Total oxidation processes -Automotive depollution and air and water treatments

Oxidation catalysis plays a key role in pollution control processes. It makes it possible to work under milder temperature and pressure conditions to achieve high levels of pollutant conversion.

Automotive catalytic converters are a prime example of what can be achieved in this field. They were first used in the exhaust line of gasoline engines. The "three-way" process uses a single catalyst to lower the levels of the three major pollutants (CO, HC, NO _x ) below the levels set by European Union standards. This process is mature, and the progress expected will come from the durability of the materials used in the converter, with manufacturers aiming for a longevity equal to or greater than 240,000 km. The situation is very different for engines operating with a lean mixture (i.e. excess air): diesel engines or "lean" gasoline engines. Since exhaust gases are highly oxidizing, the reduction of nitrogen oxides is complex and represents a challenge for the chemical industry. Solutions include ammonia reduction (from urea hydrolysis) or transient NO _x trap systems. In all cases, if we include the particulate filter, no less than three pots in series are required, making the depollution of these engines both costly and complex. The expected progress will come from making these systems more compact, by seeking to place several catalysts in the same pot, so as to get closer to the "ideal" system found in petrol engines (a single pot). At the same time, progress is being made on the durability of materials, since the same requirements apply to these systems installed in diesel exhaust systems (240,000 km).

Oxidation catalysis is also used in stationary air and water treatment processes. However, catalytic processes are not as well developed as in the automotive sector, probably because alternative processes are simpler and less costly. The removal of VOCs from the air is certainly the process best suited to catalytic treatment. The materials used are very similar to those found in catalytic converters, with a predominance of noble metal catalysts (Pt, Pd). The progress expected in this field is of the same order as in automotive catalysis, with increased durability of materials and, above all, lower catalyst costs by substituting noble metals with cheaper oxides. In this field, perovskites of the LaMnO ₃ or LaCoO ₃ type (or ternary and quaternary combinations of the various cations) occupy a prime position. Catalysis is still little used in processes for oxidizing water pollutants ("wet" oxidation or OVH). Conventional processes (adsorption, biological oxidation, non-catalyzed chemical oxidation,...