A series of Lewis acid metals monosubstituted phosphotungstic acids H_nPW₁₁MO₃₉ (HPWM, M = Cu^II, Zn^II, Cr^III, Fe^III, Sn^IV, Ti^IV, and Zr^IV; for Ti and Zr, the number of oxygen is 40) was evaluated in direct production of methyl levulinate (ML) from cellulosic biomass in a cascade reaction. One of the solid catalysts, H₅PW₁₁TiO₄₀ (HPWTi), was found to be highly efficient for generation of ML from mono- or polysaccharides, reaching 51.3% ML yield directly from cellulose. And under microwave-assistance, the efficiency could be improved to a 62.6% ML yield within 2 h, which was almost the best result so far among reported solid catalysts. Identification of the reaction intermediates and the products provided some insight into the reaction mechanism and showed the requirement of certain Brønsted/Lewis acid ratio as 2.84/1 for HPWM. Moreover, the different metals in catalysts profoundly affected the Lewis or total acidity, and therefore, the catalytic activity and selectivity to ML or methyl glucosides (MG). HPWTi acted as a heterogeneous catalyst after being calcinated at 200 °C and showed high recyclability with minor loss of performance.

中文翻译：

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使用具有Brønsted/ Lewis酸性位点的杂多酸H _n PW ₁₁ MO ₃₉催化从多糖级联生产乙酰丙酸甲酯

一系列路易斯酸金属单取代的磷钨酸H _n PW ₁₁ MO ₃₉（HPWM，M = Cu ^II，Zn ^II，Cr ^III，Fe ^III，Sn ^IV，Ti ^IV和Zr ^IV ;对于Ti和Zr，在级联反应中从纤维素生物质直接生产乙酰丙酸甲酯（ML）的过程中评估了氧气为40）。固体催化剂之一，H ₅ PW ₁₁ TiO ₄₀发现（HPWTi）从单糖或多糖产生ML的效率很高，直接从纤维素中获得51.3％的ML收率。在微波辅助下，效率可在2小时内提高至ML的62.6％，这几乎是迄今为止报道的固体催化剂中最好的结果。反应中间体和产物的鉴定为反应机理提供了一些见识，并表明对于HPWM，要求一定的布朗斯台德/路易斯酸比为2.84 / 1。此外，催化剂中的不同金属深刻影响路易斯或总酸度，因此影响了ML或甲基葡糖苷（MG）的催化活性和选择性。HPWTi在200°C下煅烧后起多相催化剂的作用，并显示出较高的可回收性，且性能损失较小。