The catalytic reduction of nitric oxide in automobile exhause gases--I. Tests of iron-containing materials.
Abstract The efficiencies of iron-containing catalysts for the reduction of nitric oxide in simulated and real exhaust gases are reported. The catalyst bed was seven times the swept volume of the engine. The best results were obtained when the engines were run about 10 per cent rich of stoicheiometric. The rate at which the catalyst was poisoned by conventional fuel additives was shown to be reduced by raising the working temperature of the reactor.
Highly conjugated organic polymers as heterogenous catalysts (II): The interaction of nitrogen monoxide and pyrolysed polyacrylonitrile
The interaction of nitrogen monoxide (nitric oxide, NO) with pyrolysed polyacrylonitrile (PANP) has been examined together with the feasibility of the use of PANP based catalysts for the removal of small quantities of NO from the exhaust systems of internal combustion engines. Kinetic studies indicated that PANP was capable of interacting with and removing NO from an inert carrier gas and that the initial specificity of this interaction was little affected by hydrogen, hydrocarbons, carbon monixide or oxygen, the initial rates of removal being appreciably higher than those obtainable with conventional inorganic catalysts or graphitised carbon. The activation energy and kinetic features of the reaction suggested that the interaction involved the odd electron nature of NO and the free spin generated at the polymer surface. Once adsorbed the nitric oxide decomposes to form dinitrogen oxide (N2O) which is further reduced to nitrogen with concurrent assimilation and rearrangement of oxygen within the polymer structure. As a result the PANP gradually loses its capacity to adsorb and decompose NO. In addition, it appears that the structural features which promote the oxidative instability of PANP also govern its NO removal ability. Consequently, the lifetime and therefore practical utility of these systems is governed by the limits of oxidative stability and catalytic capacity.
The adsorption of nitric oxide on iron oxides
Abstract Adsorption isotherms and rates were measured for NO chemisorption on supported and unsupported samples of Fe 2 O 3 and Fe 3 O 4 in the 26–150 °C temperature range. The adsorption behavior is well described by Freundlich isotherms in the pressure range from 1 to 200 Torr. Monolayer coverage is attained at 500 Torr for the reduced samples and at 25000 (by extrapolation) on the oxidized samples. Kinetic measurements were evaluated using the Elovich equation. These plots were monotonic in the case of supported Fe 2 O 3 and showed a sharp discontinuity in the case of supported Fe 3 O 4 at θ = 0.5. A close parallelism is noted with previously studied chemisorption behavior on reduced and oxidized supported chromium oxide.