User:Pieceofmetalwork/sandbox/Sintering and catalysts

Sintering is an important cause for loss of catalyst activity, especially on supported metal catalysts. It decreases the surface area of the catalyst and changes the surface structure. For a porous catalytic surface, the pores may collapse due to sintering, resulting in loss of surface area. Sintering is in general an irreversible process.

Small catalyst particles (which have the highest relative surface areas) and a high reaction temperature are in general both factors that increase the reactivity of a catalyst. However, these factors are also the circumstances under which sintering is occuring. Specific materials may also increase the rate of sintering. On the other hand, by alloying catalysts with other materials, sintering can be reduced. Especially rare earth metals have been shown to reduce sintering of metal catalysts when alloyed.

For many supported metal catalysts, sintering starts to become a significant effect at temperatures over 500 C. Catalysts that operate at higher temperatures, such as a car catalyst, use structural improvements to reduce or prevent sintering. These improvements are in general in the form of a support made from an inert and thermally stable material such as silica, carbon or alumina.