The mechanism of the lean Nox reaction over Pt-based catalysts

Insight into the Catalytic Reduction of NO by Methane: The Reaction of Nitromethane on Oxidized Mo(110)

“…The peak from ν(CN) of CH 3 N is at 1290 cm -1 , which is close to the C-N stretch frequency of 1281 cm -1 reported for methylimide in Os(NCH 3 )(CH 2 SiMe 3 ) 4 . 43 Furthermore, this peak shifts to 1275 cm -1 for 13 CH 3 NO 2 (Figure 3), in agreement with the 17 cm -1 downshift in ν(CN) observed upon 13 C isotopic substitution in gaseous CH 3 N radicals, 44 and the 19 cm -1 downshift predicted using a harmonic oscillator approximation for a C-N stretch of CH 3 N. The observation of •CH 3 desorption commencing at 550 K is also consistent with the formation of CH 3 N between 300 and 500 K. Methylimido has previously been identified on Pt(111) via decomposition of adsorbed trimethylamine, with ν(CN) reported at 1162 cm -1 . 45 Other possible intermediates, namely methylene amidogen (CH 2 N) and aminomethylidyne (CNH 2 ), are ruled out based on the absence of detectable dehydrogenation up to the onset of HCN production.…”

“…Other modes characteristic of a CH 3 N intermediate are the methyl rocking mode at 1072 cm -1 , the deformation mode at 1396 cm -1 , and two distinct peaks in the C-H stretching region at 2906 and 2844 cm -1 (Figure 2). All of these modes shift as expected upon 13 C isotopic substitution and deuteration of nitromethane, with the exception that only one peak in the C-D stretching region at 2050 cm -1 is observed for CD 3 N (Table 3). We assign the peaks at 2906 and 2900 cm -1 for CH 3 N and 13 CH 3 N, respectively, as the symmetric C-H stretch.…”

“…The intensity redistribution and shifts in peak positions are attributed to changes in the local environment of ModO moieties and in the morphology of the thin-film oxide, as previously demonstrated. 37 Notably, the persistence of these peaks to 800 K where product evolution is complete, and the invariance in their frequencies for 13 CH 3 NO 2 , CH 3 NO 2 , and CD 3 NO 2 confirm that neither C nor H contribute to these peaks (Figure 2a, inset). These results rule out any contribution from ν(CO) of methoxy (CH 3 O), which has been observed in the same frequency range on oxygen-modified Mo(110).…”

“…Despite substantial evidence that methane enhances NO x reduction over a variety of catalysts, including zeolites, , rare earth oxides, , and metal-promoted oxides, , the mechanism for this process is still not well understood. One possibility is that methyl radicals formed from methane would scavenge surface oxygen deposited from NO dissociation, which would otherwise deactivate the catalyst by occupying sites required for NO reduction.…”

Removal of Nitrogen Oxides Using Nanosized Catalysts Prepared by Dry Mechanical Coating Technique

“…Most investigations have focused on supported noble metal catalysts for reduction of NOx (Benton and Taylor, 1999) with concentrated efforts on either platinum alone due to its exceptional catalytic properties, resistance to chemical corrosion, and high mechanical strength or in combination with other metals. Well-known examples are Pt/Al 2 O 3 , Pt/Rh, and Pt/Pd/Rh (Ansell et al, 1995). Platinum alone is effective, but the presence of small amounts of rhodium improves the conversion of NO x .…”