Adsorption of Phosphorus-Containing Compounds on Alumina

To understand the complex interaction of phosphorus-containing species with alumina and with the other elements (molybdenum, cobalt, or nickel) introduced in the catalyst formulations, it is important to examine the chemistry involved in the preparation steps. In this section, adsorption of phosphorus-containing species on alumina is discussed. 

Phosphorus oxo-species adsorbed on alumina are present in a well-dispersed state up to a surface density of 2.9 x 10 P atom/pm (or 2.9 P atom/nm ) 31). IR spectroscopy measurements allowed identification of several types of hydroxyl groups on the y-alumina surface, such as type la (tetrahedral Al —OH, 3780 cm ), type lb (octahedral Al —OH, 3795 cm ), types 11a and Ilb (bridged OH between two Al atoms, 3736 

Different mechanisms of H3PO4 adsorption on alumina are proposed in the literature  

Phosphorus species adsorb electrostatically on the protonated Al—OH surface groups 51) through the following equilibria  

Phosphorus species adsorb covalently on the protonated Al-OH surface groups (52, 55)  

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