High-surface thermally stable mesoporous gallium phosphates constituted by nanoparticles as primary building blocks

Mesoporous gallium phosphates synthesized by hydrolysis of gallium alcoxide in the presence of PCl 3 assisted by surfactants form robust structures exhibiting the potential of the aerobic oxidation of toluene. [Display omitted] ► A new procedure for the synthesis of porous gallophosphates is described. ► Thermally stable porous gallophosphates have been obtained. ► The catalytic activity of porous gallophosphate for the aerobic oxidation of benzylic oxidation has been demonstrated. In constant, search for micro/mesoporous materials, gallium phosphates, have attracted continued interest due to the large pore size reported for some of these solids in comparison with analogous aluminum phosphates. However up to now, the porosity of gallium phosphates collapsed upon template removal or exposure to the ambient moisture. In the present work, we describe high-surface thermally stable mesoporous gallium phosphates synthesized from gallium propoxide and PCl 3 and different templating agents such as amines (dipropylamine, piperidine and aminopiperidine) and quaternary ammonium salts (C 16H 33(CH 3)3NBr and C 16PyCl). These highly reactive precursors have so far not been used as gallium and phosphate sources for the synthesis of gallophosphates. Conceptually, our present synthetic procedure is based on the fast formation of gallium phosphate nanoparticles via the reaction of gallium propoxide with PCl 3 and subsequent construction of the porous material with nanoparticles as building blocks. The organization of the gallophosphate nanoparticles in stable porous structures is effected by the templates. Different experimental procedures varying the molar composition of the sol–gel, pH and the pretreatment of gallium precursor were assayed, most of them leading to satisfactory materials in terms of thermal stability and porosity. In this way, a series of gallium phosphates with surface are above 200 m 2 g −1, and narrow pore size from 3 to 6 nm and remarkable thermal stability (up to 550 °C) have been prepared. In some cases, the structure tends to show some periodicity and regularity as determined by XRD. The remarkable stability has allowed us to test the catalytic activity of gallophosphates for the aerobic oxidation of alkylaromatics with notable good results. Our report reopens the interest for gallophosphates in heterogeneous catalysis.