Emission catalysts, degradation

T he successful use of platinum monolithic oxidation catalysts to control automobile emissions over many thousands of miles requires an intimate understanding of the many factors which contribute to catalyst degradation. Contamination of the active catalyst by lead and phosphorus compounds present in fuel and lubricating oil is a major factor in catalyst deterioration. 

Thermal Stability. Our initial work on catalyst degradation processes was designed to answer qualitatively several simple yet vital questions. This report is organized similarly. The question naturally arises whether platinum or palladium is best for automotive emission control. One aspect... 

Three flue gas cleaning units were built for the eight rotary furnaces. Each unit consists of an electrostatic filter and a three-stage scrubber. By 1996, these units will be retrofitted with catalysts to lower NO emissions and degrade dioxins. The plant combusted ca. 150 000 t of waste in 1992 on reconstruction, a combustion capacity of 160 000 t/a will be available after 1996 [255]-[258]. 

Double-Absorption Plants. In the United States, newer sulfuric acid plants ate requited to limit SO2 stack emissions to 2 kg of SO2 per metric ton of 100% acid produced (4 Ib /short ton Ib = pounds mass). This is equivalent to a sulfur dioxide conversion efficiency of 99.7%. Acid plants used as pollution control devices, for example those associated with smelters, have different regulations. This high conversion efficiency is not economically achievable by single absorption plants using available catalysts, but it can be attained in double absorption plants when the catalyst is not seriously degraded. 

The freshly prepared, flexible PU foams, using tertiary amines as foaming catalysts, are well known to have an unpleasant odour, characteristic of amines. The staining of vinylic films or degradation of polycarbonate sheets is produced as a consequence of the aminic catalyst emission from PU foams. This problem is serious, especially in environments where there are elevated temperatures for long periods of time, for example in an automobile interior. These problems need a reduction of migratory amine catalyst emissions. 

First, this reserve activity could be utilized to offset thermal and contaminant degradation of catalyst activity. In simplistic terms, the 4300-cm3 production prototype converter could lose 70% of its catalytic activity (with a remaining catalyst volume equivalent to 1300 cm3) without suffering degradation in the overall control of exhaust HC and CO emissions. 

The Chemistry of Degradation in Automotive Emission Control Catalysts... 

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