Synthesis of ordered mesoporous Zr–P–Al materials with high thermal stability

Abstract

A kind of mesoporous Zr–P–Al materials was synthesized by a three-step method, in which a hexagonal zirconium oxide–sulfate composite was prepared and subsequently treated with a phosphoric acid solution followed by the treatment with AlCl 3 solutions. These materials had ordered cylindrical pores, and their textual data depended on the amount of AlCl 3 and calcination temperature. Small amount of Al incorporation (Al/Zr = 0.49) leaded to a microporous material with a Brunauer–Emmett–Teller (BET) specific surface area of 314 m 2/g and a pore size of 0.6 nm. Increasing the Al/Zr ratio resulted in mesoporous materials with higher BET specific surface area. The mesoporous Zr–P–Al material exhibited a BET specific surface area of 462 m 2/g and a pore size of 2.9 nm after calcination at 773 K. 973 K calcination led to a BET specific surface area of 416 m 2/g and a pore size of 2.7 nm. Even after calcination at 1073 K, a BET specific surface area of 227 m 2/g and a pore size of 3.2 nm could still be observed. The pentacoordinated aluminium species seemed to be indispensable for the synthesis of mesoporous Zr–P–Al materials because of their effective reduction of the lattice contraction. NMR results showed that a hexacoordinated aluminium layer, a (HO) 2P(O–Zr) 2 layer and a Zr(OH) layer combined with each other were formed after AlCl 3 treatment. Upon calcination, the layers of Al 2O 3, (Zr–O) 2PO 2 and ZrO 2 formed the walls of the mesoporous Zr–P–Al materials. This unique structure was suggested to be responsible for the high thermal stability (up to 1073 K).