CROATICA CHEMICA ACTA CCACAA 60 (4) 677-686 (1987) CBA CCA-1764 YU ISSN 0011-1643 UDC 546.77 Original Scientific Paper Action of Salt Formation on the Bifunctional Nature of 12-Molybdophosphoric Acid and Their Relationship to the Catalytic Activity A. M. El-Awad and K. M. Abd El-Salaam Chemistry Department, Faculty of Science, Assiut University Assiut, Egypt Received February 17, 1987 Acidic properties and the catalytic activity of 12-molybdopho- sphates (M"nn+ H 3 -,PM0 12 0 40 ; M = Cu 2 +,BP+,Cr 3 + and X = 1-3) have been studied. The results are discussed as the effect of these catalyst components on the partial charge on oxygen atom which is in arelation with the acidity. It is shown that the oxygen- -hydrogen bond is weakened as the value of partial charge on oxygen (-bo) becomes more negative, while the vapor-phase dehydration activity of 2-propanol is explained on the basis of the reacting zone wideness taking into account the pseudo liquid phase nature of the heteropoly compounds. Correlation, the percentage conversion of 2-propanol with the fractional charge on molybdenum atom was successful to interpret the effect of the redox properties of these catalysts on their catalytic activity. INTRODUC'l'ION Heteropoly acids have recently attracted much attention as catalysts for various industrial processes, such as oxidation, dehydration, esterification, and etheration.' It' has been reported that metal salts of heteropoly acids are more active and selective than the acid form in some acid-catalyzed reactions.F" Relationships between catalytic activity and either the acidic or redox properties of these heteropoly compounds have been reported. Niiyama et aP obtained a fair correlation between the activity for alcohol dehydration and electronegativity of metal cations. Hayashi and Moffat found that the activity for methanol conversion was related to the partial charge on oxygen atom," while in considering the redox properties many schemes have been proposedt"!". Also, the participation of both the surface and bulk heteropoly salt molecules in the catalytic processes has been investigated by several wor'kers.4,11.-13 The present work, in an attempt to gain more insight into the bifunctional nature of the heteropoly salts (the acidic and redox properties), is concerned with an investigation of the acidity, dehydration activity and the electrical conductivity properties of the substituted 12-molybdophosphoric acid with Bi 3 +,Cr 3 + and Cu 2 + cations. EXPERIMENTAL BDH 12-molybdophosphoric acid was incorporated with the nitrates of Cu(II), Cr(III), and Bi(III). An aqueous solution containing the required amounts of these