在Pd催化剂上的CH4反应中,金属氧化物相互转换对C-H键激活的后果
Ya-Huei Cathy Chin1, Corneliu Buda, Matthew Neurock
1Department of Chemical and Biomolecular Engineering, University of California , Berkeley, California 94720, United States.
Journal of the American Chemical Society
|October 3, 2013
概括
这项研究揭示了 (Pd) 表面的甲 (CH4) C-H 键激活如何随氧含量而变化. 增加氧气将反应途径从氧化添加转移到H-抽象和σ-键转化,增强CH4的氧化率.
科学领域:
- 表面科学和催化剂的研究
- 计算化学计算化学
- 材料科学 材料科学 材料科学
背景情况:
- 甲 (CH4) C-H 键激活对其利用和氧化至关重要.
- (Pd) 催化剂在C-H激活方面受到广泛研究,但反应机制各不相同.
- 氧 (O) 在Pd表面对调节C-H激活通路的作用尚未完全理解.
研究的目的:
- 阐明CH4C-H键激活在赤裸的Pd集群,O*覆盖的Pd表面和PdO集群上的多种机制性途径.
- 为了研究活跃部位的演变与增加的氧含量如何影响C-H键裂解机制.
- 为了将机械学见解与CH4氧化周转率的观察变化相关联.
主要方法:
- 结合的动力和同位素实验方法.
- 密度函数理论 (DFT) 计算用于机械评估.
- 对过渡状态和沿反应坐标的电荷分布进行分析.
主要成果:
- C-H激活途径从氧化添加 (赤裸Pd) 转移到H抽象 (O*-Pd) 到σ-键转化 (PdO).
- 活性位点从Pd-Pd对演变为O*-O*对,再演变为Pd阴离子氧对 (Pd(2+) -O(2-)).
- 在赤裸的和O*覆盖的表面上,均质C-H裂变占主导地位,而在PdO上,异质裂变通过σ-键转化发生.
- PdO表面表现出明显更稳定的过渡状态,导致CH4氧化率增加.
结论:
- Pd活性位点的氧含量和化学状态决定了C-H键激活机制.
- 在Pd表面观察到的机制类似于同质有机金属复合体中的机制.
- 了解这些途径为设计有效的甲氧化催化剂提供了洞察力.
相关概念视频
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