*3.1. Materials*

Nickel nitrate hexahydrate [Ni(NO3)2.6H2O, 98%, Alfa Aesar], cerium nitrate hexahydrate [Ce(NO3)3.6H2O, 99.0% assay on Ce basis, general purpose reagent, BDH], magnesium acetate tetra-hydrate [Mg(O2CCH3)2.4H2O, 99.5-102.0%, Merck & Co., Inc., Kenilworth, NJ, USA] were commercially available and were used without further purification. γ-Alumina doped with titania (3.0 wt. % TiO2/γ-Al2O3) in the shape of pellets, was a gift from Tiancun Xiao, Senior Research Fellow, Inorganic Chemistry Laboratory, Oxford University. Ultrapure deionized water (18.2 MΩ.cm) was obtained from a Milli-Q water purification system (Millipore, Burlington, MA, USA).
