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

Abstract

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.