GENERATION OF CATALYTIC ACTIVITY IN SILICAGEL BY IONIZING RADIATIOX
in making available the complete computer programs and the guidance which they gave. We acknowledge discussions with Dr. R. AI. Hedges and the encourage-
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ment of Dr. B. J. Zwolinski. The research samples were made available through the API Research Projects 44 and 5SB.
Generation of Catalytic Activity in Silica Gel by Ionizing Radiation
by C. Barter and C. D. Wagner Shell Development Company, Emeryiille, Calijornia
(Received August $0, 1964)
In a previous paper it was reported that acid centers are generated in silica gel by the action of ionizing radiation, in vacuo. These centers persist in the gel, in the absence of radiation, but are thermally sensitive. At 25" they disappear with a half-time of a few hours, as shown by the loss of acid titer and activity for isobutylene polymerization. Further study of irradiated silica gel has disclosed that radiation generates at least two other types of chemically active centers. These are stable a t more elevated temperatures and are active for butene interconversions and for the conversion of cyclopropane to propylene.
Introduction That irradiation of silica gel with X-rays results in surface changes other than the generation of acid centers has been suggested by spectroscopic evidence. Following butylamine neutralization of the gel or thermal decay of its generated acid centers, the absorption spectrum of adsorbed p-dimethylaminoazobenzene is not at all characteristic of this indicator in its neutral form, in solution or adsorbed on unirradiated gel. The surface changes responsible for the altered spectrum are reversible; they may be due to atomic displacements, for the heating of irradiated silica gel at 500" for 10 hr. prior to adsorption of the indicator results in an absorption spectrum identical with that obtained with unirradiated ge I. The active centers studied in this work niay be similar to those observed by Mikovsky and Weisz2 as a result of neutron irradiation ( l o w n.v.t.) of silica gel; they attributed the centers to atomic displacement.
Experimental Davison 950 silica gel, 60-200 mesh, surface area 625 m.2/g., aluminum content
