Monte Carlo Studies (MCLH Simulations) of the CO−NO Reaction on Disordered Substrates and Their Relation with Experiments

Abstract

A Monte Carlo study is made of the reduction reaction of NO by CO over a uniform surface and on disordered substrates, some of them fractals, assuming a Langmuir−Hinshelwood mechanism and using experimental kinetics parameters proposed in the literature in the case of Rh as the catalyst. There is good agreement in the pressure and temperature intervals studied between the simulations and the analytic solutions of the mechanism for a uniform substrate. For nonuniform surfaces, in which the kinetics mechanism cannot be solved, MC simulations were used. The production and surface coverage diagrams and their extreme values are analyzed for the different systems, with a scaling seen for maximum CO2 and N2 production with the fraction of blocked sites in substrates from percolation clusters. The effect of structural sensitivity, temperature, reaction order, and selectivity for N2O, of special interest for experimental work, was also studied.

Rh1−x Pd x Nanoparticle Composition Dependence in CO Oxidation by NO

“…The Rh nanoparticles were very active, had a moderate decrease in activity at elevated pressures of NO, and did not undergo significant deactivation. These results are consistent with previous studies on Rh catalysts in this reaction, which found that supported Rh nanoparticles show decreased activity with increased NO pressure at 538 K [32] and that Rh shows very little deactivation for this reaction [33]. The Pd nanoparticles, however, were significantly less active in all conditions and deactivated at elevated pressure of NO.…”

Time Decay of the Activity of the Reduction Reaction of NO by CO on a Pd/Al2O3 Catalyst

“…Fortunately, as shown in Appendix A, analytic solutions can be found for the covering using the approximation that assumes an equilibrium between the adsorbed species CO(a) and NO(a) and their molecules in the gas phase. This approximation, which we have used before [14,21,26] and which assumes high adsorption and desorption rates, is reasonable within the working range of the paper, as has been commented in the literature for the CO-NO [12] reaction. The validity of the approximation has also been confirmed in one of our previous works using Monte Carlo simulations [21] and by numerical integration of the mass balance equations [14].…”

“…This approximation, which we have used before [14,21,26] and which assumes high adsorption and desorption rates, is reasonable within the working range of the paper, as has been commented in the literature for the CO-NO [12] reaction. The validity of the approximation has also been confirmed in one of our previous works using Monte Carlo simulations [21] and by numerical integration of the mass balance equations [14]. In that work it was found an excellent agreement between the analytical approximation, Appendix A, and the numerical solution.…”

“…Our main interest, however, which is probably related to the above, is the deactivation over time that this system undergoes during the process of the reaction, making it difficult to achieve the steady state. According to the literature and to our laboratory experience [14], this phenomenon does not occur with rhodium. As far as the authors are aware, this situation, which can be seen in the figures in the next section, has only been commented incidentally in a recent paper by Reiner et al [7].…”

“…The mechanism on Rh has a long and conflicting history since the early work of Hecker and Bell [15], followed by, among others, the work of Oh [16], Cho [17], Chuang and Tan [18], Peden et al [19] and Permana et al [20], and that from our laboratory [14,21], where we have considered recent experiments by Zaera's group [22]. In view of the attractive matters discussed previously with respect to this mechanism, included also in a large number of theoretical papers, with some contributions from our laboratory [23], it seems appropriate to make use of the recent interest in Pd as a catalyst to extend those studies.…”