Abstract: The selective catalytic oxidation behavior of propane over the cesium salts of heteropoly acids with different elemental compositions were systematically studied. Special attentions were paid to the series of H₃+n-xCs_xPMo_12-nV_nO₄0 catalysts(n=0₄, x=0₃) as well as the H_0.5Cs_2.5PW₁2O₄0, H₁.5Cs_2.5PW₁1VO₄0 and H_1.5Cs_2.5SiMo₁2O₄0 catalysts. The catalysts were characterized by means of BET, UV-Vis diffuse reflectance spectroscopy, FTIR, XRD, TPR and SEM to understand their physico-chemical properties. The substitution of Mo⁶⁺ with V⁵⁺ increased the acidity and oxidation ability of the HPAs of H₃+nPMo₁2-nV_nO₄0(n=0₄) samples. Substitution of proton with Cs⁺ not only modified the surface acidity, but also affected the redox property as well as the structural stability of the samples, therefore, had a substantial impact on the catalytic performance for the series of H_3+n-xCs_xPMo₁2-nV_nO₄0(n=0₄, x=0₃) catalysts. It was found that the structural stability of HPCs increased steadily with increasing the number of cesium cation up to 3. The optimal number of cesium substitution varied along with the number of vanadium atoms existing in the primary structure of heteropoly anions. The appropriate elemental composition of heteropoly anions was found to be the key factor determining the overall catalytic behavior of the Keggin type heteropoly compounds, and the best results was achieved over the H_1.5Cs_2.5PMo₁₁VO₄0 catalyst. The reaction data collected on various HPCs in this study suggest that the composition of structural atoms of heteropoly anions and the number of balanced cations are closely related to acidity, redox property and catalytic performance of HPCs, and these data also accord well with the theoretical predictions.

Key words: Keggin type heteropolycompounds, Elemental composition, Selective oxidation of propane, {Acrylic acid}