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

Abstract

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.

The use of mixed-metal single source precursors for the synthesis of complex metal oxides

“…17b). 140 Mixed-metal sulphides may also be targeted, for instance using [(Ph3P)2AgIn(SC{O}R)4] (R = Me, Ph) can access AgInS2 by direct thermolysis or AgIn5S8 films by AACVD (Fig. 17c).…”

Formation, dynamics, and long-term stability of Mn- and Fe-promoted Rh/SiO2 catalysts in CO hydrogenation

“…An improvement in the C 2+ oxygenate selectivity by the addition of Mn is well-known for Rh/SiO 2 catalysts, as reported in previous studies. 28,30,40 However, a clear explanation is still missing, and the role of Mn as a modifier or promoter for Rh-based catalysts is still elusive, to the best of our knowledge. By considering the aforementioned structural model of RhMn/SiO 2 , we propose that the MnO phase stabilizes the relatively small Rh nanoparticles and mainly prevents agglomeration.…”

“…27 Despite these conversely discussed promoter effects, it is widely accepted that a close proximity of the promoter and Rh is needed, the so-called strong metal-promoter interactions. [28][29][30] However, a lack of long-term catalytic investigations and thorough characterization of spent samples after catalytic reaction have limited atomistic insights into the Rh-promoter interface. Likewise, the specific role of each promoter and their influence on rhodium's catalytic properties over longer periods of time are not clarified yet.…”

Research progress of catalysts for synthesis of low-carbon alcohols from synthesis gas

“…In the synthesis process of low-carbon alcohols, there are many types of parallel side reactions at the same time, such as the reaction to generate various alkanes and alkenes, and the water gas shi reaction, such as reaction eqn (3) and (4). In addition, there are secondary reactions to produce aldehydes and esters (5) and (6).…”

“…Meanwhile, there are fewer harmful substances in the released gas, which is an environmentally friendly fuel; secondly, low-carbon alcohol has a higher octane number, better explosion-proof and shockresistant performance, and can replace the carcinogenic methyl tert-butyl ether as a fuel additive; nally, low-carbon alcohols can be used directly as bulk\ne chemical products, which can also be separated to obtain individual alcohols with high economic value such as ethanol, propanol, butanol, and pentanol. [4][5][6] The current methods for preparing low-carbon alcohols have major drawbacks. Take ethanol as an example.…”