NO Reduction by CO over a Pt/Al₂O₃ Catalyst:  Reaction Kinetics and Experimental Bifurcation Behavior

Abstract

The kinetic behavior of NO reduction by CO over a Pt/Al2O3 catalyst has been investigated in the temperature range of 465−520 K. The NO + CO reaction exhibits isothermal steady-state multiplicity. A high-conversion steady state was obtained starting with a net oxidizing feed composition ([NO]0 > [CO]0), and a low-conversion steady state was obtained for a net reducing initial feed composition ([NO]0 < [CO]0). A significant amount of N2O was observed as a reaction product, particularly for the high-conversion steady states. The selectivity toward N2O decreased with increasing NO conversion. For the high-conversion steady states, the N2O selectivity decreased rapidly with a decrease in the feed [NO]0/[CO]0 ratio below a critical value of 1.5. The N2O + CO reaction was found to occur to a significant extent. The steady-state bifurcation behavior has been used to discriminate among three kinetic models.

Bifurcation Analysis on Pt and Ir for the Reduction of NO by CO

“…The same qualitative behaviour is observed at other temperatures also. Sadhankar and Lynch (1997) performed experiments on 0.5%Pt/Al 2 O 3 with feed conditions of 0.45% NO (0.184 mol/m 3 ) and by changing CO concentration from 0 to 1.2% CO (0-0.491 mol/m 3 ) at 232ºC. The experimental results of Sadhankar and Lynch (1997) are shown in Figure 7b.…”

“…Sadhankar and Lynch (1997) performed experiments on 0.5%Pt/Al 2 O 3 with feed conditions of 0.45% NO (0.184 mol/m 3 ) and by changing CO concentration from 0 to 1.2% CO (0-0.491 mol/m 3 ) at 232ºC. The experimental results of Sadhankar and Lynch (1997) are shown in Figure 7b. Our simulation results (Figure 7a) are qualitatively in good agreement with these experimental results (Figure 7b).…”

“…The NO-CO reaction plays a prominent role in the catalytic converter, as the exhaust from automobiles contains suffi cient amount of CO. First reported literature (Kobylinski and Taylor, 1974) and as well as the more recent articles (Chambers et al, 2001;Granger et al, 2002) on the NO-CO reaction indicate good activity of Pt group catalysts. (Frank et al, 1997;Sadhankar and Lynch, 1997). Cobden et al (2000) observed that Ir(110) shows bifurcations for the NO-H 2 reaction at 200ºC under 10 -7 bar pressure when C NO /C H2 = 0.05.…”

Application of periodic operation to kinetic study of NO–CO reaction over Rh/Al2O3

“…Several groups published detailed analysis of the surface reaction steps and reaction mechanism using non-conventional techniques such as transient response method, Monte Carlo simulation, feed composition forcing periodic operation etc. [6,[12][13][14][15][16][17][18]. Generally, NO dissociation over catalytic site is considered as a key surface reaction step.…”

“…Since Rh has similar adsorption characteristics with Pt (NO and CO are competitively adsorbed on active sites and the adsorption strength is strong for both NO and CO), the proposed method was expected to be effective for the case of Rh/Al 2 O 3 , as well. However, infrared studies showed that several types of adsorbed species which could not be observed on Pt sites were formed on Rh sites during the reaction [15,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. NO is adsorbed on the Pt sites as linear Pt-NO whereas it is adsorbed on the Rh sites as anionic Rh-NO ␦− , cationic Rh-NO ␦+ , neutral Rh-NO and dinytrosyl Rh(NO) 2 .…”