Aqueous Catalytic Disproportionation and Oxidation of Nitric Oxide

Abstract

Nitric oxide, a byproduct of combustion exhaust, is a key species that leads to urban photochemical smog. Nitric oxide exhibits low aqueous solubility, and it has proved difficult to remove NO from gas streams by aqueous scrubbing methods. A catalyst for the aqueous disproportionation of NO to nitrous oxide and aqueous nitrite has been developed with wood-derived activated carbons. Addition of palladium or platinum metal to the carbon support significantly accelerates catalysis. The carbon-supported catalyst was not poisoned by sulfur oxides. The reaction is thought to involve the reduction of surface-bound nitric oxide dimers. The reducing equivalents stem from the oxidation of NO to NO 2 -. Addition of oxygen as an alternative electron acceptor during the reaction immediately arrested nitrous oxide formation, and all the nitric oxide was removed from the gas stream as aqueous nitrite. This demonstrates the feasibility of removing SO x and NO x simultaneously by lowtemperature aqueous scrubbing.

In Situ Attenuated Total Reflection Infrared (ATR-IR) Study of the Adsorption of NO2-, NH2OH, and NH4+ on Pd/Al2O3 and Pt/Al2O3

“…These observations also explain why on Pd/Al 2 O 3 no nitrous oxide is observed. Normally, N 2 O is thought to be produced from either dimerization of NO, dimerization of speculated “HNO” (ads) fragments, or a reaction between NO and adsorbed HNO. ,,,− Since neither NO (ads) nor “HNO” (ads) is observed on Pd/Al 2 O 3 , the formation of N 2 O was not expected, which is in agreement with our experimental findings. This also agrees well with the fact that palladium is less active for the disproportionation of hydroxylamine.…”

Mechanistic Investigation of the Heterogeneous Hydrogenation of Nitrite over Pt/Al2O3 by Attenuated Total Reflection Infrared Spectroscopy

“…From the present results, the mechanism for the formation of N 2 O, which was detected during all hydrogenation experiments in this study, is not clear yet. N 2 O can be formed either via dimerization of NO (ads) and/or “HNO” (ads) or via dissociation of NO on steps as proposed in literature. ,,,,,− Interestingly, although they cannot be converted into each other, NO (ads) 1580 cm −1 and NO (ads) 1620 cm −1 both seem to lead to N 2 O (Figure , Figure , Figure , and Figure ). Dimerization of NO (ads) 1580 cm −1 is easy to understand since the infrared signals show a dipole coupling effect, indicating that NO molecules are in each other vicinity.…”

Aqueous Absorption and Oxidation of Nitric Oxide with Oxone for the Treatment of Tail Gases: Process Feasibility, Stoichiometry, Reaction Pathways, and Absorption Rate

“…The slight increase in NO fractional conversion in the presence of O 2 is attributed to the well-known reactions of O 2 with NO to form nitrite solely and quantitatively under aqueous conditions with the overall stoichiometry [62][63][64][65] The third-order rate law for this reactions is (with k 3 ) 2.1 × 10 6 M -2 ‚s -1 at 25 °C63 and 6.0 ( 1.5 × 6 M -2 ‚s -1 at 22 °C65 ) consistent with the mechanism 63,64 The rate has been found to be unaffected by pH over the range of 1-13 and to hold with either NO or O 2 in excess. 63 However, the main loss mechanism for nitrite ion is the reaction with bisulfite ion to form the N-S compounds discussed earlier, as oxidation by oxygen is a fairly slow process.…”