Hydrogenation of carbon monoxide over rhodium/silica catalysts promoted with molybdenum oxide and thorium oxide

Abstract

R. (1987). Hydrogenation of carbon monoxide over rhodium/silica catalysts promoted with molybdenum oxide and thorium oxide. Applied Catalysis, 35(1), 109-139. DOI: 10.1016/S0166-9834(00) General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. ABSTRACTThe promotion of silica-supported rhodium catalysts in the hydrogenation of carbon monoxide by molybdenum oxide and thorium oxide has been examined. Temperature programmed reduction studies indicated the formation of rhodium molybdates, while no evidence was found for the formation of such mixed oxides in the thorium oxide-promoted catalysts. Hydrogen and carbon monoxide chemisorption were suppressed by the presence of molybdenum oxide, pointing to a coverage of the rhodium particles by this promoter oxide. The catalysts with MO: Rh ratios exceeding one even exhibited an almost complete suppression of the rhodium chemisorption capacity. In the thorium oxide-promoted catalysts the chemisorption of hydrogen and carbon monoxide were not suppressed. Infrared spectroscopy of adsorbed carbon monoxide showed that molybdenum oxide completely suppressed bridge-bonded and linearly bonded carbon monoxide, as well as the gemdicarbonyl species. Thorium oxide addition resulted in a minor decrease of the linearly bonded carbon monoxide, while the bridge-bonded carbon monoxide was suppressed to a greater extent. The IR spectra of the thorium oxide-promoted catalysts also exhibited a broad absorption band between 1300 and 1750 cm-', which is thought to be due to carbon monoxide bonded with the carbon atom to the metal and with the oxygen atom to the promoter ion.Carbon monoxide hydrogenation was greatly enhanced by the presence of both molybdenum oxide and thorium oxide. Thorium oxide-promoted catalysts had a high selectivity to C,-oxygenates, while the molybdenum oxide-promoted catalysts exhibited a high methanol selectivity. Ethylene addition to a working catalyst showed that the carbon monoxide insertion reaction, which is thought to be responsible for the formation of oxygenates, was not enhanced by molybdenum oxide, nor by thorium oxide. The ethylene addition experiments indicated that the role of the promoter is to enhance carbon monoxide dissociation. The results can be understood by assuming that side-bonded carbon monoxide, with its weakened C-O...

Manganese-promoted Rh/Al2O3 for C2-oxygenates synthesis from syngas

“…The manganese oxide reduction peaks seem to overlap with that of the rhodium oxide. The ability of a noble metal oxide to accelerate the reduction of a second surface metal oxide species with which it is in intimate contact has been reported previously [32,33]. Metallic rhodium provides sites for hydrogen adsorption and dissociation with an extremely low activation energy.…”

The Promoting Effect of Fe Doping on Rh/CeO2 for the Ethanol Synthesis

“…1974 and 1803 cm -1 were assigned to the bridged bonded CO (CO(b)) [47]. The band at 1704 cm -1 was assigned to the tilted bonded CO (CO(t)) [48], in which the C atom was bonded to a metallic Rh site, [49], and the bands assigned to the hydrogen carbonate and monodentate carbonate species appeared at ca. 1608 [50] and 1429 cm -1 [49], respectively.…”

Enhanced dispersion and the reactivity of atomically thin Rh layers supported by molybdenum oxide films

“…Mo containing additives are known to increase the catalytic activity of Rh nanoparticles in the hydroformylation reaction of ethylene and propylene [3]. While molybdenum oxides were found to suppress the uptake of CO and H 2 on Rh particles, they promoted greatly the hydrogenation of CO through enhancement of CO dissociation [4]. Since it was reported that MoO 3 did not enhance the dissociation of carbon monoxide adsorbed on Rh [5], the clarification of promotional effect of MoO X species with different compositions is of importance.…”

“…Since it was reported that MoO 3 did not enhance the dissociation of carbon monoxide adsorbed on Rh [5], the clarification of promotional effect of MoO X species with different compositions is of importance. There are several proposals to explain the promotional mechanism of molybdenum oxides [2,4], but model studies on wellcontrolled systems are rare. A recent work addressed the interaction of Pt deposit with WO 3 support, concluding that the so-called strong metal support interaction (SMSI) is responsible for the loss of CO adsorption capability on annealing the sample to 570 K [6].…”