Rhodium trioxide

Principal Compounds Rhodium trichloride rhodium trioxide rhodium (II) acetate rhodium nitrate rhodium potassium sulfate rhodium sulfate rhodium sulfite... 

Rhodium Trioxide, RhOs, separates out as a blue precipitate from the solution left, after preparing the dioxide (as indicated in (1) above), on neutralising the alkali with nitric acid. It dissolves in hydrochloric acid evolving chlorine, the trichloride remaining in solution ... 

The most active catalyst is platinum applied in finely divided form, for example platinised asbestos. Certain elements, especially arsenic and mercury, have a powerful effect in reducing the activity of the platinum, a quantity of arsenic equal to 0-2 per cent, of the weight of the platinum reducing the activity by 50 per cent.5 These poisons, as they are termed, also include less harmful substances such as antimony, lead, bismuth, etc. The presence of small quantities of rhodium, iridium or osmium in the platinum also causes diminished yields of trioxide, but the presence of palladium or ruthenium has the opposite effect.6... 

Gasolines contain a small amount of sulfur which is emitted with the exhaust gas mainly as sulfur dioxide. On passing through the catalyst, the sulfur dioxide in exhaust gas is partially converted to sulfur trioxide which may react with the water vapor to form sulfuric acid (1,2) or with the support oxide to form aluminum sulfate and cerium sulfate (3-6). However, sulfur storage can also occur by the direct interaction of SO2 with both alumina and ceria (4,7). Studies of the oxidation of SO2 over supported noble metal catalysts indicate that Pt catalytically oxidizes more SO2 to SO3 than Rh (8,9) and that this reaction diminishes with increasing Rh content for Pt-Rh catalysts (10). Moreover, it was shown that heating platinum and rhodium catalysts in a SO2 and O2 mixture produces sulfate on the metals (11). 

Several high-temperature procedures have been described in the literature for the preparation of the transition-metal dioxides. Direct oxidation of the metals, lower oxides, chlorides, or nitrate precursors provides a convenient route to the dioxides of several metals Ti, Mn, Ru, Rh, Os, Ir, and Pt.1,3-5 (Syntheses of the rutile forms of rhodium and platinum dioxides by direct oxidation requires application of high pressures.5) Reduction of higher oxides is the most common method of synthesis for these dioxides V02, Nb02, Mo02, W02, and /3-Re02.4,6-8 Stoichiometry in these reactions is most readily controlled by use of the respective metal or a lower oxide as reductant. Chromium dioxide is normally synthesized by hydrothermal reduction of the trioxide.9... 

Later work by Stevenson [72] supported this hypothesis. The preparation of PET catalysed by antimony trioxide was studied in thin films on metal surfaces that were carefully selected to avoid catalysis by surface effects or by dissolved metal as mentioned earlier, a large number of metals and their oxides, salts or other derivatives catalyse the polyesterification reaction. On inactive surfaces like silver or rhodium the catalysed polycondensation rate increased with decrease in film thickness. In the absence of added catalyst there was no tendency for the rate to increase with decreasing film thickness. Stevenson proposed that in thin films the catalyst-deactivating component was more readily lost, thereby increasing the reaction rate. 

In our first approach, a nonradioactive, representative fission-product mixture was prepared, consisting of equal masses of the desired elements. An ammonium hydroxide solution was used to dissolve molybdenum trioxide, M0O3 this solution was added to an aqueous solution containing the nitrates of cerium, palladium, and rhodium. The resulting mixture was calcined at 500°C for 17 hours, then at 550°C for an additional seven hours. The solids from the calcination were powdered and added to a blended mixture consisting of the oxides of antimony, ruthenium, samarium, strontium, yttrium, and zirconium. Cesium was then added as cesium iodide niobium was added as potassium hexaniobate,... 

As a result of the diminution in the range of oxidation states which has already been mentioned, the number of oxides formed by these elements is less than in the preceding groups, being confined to two each for cobalt (CoO, C03O4) and rhodium (RhiOB, RhOi) and to just one for iridium (IrOi) (though an impure sesquioxide IriOs has been reported — see below). No trioxides are known. 

Sulfonation of toluene with gaseous sulfur trioxide [81] Asymmetric hydrogenation of Z-methylacetamidocinnamate (mac) with rhodium chiral diphosphine complexes [82]... 

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