High surface area nickel aluminate spinels prepared by a sol–gel method

The oxide spinel NiAl2O4 and spinel-type solid solutions Al2O3–NiAl2O4 (at Ni/Al=1:4, and Ni/Al=1:8) were prepared by controlled hydrolysis of mixed metal alkoxides, followed by calcination of the resulting gels. Powder X-ray diffraction showed that all samples prepared were single phase cubic materials having the spinel-type structure. The cubic lattice parameter, ao, was found to decrease gradually with increasing aluminium content of the mixed metal oxides. The specific surface area (determined by nitrogen adsorption at 77 K) was found to be in the range of 200–300 m2 g−1. The materials were found to be basically mesoporous, the most frequent pore radius being in the range 3.2–6.4 nm. IR spectroscopy of CO adsorbed at liquid nitrogen temperature gave a main band at 2186–2195 cm−1, which was assigned to the CO stretching vibration of surface Al3+⋯CO adducts where coordinatively unsaturated Al3+ ions act as Lewis acid centres.