Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN 37831, USA.
ChemSusChem. 2013 May;6(5):840-6. doi: 10.1002/cssc.201200756. Epub 2013 Mar 7.
Nanostructured graphitic forms of carbons have shown intersting potential for catalysis research and are ideal candidates to substitute the conventional metal-oxide catalysts because they can be easily disposed, which enables a greener, more sustainable catalytic process. Few-layer graphene and its functionalized form offer the opportunity to investigate the nature of graphitic active sites for oxidation reactions in well-defined carbon-based catalysts. In this paper, we report the utilization of oxygen-functionalized few-layer graphene sheets containing variable amounts of oxygen in the heterogeneous catalytic oxidative dehydrogenation (ODH) reaction of isobutane at 400ºC. Interestingly, there is poor correlation between oxygen content and catalytic performance. Carbonyl groups were found to be highly stable, and graphene that had higher sp(2) character, the lowest oxygen content, and fewer edge sites presented the lowest specific rate of isobutane reaction, although the isobutene selectivity remained high. The reoxidation of the graphene surface occurred at the same rate as the ODH reaction suggesting a Mars-van Krevelen type of mechanism, similar to that which takes place on oxide surfaces. These results appear to suggest that a higher fraction of exposed edges where oxygen active sites can be formed and exchanged should lead to more active catalysts for ODH reactions.
纳米结构石墨形式的碳在催化研究中显示出了有趣的潜力，并且是替代传统金属氧化物催化剂的理想候选物，因为它们可以很容易地处理，这使得催化过程更加环保和可持续。少层石墨烯及其官能化形式为研究氧化反应中石墨活性位的性质提供了机会，这种研究可以在基于碳的明确催化剂中进行。在本文中，我们报告了在 400°C 下利用含有不同氧含量的含氧少层石墨烯片在异丁烷的非均相催化氧化脱氢（ODH）反应中的应用。有趣的是，氧含量和催化性能之间几乎没有相关性。研究发现，羰基基团非常稳定，而具有更高 sp(2)特征、最低氧含量和更少边缘位的石墨烯表现出最低的异丁烷反应比速率，尽管异丁烯选择性仍然很高。石墨烯表面的再氧化与 ODH 反应的速率相同，这表明存在类似于氧化物表面发生的 Mars-van Krevelen 型机制。这些结果似乎表明，形成和交换氧活性位的更多暴露边缘应该会导致 ODH 反应中更活跃的催化剂。
