Powder platinum

Figure 15B shows a screenshot displaying the spin echoes of 195Pt in platinum powder acquired by the CPMG sequence. The experiments were performed at a carrier frequency of 50.74 MHz. The 19SPt signal... 

The isomerization of neopentane has also been observed on a variety of dispersed platinum catalysts, including supported platinum as well as platinum powder, by Boudart and co-workers (121, 122). On a 1% plati-... 

Analogous studies of the chemisorption of 14C-labeled benzene on copper powder and on platinum powder showed no chemisorption on the former, and the establishment of a low surface coverage over a range of temperature on the latter (Fig. 1). Again the surface coverage of hydrogen on platinum appeared to be about three times that achieved by benzene. 

High area platinum electrodes were made by painting platinum powders as described earlier. The electrodes were electrochemically cleaned by scanning the potential 50 to 1500 mV for 3 h in 3 M sulfuric add. After that the electrolyte was exchanged with 3 M sulfuric acid with 1 M methanol. 

Fine platinum powder may explode if near an open flame. Because platinum is rather inert in its elemental metallic form, it is not poisonous to humans, but some of its compounds, particularly its soluble salts, are toxic if inhaled or ingested. 

Inelastic neutron TOF spectra have also been obtained for hydrogen adsorbed on platinum powders (31,32). Both experiments observed a sharp surface vibratory mode of the hydrogen near 400... 

In order to investigate the poisoning mechanism, the FT-IR spectra were measured for the platinum powder before and after exposed to the vapor of HN03 aqueous solution. A sharp peak which belongs to N03 characteristic absorption was observed at 1390 cm 1 as shown in Fig.3. The formation of some platinum nitrate compounds seems quite unlikely under the present experimental condition, We might conclude from these results that the poisoning was caused by the reversible adsorption of HN03 on the Pt catalyst surface. 

Platinous Selenide, Platinum Monoselenide, PtSe.—Berzelius observed that platinum and selenium unite, when heated together, to yield a grey, refractory selenide. Roessler 2 obtained the monoselenide by igniting an intimate mixture of platinum powder and half its weight of sdenium under a layer of borax at a temperature approaching the melting-point of gold (circa 1062° C.). 

The purified platinum is quite similar in types and levels of impurities to that produced by the primary purification sequences. It is therefore apparent why Wollaston found no consistent differences in the metallurgical characteristics of the platinum powder produced from the crude ore or the retreated residuum by either of his two purification processes. 

We obtained initial rates for the reaction of neopentane on supported platinum and platinum powder catalysts at 300°, 1 atm total pressure, and a hydrogen-to-neopentane ratio equal to 10. As before, surface platinum atoms were titrated by selective chemisorption of hydrogen (27). Before discussing the results, it is important to stress the reproducibility of the results on samples of different origin but nearly identical dispersion and pretreatment. Thus, the same value of the selectivity to isomerization was found on two catalysts an experimental catalyst containing 2% platinum on t -alumina and a commercial sample with 0.6% platinum on y-alumina. Percentage dispersion of the metal was 64 and 73, respectively, and the selectivity was 1.5. Both samples were reduced at 500° under identical standard conditions. 

CUSO4 and CUO.CU8O4 decomposed between 700 and 780 K to give only SO3. These reactions were not catalyzed by platinum powder, which did, however, promote dissociation of 8O3 ( 8O2 + V2O2). 

A stream of gaseous H2 is directed onto finely divided platinum powder in the open air. The metal immediately glows white-hot and continues to do so as long as the stream continues. Explain. 

Van Straeten M., Swenters K., Gijberls R., Verlinden J. and Adriaenssens E. (1994) Analysis of platinum powder by glow discharge mass spectrometry, J Anal At Spectrom 9 1389-1397. 

F.H.M. Dekker, J.G. Nazloomian, A. Bliek, F. Kapteijn, J.A. Moulijn, D.R. Coulson, P.L. Mills, and J.J. Lerou, Carbon Monoxide Oxidation over Platinum powder A comparison of TAP and Step-Response Experiments, Appl. Catal. A, accepted for publication (1996). 

For platinum powder before and after dosing with dihydrogen peak positions and assignments in the INS spectrum are given in Table 7.5 [50]. The platinum was in the form of a 55.7 g cylinder of compressed platinum powder which had been reduced in dihydrogen, evacuated and then dosed with dihydrogen. 

The INS spectrum of ethyne adsorbed by platinum black at 120 K was fitted to a force field with a deformed ethyne (Z H-C-C, 143.5°) [64]. The peak positions are close to those reported by HREELS [65] of ethyne on Pt(lll) (the predominant exposed crystal face of platinum powder). The spectra may be assigned with reference to ethyne and the ethyne complexes [Co2(CO)6(p2-Tl -C2H2)] [66] and [Os3( li2-CO)(CO)9 (p,3-T -C2H2)] [67]. Spectra are shown in Fig. 7.12 and peaks are listed in Table 7.7. The stmctures and INS spectra of the ethyne complexes are discussed further in 7.3.2.2. 

C.M. Sayers C.J. Wright (1984). J. Chem. Soc. Faraday Trans. I, 80,1217-1220. Hydrogen adsorbed on nickel, palladium and platinum powders. 

However, there is also evidence that dehydrocyclization may proceed by another route involving only the metal component of the catalyst. It has been observed that unsupported platinum powders catalyze the dehydrocyclization of n-heptane (21). Also, Dautzenberg and Platteeuw (25) report that dehydrocyclization of n-hexane to benzene occurs over a catalyst in which platinum is supported on a nonacidic alumina. Since bifunctional catalysis with participation of acidic sites is then presumably eliminated, the activity is attributed to the platinum itself. 

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