Rhodium Sponge

The massive metal is inert, but very finely divided forms are more reactive, absorbing large quantities of either CO or H2. While rhodium black or rhodium sponge dissolves in aqua regia or aqueous chlorine under pressure, larger pieces must be fused with sodium hydrogen sulfate to effect dissolution. 

Five grams (0.048 mol) of rhodium sponge and 10.9 g. (0.146 mol) of finely pulverized potassium chloride are ground together in a mortar. The mixture is then placed in an unglazed porcelain boat in the center of a ceramic tube inserted in a furnace heated to 550 to 575°. This temperature is maintained for 45 to 60 minutes while chlorine is... 

The (NH4)3RhCla HgO is ignited to rhodium sponge and post-reduced with hydrogen. 

Properties of the palladium metals and platinum. Ruthenium, osmium, rhodium, iridium, palladium, platinum. Osmium tetroxidc. Chloropailadous acid, chlo-ropaliadic acid, chloroplatinous at id. rhloroplatinic acid. Platinum sponge, platinum black. Uses of the palladium and platinum metals. 

On treatment with proton sponge 1, cationic rhodium complexes of type 262 have been shown to undergo double intramolecular dehydrofluorinative/C—C coupling to produce quantitatively rhodium complexes of hybrid cyclopentadienyl-phosphine ligands 263 (equation 27)240. 

Carbonyl compounds are formed with platinous derivatives, as, for example, by passing carbon monoxide over platinous chloride at 250°. Under these conditions there is obtained a mixture of PtCl - 2 CO, and 2 PtClj 3 CO, which on further heating gives PtClj CO. Other platinous compounds yield similar derivatives. Carbonyl compounds may also be prepared by passing an equimolecular mixture of carbon monoxide and chlorine over platinum sponge or foil at 240°-250°. This reaction is sometimes used to detect the presence of small amounts of rhodium or certain base metals in platinum. ... 

Saunders et al. have studied the G-G coupling in rhodium and iridium complexes that links fluorinated aromatic substituents on phosphine ligands to the methyl substituents of cyclopentadienyl ligands. These reactions involve HF elimination and can be induced by heat or base. The most effective bases are proton sponge (l,8-bis(dimethyl-amino)naphthalene) and BU4NF. One example is shown in Scheme ZZ ... 

The platinum group metals occur jointly as alloys and as mineral compounds in placer deposits of varying compositions. Ru and Os are separated from the PGM mix by distillation of their volatile oxides, whereas platinum, iridium, palladium, and rhodium are separated by repeated solution and precipitation as complex PGM chlorides, or by solvent extraction and thermal decomposition to sponge or powder. PGM scrap is recycled by melting with collector metals (lead, iron, or copper) followed by element-specific extraction. 

Production. Rhodium is produced as powder and sponge by chemical reduction or thermal decomposition of the chloro-ammonia complex (NHjlsIRHCl ]. Bars, rods, and wires are produced by powder compacting and extrusion, while coatings are produced galvanically, by evaporation or by sputtering. 

Rh nor rhodium oxide, but probably Rh+. Mallens et al. studied the response of pulsing methane, oxygen or a mixture of the two over Rh sponge and reported that CO and H2 were the primary products, from transient response curves where these products appeared before CO2 and H20. Similar studies and results are reported for several noble metal catalysts on various supports (see, for example. Ref. 57 and the references therein). However, even for noble metal catalysts, steep temperature gradients, indicating a combustion-reforming reaction scheme, are observed for reactants under atmospheric pressure. ... 

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