Identification of Active Sites in the Catalytic Oxidation of 2‐Propanol over Co1+xFe2–xO4 Spinel Oxides at Solid/Liquid and Solid/Gas Interfaces

• Published in: ChemCatChem Vol. 13; no. 12; pp. 2942 - 2951
• Main Authors: Falk, Tobias, Budiyanto, Eko, Dreyer, Maik, Pflieger, Christin, Waffel, Daniel, Büker, Julia, Weidenthaler, Claudia, Ortega, Klaus Friedel, Behrens, Malte, Tüysüz, Harun, Muhler, Martin, Peng, Baoxiang
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 18-06-2021
• Subjects: Catalysts; Catalytic oxidation; cobalt ensemble; cobalt iron oxide; Cobalt oxides; liquid phase; Liquid phase oxidation; nanocasting; Nanowires; Photoelectrons; Reaction kinetics; Selective oxidation; Silicon dioxide; Spinel; Water vapor
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.202100352

A series of Co1+xFe2–xO4 (0≤x≤2) spinel nanowires was synthesized by nanocasting using SBA‐15 silica as hard template, which was characterized by X‐ray powder diffraction, X‐ray photoelectron spectroscopy, and transmission electron microscopy. The Co1+xFe2–xO4 spinels were applied in the aerobic oxidation of aqueous 2‐propanol solutions to systematically study the influence of exposed Co and Fe cations on the catalytic properties. The activity of the catalysts was found to depend strongly on the Co content, showing an exponential increase of the reaction rate with increasing Co content. Ensembles of Co3+cus (coordinatively unsaturated) sites were identified as the active sites for selective 2‐propanol oxidation, which are assumed to consist of more than six Co ions. In addition, gas‐phase oxidation with and without water vapor co‐feeding was performed to achieve a comparison with liquid‐phase oxidation kinetics. An apparent activation energy of 94 kJ mol−1 was determined for 2‐propanol oxidation over Co3O4 in the liquid phase, which is in good agreement with the gas‐phase oxidation in the presence of water vapor. In contrast to gas‐phase conditions, the catalysts showed high stability and reusability in the aqueous phase with constant conversion in three consecutive runs.
Selective oxidation: A series of Co1+xFe2–xO4 (0≤x≤2) spinel nanowires was applied in the aerobic oxidation of 2‐propanol in the aqueous phase. The exponential increase of the reaction rate with increasing Co content indicated large Co cation ensembles to be the active site. Fe cations inhibit the catalytic activity by affecting the electronic structure. Gas‐phase oxidation was performed with co‐feeding of water demonstrating its beneficial effect on deactivation.