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)

[Photoelectron spectroscopy: its possibilities in application to heterogeneous catalysis. [Review]]

Francai

Influence of reducing and sulfiding treatments on Co/Al/sub 2/O/sub 3/ and Mo/Al/sub 2/O/sub 3/ catalysts. An X-ray photoelectron spectroscopy study

X-ray photoelectron spectroscopy (XPS) has been used to investigate the phase transformations induced by various pretreatments of Co/Al/sub 2/O/sub 3/ and Mo/Al/sub 2/O/sub 3/. Upon sulfiding by H/sub 2/-H/sub 2/S, Co/sup 2+/ is partly reduced to Co/sup 0/ while the Mo/sup 6+/ species is completely transformed into MoS/sub 2/. The behaviour of molybdenum is similar to that observed in Co-Mo/Al/sub 2/O/sub 3/ hydrodesulfurization catalysts. In contrast, cobalt gives Co/sup 0/ in Co/Al/sub 2/O/sub 3/ systems whereas Co/sub 9/S/sub 8 / is observed for HDS catalysts. A nonreducible alumina bound Co is also observed in both the presence and absence of molybdenum. In the oxide form, molybdenum species are in strong interaction with the support but this interaction does not exist after sulfiding.Anglai

Comparative study of unsupported and supported Co-Mo hydrodesulphurisation catalysts

Catalytic activities of unsupported and alumina- or silica-supported cobalt-molybdenum catalysts in the oxidic and sulphided form are compared. Silica-supported catalysts behave essentially as unsupported catalysts. The behaviour of alumina-supported catalysts is quite different. The synergistic effect is much stronger, especially in the sulphided form, and the domain in which the synergism is exhibited is much broader. In addition, alumina brings about a strong hydrogenating activity. ESCA measurements have helped to investigate further the interaction between the cobalt-molybdenum system and alumina.Anglai