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

Abstract

An experimental study is made of the time decay of activity of the CO-NO reaction on a Pd/Al2O3 looking at the effect on reaction order and apparent activation energy. The optimum kinetics parameters fitting the steady state data at moderate pressures are determined. The time decay curves are analyzed through various catalyst deactivation models.The authors acknowledge the financial support of this work by FONDECYT under Project 1070351

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

“…The Pd nanoparticles, however, were significantly less active in all conditions and deactivated at elevated pressure of NO. These results, again, are consistent with previous studies on Pd catalysts in this reaction, which found that the activity of Pd is positive order in NO [34], and the deactivation of Pd is quite significant [14,15]. The behavior of the bimetallic catalysts in the P NO = P CO condition is fairly similar to the behavior of a linear combination of monometallic catalyst.…”

“…This model is supported by the work of Vesecky, Rainer, and Goodman, who used Temperature Programmed Desorption (TPD) to show that high surface area Pd catalysts and Pd (100) single crystals are poisoned by stable adsorbed nitrogen atoms, and that free surface oxygen is removed so quickly by CO to form CO 2 that it is unlikely to play a role in the catalyst deactivation [36]. This explanation for deactivation seems more likely than previously suggested mechanisms, such as reaction inhibition by carbon deposition on the surface [14] or self-inhibited NO adsorption on the Rh surface [11] because deactivation was not observed on the pure-Rh catalyst despite identical reaction conditions, and because the sample activity was closely correlated with the Rh molar fraction after deactivation. The importance of nitrogen in this deactivation is further supported by the observation that N 2 O and N 2 production were not significantly enhanced prior to catalyst deactivation.…”

“…Rhodium is acknowledged to be the best catalyst for this reaction, with intense efforts devoted to understanding its behavior [3][4][5][6][7][8][9][10][11][12][13]. However, in recent years much research has also been aimed at understanding the role of Pd in the reaction [1][2][3][14][15][16][17][18][19] because of the relatively high cost of rhodium catalysts, palladium's improved resistance to sintering, and because new improvements in gasoline purification have helped reduce the significance of previous problems with Pd site poisoning by sulfur and lead [15]. Pd has been found to have lower activity than Rh for the reaction of NO with CO [16] and has also been shown to suffer from deactivation [14].…”

Rh1−xPdxnanoparticle composition dependence in CO oxidation by oxygen: catalytic activity enhancement in bimetallic systems

“…Among the large number of possible nanoparticle compositions, Rh, Pt, and Pd-based mono-, bi-, and trimetallic nanocrystals with controlled composition, size, and shape are of special interest because of their role in three-way automotive exhaust catalysis. 12 Although CO oxidation has been studied extensively, many open questions remain regarding catalyst behavior in these systems, especially with regard to composition and oxidation state 13,14 and how these factors affect catalyst deactivation, 15 synergism, 16 and surface segregation. 17 Previous work in our lab on 15 nm Rh 0.5 Pd 0.5 bimetallic Pd-core Rh-shell nanoparticles supported on Si wafers used ambient pressure X-ray photoelectron spectroscopy (APXPS) to examine the dependence of surface composition and oxidation state on the local chemical environment.…”