Metal-Substituted Microporous Aluminophosphates

This chapter aims to present the zeotypes aluminophosphates (AlPOs) as a complementary alternative to zeolites in the isomorphic incorporation of metal ions within all-inorganic microporous frameworks as well as to discuss didactically the catalytic consequences derived from the distinctive features of both frameworks. It does not intend to be a compilation of either all or the most significant publications involving metal-substituted microporous aluminophosphates. Families of AlPOs and zeolites, which include metal ion-substituted variants, are the dominant microporous materials. Both these systems are widely used as catalysts, in particular through aliovalent metal ions substitution. Here, some general description of the synthesis procedures and characterization techniques of the MeAPOs (metal-contained aluminophosphates) is given along with catalytic properties. Next, some illustrative examples of the catalytic possibilities of MeAPOs as catalysts in the transformation of the organic molecules are given. The oxidation of the hardly activated hydrocarbons has probably been the most successful use of AlPOs doped with the divalent transition metal ions Co2+, Mn2+, and Fe2+, whose incorporation in zeolites is disfavoured. The catalytic role of these MeAPOs is rationalized based on the knowledge acquired from a combination of the most advanced characterization techniques. Finally, the importance of the high specificity of the structure-directing agents employed in the preparation of MeAPOs is discussed taking N,N-methyldicyclohexylamine in the synthesis of AFI-structured materials as a driving force. It is shown how such a high specificity could be predicted and how it can open great possibilities in the control of parameters as critical in catalysis as crystal size, inter-and intracrystalline mesoporosity, acidity, redox properties, incorporation of a great variety of heteroatom ions or final environment of the metal site (surrounding it by either P or Al)

Correlation between benzene hydrogenation activity and zeolite basicity in Pt-faujasites

Benzene hydrogenation has been carried out on a scries of Pt-faujasites covering a whole range of acidic to basic zeolites. The turn over frequency decreases and the apparent activation energy increases as the zeolite basicity increases. This is explained in terms of an electron transfer in basic zeolites from the zeolite to the Pt particles

Etude du comportement de zeolithes protoniques en solution sodique

Le comportement d'une série de zéolithes protoniques : Y stabilisée, ZSM-5, offretite, Ω et de 4 mordénites de rapport atomique Si/Al compris entre 7,5 à 70 a été étudié au cours de leur échange par Na+ en solution aqueuse. L'échange d'ions provoque le passage en solution d'espèces aluminiques et siliciques, la dissolution étant d'autant plus importante que les sites acides sont plus faibles. L'étude de l'équilibre et de la cinétique du phénomène d'échange d'ions, ainsi que de la dissolution qui l'accompagne, permet de classer les zéolithes en fonction de leur acidité. Le classement obtenu est voisin de celui trouvé par une méthode classique de mesure d'acidité : l'adsorption d'ammoniac suivie par calorimétrie