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

Aluminum doped cesium salts of tungstophosphoric acid, AlxCs2.5-3xH0.5PW12O40 (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 C-13 MAS NMR technique and 1-C-13-n-butane as the reactant. All AlxCs2.5-3xH0.5PW12O40 catalysts show higher catalytic activity than Cs2.5H0.5PW12O40. Among them, Al0.1Cs2.2H0.5PW12O40 exhibits the best performance. The MAS NMR technique was further employed to characterize the acidity of the catalysts using trimethylphosphine and 2-C-13-acetone as the basic probe molecules. Al0.1Cs2.2H0.5PW12O40 possesses higher Bronsted acid strength than Cs2.5H0.5PW12O40, which parallels the activity of the catalysts. For a catalyst used in n-butane isomerization reaction, to enhance its Bronsted acid strength rather than to increase its acid density is more important for improving the activity of the catalyst.