A synthetic gallophosphate molecular sieve with a 20-tetrahedral-atom pore opening

Abstract

THE most widely used catalyst in petroleum cracking and reforming processes is the synthetic zeolite Y. Its unique properties arise from the fact that the enormous inner surface area created by the three-dimensional channel system is accessible to sorbed molecules through 12-ring pore openings. These windows, with free diameters of 7-8Å, allow both aliphatic and small aromatic molecules to enter the zeolite. Attempts to synthesize zeolitic structures with even wider pores, to accommodate larger molecules, have produced two aluminophosphates with one-dimensional channels: VPI-5 (ref. 1), which has 18-ring channels with free diameters of 12-13Å, and AlPO₄8 (refs 2, 3), with oval 14-ring channels. We now report the structure of a new cubic gallophosphate with a pore opening comprising 20 tetrahedrally coordinated atoms in the shape of a four-leafed clover (Fig. 1) and a three-dimensional channel system. The unusual shape of the window is due to the presence of terminal hydroxyl groups in the framework, and provides new possibilities for shape-selective sorption. The supercage formed aHhe intersection of the channels has a body diagonal of 29-30 Å, and could thus accommodate larger intermediates in zeolite catalytic processes.