Mandy W. McQuire

In situ FTIR study of CO/H2 reactions over Rh/SiO2 catalysts at high pressure and temperature

Abstract Infrared spectra are reported of CO(5 atm) and CO(5 atm)/H 2 (10 atm) over Rh/SiO 2 catalysts at high temperatures. Three stages of reaction involved initial CO adsorption, followed by the appearance of a band ascribed to a reactive hydrocarbonaceous residue, and finally the slow generation of methane, adsorbed methoxy and ethoxy groups and a methylene-containing hydrocarbon product. The alkoxy groups existed predominantly on the surface of the silica support.

Fourier-transform infrared study of Rh/SiO2 catalysts exposed to CO–H2 mixtures at high pressure and temperature

FTIR spectra are reported of Rh/SiO2 exposed to 1 : 2 and 2 : 1 mixtures of CO : H2 at 3 atm total pressure and 503, 523 and 553 K. Linear and bridged CO existed on Rh during reaction which led to methane, methanol and ethanol as the dominant products. IR bands due to adsorbed CH3 and CH2 groups primarily resulted from alcohol adsorption on the silica support giving surface methoxy and ethoxy groups. An IR band at 3124 cm–1 is ascribed to an unsaturated hydrocarbonaceous residue, the build-up of which displaces linearly bonded CO from the Rh surface and also decreases the catalyst selectivity for methane formation.

Syngas reactions over Rh/SiO2 at high pressure and temperature studied by Fourier-transform infrared spectroscopy

In situ FTIR spectra are reported of Rh/SiO2 at 473, 503, 523 and 553 K exposed to CO–H2 mixtures with CO : H2 ratios of 1 : 14 and 14 : 1 and a total pressure of 1.5 MN m–2 and also with a CO : H2 ratio of 1 : 2 and a total gas pressure of 0.3–5.0 MPa. The dominant detectable products were adsorbed CO on Rh, OMe and OEt groups on silica, CH4(g) and adsorbed higher hydrocarbon. Selectivities varied widely from ca. 100% to methoxy/methanol for the 1 : 14 ratio at 473 K to ca. 100% to higher hydrocarbon for the 14 : 1 ratio at 523 K. The dominant factor influencing selectivity was the CO : H2 ratio, although temperature, total gas pressure and time of reaction also had an effect. Selectivity to methanol rather than ethanol was favoured by low temperature and high pressure.

Comparative FT-IR and MAS NMR spectroscopic studies of Rh/SiO2 catalysts exposed to CO/H2 at high temperature and pressure

Abstract 13 C and 1 H MAS NMR spectra of Rh/SiO 2 catalysts after exposure to methanol and ethanol at 473 K or to CO: HZ mixtures at 15 atm (ratios 1 : 14, 1 : 2, and 14 : 1) and 473, 523, or 553 K are reported. The NMR spectra complement FT-IR spectra and confirm that adsorbed OMe and OEt groups resulting from CO/H 2 reactions over Rh/SiO 2 , exist predominantly on the silica surface. NMR was better than FT-IR for distinguishing adsorbed OMe, OEt, and hydrocarbon species and also enabled identification of immobile chemisorbed species and weakly adsorbed mobile product molecules. Changes in the CO : H 2 ratio had a profound effect on the nature of resulting surface species in situ under reaction conditions.

In situ FTIR study of CO–H2 reactions over RH/TiO2 catalysts at high pressure and temperature

IR spectra are reported of Rh/TiO2in situ in CO–H2 mixtures (1 : 14, 1 : 2, 2 : 1 and 14 : 1 ratios) at high pressure (0.3 or 1.5 MN m–2) and temperature (473, 523 or 553 K). The spectra allowed the surface hydroxy groups and water on TiO2, CO adsorbed on Rh and gaseous CO, CO2 and CH4 to be monitored together with OMe–, OEt–, HCO2– and MeCO2– species on TiO2 and surface CH2-containing hydrocarbon.Titania alone catalysed the CO–H2 reactions but the dominant products with Rh/TiO2 were formed by catalysis over Rh followed by spillover of oxygenates onto the support. Surface carbonyl and carbonyl hydride complexes of rhodium, present during the reaction, are believed important, possibly as precursor intermediate species influencing the catalytic selectivity for methanol, ethanol, methane and higher linear hydrocarbon production.

In situ Fourier-transform infrared study of CO–H2 reactions over Rh/Al2O3 catalysts at high pressure and temperature

Infrared spectra are reported of methanol and ethanol adsorbed on Rh/Al2O3 at 473 K, and of the adsorbed products of the reaction of CO(1 MPa)–H2(2MPa) over alumina and Rh/Al2O3 at 553 K. Catalysis by rhodium leads to production of methanol and ethanol over Rh/SiO2, but the alcohols interact further with the alumina support in Rh/Al2O3 to give surface methanoate and ethanoate anions. Methanoate species are also formed from CO–H2 over alumina alone in the absence of rhodium. Rh/Al2O3 showed a higher selectivity towards methane than Rh/SiO2 possibly via the involvement of methanoate as an intermediate species.

In situ Fourier-transform infrared studies of CO–H2 reactions over Ru–Rh/SiO2 catalysts at high pressure and temperature

Infrared spectra of Ru–Rh/SiO2 catalyst in situ in CO–H2 mixtures (ratios 1 : 14, 1 : 2 and 14 : 1) at high pressure (0.3, 1.5 and 3 MN m–2) and temperature (473, 503, 553 K) are compared with corresponding results for Rh/SiO2 and Ru/SiO2. The mixed metal catalyst gave results suggesting that the surfaces of the metallic particles contained primarily Rh rather than Ru atoms, a conclusion which was substantiated by data for the adsorption of CO and methanol or ethanol. Particles possibly consisted of a monoatomic sheath of Rh surrounding a core of Ru. The nature of the precursor metal salts probably has a strong influence on the structures of individual metal particles after reduction.