Choosing a suitable support for Co3O4 as an NH3 oxidation catalyst

Abstract

Co 3 O 4 as an NH 3-oxidation catalyst may transform reversibly to CoO under reaction conditions, even in the presence of excess oxygen. The use of alumina may then result in the formation of cobalt aluminate rendering the catalyst inactive. The formation of cobalt aluminate can be avoided by using ZnAl 2 O 4 as a support.

Selective catalytic oxidation of ammonia to nitrogen over MnO2 prepared by urea-assisted hydrothermal method

“…Moreover the exorbitant price of noble metals also limited their widespread application. Relatively cheap transition-metal-oxide catalysts, including CeO 2 [6,7] and Co 3 O 4 [8], also showed appropriate activities for NH 3 -SCO, but the operation temperature remained unsatisfactory (300-450 • C). Therefore, it is essential to develop the efficient transition-metaloxide catalysts for the removal of NH 3 at low temperatures.…”

Molecular modelling of the decomposition of NH3 over CoO(100)

“…Clearly, the dominant factor in the loss of catalytic activity of CoO towards NH x dehydrogenation compared to that of the Co 3 O 4 (100) surface is associated to the inability of lattice oxygen to assist the hydrogen abstraction process, rather than the stability of the NH x species at the surface. [14]. The information provided in this study indicates that CoO may not only decrease the conversion of NH 3 but also affects the NO selectivity since the NO desorption energy -leaving an O vacant site-from the CoO surface is 207 kJ mol À1 more endothermic than NO desorption leaving a vacant site at the Co 3 O 4 surface [16].…”

“…Co 3 O 4 is not suitable for high-temperature operations because it loses oxygen above 750 C under oxygen atmospheric pressure, forming less active CoO [13]. Experiments on the oxidation of NH 3 oxidation on unsupported Co 3 O 4 pellets between 450 and 800 C show a decrease of approximately 15% in the NH 3 conversion when the reaction temperature is increased from 640 to 800 C, which has been ascribed to the formation of small CoO crystallites [14]. Limited studies are available that demonstrate the reduced activity of CoO for NH 3 oxidation under industrial oxidation conditions [14].…”

“…Experiments on the oxidation of NH 3 oxidation on unsupported Co 3 O 4 pellets between 450 and 800 C show a decrease of approximately 15% in the NH 3 conversion when the reaction temperature is increased from 640 to 800 C, which has been ascribed to the formation of small CoO crystallites [14]. Limited studies are available that demonstrate the reduced activity of CoO for NH 3 oxidation under industrial oxidation conditions [14]. Evidence at molecular level of the low activity of CoO comes from FTIR analysis of Co 3 O 4 samples reduced in H 2 at 200 Torr and 523 K, which were exposed to NH 3 at room temperature.…”

MnO2‐Based Materials for Environmental Applications

“…At present, noble‐metal‐oxides such as Ag 2 O [ 546 ] and RuO 2 [ 547 ] with high catalytic activity can completely remove NH 3 at 180 and 240 °C, respectively, but these materials also have significant disadvantages, such as low nitrogen selectivity (38% and 78%) and high costs, which limit their practical application. Relatively cheaper transition metal oxide catalysts such as CeO 2 [ 548 ] and Co 3 O 4 [ 549 ] also demonstrate catalytic activities for the oxidation of NH 3 . However, the problem with these materials is that the temperature required for catalytic reactions is too high (300–450 °C).…”