合成气直接制二甲醚用新颖嵌入式分级核壳双功能催化剂的构筑与调控

The catalytic transformation of coal-based synthesis gas to chemicals and clean fuels has been considered as a significant way for efficient and clean use of coal resources. Dimethyl ether (DME) is considered as an excellent clean fuel, and also as one of the most important chemical materials. DME can be synthesized through one-step method and the two-step method. The direct transformation of synthesis gas through the one-step method over bifunctional catalysts containing methanol synthesis catalyst (MSCAT) and methanol dehydration catalyst (MDCAT) can be considered as a promising approach, owing to its notable merits from the thermodynamic and economic viewpoints. The well-designed core-shell structured bifunctional catalyst provides a confined reaction environment, which overcomes the unavoidable issue for conventional hybrid or supported bifunctional catalysts that the formed methanol over CuZn based methanol synthesis catalyst leaves from catalyst surface before it transfers into DME via dehydration over solid acid catalyst. However, the improvement in catalytic performance including catalytic activity, selectivity, and stability of the core-shell structured catalyst is highly desirable. Therefore, the proposed work aims to investigate the fabrication and tuning of novel embedded-type hierarchical core-shell structured bifunctional catalysts towards direct production of DME from synthesis gas. The purpose is to significantly improve catalytic performance including catalytic activity, selectivity and stability of current bifunctional catalysts for direct production of DME from synthesis gas by improving the dispersity, reducibility, accessibility, and the stability of the architecture under the reaction conditions towards CuZn MSCAT unit of bifunctional catalyst through the tailoring of the nano-/micro-structure and the modification of MSCAT, as well as by improving the activity, inhibiting hydrocarbon formation, and suppressing the coke-deposition on the MDCAT unit of the bifunctional catalyst via the adjustment of the crystal size of HZSM-5 as well as the thickness and acidic properties of HZSM-5 zeolite shell encapsulated on the millimeter-level shaped CuZn embedded hollow mesoporous MSCAT particles. Furthermore, this proposed research is also devoted to reveal the inherent rule and mechanism for the significantly promoted catalytic performance, as well as the structure-performance relationship of the developed novel embedded-type hierarchical core-shell structured catalysts in direct production of DME from synthesis gas through comparing the change in catalyst nature of fresh and spent catalysts along with correlating to catalytic reaction data. The main objective for the proposed research is to provide some academic guidance for developing excellent bifunctional catalysts for direct production of DME from synthesis gas.

以煤基合成气为原料催化转化制化学品和清洁燃料是煤炭高效洁净利用的重要途径。二甲醚既是理想清洁燃料，又是重要化工原料，可由合成气经两步法或一步法制得。双功能催化剂催化一步直接制二甲醚，热力学和经济上优势明显，前景广阔。核壳双功能催化剂提供受限微环境，克服了常规双功能催化剂存在的部分甲醇未经脱水而直接离开床层的问题，但催化性能仍亟待提升。为此，拟研究合成气直接制二甲醚用新颖嵌入式分级核壳双功能催化剂的构筑与调控，通过对甲醇合成单元微结构调变和改性来提高铜锌分散度、可还原性、可及性、抗烧结性和反应条件下结构稳定性，并通过调节甲醇脱水单元分子筛壳层酸性、晶粒尺寸和厚度来提高脱水活性并抑制烃副产和积碳，以显著提升现有核壳双功能催化剂的催化性能。通过反应前后催化剂特征对比分析并结合反应数据，探究性能提升的本质规律及机制，并揭示构效关系。旨在为合成气直接制二甲醚用性能优良双功能催化剂的创制提供理论指导。

以煤基合成气为原料催化转化制化学品和清洁燃料是煤炭高效洁净利用的重要途径。二甲醚既是理想清洁燃料，又是重要化工原料，可由合成气经两步法或一步法制得。双功能催化剂催化一步直接制二甲醚，热力学和经济上优势明显，前景广阔。核壳双功能催化剂提供受限微环境，克服了常规双功能催化剂存在的部分甲醇未经脱水而直接离开床层的问题，但催化性能仍亟待提升。本项目针对现有核壳双功能催化剂的不足，开展了二甲醚直接合成用新型核壳双功能催化剂的制备、催化性能及构效关系研究。主要包括以下几个方面：1）针对现有包覆过程对CuZnAl核的破坏问题，开展了分子筛包覆新方法的探索，建立胶囊型CuZn@HZSM-5核壳双功能催化剂的制备新方法；2）针对胶囊型毫米尺寸CuZnAl@HZSM-5核壳双功能催化剂存在的过渡金属活性组分利用率低的问题，开展了新型植入式微纳CuZn@m-Al2O3核壳双功能催化剂的研究；3）为了进一步提高过渡金属利用率，开展了新型植入型MOF衍生多孔CuZn@Al2O3核壳双功能催化剂的研究。固体酸、纳微碳和负载型催化剂的制备和调控研究，为后续开展新型核壳双功能催化剂的研究奠定了坚实基础。此外，还开展了CO2加氢制甲醇用胶囊型核壳催化剂的研究，为后续核壳双功能催化剂上CO2及包含CO2的合成气的转化直接制二甲醚及其他化学品的研究提供参考。通过该研究，制备了系列性能优良的合成气直接制二甲醚用新型核壳双功能催化剂，催化活性和选择性得到了显著提高，并建立了制备此类催化剂的一些新方法。关联表征结果和反应性能，揭示了催化剂的构效关系，基本弄清了所制备的核壳双功能催化剂催化合成气直接制二甲醚反应具有优良催化性能的原因和机制，并发现了一些有价值的调控规律。铜基催化剂价格低、性能好，用于合成气的高值转化，具有广阔前景。本项目的研究成果，对合成气直接制二甲醚用性能优良双功能催化剂的创制，具有一定借鉴意义。