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

1999; Elsevier BV; Volume: 141; Issue: 1-3 Linguagem: Inglês

10.1016/s1381-1169(98)00258-1

1873-314X

Yanyong Liu,

Chemical Synthesis and Characterization

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 mixture of Cs2.5 and Pt/Al2O3 (Pt+Cs2.5), were used to catalyze the isomerization 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 suppressed the deactivation and increased the selectivity to isopentane. High stationary 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 pressure (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 remarkable 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. Increase in the hydrogen pressure decreased the initial activity probably due to a decrease in the concentration of pentenes or pentyl carbenium ion.