An aluminum promoted cesium salt of 12-tungstophosphoric acid: a catalyst for butane isomerization

Abstract

Aluminum doped cesium salts of tungstophosphoric acid, Al_xCs_2.5–3xH_0.5PW₁₂O₄₀ (x = 0.05, 0.1 and 0.15), were prepared via a solid state synthesis method and their catalytic activity in n-butane isomerization reaction was tested using the ¹³C MAS NMR technique and 1-¹³C-n-butane as the reactant. All Al_xCs_2.5–3xH_0.5PW₁₂O₄₀ catalysts show higher catalytic activity than Cs_2.5H_0.5PW₁₂O₄₀. Among them, Al_0.1Cs_2.2H_0.5PW₁₂O₄₀ exhibits the best performance. The MAS NMR technique was further employed to characterize the acidity of the catalysts using trimethylphosphine and 2-¹³C-acetone as the basic probe molecules. Al_0.1Cs_2.2H_0.5PW₁₂O₄₀ possesses higher Brönsted acid strength than Cs_2.5H_0.5PW₁₂O₄₀, which parallels the activity of the catalysts. For a catalyst used in n-butane isomerization reaction, to enhance its Brönsted acid strength rather than to increase its acid density is more important for improving the activity of the catalyst.