Nov., 1959
NOTES
1981
The existence of a Rh(OH)++ species is contra- Higher areas were in general obtained with larger samples. largest samples (10 g. or more) a fast exothermic dictory to the findings of Grube and c o - ~ o r k e r s ~With ~ ~ thestarted at 350" and the temperature in the solid who postulated the formation of Rh(OH)2C104 reaction mass rose quickly above 400' for a brief period. It appeared from titration of rhodium hydroxide with perchloric that this temperature runaway was related to the surface acid; no strong evidence for the Rh(OH)2+ ion area variations, probably because of effects on rate of reducIt seemed likely that the temperature in small samples was found in the present study. A very slight tion. g. or less) remained nearly the same as that of .the hyirregularity in the titration curves of Fig. 2 and 3 (0.1 drogen during heating and that the rate of reduction was may be observed at [OH-]/[Rh+++] ratios of 2; therefore slower. A number of experiments are described below in which the however, these can hardly be noticed above the of reduction of small samples was controlled and varied; experimental scattering of the data. If Rh(OH)2+ rate results are shown in Table I. The reduction was carried out was present in the solutions, its concentration was in a 5-ml. glass cell having a sintered glass plate to support negligible compared to the observed species. the sample. The same cell was employed as the adsorption Several strong indications for oxy or hydroxy cell for B.E.T. measurement of the surface area. bridges were evident during the study. I n the TAbLE 1 preparation of rhodium per~hlorate,~ extensive SURFACE AREAS OF MoSz PREPARED FROM MoSa boiling of the solutions ultimately led to a color Gas flow rate, 5 ml. per min., atmospherk pressure; outchange from light yellow to dark brown. Crys- gassing temp. for area measurements, 500 ; 30 mg. MoS tals of rhodium perchlorate hexahydrate could not ( < 20 mesh) be isolated from the darkened solution. If, Final Surface Rate of tpp., area, however, these solutions were refluxed with hydroGas heatinga C. m.Z/g. chloric acid and the rhodium was reconverted to .. Untreated tri..
