丙烷选择氧化用BiCeVMoO复合氧化物催化剂中Ce组分的作用

Effect of Cerium Component on Selective Oxidation of Propane over BiCeVMoO Composite Oxide Catalyst

用X射线衍射 (XRD)、激光拉曼光谱 (LRS)、程序升温还原 (TPR)、催化剂晶格氧反应性和微反测试等手段考察了BiCeVMoO复合氧化物催化剂的组成、结构、氧化 还原性质与催化丙烷选择氧化性能 .结果表明 ,n(Ce) /n(Ce+Bi) ≤ 0 15时 ,Ce组分可能占据BiVMoO结构中Bi离子所处的晶格位置 .催化剂对丙烷选择氧化的催化性能与Ce组分的含量密切相关 ,随着Ce含量的增加 ,丙烯醛选择性显著升高 ,在n(Ce) /n(Ce+Bi) =0 15时达极大值 .随着Ce含量的进一步增加 ,丙烯醛选择性下降 ,完全氧化产物COx 选择性上升 .可以认为 ,适量Ce组分的引入提高了催化剂晶格氧物种的反应活性 。

Direct oxidation of propane to acrolein is an interesting alternative of propylene oxidation. In this work, we try to improve the catalytic properties for propane oxidation ulteriorly by introducing Ce(Ⅲ) into BiVMoO composite oxide catalyst. The composite oxide catalyst BiCeVMoO was prepared by evaporating a desired complex metal ions solution of citric acid and oxalic acid. Ce(Ⅲ) was introduced into Bi 0.85 V 0.55 Mo 0.45 O 4 as (Ce+Bi) 0.85 V 0.55 Mo 0.45 O 4 and Bi(Ⅲ) was substituted by Ce(Ⅲ) step by step. The structure of BiCeVMoO composite oxide catalyst with different composition and its catalytic properties for selective oxidation of propane have been investigated by XRD, LRS, TPR, lattice oxygen reaction and micro reaction tests. It has been shown that Bi can be substituted by a low amount of Ce while the scheelite structure of BiVMoO remains unchanged. With the increase of Ce content ( n (Ce) / n (Ce+Bi) >0 15), new phases such as CeVO 4 and Ce 2 (MoO 4) 3 formed. The composition and structure of catalyst exert great influence on the catalytic properties for selective oxidation of propane. The Ce which entered into the lattice of BiVMoO promotes the formation of target acrolein, and the selectivity for acrolein increases to a maximum at n (Ce) / n (Ce+Bi) =0 15. Further increasing Ce content results in further oxidation of propylene and acrolein to CO x owing to the strong oxidative ability of catalyst. The low amount of introduced Ce which occupied the lattice sites of Bi enhanced the oxidative ability of catalyst moderately by increasing the activity and the amount of surface active oxygen species.