Researchers Discover That Fullerenes Support Hydrogenation Without Noble Metal Catalysts Under Mild Conditions

2 November 2009

Fullerenes can drive hydrogenation under mild conditions. Credit: ACS, Li and Xu. Click to enlarge.

Researchers at Nanjing University in China have shown that fullerenes (cage-like, all-carbon nanostructures) can function effectively as novel non-metal hydrogenation catalysts. Catalytic hydrogenation—used to refine crude oil, synthesize ammonia, and now in multiple processes to produce bio-hydrocarbon fuels from renewable fats and oils—conventionally relies on transition-metal catalysts.

Current catalysts and processes typically require high temperatures and pressures. The ability to replace these catalysts with carbon-based substitutes operating under milder conditions could reduce process costs—as well we environmental effects from metal pollution.

In a paper published online 21 October in the Journal of the American Chemical Society, Baojun Li and Zheng Xu showed the hydrogenation of aromatic nitro compounds to amino aromatics with high conversion and selectivity under 1 atmospheric pressure of H₂ and light irradiation at room temperature, or under conditions of 120-160 °C and 4-5 MPa H₂ pressure without light irradiation.

The catalytic performance is comparable with that of the noble metal catalyst. Also, it exclusively catalyzes the reduction of a nitro group without the need to add metal salts and avoids the accumulation of the corresponding hydroxylamine and the formation of azoxy and azo compounds and is a highly selective and environmentally friendly catalyst.

These findings foreshadow a new catalytic system available for applications both in academic laboratories and in industry, allowing stoichiometric reductions mediated by Fe or Na₂S to be performed in a catalytic fashion and greatly reducing subsequent waste production. Moreover, the catalyst developed here could replace expensive precious metal catalysts, therefore offering the potential benefit of lowering cost and diminishing the environmental impact from heavy-metal pollutants.

—Li and Xu

Li and Xu said that the exact reaction mechanism is not yet clearly understood; more study is underway. They said that they anticipated the discovery would be a starting point for more effective all carbon molecular-based nonmetal catalyst systems for molecular hydrogen activation and will promote the development of electronically excited state reactions and novel molecular H₂ activation and storage systems.

Resources

• Baojun Li and Zheng Xu (2009) A Nonmetal Catalyst for Molecular Hydrogen Activation with Comparable Catalytic Hydrogenation Capability to Noble Metal Catalyst. J. Am. Chem. Soc., Article ASAP doi: 10.1021/ja9061097