Nanoparticles for Catalytic Converters.

The Mazda Motor Corporation has revealed a new class of catalytic converters which use between 70% and 90% less precious metals such as platinum than are required in current devices. Since around 40% of all platinum produced in the world goes into making catalytic converters (about the same as is used to make jewelry), this would suggest a significant reduction in the demand placed on a resource which presently exceeds its supply. In the new models, the metal is employed in the form of nanoparticles (i.e. with a size of perhaps around 10-100 nanometres. For reference, 1000 nanometres is one micron, and the width of a human hair is about 70 microns, so they are tiny).

The function of the metal is to provide a surface on which chemical reactions are catalyzed, and for example, toxic emissions from exhausts of NO2 (which contributes to ozone formation at ground level and to photochemical smog) are eliminated. In the specific case of NO2, which arises from the combination of atmospheric O2 and N2 drawn into internal combustion engines, at the relatively high temperatures within them, the catalyst simply reverses the process, and breaks it down to O2 and N2 again:

2NO2 --> N2 + 2O2.

How effective a catalyst is depends very closely on the actual area of the surface and simply, the greater that is, the more active the catalyst is expected to be. By using the metals in the form of nanoparticles, a smaller mass of metal is required to provide the same surface area is in current CC's, since the surface area scales roughly with the square of the particle diameter. Prior efforts to implement this technology had been unsuccessful because at the temperature of the exhaust, metal particles can migrate over the surface of the supporting ceramic bead and then coalesce (agglomerate) into larger particles, with naturally smaller surface areas and hence lower catalytic efficiencies. Mazda apparently have invented a means unspecified that can immobilise the metal particles by embedding them at fixed positions in the ceramic surface, which obviates the problem.

Now, the question remains of how useful this will be in the future. Oil prices have just hit $96 a barrel, and they will continue to rise. Inevitably, then, the cost of fuel or simply its reduced availability (since the rising cost will mirror the dearth of petroleum derived fuel, post peak oil) will begin to force cars off the road, thus cutting pollution in any case. When there is less fossil fuel to burn, carbon emissions will necessarily fall too. Can this technology be implemented quickly enough to make any real difference in comparison with the emissions-reductions that will be in any case implemented by the falling number of cars expected during the next 20 years say, as we slip into the age when cheap oil has certainly gone? Or do we still believe that the number of cars will rise interminably into the future; and if so, as fuelled by what means?


Related Reading.
"Catalytic Converters go nano," Ned Stafford, Chemistry World, November 11, 2007, p16.