Promoters are materials that are incorporated into the catalyst system to improve performance. Although not catalytic per se, they nonetheless accelerate the chemical reaction. Frequently, promoters help initiate the reaction while the system is cold or when one reactant is in short supply. For example, cerium oxide, which can store oxygen, is frequently used to provide oxygen storage during the first few seconds of automobile engine operation. In addition to cerium oxide, Ultramet has used other metal oxides for oxygen storage in more severe applications.
Ultramet open-cell foam catalyst supports are made from materials such as silicon carbide, silicon nitride, dendritic rhenium, and metal oxides. The unique structure of the open-cell foam allows the fluid excellent access to the catalytic surface. The foams are compact, provide excellent heat and mass transfer, and generate little pressure drop on the flowing fluid, all of which are distinct advantages over conventional honeycombs.
Gas moving through Ultramet catalyst support, showing excellent mixing and low pressure drop
Because the mass and heat capacity are low, Ultramet foam catalyst supports are well suited for applications in which fast heatup and rapid lightoff are important. Several Ultramet foams are electrically conductive and are appropriate for resistive heating, thus enabling the catalyst to be preheated before use.
Ultramet washcoats can be used to increase the surface area of a foam or honeycomb support. Gamma alumina offers excellent surface area for low temperature applications, and zirconium oxide offers surface area enhancements for higher temperature applications.