Characterization of aluminosilicate on rutile surface by high resolution solid state NMR

Pigments of titanium dioxide rutile, coated with SiO2>-Al2O3, have been characterized by high-resolution solid state NMR. The model samples were prepared following four synthesis routes differing by the aluminate and silicate salts addition sequence. From 27Al single pulse MAS and 3Q-MAS NMR experiments, we characterize short range order around Al and distinguish several types of environment: AlIV, AlV, AlVI and AlVI linked to Ti, depending upon synthesis route and thermal treatment. The major difference between the different samples is observed after heat treatment at 750 °C. Rotational echo double resonance 27Al-1H and cross-polarization H-Si experiments provide longer range distance information through dipolar coupling to proton. Two types of surface treatment can be distinguished from 27Al-1H Redor by the presence of proton free alumina domain in the surface treatment.