Effect of potassium on the catalytic activity of TS-1 Original Research Article

Titanium silicate-1 (TS-1) samples contained a significant amount of potassium 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 with 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 corresponds to the presence of Ti in the framework. The potassium ion exchange is considered to occur mainly on the Si–OH group adjacent to the ‘open’ Ti site. The presence of potassium retarded the oxidation of organic compounds with aqueous H2O2 to a different extent depending on the substrates. The retarding effect decreased in the order hexane>2-hexene>2-penten-1-ol and there was little inhibition in the oxidation of 2-penten-1-ol. This could be interpreted in terms of polarities of substrates and active sites in TS-1; non-polar hexane was less easily accessible to the Ti environment made more polar by adjacent potassium. In a similar manner, promotion of the oxidation of the alcoholic group in the reaction of 2-penten-1-ol over the K-type TS-1 might be ascribed to increased interaction of the alcoholic group with the active Ti site.