Manganese-cerium mixed oxides

Adsorption ofNHs and NO on manganese-cerium mixed oxides... 

PulseTA can be used not only for determination of the amount of adsorbed species, as described above, but also for gaining some insight into the mechanisms of gas-solid reactions in which adsorption of reactive species plays an important role. This is illustrated by studies of the selective catalytic reduction (SCR) of NO by ammonia over manganese-cerium mixed oxide that elucidated the relation between adsorption, redox and catalytic behaviour of the investigated samples [39]. All these reactions were investigated by PulseTA . 

Precipitation of the coating from aqueous solutions onto the suspended Ti02 particles. Batch processes in stirred tanks are preferred various compounds are deposited one after the other under optimum conditions. There is a very extensive patent literature on this subject. Continuous precipitation is sometimes used in mixing lines or cascades of stirred tanks. Coatings of widely differing compounds are produced in a variety of sequences. The most common are oxides, oxide hydrates, silicates, and/or phosphates of titanium, zirconium, silicon, and aluminum. For special applications, boron, tin, zinc, cerium, manganese, antimony, or vanadium compounds can be used [2.40], [2.41],... 

In addition to change of concentration by mixing processes, the relative concentrations of lanthanides may be changed by oxidation-reduction reactions followed by diflFerential mineral uptake (as for manganese nodules (4, JO), or phosphorites (4)), or by diflFerential solubility or ion-exchange processes aflFected by variations in ionic radius. The lanthanides are the group of elements for which such processes are known to be least effective only two, cerium and europium, are expected to exhibit stable ions other than trivalent, and as summarized by Moeller et aL (13), lanthanide complexes are typically weak, and show within the series, only modest variations in strength. 

A series of mixed ceria-mangania solids were synthesised covering the whole concentration range from 0% to 100% cerium. It was shown that at high cerium concentrations a single phase was obtained, whereas at low concentrations the samples consisted of two phases. The behaviour of manganese oxide under heat treatment was modified in the presence of cerium ions, both in the nature of oxide phases (and oxidation states) produced at various temperatures, as well as the temperature at which the phase change occurred. The surface properties and texture of the solids prepared were characterised. 

The mixed cerium-manganese oxide samples were prepared by homogenous co-preciintation fiom aqueous solutions, using IM ammonia solution as base. The metal precursors u%d were cerium (IV) ammonium nitrate and hydrated manganese (II) nitrate or chloride O.IM solutions mixed in the appropriate ratios. The pr ipitate was left to stand in ftie mother liquor for 24h, centrifuged and dried at 473K for 24h. 

We have successfully synthesized pure and mixed manganese and cerium oxides using the surfactant assisted wet-chemistiy route followed by acidic treatment. The XRD analyses of calcined samples reveal the substitution of Ce" by Mn species in the fluorite structure forming a sohd solution with a solubihty limit of 50% Mn. For all the solids, the acidic treatment has important effect in the BET surface area. For the binary oxides a narrow pore size distribution was created after H2SO4 treatment, with a major extension for solids having high Mn content. 

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