催化学报 ›› 2024, Vol. 63: 133-143.DOI: 10.1016/S1872-2067(24)60083-5

• 论文 • 上一篇    下一篇

调控含钛材料中钛位点的微环境与金位点协同促进丙烯环氧化

施树栋,1, 张志华,1, 井运道, 杜威, 段学志*(), 周兴贵*()   

  1. 华东理工大学化工学院, 化学工程国家重点实验室, 上海 200237
  • 收稿日期:2024-04-05 接受日期:2024-06-18 出版日期:2024-08-18 发布日期:2024-08-19
  • 通讯作者: *电子信箱: xzduan@ecust.edu.cn (段学志),xgzhou@ecust.edu.cn (周兴贵).
  • 作者简介:

    1共同第一作者.

  • 基金资助:
    国家重点基础研究发展计划(2021YFA1501403);国家自然科学基金(22038003);国家自然科学基金(21922803);国家自然科学基金(22178100);国家自然科学基金(22208093);上海市优秀学术/技术研究带头人计划(21XD1421000);上海市科技创新行动计划(22JC1403800)

Tailoring the microenvironment of Ti sites in Ti-containing materials for synergizing with Au sites to boost propylene epoxidation

Shudong Shi,1, Zhihua Zhang,1, Yundao Jing, Wei Du, Xuezhi Duan*(), Xinggui Zhou*()   

  1. State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China
  • Received:2024-04-05 Accepted:2024-06-18 Online:2024-08-18 Published:2024-08-19
  • Contact: *E-mail: xzduan@ecust.edu.cn (X. Duan), xgzhou@ecust.edu.cn (X. Zhou).
  • About author:

    1Contributed equally to this work.

  • Supported by:
    Ministry of Science and Technology of the People’s Republic of China under the Research Fund for National Key R&D Program of China(2021YFA1501403);Natural Science Foundation of China(22038003);Natural Science Foundation of China(21922803);Natural Science Foundation of China(22178100);Natural Science Foundation of China(22208093);Program of Shanghai Academic/Technology Research Leader(21XD1421000);Shanghai Science and Technology Innovation Action Plan(22JC1403800)

摘要:

环氧丙烷(PO)作为丙烯的重要下游产品, 广泛用于丙二醇、聚醚多元醇、丙二醇醚等高附加值化工产品的合成. 其中, 70%以上的PO被用于合成聚醚多元醇, 而这些聚醚多元醇又是蓬勃发展的聚氨酯工业的重要原料. 与传统的氯醇法和共氧化法相比, 丙烯在氢气和氧气氛围下直接气相环氧化反应生成PO(HOPO)的工艺因其环保和经济性优势, 成为学术界与工业界关注的焦点. 目前, 高度分散的金纳米颗粒协同含有孤立四配位钛位点的钛材料(Au/Ti)被视为该反应最具潜力的催化剂, 这主要是因为其独特的反应机理: 在金位点上形成的过氧化氢(HOOH)物种与附近孤立的Ti4+位点作用, 生成Ti-OOH中间物种, 进而环氧化丙烯生成PO. 因此, 构筑和调控钛位点的微环境, 建立其与丙烯及PO吸脱附的构效关系, 对于高效利用金位点上的HOOH物种是一个重要且充满挑战的研究方向.

本文深入探讨了具有不同钛配位状态(包括TiVI, TiVI+IV和TiIV)的含钛材料, 通过统一的热处理策略调控钛位点的微环境, 并与金位点协同作用, 显著提升了HOPO过程中的PO选择性和氢气利用效率. 以含TiVI材料为例, 详细分析了钛位点的理化性质、PO进一步转化的潜能及其与HOPO催化性能之间的内在联系. X射线衍射(XRD)和拉曼光谱(Raman)分析显示, 含TiVI样品在经过热处理后, TiVI-L(500 °C)和TiVI-M(800 °C)仍然保持锐钛矿晶相, 而TiVI-H(1000 °C)则完全转变为金红石结构, 高分辨率透射电镜观察进一步证实了这一结构转变. 此外, 氨气程序升温脱附(NH3-TPD)与吡啶红外光谱(Py-IR)测试结果表明, 随着热处理温度的升高,含TiVI样品表面的酸性位点减少, 这与表面羟基数量的减少趋势相吻合. 傅里叶变换红外(FTIR) 进一步证实, 相较于TiVI-L和TiVI-M, TiVI-H含有更少的表面羟基. 原位漫反射红外光谱(In-situ DRIFTS)实验揭示了表面羟基数量对PO吸附和转化行为的影响: TiVI-H样品因表面羟基和酸性位点较少, 抑制了目标产物PO的吸附和后续转化; 而TiVI-L上则发生PO的强吸附, 并促进了其进一步转化为双齿基含碳物种. PO转化实验结果显示, TiVI-L样品具有高PO转化率(转化为丙醛和丙酮), 约为66%, 分别是TiVI-M和TiVI-H样品的11倍(6%)和13倍(5%). 此外, 动力学分析结果表明, TiVI-M相较于TiVI-L具有更高的PO转化活化能, 同样证实其更弱的PO转化能力; 而TiVI-H具有更低的活化能, 但其PO转化率却最低, 这可能是由于其表面PO吸附转化的活性位点发生了改变. 综合分析含TiVI样品的理化性质和PO吸附转化能力, 结果表明, 高温热处理后的TiVI-H样品相比于TiVI-L和TiVI-M含有更少的表面羟基和酸性位, 因此有效提升了PO的脱附能力. 正因为PO在TiVI-H样品上的吸附和转化被抑制, 所以相比TiVI-L, TiVI-H在协同金位点用于HOPO反应中表现出更好的催化性能, PO选择性和氢效分别提高了7倍和4倍. 正如预期, 含TiVI+IV和TiIV的材料在经过相同的热处理调控后,也表现出与TiVI样品一致的构效关系.

综上所述, 本文对含有不同钛配位的材料通过热处理的方式改变了钛位点周围的微环境. 结果表明, 含有较少表面羟基的钛材料和金位点共同用于HOPO过程时, 获得了更高的PO选择性和氢气利用效率, 实现了更高效的金钛协同作用. 此外, 本文进一步阐明了钛位点的微环境对PO转化的作用机制, 为后续含钛材料的设计和优化提供了参考.

关键词: 丙烯环氧化, 微环境, 含钛材料, 金-钛协同, 表面羟基

Abstract:

Au sites supported on Ti-containing materials (Au/Ti-containing catalyst) are currently considered as a promising catalyst for the propylene epoxidation owing to the synergistic effect that hydrogen peroxide species formed on Au sites diffuses to the Ti sites to form the Ti-hydroperoxo intermediates and contributes to the formation of propylene oxide (PO). In principle, thermal treatment will significantly affect the chemical and physical structures of Ti-containing materials. Consequently, the synergy between tailored Ti sites with different surface properties and Au sites is highly expected to enhance the catalytic performance for the reaction. Herein, we systematically studied the intrinsic effects of different microenvironments around Ti sites on the PO adsorption/desorption and conversion, and then effectively improved the catalytic performance by tailoring the number of surface hydroxyl groups. The TiVI material with fewer hydroxyls stimulates a remarkable enhancement in PO selectivity and H2 efficiency compared to the TiVI material that possessed more hydroxyls, offering a 7-fold and 4-fold increase, respectively. As expected, the TiVI+IV and TiIV materials also exhibit a similar phenomenon to the TiVI materials through the same thermal treatment, which strongly supports that the Ti sites microenvironment is an important factor in suppressing PO conversion and enhancing catalytic performance. These insights could provide guidance for the rational preparation and optimization of Ti-containing materials synergizing with Au catalysts for propylene epoxidation.

Key words: Propylene epoxidation, Microenvironment, Ti-containing material, Au-Ti synergy, Hydroxyl group