Kinetic study of NO reduction on carbon-supported chromium catalysts

Direct reduction of NO on carbon supported chromium catalyst and in the presence of reducing agent, such as C3H6 and CO, has been studied. For the direct NO reduction on the catalyst, a kinetic study has been carried out considering that adsorption of NO takes place on an activated chromium site. This activated chromium site, an oxygen deficient chromium catalysts, is generated by the reaction between a chromium site and an unstable carbon site, obtained by decomposition of carbon–oxygen complexes. The following step was the dissociative chemisorption of adsorbed NO by a neighboring carbon site. The rate determining step for the direct NO reduction is the formation of CO2, associated to the chromium catalyst regeneration. In the presence of a reducing agent, the proposed mechanism considers the chemisorption of C3H6 or CO on the chromium site, followed by the activation (reduction) of this site to obtain an oxygen-deficient species, which interacts with NO in gas phase, when propylene is used as reducing agent. The presence of CO favors other reaction pathway for the regeneration of the chromium catalyst, increasing the activity. Both models represent reasonably well the experimental data. XPS and thermodynamic results support the validity of the models proposed.