Abstract
The catalytic acitivity of Rh/TiO 2and Rh/A1 20 3 catalysts for the hydrogenation of CO at atmospheric pressure and 523 K was investigated. Normal, non-SMSI state Rh/TiO 2 as well as Rh/TiO 2 catalysts in the SMSI state with varying dispersion were studied. In all cases only hydrocarbons and no oxygenated products were formed. When measured at equal dispersions the activities of Rh/A1 20 3 and non-SMSI Rh/TiO 2 catalysts hardly differed. The specific activity of Rh/TiO 2 catalysts increased an order of magnitude when changing the dispersion from 1.10 to 0.12. This increase in specific activity was acompanied by an increase in the olefin-to-paraffin ratio, but neither the selectivity to methane nor the probability for chain growth was affected much. Reduction of the Rh/TiO 2 catalysts at 773 K decreased their initial activities substantially compared to reduction at 523 K. whereas the steady-state activities were hardly affected. Apparently the SMSI state is removed to a great extent during CO hydrogenation. The lowering effect of SMSI on activity was a function of dispersion. The effect was much more pronounced for small metal particles, indicating that SMSI might be due to covering.
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