Skeletal isomerization of n-pentane over Pt-promoted cesium hydrogen saltsof 12-tungstophosphoric acid

Two kinds of Pt-promoted Cs2.5H0.5PW12O40 (Cs2.5H0.5PW12O40 will be denoted by Cs2.5), Pt directly impregnated on Cs2.5 (Pt/Cs2.5) and a physical mixt ure of Cs2.5 and Pt/Al2O3 (Pt + Cs2.5), were used to catalyze the isomeriza tion of n-pentane in the presence of hydrogen at 453-573 K. Cs2.5 showed a high initial activity but deactivated rapidly. Addition of Pt greatly suppr essed the deactivation and increased the selectivity to isopentane. High st ationary conversion (34.8%) and selectivity (96.9%) were obtained by using Pt + Cs2.5 at a relatively low temperature (453 K) and a low hydrogen press ure (0.05 atm, hydrogen/pentane = 1). Under these reaction conditions, the stationary activity and selectivity of Pt + Cs2.5 were significantly higher than those of Pt-promoted H-ZSM-5 or SO42-/ZrO2. It was deduced that the r emarkable effect of Pt in suppressing the catalyst deactivation was brought about by activated hydrogen, which were formed on Pt, transferred to Cs2.5 , and utilized to remove carbonaceous deposits or their precursors. Increas e in the hydrogen pressure decreased the initial activity probably due to a decrease in the concentration of pentenes or pentyl carbenium ion. (C) 199 9 Elsevier Science B.V. All rights reserved.