The activation of a dimethylgallium/ZSM-5 precursor to well-defined reduced and oxidized species is studied by in situ Ga K edge XANES. The precursor is prepared by chemical implanting of trimethylgallium on acidic HZSM-5. Subsequent reduction leads to charge-compensating Ga + species. Direct oxidation of the trimethylgallium precursor leads to various forms of gallium oxide and regeneration of Brønsted acid protons. Oxidation of the reduced Ga + species yields predominantly to GaO + species. The GaO + species exhibit a much higher H 2 /D 2 exchange activity than reduced Ga + species.

Nanoscale, high surface area cerium oxide (ceria) powders and stable, high-concentration (>1 M) ceria sols were prepared by a new method based on homogeneous precipitation in an acidic environment using cerium(IV) nitrate as the precursor. The results are compared with ceria powders and sols prepared by a hydrothermal method in a basic environment with cerium(III) nitrate as the precursor. Hydrolysis and condensation of the cerium(IV) and cerium(III) nitrates yield the ceria precursor precipitates with molecular formula of CeO 2 ‚2H 2 O [or Ce(OH) 4 ] and CeO 2 ‚H 2 O [or Ce(OH) 2 O], respectively. The dried ceria precursor powders from Ce(IV) and Ce-(III) are well dispersed in the form of primary particles of about 4 nm in size. Calcination at 450 °C causes phase transformation of the amorphous portion accompanying growth of the Ce(IV)derived ceria crystallite or aggregation of the Ce(III)-derived ceria particles. The Ce(III)-derived ceria crystallites have a smaller lattice parameter than the Ce(IV)-derived sample whose lattice parameter decreases with increasing calcination temperature. Stable ceria sols at a solid concentration up to 300 g of CeO 2 /L were obtained from a Ce(IV)-derived ceria precursor powder, as compared to a maximum stable solid concentration of 20 g of CeO 2 /L for the Ce(III)-derived ceria sols. These results are discussed in terms of the shape and aggregation tendency of the primary ceria particles prepared by the two different methods.

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