Rare earth oxide elements introduction

Activity and selectivity of monometallic Ag catalysts can be controlled by the preparation conditions leading to micro- and meso- to macroporous catalysts which are active and selective in the hydrogenation of crotonaldehyde. In Ag catalysts modified by a second metal, bimetallic sites exhibiting surface polarity and Ag particles in close contact with a partially reduced early transition metal or a rare earth element, or Ag species stabilized and incorporated in these oxides were concluded to be the active species in the working state of these catalysts. Simultaneous introduction of both metals during the sol-gel process under optimized hydrolyzing conditions could further increase the metal-promoter interaction and lead to well-tailored new hydrogenation catalysts. 

Fig. 12. Trace element/Ca ratios of foraminifera subject to different cleaning procedures, (a) Mn/Ca, (b) Mg/Ca and (c) Sr/Ca. Samples cleaned using procedure A were subject to ultrasonication in methanol, oxidation and a weak acid leach. Those cleaned using procedure B were subject to additional reductive cleaning, and those cleaned using procedure C were subject to additional reductive cleaning as well as cleaning in DTPA (diethylene triamine pentaacetic acid). DTPA removes refractory phases rich in Ba and the rare earth elements (e.g. Haley Klinkhammer 2002). Note that the introduction of the reductive cleaning step significantly lowers Mn/Ca and also lowers Mg/Ca. Reductive cleaning has no resolvable effect on Sr/Ca. DTPA has little effect on Mn/Ca, Mg/Ca or Sr/Ca. Error bars (where visible) represent the standard deviation of the mean of two (0. universa) or three (G. conglomerata) separate analyses. Data are from Hathorne (2004).

The introduction of isovalent and aliovalent elements into a ceria lattice can induce important modifications of its textural, structural and redox properties and this can deeply affect its catalytic properties. " Ceria-zirconia still represents the best example showing how the incorporation of an isovalent element like Zr into the ceria structure can enhance the thermal, redox and catalytic properties. " The state-of-the-art material for oxygen storage in TWC is in fact appropriate amounts of zirconia-modified ceria mixed oxides including small amounts of other rare-earth elements, which are added to further enhance the redox and textural features of ceria. ... 

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