https://doi.org/10.1351/goldbook.13999
Site at which catalysed chemical transformations take place.
Notes:
- 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.
- 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.
- 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.
See: BET surface area