When you look inside a catalytic converter you will notice a silicon based ceramic monolith that mimics the shape of a honeycomb. Each little square or cell are channels that the exhaust produced from your vehicle’s engine goes through. These channels are where precious metals are hosted as it is there chemical responsibility to converts those toxic gases into breathable air.  

When we look at catalytic converter generational advancements, it is usually in response to meeting higher air quality standards. Increasing the precious metal loadings in catalytic converters is the most effective way to meet these standards. To accomplish this, the number of channels that host precious metals must be increased. This is not as simple as it sounds because as the number of channels increases, the walls between them become thinner and thinner. Thinner walls, as expected, mean less durability. The channels quadrupled over time, and there are now about 600 cells per square inch. 

Air quality standards continue to rise, necessitating further catalytic converter innovation to meet the demands. From an engineering standpoint, increasing precious metal loadings to where they are now is already very impressive. They are now confronted with a new problem. The silicon-based ceramic monolith (honeycomb) can no longer accommodate any more channels without becoming frail. The channel walls would become too thin, and with average road conditions, catalytic converters would begin to fail, which would be detrimental to the components’ function. 

Manufacturers have been forced to look for alternative chemistries to create monoliths from other materials. Aluminum titanate is one of these options because it is a stronger material for a monolith than silicon-based ceramic and can handle real-world driving conditions with many more channels. Aluminum titanate has the potential to boost cell density per square inch from 600 to 1200 and beyond. More precious metals could thus be loaded into the catalytic converter, transferring more harmful gas into clean, breathable air. 

While aluminum titanate is an excellent material for forming next-generation monoliths in catalytic converters, it has a significant disadvantage that is not readily apparent. On the automotive recycling front, this issue arises as these converters reach the end of its life cycle. Smelting operations currently use a furnace to melt down scrap monoliths and separate precious metals such as platinum, palladium, and rhodium. These precious metals can now be used again, which is extremely beneficial to the environment because it reduces the amount of mining required. 

Because aluminum titanate is such a strong material, it will not melt, and the precious metals will become entangled in the slag. Finally, because the precious metals are not recovered, it complicates the recycling process. Smelters would lose money, and we would have to mine more precious metals. Obviously, these initiatives to innovate the catalytic converter are in response to air quality standards, so the intention is good; however, losing precious metals and not recovering them properly is counterproductive in terms of pollution because it leads to more mining. 

Aluminum titanate is already being used as a monolith in catalytic converters. Because the material is still new and the cars have yet to fail, we have yet to see it reach the recycling end of the loop. When that day comes, as many cars reach the end of their lives or have their catalytic converters replaced for various reasons, wet chemistry is the best method to recover the rare metals on the recycling end. 

Learn more about wet chemistry options and our recent collaboration with pH7 Technologies, who will aid us in developing these future solutions.