Reduction of 12-Molybdophosphates by Carbon Monoxide

Abstract

The reducibilities of heteropoly compounds with carbon monoxide (CO) was drastically affected by their countercations. Among the following salts of H₃PMo₁₂O₄₀, i e., A g⁺, Na⁺, K⁺, Cs⁺, Ni2⁺, cu²⁺, zn²⁺, , mg²⁺, Ca²⁺ and Fe³⁺, nickel salt was most readily reduced and copper salt was next (Fig.1). Other salts were less reducible than the two and show ed almost the same or even lesser reducibility than H₃PMo₁₂O₄₀ tself. Silver salts, whic h was highly reducible by hydrogen, was hardly reduced by CO. It was found in Fig.4 that t he reduction of copper salt occurred through two stage processes: in the first stage the counterc a tions, Cu(II), were reduced to a lower valency state and in the second stage M o(VI) in polyanions were reduced. Temperature programmed desorption of CO for a variety of oxidize d and reduced 12-molybdophosphates revealed that the reduced salts of nickel and copp er had an ability for CO adsorption while oxidized salts and reduced acid as well had no abili t y.. These findings indicate that the role of countercations in the reduction is to adsorb CO which then react with polyanions. This clearly explains the presence of induction period which was found in the low temperature reduction of copper salt.