介孔碳负载纳米WO3-Ta2O5的可控合成及催化菊芋转化乙酰丙酸研究

With the decreasing of fossil resource substantially, it's imperative for catalyst researchers to develop a green and efficient way immediately to transform biomass energy into bio-chemicals or energy substitutes. Levulinic acid (LA) is considered as a bio-based platform compound, and it's conventional preparation methods predominantly employ corrosive homogeneous acids, which make the process unfavorable. Most solid acids have poor performance on catalytic conversion biomass into levulinic acid.. According to our previous study, tantalum oxide is excellent in catalytic dehydration of biomass into 5-hydroxymethylfurfural. In order to improve the catalytic selectivity of bio-chemicals, we will modulate the physicochemical properties of tantalum oxide by doping with tungsten oxide, and the properties of the catalysts such as the composition, size, acidity, surface area and so on can be controlled. The nature and property of the catalyst, and the reaction intermediates and products will be characterized and analysed, and the relationship between the catalyst structures and the catalytic performance will be explored on preparation of LA from Jerusalem artichoke. This project will also elucidate the mechanisms of biomass conversion catalyzed by the solid acids. The implementation of this project will provide theoretical and experimental basis on development of efficient solid acid catalysts for direct biomass conversion.

随着石化资源急剧减少，将生物质绿色、高效、定向转化为能源替代品或目标化学品是催化学科亟待解决的一个重要课题。乙酰丙酸作为一种生物基平台化合物，常规制备方法多采用强腐蚀性质子酸作为催化剂，存在诸多弊端；而大多数固体酸对催化生物质制备乙酰丙酸性能较差。申报人前期研究发现钽氧化物是一种性能优异的固体酸，对催化生物质糖脱水制备5-羟甲基糠醛具有很好的催化活性。为进一步提高其制备生物基化学品的催化性能，本项目拟通过加入钨氧化物对钽氧化物催化性质进行调变，通过控制催化剂合成条件，制备组成、尺寸、孔径、表面性质等均可控的催化剂是本项目需要解决的关键科学问题之一。通过对催化剂和反应中间体和产物类型及其分布进行分析表征，探究催化剂与菊芋转化乙酰丙酸之间的构效关系，阐明固体酸催化生物质转化过程的机理及科学问题。本项目的实施将为开发高性能固体酸催化剂催化生物质定向转化提供理论及实验依据。

本报告主要研究了在固体酸催化下将可再生生物质资源转化为平台化合物5-羟甲基糠醛（HMF）和乙酰丙酸（LA）。采用共沉淀方法制备出双金属氧化物固体酸WO3-Ta2O5，研究表明，WO3-Ta2O5的酸性（Bronsted酸和Lewis酸）随着催化剂中W和Ta的元素比例改变而改变，Ta2O5加入WO3后，L酸减弱直至消失，从而影响催化糖转化HMF和LA的反应效果：未加入WO3的Ta2O5催化剂，其酸性位点主要为Lewis酸，对催化糖（葡萄糖、果糖、菊粉、菊芋汁等）转化为HMF表现出很好的选择性和可重复实用性，HMF收率可达90%，催化剂重复使用15次后，其活性和催化效果未发生明显改变。加入WO3后，催化剂Lewis酸位点酸性减弱，催化糖转化HMF的选择性和收率随着WO3含量增加而降低，而产物中LA含量随着WO3的加入呈现先升高后降低的变化趋势，LA收率最高可达90%（远高于其他固体酸催化生物质制备LA）；进一步提高催化剂中WO3含量，产物中LA含量稍有降低。研究表明：具有Lewis酸位点的Ta2O5对于生物质糖脱水转化为HMF表现出很好的活性和选择性，加入WO3后，+5价的Ta被+6价的W取代后，Lewis酸位点酸性减弱，更有利于HMF发生水合反应生成LA。