Promotion effects of vanadium, niobium, molybdenum, tungsten, and rhenium oxides on surface reactions in the CO hydrogenation over Ru/Al2O3 catalyst

By use of the PSRA (pulse surface reaction rate analysis) apparatus equipped with an EDR (emissionless infrared diffuse reflectance spectrometer) and an FID (flame ionization detector), the promotion effects of oxides of V, Nb, Mo, W, and Re have been investigated for the surface hydrogenation reaction of CO over Ru/Al₂O₃ catalysts. These promoters markedly increase the rate constant for the dissociation of CO to form (CH_x)_ad (k_CO), while decreasing the rate constant for the hydrogenation of (CH_x)_ad to CH₄ (k_CHx). In accordance with the observed change in rate constants, it was found that the surface concentration (CH_x)_ad species on the catalyst increased during the steady-state reaction, resulting in an increase in the yield of higher molecular weight hydrocarbons. The promotion mechanism leading to the dissociation of CO is discussed on the basis of the results obtained from PSRA.