Comparison of the preparation of cerium oxide nanocrystallites by forward (base to acid) and reverse (acid to base) precipitation

The morphological and structural characterization of CeO₂ nanocrystallites prepared by forward and reverse precipitation techniques were investigated and compared by powder x-ray diffraction (PXRD), nitrogen adsorption (BET) and high resolution transmission electron microscopy (HRTEM) analysis. The two routes gave quite different materials although in both cases the products were essentially highly crystalline, dense particulates. It was found that the reverse precipitation technique gave the smallest crystallites with the narrowest size dispersion. This route also gave as-synthesized materials with higher surface areas. HRTEM confirmed the observations made from PXRD data and showed the two methods resulted in quite different morphologies and surface chemistries. The forward route gives products with significantly greater densities of Ce³⁺ species compared to the reverse route. Data are explained using known precipitation chemistry and kinetic effects.