Hydrocarbons activation during oxidation

The use of supported mixed oxides in both catalytic combustion and NO reduction are challenging applications. In the case of high-temperature catalytic combustion there is an unsatisfied need to obtain solids able to maintain high combustion activity during extended operation, i.e., high-surface-area structurally stable solids. Another hot subject that deserves exploration is the use of washcoated highly dispersed mixed oxides for the selective reduction of NO with CO and hydrocarbons. These studies should be conducted in the presence of both SO2 and H2O to evaluate the potential practical application of these catalysts. 

Saturated and unsaturated hydrocarbons with odd and even numbers of carbon atoms in the molecule (about C11-C35) are present as the primary substances in all vegetable oils and animal fats. Alkanes, alkenes, alkadienes and alkatrienes also arise as oxidation products of unsaturated fatty acids, catalysed by lipoxygenases or by autoxidation of fatty acids during food storage and processing. Only the lower hydrocarbons can play a role as odour-active substances. The main hydrocarbons resulting from oxidation of unsaturated fatty acids are ethane from Hnolenic acid, pentane and butane from Hnoleic acid and hexane and octane from oleic acid. The immediate precursors of hydrocarbons are the fatty acid hydroperoxides (Table 8.4). The unsaturated hydrocarbons are predominantly (Z)-isomers. Numerous other hydrocarbons, including ahcycHc hydrocarbons, appear as secondary hpid oxidation products. 

Using cobalt nitrates as precursor, the possible cobalt insertion in the srrrface ceria lattice leads to a synergistic coupling of the redox properties of ceria and C03O4. By the addition of ethylenediamine during the catalyst preparation, Co species do not enter in the ceria due to the preliminary formation of Co-ethylenediamine complex, but rather contribute to well dispersed C03O4 phase after activation treatment. Consequently CoEn is more active than CoNit in the propylene (model molecule to mimic the total catalytic oxidation of a VOC of hydrocarbon type) total oxidation the T50 is lowered by 20°C. 

Zinc oxide is a common activator in mbber formulations. It reacts during vulcanization with most accelerators to form the highly active zinc salt. A preceding reaction with stearic acid forms the hydrocarbon-soluble zinc stearate and Hberates water before the onset of cross-linking (6). In cures at atmospheric pressure, such as continuous extmsions, the prereacted zinc stearate can be used to avoid the evolution of water that would otherwise lead to undesirable porosity. In these appHcations, calcium oxide is also added as a desiccant to remove water from all sources. 

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