Editing Sintering (section)

==Sintering of catalysts==
Sintering is an important cause for loss of [[catalyst|catalytic activity]], especially on supported metal catalysts. It decreases the surface area of the catalyst and changes the surface structure.<ref name="Kuczynski2012">{{cite book|author=G. Kuczynski|title=Sintering and Catalysis|url=https://books.google.com/books?id=mI3kBwAAQBAJ|date=6 December 2012|publisher=Springer Science & Business Media|isbn=978-1-4684-0934-5}}</ref> 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.<ref>{{cite journal|doi=10.1016/S0926-860X(00)00843-7|url=https://www.researchgate.net/publication/223902508|title=Mechanisms of catalyst deactivation|journal=Applied Catalysis A: General|volume=212|issue=1–2|pages=17–60|year=2001|last1=Bartholomew|first1=Calvin H|doi-access=free|bibcode=2001AppCA.212...17B }}</ref>

Small catalyst particles have the highest possible relative surface area and high reaction temperature, both factors that generally increase the reactivity of a catalyst. However, these factors are also the circumstances under which sintering occurs.<ref name="Harris1986">{{cite journal|last1=Harris|first1=P|title=The sintering of platinum particles in an alumina-supported catalyst: Further transmission electron microscopy studies|journal=Journal of Catalysis|volume=97|issue=2|year=1986|pages=527–542|doi=10.1016/0021-9517(86)90024-2}}</ref> Specific materials may also increase the rate of sintering. On the other hand, by [[alloy]]ing catalysts with other materials, sintering can be reduced. [[Rare-earth metals]] in particular have been shown to reduce sintering of metal catalysts when alloyed.<ref name="Figueiredo2012">{{cite book|author=Figueiredo, J. L. |title=Progress in Catalyst Deactivation: Proceedings of the NATO Advanced Study Institute on Catalyst Deactivation, Algarve, Portugal, May 18–29, 1981|url=https://books.google.com/books?id=b-HzCAAAQBAJ&pg=PA11|date=2012|publisher=Springer Science & Business Media|isbn=978-94-009-7597-2|page=11}}</ref>

For many [[Catalyst support|supported metal catalysts]], sintering starts to become a significant effect at temperatures over {{convert|500|C|F}}.<ref name="Kuczynski2012"/> Catalysts that operate at higher temperatures, such as a [[Catalytic converter|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]].<ref name="ChorkendorffNiemantsverdriet2006">{{cite book|author1=Chorkendorff, I. |author2=Niemantsverdriet, J. W. |title=Concepts of Modern Catalysis and Kinetics|url=https://books.google.com/books?id=p34rVviEVWsC|date=6 March 2006|publisher=John Wiley & Sons|isbn=978-3-527-60564-4}}</ref>