催化学报 ›› 2025, Vol. 74: 365-376.DOI: 10.1016/S1872-2067(25)64726-7

• 论文 • 上一篇    下一篇

碳化钼催化氨分解制氢: Mo/C比调控与相变动力学机制研究

孙博文a,1, 穆思允a,1, 陈冰冰a,*(), 胡国骏a, 高瑞b,*(), 石川a,*()   

  1. a大连理工大学化学学院, 精细化工国家重点实验室, 辽宁大连 116024
    b内蒙古大学化学化工学院, 内蒙古呼和浩特 010021
  • 收稿日期:2024-12-31 接受日期:2025-04-17 出版日期:2025-07-18 发布日期:2025-07-20
  • 通讯作者: *电子信箱: chuanshi@dlut.edu.cn (石川),gaorui@imu.edu.cn (高瑞),chenbb@dlut.edu.cn (陈冰冰).
  • 作者简介:1共同第一作者.
  • 基金资助:
    国家重点研发计划(2021YFA1501102);国家自然科学基金(21932002);国家自然科学基金(22276023);国家自然科学基金(22402019);国家自然科学基金(22172083);前沿科学中心基金(DUT22LAB602);辽宁滨海实验室资助项目(LBLF-2023-06)

Hydrogen production via ammonia decomposition on molybdenum carbide catalysts: Exploring the Mo/C ratio and phase transition dynamics

Bowen Suna,1, Siyun Mua,1, Bingbing Chena,*(), Guojun Hua, Rui Gaob,*(), Chuan Shia,*()   

  1. aState Key Laboratory of Fine Chemicals, School of Chemistry, Dalian University of Technology, Dalian 116024, Liaoning, China
    bCollege of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot 010021, Inner Mongolia, China
  • Received:2024-12-31 Accepted:2025-04-17 Online:2025-07-18 Published:2025-07-20
  • Contact: *E-mail: chuanshi@dlut.edu.cn (C. Shi), gaorui@imu.edu.cn (R. Gao), chenbb@dlut.edu.cn (B. Chen).
  • About author:1Contributed equally to this work.
  • Supported by:
    National Key R & D Program of China(2021YFA1501102);National Natural Science Foundation of China(21932002);National Natural Science Foundation of China(22276023);National Natural Science Foundation of China(22402019);National Natural Science Foundation of China(22172083);Fundamental Research Funds for the Central Universities(DUT22LAB602);Liaoning Binhai Laboratory Project(LBLF-2023-06)

摘要:

氨(NH3)作为无碳氢能载体, 具有储氢密度高(17.8 wt%), 能量密度大(3000 Wh/kg), 及制造和运输技术成熟等优势. 通过氨分解制氢(ADR)是分布式氢能供应的重要途径. 然而, 该技术面临非贵金属催化剂活性不足与结构失稳的挑战. 尽管氮化钼(Mo2N, MoN)在ADR中研究广泛, 但同属间隙化合物的碳化钼(α-MoC, β-Mo2C)的催化行为与构效关系尚不明确.

碳化钼的独特性质在于其多相结构, 不同晶相的催化行为有明显差异. 在涉及氨的反应中, 碳化钼的动态结构变化对反应机理和反应效率至关重要. 本文聚焦于碳化钼(α-MoC和β-Mo2C)催化剂在氨分解反应中的应用, 系统探究了不同Mo/C比例对催化性能及结构演变的影响. 实验通过程序升温碳化法制备了立方相α-MoC和六方相β-Mo2C, X射线光电子能谱结果表明, 二者表面Mo/C比例存在显著差异(β-Mo2C的Mo/C为1.48, α-MoC为0.73). 催化性能测试表明, 具有高Mo/C比的β-Mo2C在450 °C下的周转频率为1.3 s-1, 是α-MoC(0.1 s-1)的十余倍, 且表观活化能更低(89.8 vs. 107.4 kJ/mol). 此外, 在600 °C的ADR稳定性评价中, α-MoC略微下降后维持稳定. β-Mo2C在15 h内很快失活22.3%, 但在随后100 h的测试过程中实现了稳定的氨转化. 随后的表征结果表明, α-MoC和β-Mo2C都发生了拓扑相变, 其中α-MoC相变为Mo2N, β-Mo2C相变为MoN. 进一步研究表明, 表面Mo/C比例的提升直接促进了氢气产率, 其机制源于β-Mo2C更优的氮物种结合能力. 通过氨气脉冲和程序升温氮气脱附表面反应结合密度泛函理论计算证实, 氮物种的结合步骤为ADR的速率控制步骤, β-Mo2C通过降低该步骤能垒(1.68 vs. 2.33 eV)显著加速N2脱附. 此外, 碳化钼向氮化钼的相变是由于氮物种无法脱附而在催化剂表面累积, 进而向体相迁移的结果, 高温反应(810 °C)下, N物种缔合脱附速率加快, β-Mo2C可维持碳化物相, 避免因氮渗透导致相变, 而α-MoC在H2/NH3气氛中易发生结构崩塌.

综上所述, 本研究阐明了碳化钼(α-MoC和β-Mo2C)表面组成与相变动力学的内在关联, 通过调控Mo/C比例及优化反应温度, 实现了β-Mo2C兼具高活性与抗相变的能力, 为设计高效稳定的氨分解催化剂提供了新思路.

关键词: 碳化钼, 相变, 氮化, 重组, 氨分解反应

Abstract:

The deployment of non-precious metal catalysts for the production of COx-free hydrogen via the ammonia decomposition reaction (ADR) presents a promising yet great challenge. In the present study, two crystal structures of α-MoC and β-Mo2C catalysts with different Mo/C ratios were synthesized, and their ammonia decomposition performance as well as structural evolution in ADR was investigated. The β-Mo2C catalyst, characterized by a higher Mo/C ratio, demonstrated a remarkable turnover frequency of 1.3 s-1, which is over tenfold higher than that of α-MoC (0.1 s-1). An increase in the Mo/C ratio of molybdenum carbide revealed a direct correlation between the surface Mo/C ratio and the hydrogen yield. The transient response surface reaction indicated that the combination of N* and N* derived from NH3 dissociation represents the rate-determining step in the ADR, and β-Mo2C exhibited exceptional proficiency in facilitating this pivotal step. Concurrently, the accumulation of N* species on the carbide surface could induce the phase transition of molybdenum carbide to nitride, which follows a topological transformation. It is discovered that such phase evolution was affected by the Mo-C surface and reaction temperature simultaneously. When the kinetics of combination of N* was accelerated by rising temperatures and its accumulation on the carbide surface was mitigated, β-Mo2C maintained its carbide phase, preventing nitridation during the ADR at 810 °C. Our results contribute to an in-depth understanding of the molybdenum carbides’ catalytic properties in ADR and highlight the nature of the carbide-nitride phase transition in the reaction.

Key words: Molybdenum carbides, Phase transition, Nitridation, Recombination, Ammonia decomposition reaction