderived esters on bifunctional solid catalysts: esters hydrogenate to hemiacetals on Pd, Rh, and Pt nanoparticles and diffuse to nearby Brønsted acids sites to form ethers or alcohols. Ester reduction rates are determined by H* addition to the C=O bond on metal sites and cleavage of C−O bonds on acid sites.