Influence of cesium in Pt/NaCs beta on the physico-chemical and catalytic properties of the Pt clusters in the aromatization of n-hexane

Various Pt/NaCs beta catalysts with decreasing Na/Cs ratios and a Pt/KL sam ple taken as a reference catalyst for aromatization of n-hexane, have been prepared by exchange of NaCs beta and KL zeolites in a Pt tetraammine solut ion then calcination and reduction. The increase of the Cs content in the N aCs beta zeolitic support results in a decrease of the cyclohexane adsorpti on and Pt exchange capacities. The Pt/Cs beta and Pt/KL samples show simila r behaviors which strongly differ from those of the Na-containing Pt/NaCs b eta samples in terms of(i) reducibility of the Pt ions after calcination, ( ii) shape of the FTIR spectra of CO adsorbed on the Pt clusters after reduc tion, and (iii) catalytic activity of these clusters in the conversion of n -hexane. In particular, the selectivity to aromatization is much higher on the Pt/Cs beta and Pt/KL catalysts than on the Na-containing Pt/NaCs beta o nes. The reasons for the specific behaviors of the Pt/Cs beta and Pt/KL sam ples are discussed. (C) 1999 Academic Press.