From a Molecular Single‐Source Precursor to a Selective High‐Performance RhMnOx Catalyst for the Conversion of Syngas to Ethanol

• Published in: ChemCatChem Vol. 11; no. 2; pp. 885 - 892
• Main Authors: Preikschas, Phil, Bauer, Julia, Huang, Xing, Yao, Shenglai, Naumann d'Alnoncourt, Raoul, Kraehnert, Ralph, Trunschke, Annette, Rosowski, Frank, Driess, Matthias
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 23.01.2019
• Subjects: Carbonyls; Catalysis; Catalysts; Clusters; Conversion; Ethanol; Heterobimetallic Catalysis; Hydrogenation; Manganese; Metathesis; Nanoparticles; Oxygenates; Precursors; Rhodium; Selectivity; Silicon dioxide; Synthesis gas
• ISSN: 1867-3880; 1867-3899
• DOI: 10.1002/cctc.201801978

The first molecular carbonyl RhMn cluster Na2[Rh3Mn3(CO)18] 2 with highly labile CO ligands and predefined Rh‐Mn bonds could be realized and successfully used for the preparation of the silica (davisil)‐supported RhMnOx catalysts for the conversion of syngas (CO, H2) to ethanol (StE); it has been synthesized through the salt metathesis reaction of RhCl3 with Na[Mn(CO)5] 1 and isolated in 49 % yields. The dianionic Rh3Mn3 cluster core of 2 acts as a molecular single‐source precursor (SSP) for the low‐temperature preparation of selective high‐performance RhMnOx catalysts. Impregnation of 2 on silica (davisil) led to three different silica‐supported RhMnOx catalysts with dispersed Rh nanoparticles tightly surrounded by a MnOx matrix. By using this molecular SSP approach, Rh and MnOx are located in close proximity on the oxide support. Therefore, the number of tilted CO adsorption sites at the RhMnOx interface increased leading to a significant enhancement in selectivity and performance. Investigations on the spent catalysts after several hours time‐on‐stream revealed the influence of rhodium carbide RhCx formation on the long‐term stability. Catalysts Birth. The first carbonyl RhMn cluster Na2[Rh3Mn3(CO)18] has been synthesized, structurally characterized and utilized as well‐defined molecular single‐source precursor (SSP) for the low‐temperature preparation of selective high‐performance RhMn catalysts for the conversion of syngas to ethanol (StE). Highly dispersed Rh nanoparticles in a tightly surrounded MnOx matrix lead to a superior selectivity towards ethanol.