Kinetics of the CO+NO Reaction over Rhodium and Platinum–Rhodium on Alumina

Mesoporous Pt–SiO2 and Pt–SiO2–Ta2O5 Catalysts Prepared Using Pt Colloids as Templates

“…A similar structural sensitivity is also reported during the reduction of NO by hydrocarbons under lean conditions, with the higher dispersions corresponding to the less active catalysts. [38] In line with this, it has been suggested that the oxidation of NO into NO 2 within the overall reduction process of NO could be rate determining. On the other hand, a strong interaction between hydrocarbons, such as alkenes, and Pt particles would prevent the accumulation of oxygen at the surface, further preserving the metallic character of Pt.…”

Infrared investigation of the transformation of NO over supported Pt‐ and Rh‐based three‐way catalysts

“…The lack of observation of gem-dinitrosyl species Rh(NO) 2 . The low N-O frequency for the anionic species formed on Rh compared with gas-phase NO suggests that the N-O bond breaking is more facilitated in the negatively charged NO species than in the neutral or positively charged species.…”

“…In contrast to what was observed on Pt, CO does not completely remove NO from the Rh surface, which could be related to a stronger NO adsorption on Rh than on Pt. 2 The spectrum of the CO adsorbed species obtained after a reductive treatment in hydrogen (see Fig. 3(B.c)) shows a strong attenuation of the gem-dicarbonyl band parallel to the appearance of an intense band at 2042 cm 1 , corresponding to CO linearly bound to Rh 0 .…”

“…The absence of a significant infrared band associated with NO adsorbed on Pt or Rh could be explained tentatively by a balance between competitive adsorptions, in favour of CO on Pt and of NO on Rh, and a faster dissociation of NO on Rh than on Pt, as found previously. 2,13 The appearance/disappearance of the gem-dicarbonyl species on Rh/Al 2 O 3 during the CO C NO reaction could be easily explained by the accumulation of oxygen on Rh via the dissociation of NO at low temperature, leading to the formation of surface oxidic Rh species, whereas at higher temperature the oxygen removal would act predominantly in the presence of CO, via step (7), preserving Rh sites in their metallic state. In the light of these results, changes in the oxidation state of metals during the CO C NO reaction, being initially oxidized and then recovering their metallic state, could partly explain changes in the selectivity of NO transformation, particularly during the cold start where the formation of N 2 O is mainly promoted on Rh/Al 2 O 3 .…”

“…5,6 Recently Chafik et al 10,11 proposed that the formation of N 2 O would occur mainly via the formation of dinitrosyl species Rh(NO) 2 on oxidic rhodium sites instead of a reaction path involving chemisorbed nitrogen atoms and adsorbed NO molecules. This proposal differs from earlier kinetic features obtained in our laboratory, suggesting that the following mechanism is the most representative to describe the CO C NO reaction on Rh/Al 2 …”