Surface reaction of 2-propanol on modified Keggin type polyoxometalates: In situ IR spectroscopic investigation of the surface acid-base properties

In order to investigate the influence of modified Keggin-polyoxometalates and supported gold particles on reactivity and reaction pathways in thermal 2-propanol oxidation, titanium-substituted, insoluble Cs⁺-salts of the Keggin-heteropolytungstate (H₃PW₁₂O₄₀) Cs₃PW₁₂O₄₀ 1, Cs₅PW₁₁TiO₄₀·nH₂O 2, and supported gold composite Au/Cs₅PW₁₁TiO₄₀·nH₂O 3 were synthesized and characterized as molecular model catalysts. The Ti-substituted polyoxometalate 2 did not show any observable activity in the gas phase oxidation of 2-propanol. The presence of gold nano-particles activates the supporting polyoxometalate 3 and enhances formation of different oxidation products (acetone, diisopropyl ether) depending on the presence of different types of active sites. The formation of the diisopropyl ether involves two adjacent 2-propanol molecules adsorbed on two different types of active sites, whereas the dehydrogenation reaction for the acetone formation involves the initial adsorption of 2-propanol on one type of active site.