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正丁烷选择性氧化制备顺丁烯二酸酐（MA）是目前唯一实现工业化的低碳烷烃选择性氧化的过程，对于低碳烷烃的高值化利用具有重要的意义。钒磷氧（VPO）催化剂是目前针对该反应最有效的催化剂。然而VPO催化剂存在晶相不纯、结晶性差、暴露活性晶面少等问题，导致在催化过程中转化率低、过度氧化，本文针对VPO催化剂存在的问题，以提高目标产物MA的收率为目标，设计合成了一系列的低共熔类离子液体，在VPO催化剂前体合成过程中，利用所设计的低共熔类离子液体调控其成核生长过程，进而获得高性能的VPO催化剂。研究了低共熔溶剂对催化剂物化性质（晶体结构、形貌、表面价态、氧化还原特性、酸碱性）的影响，关联了催化剂物化特性与其催化活性之间的构效关系，并对催化剂的反应条件进行优化考察，得到了最佳的反应条件。主要的创新性工作如下：（1）针对该催化剂晶相不纯、结晶性差的问题，设计合成了草酸类低共熔离子液体（ChCl/OA DES）调控VPO催化剂的合成，通过ChCl/OA DES与催化剂前体溶液之间的络合性，形成草酸钒的低共熔络合物，降低了体系的成核数量，控制了成核速率，获得了表面单晶的催化剂前体，经过原位处理活化后，得到了结晶性高、杂相含量少的VPO催化剂。同时，ChCl/OA DES作为晶面诱导剂和表面化学改性剂，显著诱导了催化剂（020）晶面的增长，降低了V的平均价态和还原活化能，其催化效果相比未改性的而言，MA的质量收率提高了18%；（2）针对VPO催化剂暴露活性位点少的问题，基于上述工作，设计合成了多羟基的葡萄糖类低共熔溶剂（ChCl/GLU DES）作为结构导向剂和模板剂。通过ChCl/GLU DES 对催化剂前体合成过程的调控，诱导了前体活性面的生长，在催化剂活化过程中，ChCl/GLU DES逐步分解，得到高结晶性的多孔VPO催化剂，多孔性使其暴露了更多的活性位点，同时降低了催化剂表面的酸性，避免了产物的过度氧化。催化性能结果表明，改性后催化剂MA质量收率提高12%；（3）在列管式固定床反应器中对催化剂的反应条件进行优化，考察了反应温度、反应空速（GHSV）对催化效果的影响，总结了反应器反应参数对催化结果的影响规律。结果表明，最佳的反应参数为：反应温度420 oC，空速为2000 h-1。;Selective oxidation of light alkanes (C1?C5) to valuable functionalized chemicals has been widely studied due to their economy and environmental friendliness. Up to now, the most successful example is the partial selective oxidation of n-butane to maleic anhydride (MA) by vanadium phosphorus oxide (VPO) catalysts in industry. However, there are many problems of VPO catalysts, like impurity phase, poor crystallization, poor active sites etc., which result in the low conversion of n-butane and poor selectivity of MA. In this thesis, we intend to these problems with the purpose of improving the yield of MA, some functionalized deep eutectic solvents (DES) were designed and synthesized. The process of nucleation and growth of precursors was adjusted by DES, resulting in the higher catalytic performance of VPO. Meanwhile, the effect on physicochemical properties (crystal structure, microstructure, surface chemical state, redox characteristic and acid-base property) of DES was investigated in detail. The combination of characterizations with the performance was considered to understand the essential effects of DES. In addition, reaction parameters were optimized in the research. The main results are summarized in below:(1) The oxalic acid-base DES (ChCl/OA DES) was synthesized to solve the problem of poor crystallization and impurity phase of VPO catalysts. ChCl/OA DES can interact with V2O5 and form a new vanadium complex, which affects the process of nuclei formation of precursors by acting like a “buffer agent” in this process and obtained a single-crystal structure on the surface of precursor, correspondingly, topological transformation to the single-crystal active phase under the activation conditions accompany the decomposition of DES. What’s more, ChCl/OA DES as crystal induced agent and structural modifier could induce the growth of (020) plane, reduce the average valence state of V and reduction activation energy. Catalytic performance showed that the ChCl/OA DES improved the yield of MA about 18%;(2) Based on the above work, the glucose-based DES (ChCl/GLU DES) was synthesized as structure direct agent and template agent to solve the problem of poor crystallization and poor active sites of VPO catalysts. The active crystal plane was induced by ChCl/GLU DES, which result from the –OH group can selectively adsorb to certain faces to decrease their surface energy and further the growth rate of these faces. After activation, polyporous and high crystallinity VPO catalysts were obtained with the decomposed of ChCl/GLU DES. Meanwhile, the surface acidity of VPO was reduced, which avoid the deep oxidation of MA. Catalytic performance showed that the ChCl/OA DES improved the yield of MA about 12%;(3) The reaction conditions were optimized in the tube fixed-bed reactor, mainly contain the reaction temperature and the gas hourly space velocity (GHSV). The tendency between reaction parameters and catalytic performance was summarized.
|贺滨. 低共熔溶剂强化丁烷氧化制顺酐钒磷氧催化剂研究[D]. 中国科学院大学,2019.|
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