Heteropolyanions Catalysts for n-Heptane Conversion: Effect of the Counter Cation and the Addenda Atoms

Abstract

Different heteropoly compounds (HPC) H₃PW₁₂O₄₀, H₃PMo₁₂O₄₀, H₄PMo₁₁VO₄₀ and Cu_1.5PMo₁₂O₄₀ were prepared and characterized by means of FTIR and thermogravimetry. Their catalytic properties for the n-heptane reaction were evaluated at 300 ºC. In this study the effect of the addenda atoms (W, Mo and V) and the counter cations (H⁺ and Cu²⁺) was investigated. The substitution of W atoms with Mo ones increased the conversion and favoured the cracking selectivity to the detriment of that of cyclization while isomerization selectivity remained unchanged. When the protons were replaced with copper ions, cracking and cyclization reactions were favoured to the detriment of that of isomerization. Heteropolyacids have been found more active than the copper heteropolymolybdate salt. Increasing hydrogen pressure favoured cyclization and cracking reactions to the detriment of isomerization one.