Thermally Induced Solid-Phase Quasi-Intramolecular Redox Reactions of [Hexakis(urea- O)iron(III)] Permanganate: An Easy Reaction Route to Prepare Potential (Fe,Mn)Ox Catalysts for CO2 Hydrogenation

Kende Attila Béres; Zoltán Homonnay; Libor Kvitek; Zsolt Dürvanger; Martina Kubikova; Veronika Harmat; Fanni Szilágyi; Zsuzsanna Czégény; Péter Németh; Laura Bereczki; Vladimir M Petruševski; Mátyás Pápai; Attila Farkas; László Kótai

doi:10.1021/acs.inorgchem.2c02265

Thermally Induced Solid-Phase Quasi-Intramolecular Redox Reactions of [Hexakis(urea- O)iron(III)] Permanganate: An Easy Reaction Route to Prepare Potential (Fe,Mn)O_x Catalysts for CO₂ Hydrogenation

Inorg Chem. 2022 Sep 12;61(36):14403-14418. doi: 10.1021/acs.inorgchem.2c02265. Epub 2022 Aug 31.

Authors

Kende Attila Béres^{1

2}, Zoltán Homonnay², Libor Kvitek³, Zsolt Dürvanger⁴, Martina Kubikova³, Veronika Harmat^{4

5}, Fanni Szilágyi^{1

6}, Zsuzsanna Czégény¹, Péter Németh⁷, Laura Bereczki¹, Vladimir M Petruševski⁸, Mátyás Pápai⁹, Attila Farkas¹⁰, László Kótai^{1

11}

Affiliations

¹ Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar Tudósok krt. 2, H-1117 Budapest, Hungary.
² György Hevesy PhD School of Chemistry, Institute of Chemistry, ELTE Eötvös Loránd University, Pázmány Péter s. 1/A, H-1117 Budapest, Hungary.
³ Faculty of Science, Department of Physical Chemistry, Palacky University Olomouc, 17. Listopadu 12, Olomouc 77146, Czech Republic.
⁴ Structural Chemistry and Biology Laboratory, Institute of Chemistry, ELTE Eötvös Loránd University, Pázmány Péter s. 1/A, H-1117 Budapest, Hungary.
⁵ ELKH-ELTE Protein eModelling Research Group, Pázmány Péter s. 1/A, H-1117 Budapest, Hungary.
⁶ Bay Zoltan Ltd. for Applied Research, Production Division (BAY-PROD), 1 Kondorfa, H-1116 Budapest, Hungary.
⁷ Institute for Geological and Geochemical Research, Research Centre for Astronomy and Earth Sciences, ELKH, Budaörsi street 45, H-1112 Budapest, Hungary.
⁸ Faculty of Natural Sciences and Mathematics, Ss. Cyril and Methodius University, Skopje MK-1000, North Macedonia.
⁹ Wigner Research Centre for Physics, H-1525 Budapest, P.O. Box 49, Hungary.
¹⁰ Department of Organic Chemistry, Budapest University of Technology and Economics, Műegyetem rakpart 3, H-1111 Budapest, Hungary.
¹¹ Deuton-X Ltd., Selmeci u. 89, H-2030, Érd, Hungary.

Abstract

Research on new reaction routes and precursors to prepare catalysts for CO₂ hydrogenation has enormous importance. Here, we report on the preparation of the permanganate salt of the urea-coordinated iron(III), [hexakis(urea-O)iron(III)]permanganate ([Fe(urea-O)₆](MnO₄)₃) via an affordable synthesis route and preliminarily demonstrate the catalytic activity of its (Fe,Mn)O_x thermal decomposition products in CO₂ hydrogenation. [Fe(urea-O)₆](MnO₄)₃ contains O-coordinated urea ligands in octahedral propeller-like arrangement around the Fe³⁺ cation. There are extended hydrogen bond interactions between the permanganate ions and the hydrogen atoms of the urea ligands. These hydrogen bonds serve as reaction centers and have unique roles in the solid-phase quasi-intramolecular redox reaction of the urea ligand and the permanganate anion below the temperature of ligand loss of the complex cation. The decomposition mechanism of the urea ligand (ammonia elimination with the formation of isocyanuric acid and biuret) has been clarified. In an inert atmosphere, the final thermal decomposition product was manganese-containing wuestite, (Fe,Mn)O, at 800 °C, whereas in ambient air, two types of bixbyite (Fe,Mn)₂O₃ as well as jacobsite (Fe,Mn)^T-4(Fe,Mn)^OC-6₂O₄), with overall Fe to Mn stoichiometry of 1:3, were formed. These final products were obtained regardless of the different atmospheres applied during thermal treatments up to 350 °C. Disordered bixbyite formed first with inhomogeneous Fe and Mn distribution and double-size supercell and then transformed gradually into common bixbyite with regular structure (and with 1:3 Fe to Mn ratio) upon increasing the temperature and heating time. The (Fe,Mn)O_x intermediates formed under various conditions showed catalytic effect in the CO₂ hydrogenation reaction with <57.6% CO₂ conversions and <39.3% hydrocarbon yields. As a mild solid-phase oxidant, hexakis(urea-O)iron(III) permanganate, was found to be selective in the transformation of (un)substituted benzylic alcohols into benzaldehydes and benzonitriles.