Studies on the identification of the heteropoly acid generated in the H3PO4–WO3–Nb2O5 catalyst and its thermal transformation process
Studies on the identification of the heteropoly acid generated in the H3PO4–WO3–Nb2O5 catalyst and its thermal transformation process
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DOI：
10.1016/j.jcat.2006.09.021
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发表时间：
2007
影响因子：
7.3
通讯作者：
K. Okumura;K. Yamashita;Kazuhiro Yamada;M. Niwa
中科院分区：
文献类型：
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作者：
K. Okumura;K. Yamashita;Kazuhiro Yamada;M. Niwa
由H3PO4-WO3-Nb2O5组成的混合金属氧化物催化剂的前体在Friedel-Crafts烷基化中表现出优异的活性，并通过31P NMR进行了鉴定。结果表明，Keggin 型混合杂多酸 H4PNbW11O40 是在 H3PO4-WO3-Nb2O5 催化剂的制备过程中自发生成的。 H4PNbW11O40 在 673-823 K 的温度范围内发生部分分解，生成具有布朗斯台德酸特性的无定形氧化物。根据结构和酸性研究的结果，通过煅烧 H3PO4-WO3-Nb2O5 获得的活性物质归因于 H4PNbW11O40 在 WO3-Nb2O5 载体上热分解过程中的瞬态。事实上，通过混合 H4PNbW11O40、草酸铌和钨酸铵溶液，然后在 773 K 下煅烧而制备的催化剂，在苯甲醚与羧酸的弗里德尔-克来福特酰化反应中表现出优异的活性。
The precursor of the mixed metal oxide catalyst composed of H3PO4–WO3–Nb2O5, which exhibits excellent activity in Friedel–Crafts alkylations, was identified with31P NMR. It was revealed that the Keggin-type mixed heteropoly acid, H4PNbW11O40, was spontaneously generated during preparation of the H3PO4–WO3–Nb2O5catalyst. The partial decomposition of H4PNbW11O40occurred in the temperature range of 673–823 K to give an amorphous oxide that had a Brønsted acid character. Based on the results of structural and acidic studies, the active species obtained through the calcination of H3PO4–WO3–Nb2O5was ascribed to the transient state in the course of the thermal decomposition of the H4PNbW11O40over the WO3–Nb2O5support. In fact, the catalyst prepared by mixing H4PNbW11O40, niobic oxalate, and ammonium tungstate solutions, followed by calcination at 773 K, exhibited excellent activity in the Friedel–Crafts acylation of anisole with carboxylic acids.