Behaviour of NiO and Ni^o phases at high loadings in SBA-15 and SBA-16 mesoporous silica matrices

NiO nanocrystals were inserted into SBA-15 and SBA-16 mesoporous silica matrices by gelation on nickel hydroxide with propylene oxide inside the nanotubular channels followed by thermal dehydration. The NiO crystals size was higher inside the SBA-15 (5.5-7 nm) than inside SBA-16 (3-3.5 nm) increasing with NiO loading from 22 to 69 wt.% This reflects the lower mesopore diameter in SBA-16 compared with SBA-15. At all NiO loadings the nanocrystals were located inside the nanotubular channels of mesoporous silicas (XRD, SEM, HRTEM, EDS) without blocking them (Na-adsorption). The small NiO nanocrystals contributed significantly to the surface area of NiO/SBA composites especially at high loadings. After reduction with hydrogen large 16-20 nm Ni^o particles were formed with liberating the nanotubular channels which remain intact. The possible mechanism of nickel phase movement after NiO reduction from the internal mesopores to the external surface of the mesoporous silica microcrystals is discussed.