杂多钼酸盐中心原子(P,As)对催化氧化性能的影响

合成了具有不同中心原子Keggin阴离子结构的杂多钼酸盐M₃(XMo₁₂O₄₀)(M=K⁺,NH₄⁺,X=P,As)。利用FTIR、TPD、ESR和CV等手段考查了各化合物的氧化还原性质和酸性。比较两种不同中心原子的杂多钼酸盐,其中砷为中心原子的更容易被还原及有较低的酸强度,这类催化剂对异丁醛氧化脱氢活性较低,而对异丁醛氧化为甲基丙烯酸有较高的选择性,中心原子对活性和选择性的影响分别与它们氧化还原电位的升高关联,也与更易给出轿式氧有关。

Effects of Center Atom (P,As) in Heteropolymolybdate on Catalytic Oxidation

The heteropolymolybdates of Keggin structural anion with different center atoms, M3(XMo12O40) in which M=K+, NH4+; X=P, As, were synthesized. Their redox and acidic proper-ties were examined by means of FTIR, ESR, TPD, and cyclic voltammetry techniques. Based on a comparison of heteropolymolybdate of both kinds of center atom(P, As), we found that the one con-tainning As atom is easier reducible and possesses lower acid strength. As a result, the catalyst con-tainning As anion is less active for the oxidative dehydrogenation of isobutylaldehyde, however, is more selective for the formation of methacrylic acid. These effects of center atom in heteropolyacid salt on the oxidative dehydrogenation activity and the oxidation selectivity may be related to the increasing of oxidation-redaction potential and facility of donating bridged oxygen of the As anion.