2015 was an uneasy year for automakers because of Nitrogen Oxide (NOx) emission scandal in tests. Up to 40-times higher NOx emission was reported in some diesel engine cars. NOx gases are very hazardous to the environment and because of this they must be constrained by special norms like Euro 6 and preceding.
All internal combustion engine vehicles have catalytic converters. Those structures basically convert NOx and other hazardous gases into less hazardous gases, such like Nitrogen (N2) and Carbon Dioxide (CO2). Some structures could also trap CO2 and lower overall hazardous emission. In fact, those converters are composed of ceramics and platinum as a catalyst, which are fairly costly. At the same time, platinum does not work efficiently at low temperatures and high humidity.
Selective Catalytic Reduction (SCR) technology handles the divulged catalysis problem by introducing fluids like ammonia and urea, which could trap NOx and help them to be adsorbed by the catalyst. The conversion rate gets increased, but it needs special equipment inside the exhaust system, such as fluid store, pump and flow rate sensor. Those increase the overall cost and meanwhile, drivers should add those fluids periodically.
InnoCat Technology presented here introduces a low-cost structure, which could be applicable to new and old cars. The filter or skeleton of the converter is carbon, unlike other ceramic converters. This makes the structure low weight, durable and also low-cost. Also, it has a higher surface area, which increases the conversion rate. As could be seen in the first figure, there are many "windows" inside the structure and the flowing gases could interact with the struts of the foam-like structure more frequently. Unlike one-way interaction inside the tubes in ceramic comb, flow is everywhere without any gas stuck. This was verified via COMSOL Multiphysics by looking at the porosity-flow relation in the second figure.
Fabrication of the structure is very straightforward: Polymer foam with desired porosity was pyrolyzed and this yielded graphitic porous structure. But in the pilot-scale application, the polymer foam was washed with solvents that contains transition metal salts before pyrolysis. So, obtained structure is containing metal nanoparticles on struts of graphite foam and those would work as the catalysts in conversion. Shiny particles could be seen in the first figure.
As discussed before, this new structure could be applicable to old cars. Since it could be fabricated to any scale and post-processable for any specific application, it was adapted to a 2006 model Diesel engine car. Before starting the tests, old converter inside the car was replaced with a new commercial converter and its emission was recorded for 1000 km. Then our structure was adapted to the car and tested for 5000 km with 250 km intervals. The replacement could be seen in the third figure.
Our structure was 4 times lower in NOx emission with respect to the commercial converters. Also it was estimated that this new converter is 6 times cheaper and for Euro 6 norms, it could drop the costs much lower, by eliminating the need for SCR technology.