Selective Oxidation Of Ammonia Research Articles

Ammoximation: III. The selective oxidation of ammonia with a number of ketones to yield the corresponding oxime

A variety of ketones have been shown to undergo a selective oxidative amination to the corresponding oxime. The “ammoximation” of ketones described is limited by the competitive formation of a by-product which deposits on the catalyst during the course of the reaction. However, the amount of by-product which is formed is related to the ease with which the ketone reacts separately with ammonia. Further, pretreating the catalyst with a mixture of cyclohexanone, ammonia, and oxygen serves to activate the original catalyst (in this case a silica) toward other ketones. In general, the direct ammoximation of ketones does offer an attractive and alternative route for the preparation of speciality oximes where the conventional method(s) may prove to be more awkward.

Catalytic oxidation of ammonia: II. Relationship between catalytic properties of substances and surface oxygen bond energy. General regularities in catalytic oxidation of ammonia and organic substances

Catalytic activity and selectivity of oxides of cobalt, manganese, copper, iron, vanadium and molybdenum with respect to ammonia oxidation to N 2 and N 2O have been studied. The activity decreases in the above-mentioned sequence of oxides. The specific activity of metallic platinum is much higher than that of the most active oxide catalysts. Generally, the selectivity towards mild oxidation (the formation of N 2) increases with decreasing activity of oxides. On the basis of the reaction mechanism proposed in the previous paper (Part I) the relationship between surface oxygen bond energy, q s , and catalytic behavior of oxides has been deduced theoretically. Catalytic activity, r, is expected to pass through a maximum which corresponds to low values of q s . For the majority of catalysts the activity must decrease with increasing q s . At the same time the selectivity for the formation of N 2 must increase while the selectivity for N 2O must fall. The experimental data obtained confirm these conclusions. In accordance with the theory, for the high temperature oxidation of ammonia to NO the selectivity in NO decreases with increasing q s . The following rule has been stated: more oxygen-catalyst bonds are broken in the formation of the activated complex of a stage leading to a deep oxidation product than in the formation of a mild oxidation product. This gives rise to an increase in selectivity in mild oxidation with q s . The above rule has been shown to be rather general and also applicable to the oxidation of organic substances. Thus, the similarity between selective oxidation of ammonia and organic molecules has been found. Some general regularities concerning heterogeneous catalytic oxidation are formulated.