催化学报 ›› 2024, Vol. 67: 91-101.DOI: 10.1016/S1872-2067(24)60138-5

• 论文 • 上一篇    下一篇

用于间甲酚高效加氢脱氧制芳烃的负载型W2C纳米催化剂的活性位研究

杨艳玲a,b,c,1, 韩沛杰a,1, 张元宝a,1, 林敬东a, 万绍隆a, 王勇d, 刘海超e, 王帅a()   

  1. a固体表面物理化学国家重点实验室, 能源材料化学协同创新中心, 厦门大学化学化工学院, 福建厦门 361005, 中国
    b集美大学轮机工程学院, 福建厦门 361000, 中国
    c厦门市海洋腐蚀与智能防护材料重点实验室, 福建厦门 361000, 中国
    d华盛顿州立大学化学工程与生物工程学院, 华盛顿州, 美国
    e北京大学化学与分子工程学院, 北京分子科学国家研究中心, 北京 100871, 中国
  • 收稿日期:2024-06-27 接受日期:2024-09-09 出版日期:2024-12-18 发布日期:2024-11-30
  • 通讯作者: 王帅
  • 作者简介:

    1共同第一作者.

  • 基金资助:
    国家重点研发计划(2021YFA1501104);国家自然科学基金(21922201);国家自然科学基金(22202041);国家自然科学基金(21872113);中央高校基本科研基金(20720220008)

Site requirements of supported W2C nanocatalysts for efficient hydrodeoxygenation of m-cresol to aromatics

Yanling Yanga,b,c,1, Peijie Hana,1, Yuanbao Zhanga,1, Jingdong Lina, Shaolong Wana, Yong Wangd, Haichao Liue, Shuai Wanga()   

  1. aState Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian, China
    bCollege of Marine Engineering, Jimei University, Xiamen 361000, Fujian, China
    cKey Laboratory for Marine Corrosion and Intelligent Protection Materials of Xiamen, Jimei University, Xiamen 361000, Fujian, China
    dVoiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, United States
    eBeijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
  • Received:2024-06-27 Accepted:2024-09-09 Online:2024-12-18 Published:2024-11-30
  • Contact: Shuai Wang
  • About author:

    1Contributed equally to this work.

  • Supported by:
    National Key Research and Development Program of China(2021YFA1501104);National Natural Science Foundation of China(21922201);National Natural Science Foundation of China(22202041);National Natural Science Foundation of China(21872113);Fundamental Research Funds for the Central Universities(20720220008)

摘要:

生物质作为地球上最主要的可再生有机碳资源, 其高效转化制取液体燃料和化学品对推动“碳中和”具有重要意义. 木质素是仅次于纤维素的第二大类生物质组分, 含有丰富的含氧官能团和芳香环结构. 将木质素衍生物通过选择性加氢脱氧反应制取芳香族化合物为木质素资源的优化利用提供了一条极具潜力的途径. 加氢脱氧反应通常使用过渡金属为催化剂, 但该类催化剂在促进木质素衍生物中C-O键断裂的同时, 往往会造成芳香环的过度加氢, 导致反应选择性不理想. 近年研究表明, 金属碳化物催化剂兼具较好的促进C-O键氢解能力和抑制C=C键加氢能力. 但这些研究多以块体催化剂为主, 对催化剂的构-效关系尚缺乏深入认识, 严重阻碍了金属碳化物催化剂的合理设计与优化.

合成粒径均一且可调变的金属碳化物纳米粒子有利于深入考察金属碳化物催化剂在加氢脱氧反应中的构-效关系. 本文采用液相原子层沉积法在较宽的负载量范围(WO3: 1.0 wt%-50 wt%)内将WO3前驱体嫁接于SiO2载体表面. 紫外-可见光谱和高分辨透视电镜表征结果证实, 此合成方法可将WO3均匀分散在SiO2载体上. 以此为基础, 在优化条件下对WO3/SiO2前体进行碳化处理, 获得了相应W2C粒径均一且可在0.7-15 nm范围调控的W2C/SiO2催化剂. 以木质素衍生物间甲酚的加氢脱氧转化为模型反应, 不同W2C粒径的W2C/SiO2催化剂在350 °C下均表现出较好的甲苯选择性(>95%). 在其他氧化物载体上负载W2C催化剂(如TiO2, ZrO2等)或以其他木质素衍生物为加氢脱氧反应的底物(如苯甲醇、苯甲醚、愈创木酚等)同样可获得高C-O键氢解选择性, 体现了W2C在催化C-O键氢解反应中的优越性. 基于W2C单位质量考察催化活性, 粒径为~7 nm的W2C/SiO2催化剂上的加氢脱氧速率最高; 而将催化活性为归结至催化剂表面暴露的W位点时结果表明, 在0.7-15 nm粒径范围内, 随W2C粒径的逐渐增大, 催化剂表面W位点的本征活性呈单调上升变化. 高分辨率透射电镜结果则表明, 该粒径效应与负载在SiO2上的大粒径W2C表面易暴露高指数晶面相关. 结合催化动力学、多种探针分子的程序升温脱附实验及理论计算结果表明, W2C纳米颗粒在反应条件下被间甲酚或由其衍生得到的反应中间体所覆盖饱和, 且间甲酚加氢脱氧反应的速控步骤为H原子进攻C7H7*中间体生成甲苯, 而非间甲酚的C-O键断裂步骤. 此外, 以W2C(001)和W2C(102)表面模型来考察W2C催化剂的粒径效应. 理论计算表明, 相较于低指数晶面, 高指数晶面上所暴露出的高不饱和度位点能够更为有效地稳定反应中间体和过渡态, 进而带来更高的加氢脱氧活性.

综上, 本文通过系统考察负载型W2C催化剂的构-效关系, 揭示了W2C催化剂在木质素衍生物加氢脱氧反应中独特的粒径效应. 该独特性源于由W2C强亲氧性所诱导的催化活性位与氧化物载体之间的强相互作用, 可为进一步设计和构筑高性能金属碳化物基催化剂提供有益参考.

关键词: 木质素衍生物, 加氢脱氧, 碳化钨, 多相催化, 构-效关系, 尺寸效应, 动力学, 密度泛函理论计算

Abstract:

Selective hydrodeoxygenation of lignin derivatives into aromatic compounds is a promising route for the upgrading of lignin feedstocks. Metal carbide catalysts have exhibited excellent selectivity in hydrodeoxygenation reactions, while their structure-activity relationship is still in ambiguity. Herein, a liquid-phase atomic layer deposition method was employed to synthesize W2C/SiO2 catalysts with uniform and size-controllable W2C nanoparticles. For gas-phase hydrodeoxygenation of lignin-derived m-cresol at 350 °C, these W2C/SiO2 catalysts showed superior toluene selectivities (>95%) regardless of the W2C particle size. An optimal W2C particle size of ~7 nm was obtained for achieving the highest W2C-based hydrodeoxygenation rate. In contrast, the turnover rate per surface W site increased almost monotonously as the W2C particle size increased within 0.7‒15 nm, attributable to high-index planes appeared on the larger W2C nanoparticles. Kinetic effects of m-cresol and H2, taken together with temperature-programmed desorption of probe molecules and theoretical treatments, further indicate that the W2C surface is nearly saturated by adsorbed m-cresol or its derivates under the reaction condition and the H-addition of the C7H7* intermediate to form toluene, instead of the initial C-O cleavage in m-cresol, acts as the rate-determining step. A side-by-side comparison between W2C(102) and W2C(001) catalyst surfaces in theoretical simulations of m-cresol hydrodeoxygenation verifies that high-index planes can stabilize kinetically-relevant transition states more effectively than the low-index ones, as a result of more available less-coordinated active sites on the former. The above findings bring new mechanistic insights into the site requirements of supported W2C nanocatalysts, distinct from those metal-catalyzed hydrodeoxygenation of oxygenates.

Key words: Lignin derivative, Hydrodeoxygenation, Tungsten carbide, Heterogeneous catalysis, Structure-activity relationship, Size effect, Kinetics, Density functional theory calculation