Structure, texture and surface acidity studies of a series of mixed zinc-aluminum (60-90 molar % Al) phosphate catalysts

A series of mixed zinc-aluminum phosphate (ZnAlP) catalysts containing 40-9 0 aluminum molar % were synthesized by a coprecipitation method and charact erized by nitrogen adsorption-desorption, X-ray diffraction, FTIR spectrosc opy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and t emperature programmed desorption (TPD) of ammonia. The presence of aluminum greatly affected the surface properties of Zn-3(PO4)(2) by delaying the cr ystallization process of Zn-3(PO4)(2). All amorphous samples were shown to be mesoporous and they contained two types of aluminum surface hydroxyl gro ups and one type of phosphorus hydroxyl group, as shown by DRIFT spectra. T he specific surface area and the acidity of ZnAlP increased on increasing t he aluminum content. On the other hand, a great difference in the texture a nd the concentration of surface acid sites was found by changing the precip itating agent and calcination temperature. Thus these factors also play an important role in the final properties of these catalysts. (C) 2001 Society of Chemical Industry.