由锆系MOFs可控制备硫酸化氧化锆及其杂化材料的方法与Friedel-Crafts反应催化性能的研究

As a solid superacid catalyst, sulfated zirconia (SZ) is widely used for many catalytic applications, and much interest has been put on the synthesis and modification of SZ for both scientific and practical purposes. However, traditional SZ, which is produced via precipitation, should be improved in several aspects, such as reproducibility, loading amounts of sulfate species, mass transfer efficiency and chemical stability. This proposed research will be focused on the synthesis of SZ from zirconia based metal-organic frameworks (MOFs) and the mechanism of conversion from MOFs to SZ. As the precursors of SZ, Zr based MOFs have the following advantages, such as good reproducibility, uniform size of zirconia nanoclusters and tunable composition and porous structure, and high surface areas, etc. These new precursors can enhance the loading amounts of sulfate species, reduce mass transfer resistance and improve the stability of SZ. The particle size and morphology, as well as the pore structure of SZ will be finely controlled to provide more exposed acid sites and improve mass transfer rates. The uniform hybrid materials of SZ and carbon will be synthesized with Zr based MOFs, which has the organic and inorganic portions distributed uniformly in the frameworks on molecular levels. Due to the presence of carbon materials, the surface of hybrid catalysts will be more hydrophobic, as well as the reaction stability of SZ. The SZ catalysts will then be tested in Friedel-Crafts acylation and benzoylation reactions with two kinds of aromatic compounds as substrates. The relationship between the pore structure, particle morphology, surface properties of SZ and the acid catalytic performance will also be discussed. The proposed research will provide a new method in synthesis of metal-oxide based solid acids.

作为用途广泛、性能优越的固体超强酸，硫酸化氧化锆（SZ）具有重要的科学和应用研究价值。传统沉淀法制备的SZ在重复性、活性组分担载量、活性位暴露程度和稳定性等方面有待改进。本项目拟采用锆系金属有机框架聚合物（MOFs）为前驱体，利用MOFs制备重复性好、比表面积大、氧化锆团簇均一可调变的特点，开发制备高效SZ的新方法，以达到提高SZ活性组分担载量、降低SZ传质阻力和提高催化剂稳定性的研究目标，揭示MOFs制备SZ的合成机理。调变SZ的孔道结构和形貌、粒径，提高催化剂活性位暴露程度和传质速率。利用MOFs中有机和无机组分分布均匀的特点，实现SZ与碳材料的均一杂化，创造疏水微环境以提高催化剂稳定性。以双芳香类底物的Friedel-Crafts芳基化和酰基化反应作为模型反应，建立SZ的催化性能同结构、形貌、表面性质间的构效关系。本研究将为可控制备高性能金属氧化物类固体酸催化剂提供新的思路。

酸碱催化反应在现代化工中占据着重要地位，以多孔的固体酸（碱）代替传统的均相液体酸（碱），可以避免腐蚀设备和环境污染等缺点，同时可以精确调控固体催化剂的孔道结构和表面性质，改进其催化性能。不同于传统的浸渍法和共沉淀法，本研究以锆系MOFs为前驱体，制备出高效的氧化锆基多孔固体酸（碱），并且系统研究了催化剂的制备方法同结构效能之间的关系。.以UiO-66为前驱体，通过双溶剂浸渍的方法，制备出客体物种均匀分布的多孔WZ型固体酸催化剂（担载氧化钨的氧化锆）。通过调变偏钨酸铵的担载量，可以制备出表面担载有高度暴露的氧化钨团簇的多孔氧化锆，而WZ催化剂的酸量和催化性能直接决定于其表面担载的钨物种的状态。本方法制备的WZ同传统的氢氧化锆法制备的WZ相比，具有更高的酸量和催化活性，这得益于UiO-66前驱体的高比表面积。.通过双步煅烧的方法，以担载KNO3的UiO-66为前驱体，制备出多孔的KZ型固体碱（担载钾物种的氧化锆）。将KNO3@UiO-66首先转化为碳杂化的KZ材料，将UiO-66的有机组分转化为碳层以保护和支撑氧化锆骨架。这些碳基体可以作为介孔模板，同时加强介孔KZ的结构，提高抗碱能力防止骨架坍塌。由于比表面积的增加和碱中心的高度暴露，介孔KZ的反应速率优于KNO3@UiO-66通过单步煅烧合成的无孔对应物。与用传统的氢氧化锆作为前体制备的KZ相比，所得的介孔KZ也表现出优异的催化性能。.综上所述，以锆系MOFs为前驱体，通过改变制备条件，成功制备出了高孔隙率和活性组分高度暴露的氧化锆型固体酸（碱），同时研究了催化剂性能同结构组成之间的关系，进而通过调控制备条件来精确控制催化剂的结构性能，为开创一条新的可控制备性质可调的固体氧化物型催化剂拓展了思路，进行了前瞻性研究。