Effect of potassium on the catalytic activity of TS-1

Titanium silicate-1 (TS-1) samples contained a significant amount of potass ium derived from contaminants in an aqueous solution of Pr4NOH. By washing with H2SO4, the alkali-exchanged sites were converted to sites with two OH groups or 'closed' Ti(OSi)(4) sites. Treatment of the acid-washed samples w ith an aqueous solution of K2CO3 led to the incorporation of potassium with a K/Ti ratio of around unity, suggesting that K ion exchange on TS-1 corre sponds to the presence of Ti in the framework. The potassium ion exchange i s considered to occur mainly on the Si-OH group adjacent to the 'open' Ti s ite. The presence of potassium retarded the oxidation of organic compounds with aqueous H2O2 to a different extent depending on the substrates. The re tarding effect decreased in the order hexane>2-hexene>2-penten-1-ol and the re was little inhibition in the oxidation of 2-penten-1-ol. This could be i nterpreted in terms of polarities of substrates and active sites in TS-I; n on-polar hexane was less easily accessible to the Ti environment made more polar by adjacent potassium. In a similar manner, promotion of the oxidatio n of the alcoholic group in the reaction of 2-penten-1-ol over the K-type T S-I might be ascribed to increased interaction of the alcoholic group with the active Ti site. (C) 2000 Published by Elsevier Science B.V.