Nickel-Containing Ceria-Zirconia Doped with Ti and Nb. Effect of Support Composition and Preparation Method on Catalytic Activity in Methane Dry Reforming

Nickel-containing mixed ceria-zirconia oxides also doped by Nb and Ti have been prepared by a citrate route and by original solvothermal continuous flow synthesis in supercritical alcohols. Nickel was subsequently deposited by conventional insipient wetness impregnation. The oxides are comprised of ceria-zirconia solid solution with cubic fluorite phase. Negligible amounts of impurities of zirconia are observed for samples prepared by citrate route and doped by Ti. Supports prepared by supercritical synthesis are single-phased. XRD data, Raman, and UV-Vis DR (diffuse reflectance) spectroscopy suggest increasing lattice parameter and amount of oxygen vacancies in fluorite structure after Nb and Ti incorporation despite of the preparation method. These structural changes correlate with the catalytic activity in a methane dry reforming reaction. Catalysts synthesized under supercritical conditions are more active than the catalysts of the same composition prepared by the citrate route. The catalytic activity of samples doped with Ti and Nb is two times higher in terms of TOF (turnover frequency) and increased stability of these catalysts is attributed with the highest oxygen mobility being crucial for gasification of coke precursors.

Flow supercritical synthesis of brucite and magnesian T-O, T-O-T phyllosilicates: an opportunity to tune the structure with the solvent composition

ABSTRACTThis work presents the synthesis of minerals with a layered structure in supercritical water/ethanol mixtures to decrease the critical coordinates of the solvent regarding water. Depending on the water/ethanol ratio of the solvent, we obtained three different minerals adopting an octahedral brucitic sheet: (1) without a Si-tetrahedral sheet (O); (2) associated with one Si-tetrahedral sheet (T-O); or (3) intercalated between two Si-tetrahedral sheets (T-O-T). We have thus shown that ethanol in a supercritical water/ethanol mixture changes the solubility of silicon with a direct consequence on the formation of the tetrahedral silicon sheets and thus makes it possible to control the structure of the synthesized layered material.

Moderate supercritical synthesis as a facile route to mixed-valent uranium(iv,v) and (v,vi) silicates

The synthesis of five new U(iv,v) and U(v,vi) silicates points toward moderate supercritical synthesis as a new route to the stabilization of mixed-valent uranium compounds.