Publication details

Aluminophosphate and -phosphonate Xerogels by Non-Hydrolytic Sol-Gel Reactions

Authors

PINKAS Jiří MACHÁČ Petr PODHORSKÝ Ján MORAVEC Zdeněk STÝSKALÍK Aleš

Type Conference abstract
MU Faculty or unit

Faculty of Science

Citation
Description We have investigated the preparation of high-surface area mesoporous aluminophosphates and aluminophosphonates by non-hydrolytic sol-gel reactions. The first synthetic method is based on reactions of EtAlCl2 with trialkylesters of phosphoric acid (OP(OR)3, R = Me, Et, iPr, nBu, in dry organic solvents. The condensations proceed by alkylchloride elimination. Various reaction and calcination conditions were examined. Porosity is obtained after calcination by removal of organic residual groups. This thermal processing at 300 °C of as-synthesized precursor gels leads to amorphous aluminophosphate xerogels with surface areas of 400–500 m2 g–1 provided by small mesopores (2–8 nm). Changes in coordination environment of aluminium from six- to four-coordinate are evidenced by shift of 27Al MAS NMR resonances. The second method involves reaction of Al(NMe2)3 with trimethylsilylated phosphate, phosphonate, and bis-phosphonate esters in dry toluene. The reactions proceed by silylamine elimination and provide organic-inorganic hybrid xerogels with properties influenced by organic substituents and the Al:P ratio of the precursors. Dried xerogels exhibit large surface areas (up to 1000 m2 g-1) and Al–O–P networks stay stable under medium high thermal conditions. 27Al, 13C, and 29Si MAS NMR was employed to characterize aluminum coordination and residual amido and trimethylsilyl groups. The amount of residual groups was determined by gravimetric measurements and by thermal TG-DSC analysis. These unreacted groups have the potential to be used in post-synthetic grafting of catalytically active metal centers.
Related projects: