Performance of several Keggin heteropoly acids/salts for adsorption of NOx

Aiming at controlling pollution caused by NO_x, several Keggin heteropoly acids/salts were evaluated concerning their activities in adsorbing NO_x from gas stream. All experiments were conducted in a fixed-bed reactor. The candidate heteropoly acids/salts examined comprise H₄PVMo₁₁O₄₀, H₅PV₂Mo₁₀O₄₀, H₆PV₃Mo₉O₄₀, (NH₄)₃PW₁₂O₄₀, (NH₄)₃PMo₁₂O₄₀, K₃PW₁₂O₄₀, K₂HPW₁₂O₄₀, KH₂PW₁₂O₄₀. Results showed that substitution of coordination atom Mo in the [PMo₁₂O₄₀]^3- anion by one or more V atoms leads to only slight change in NO_x adsorption activity; however, it is for the first time that nano (NH₄)₃PW₁₂O₄₀ was found to have an up to 10.6% enhancement in NO_x adsorption efficiency in comparison with the same catalyst of normal particle size; substitution of H⁺ in H₃PW₁₂O₄₀ by metal cation tends to lower the adsorption activity, regardless of the metal cations introduced. By IR analysis, NO was found to be adsorbed via interaction with the proton of HPW structure.