Skeletal isomerization of n-butane over caesium hydrogen salts of 12-tungstophosphoric acid

Abstract

Skeletal isomerization of n-butane to isobutane has been studied with a flow reactor, mainly at 573 K, over caesium hydrogen salts of 12-tungstophosphoric acid (trihydrogen phosphododecatungstate), Cs_xH_3–xPW₁₂O₄₀. The activity was highly dependent on the caesium content, being a maximum for x= 2.5 where the number of acid sites on the surface was greatest. The initial rate was first order with respect to the butane pressure (ca. 0.05–0.5 atm) at both 423 and 573 K on Cs_2.5H_0.5PW₁₂O₄₀. Cs_2.5H_0.5PW₁₂O₄₀ was found to be much more active and selective (83%cf. 60%) than SO₄^2–/ZrO₂ at the steady state at 573 K. H-ZSM-5 showed a higher activity than Cs_2.5H_0.5PW₁₂O₄₀ and SO₄^2–/ZrO₂ but the selectivity was only 14%. Cs_2.5H_0.5PW₁₂O₄₀ is a promising catalyst for this reaction and the low deactivation of Cs_2.5H_0.5PW₁₂O₄₀ is probably responsible for the high catalytic activity.