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The electron paramagnetic resonance ahsorption of ehroniia supported on alumina has been investigated a t X-band (9.5 khfcps.) and K-band (23.9 kMcps.). Spectra of chroinia-alumina reduced in hydrogen a t 500" show two distinct phases: a dispersed (6) phase whic,h predominates a t low concentrations of chromium and a bulk ( B ) phase which is prevalent at, the higher concentrations. 1 he temperature dependence of the intensity of these phases indicates the &phase consists of rather isolated Cr+3 ions not coupled electronically and the p-phtHe consists of clusters of Cr+3 ions with strong exchange roupling of 3d electrons. Intensity calibrations of e.p.r. spectra have been made and these indicate all the chromium present in the rcduced catalysh to be in the trivalent state.A relatively sharp resonance absorption appears upon oxidation of reduced chromia-alumina with oxygen. A spin-Hamiltonian for each of the observed types of resonances is proposed and discussed.Absolute amounts of 6-and @-phase chromium also arc given.

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A study has been made of the adsorption of some lower molecular weight alkanes by silica-alumina cracking catalysts and related materials. The adsorption measurements were carried out using both a volumetric procedure and a radiotracer technique. The latter was capable of measuring isobutane adsorptions as low as 10~5 6 cc.(STP)/g. The adsorptions on silica-alumina of propane and «-butane at 760 mm. and of isobutane at 760 and 4 mm. were investigated by use of the volumetric technique. Over the temperature range from 100 to 350°, the adsorptions were found to decrease continuously with increasing temperature up to the point at which incipient adsorbate decomposition occurred. In general, no traces of chemisorption could be detected by the use of this method. By application of the more sensitive radiotracer technique, it was found that silica-alumina, dried at 500°, chemisorbed about 0.003 cc.(STP)/g. of isobutane at 10 mm. and at 25 and 150°. Also, it appeared that both a reversible and irreversible chemisorption were involved. The former constituted about 80% of the total and was capable of exchanging with the gas phase isobutane. The latter required a combustion process to effect its removal from the surface. Both water, added back to the dried catalyst, and metal ions partially poisoned the silica-alumina with respect to isobutane chemisorption. Pure silica gel and pure alumina were found to chemisorb only about Vio as much isobutane as silica-alumina. Further, the adsorption on the silica was entirely reversible, while with alumina it was for the most part irreversible.

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