Catalytic converters temperature limitations

Because of this type of behavior, a sharp transition at stoichiometry but low sensitivity and temperature effects either rich or lean of this point, the oxygen sensor is most useful in controlling at the stoichiometric point. It is of limited usefulness at other exhaust compositions. However, as shown in Figure 5, this is exactly the point at which a three-way or dual bed catalytic converter is most efficient. Only when the exhaust composition is near the stoichiometric point will both the oxidation of the HC and CO and the reduction of the NO occur satisfactorily. 

Elemental phosphorus itself exists in several polymeric forms. If the white allotropic form, which consists of P4 tetrahedral molecules, is put under high pressure, preferably at elevated temperatures, it can be catalytically converted to other modifications.41 It first becomes red, then violet, then black as the degree of polymerization increases. These materials are very difficult to characterize because of branching and the formation of cyclics. In the extreme limit, the structure approaches that of graphite, and shows good electrical conductivity.42 No evidence exists at all for the formation of high-molecular-weight, linear chains of elemental phosphorus. 

For the conversion of syngas into methanol, the pressure is raised from 25 to 100 bar. The gas mixture is catalytically converted at temperatures between 250 and 300 °C. The synthesis of methanol is exothermic and strongly equilibrium limited. In conventional operation, the conversion of hydrogen typically does not exceed 30%. In the large-scale plant, methanol and the by-product, water, are flashed off and the unconverted gas is recompressed and recycled to extinction. 

Cobalt hydrocarbonyl is a volatile substance of limited stability at or above ambient temperature. Its tendency to decompose at undesirable sites in a process has posed a severe problem for commercial operations. Consequently, the patent literature contains numerous references to a variety of schemes for selectively removing cobalt from product and converting it to a form suitable for catalytic reuse. 

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