The role of carbon monoxide in the NO-carbon reaction

The enhancement of the NO/carbon reduction reactions by carbon monoxide has been demonstrated for carbons of widely varying nature (coal char, phenolic resin-derived char and graphite). The evidence supports enhancement of NO reduction via a carbon-surface-catalyzed reaction such as NO + CO --> 1/2N(2) + CO2. This reaction appears to be characterized by an activation energy of around 116 kJ/mol, and by zero order with respect to CO, in the range of CO pressures examined here (up to order 500 ppm). This suggests that an oxide stripping reaction, e.g., CO + C(O) --> CO2 + C*, cannot be invoked in its usual form, to explain the rate enhancement. The reaction appears to be first order with respect to NO, at high temperatures and at NO concentrations of above roughly 100 ppm, but kinetic analysis is complicated by the fact that the NO-carbon reaction itself does not have a unique order at low temperatures. It is also shown that kinetic analysis can be greatly complicated in the presence of other oxidizing gases or surface oxides deposited by these gases.