Influence of vanadium and cerium additives in the development of porosity and surface acid catalytic properties of mesoporous aluminophosphates

 
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1998 (EN)
Influence of vanadium and cerium additives in the development of porosity and surface acid catalytic properties of mesoporous aluminophosphates (EN)

Galanos, E. (EN)

Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας (EL)
Galanos, E. (EN)

Mesoporous materials promise to generate a new range of catalysts. Mesoporous aluminophosphates containing vanadium or cerium additives and having the general formula Al100PXMY (X,Y=0,5,10,20, M=V,Ce) have been prepared by precipitation with NH3 and calcination at 600 degrees C XRD analysis of the resulting solids showed that vanadium is incorporated into the amorphous mesoporous aluminophosphate solids except for Y=20 where the phase of V2O5 is apparent. On the contrary, cerium is not incorporated into the aluminophosphate structure and CeO2 is apparent for Y=5 to 20 while in the last case some CePO4 also appears in the XRD patterns. The calcined solids were examined for their surface area and porosity by N-2 adsorption. At zero or constant concentration of phosphorous, the addition of vanadium increases the specific surface area (ssa) of the parent Al100P0M0 (201 m(2)/g) solid, its influence maximized at Al100P5V10 (360m(2)/g) and at Al100P10V5 (386 m(2)/g). On the contrary, the addition of cerium results in a gradual drop of ssa to similar to 150 m(2)/g depending on the P content. All the materials Al100PXMY were essentially mesoporous in nature with mean pore diameters (dp)=5-12 nm. The surface acidity of each of the solids was determined by NH3 adsorption in a flow system and a surface density between 0.6 to 2.4 acid sites.nm(-2) was found for the vanadium containing solids while for the cerium containing ones it was about one order of magnitude lower, depending on the sample. The acid catalytic behaviour of these mesoporous materials was examined using the isopropanol decomposition as a probe reaction. The main products obtained were propene and di-iso-propyl-ether while for the vanadium containing solids some dehydrogenation was also observed towards acetone. These differences in catalysis between the vanadium and the cerium containing mesoporous aluminophsphates solids are discussed in relation to their surface acid density while the variations in selectivity are discussed in terms of apparent activation energies. (EN)

alumina aluminum phosphate (EN)

Πανεπιστήμιο Ιωαννίνων (EL)
University of Ioannina (EN)

Preparation of Catalysts Vii (EN)

English

1998

<Go to ISI>://000076264000097

Elsevier (EN)



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