{"term":{"id":"13999","title":"catalytic site","longtitle":"IUPAC Gold Book - catalytic site","doi":"10.1351\/goldbook.13999","code":"13999","status":"current","definitions":[{"id":1,"text":"Site at which catalysed chemical transformations take place.","notes":{"1":"The area-related parameters do not characterise the catalyst in heterogeneous photocatalysis as they do in heterogeneous dark catalysis, inasmuch as the density and concentration of active sites are often unknown. Thus, the properties of a photocatalyst are not directly proportional to their area, in view of the fact that light does not equally reach every part of the surface or particle. Note also that photocatalysts may include several phases, in which case the overall area is physically not meaningful.","2":"If the assumption can be made that the active sites are distributed over the entire (photo)catalyst surface, then the heterogeneous reactions are described \"per area\". The generally accepted \\(\\rm{BET}(\\ce{N2})\\) surface area is used. In spite of the fact that there is no direct correlation between the number of active sites and the \\(\\rm{BET}(\\ce{N2})\\) area, the use of the latter may help when no alternative exists.","3":"Quantities expressed in terms of \"per \\(\\rm{BET}(\\ce{N2})\\) area\" should be denoted as area-related, which also implies that a lower limit of the quantity is given, because the surface determined by \\(\\ce{N2}\\) adsorption will be larger than that reached by the radiation."},"links":[{"term":"BET surface area","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/13997"},{"term":"area-related parameters","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/13992"}],"sources":["PAC, 2011, 83, 931. 'Glossary of terms used in photocatalysis and radiation catalysis (IUPAC Recommendations 2011)' on page 943 (https:\/\/doi.org\/10.1351\/PAC-REC-09-09-36)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/13999\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/13999\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/13999\/plain"},"citation":"Citation: 'catalytic site' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351\/goldbook.13999","license":"The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/) for individual terms.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.","accessed":"2026-05-07T00:13:18+00:00"}}