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.
The effect of group IIIA–VIA elements and their oxides on graphite oxidation
Abstract The effect of group IIIA–VIA elements and oxides on graphite oxidation was determined. Additives were moulded with spectroscopically pure graphite powder. The concentration was maintained constant at 0.1 mole per cent based on the element. The rate of reaction with 1 atm of air was measured at 700 and 800°C. Air flow rate from 2000 to 3000 cm 3 /min had no effect on the oxidation rate of the pure graphite at 700, 750 and 800°C, indicating that reaction was not occurring in zone III. The calculated E a of 54 kcal/mole suggested reaction in zone 1. Visual inspection of the rods after reaction substantiated this conclusion. The reaction was first order with respect to oxygen partial pressure at 700 and 800°C. B, B 2 O 5 , P and P 2 O 5 inhibited the oxidation of graphite at 700 and 800°C, while the other elements and oxides catalysed the reaction to various degrees. The reaction remained kinetically of the first order when inhibited. A systematic variation in reaction rates appears to follow the diagonals of the periodic relationship of the element from the upper left to the lower right. These variations can be correlated with average ionization energy or electron affinity.
Forms of oxygen bonds on the surface of oxidation catalysts
The study of the isotopic exchange of oxygen on oxides and metals affords additional information about the form of the oxygen bond at the surface of catalysts. As a result of high temperature treatment of oxides, there appears on the surface a form possessing the catalytic activity for isotopic exchange of oxygen at very low temperatures. One may suppose that under these conditions the exchange of oxygen proceeds through an intermediate formation of many-atom, strictly oriented, complexes.For oxides and metals having an equilibrium content of oxygen in the surface layer, the activity in a homomolecular exchange may serve as a measure of the reactivity of the surface oxygen and is well correlated with the catalytic activity in a series of oxidation reactions.