in heterogeneous catalysis we always need to determine the porosity (pore size and volume and specific surface area) of the solid materials synthesized in the laboratory, in order to find an explanation for their catalytic acid or basic activity in a chemical reaction, but sometimes we find that the catalyst is very active despite its low porosity.
is there a relationship between porosity and catalytic activity? for example, if we take two catalysts, one of which has a high porosity and the other of low porosity, can we conclude that the one of high porosity is the most active?
cher said je crois que l'activité reste la même pour les deux cas , puisque la composition chimique de matériaux ne change pas , ce dernière s'influence directement dans la création des sites actifs ( soit pour activer une réaction chimique qui se ne déroule plus, ou bien accélérer d'autre réaction). donc ici la porosité peu s'influence au plan productivité ( rendement) .d'autre part puisque on parle de la catalyse de contacte ( surface extérieure de matériaux ) ....la porosité reste un paramètre qui confirme la taille des particules déterminer auparavant par DRX,
mes salutations....
In theory both concepts are related. The actives sites are formed tipically in the surface of the catalyst, so, if the material has more porosity, it has more surface area to form the actives sites and this usually lead to greater activities.
However, people characterize the fresh catalyst before reaction and sometimes this is not the final form of the catalyst. For example, if you need a reduction step before the reaction, this step could result in morphological changes of the catalyst, so even catalyst wich have more surface area could suffer changes that affect the activity.
Both of the concepts are related to each other which is mean the actives sites on the surface of the catalyst. The catalyst has more porosity will be more active than that has lower porosity because it has more surface area to form the actives sites and this usually leads to greater activities.
Textural properties (as specific surface area, pore size, pore volume) are usually characterized in the catalysis field and frequently we associate the high specific surface area with high activity. Although is true that a high specific surface area can improve the dispersion which can be related to smaller metal particle size and also with a major amount of active sites, it is not enough. Catalysis performance is a consequence of a sum of factors as material characteristics and operational conditions and it is difficult to associate the activity just to one factor. For example, sometimes the specific surface area is high and the activity low, one reason can be for example high specific surface area because microporosity; so the reactive is not available to diffuse to the active sites. Another example is that high area promotes a high dispersion and very small particle size (depends of the material), so metal support interactions increase and the activity decrease.
Regards!
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