Hydrocarbon-Based Fuel from Carbon Dioxide

Changing carbon dioxide (CO₂) into hydrocarbon-based fuels such as methane using light would be one step towards CO₂ neutrality and the alleviation of the greenhouse effect and energy crisis.

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A highly effective photocatalyst, presented by a Chinese research team, is based on gold atoms to render this transformation viable. Details of the research can be found in the journal Angewandte Chemie.

The photocatalytic conversion of CO₂ takes place through a sequence of processes wherein electrons are shifted. This can bring about different products, including carbon monoxide (CO), methane (CH₄), methanol (CH₃OH), and other hydrocarbons.

Eight electrons must be shifted from CO₂ to CH₄ — beyond other C1 products. Methane is the thermodynamically advantageous end product; however, the competing reaction to produce CO needs two electrons and is much faster, so it is kinetically supported. Effective and selective methanization is, therefore, particularly difficult.

Recently, a team headed by Hefeng Cheng (Shandong University, Jinan, China) and co-workers formulated a practical method to turn CO₂ into CH₄ using solar energy successfully, involving a unique catalyst with single gold atoms. Since gold atoms aggregate in traditional preparative approaches, the researchers formulated a new approach that uses a multifaceted exchange to create the catalyst.

Owing to their exclusive electronic structures, single-atom catalysts behave differently from traditional metal nanoparticles. Moreover, almost all single atoms are accessible as active catalytic centers when adhered to ideal support.

In the case of the new catalyst, single gold atoms are adhered to an ultrathin zinc–indium sulfide nanolayer and are each matched to only two sulfur atoms. The catalyst was shown to be highly active when exposed to sunlight, with a CH₄ selectivity of 77%.

A photosensitizer (a ruthenium complex) captures light, becomes stimulated, and accepts an electron that is provided by an electron donor (triethanolamine). Next, it moves the electron onto the catalyst. The solo gold atoms on the support's surface serve as “electron pumps.” They trap the electrons considerably more efficiently than gold nanoparticles and shift them to CO₂ molecules and intermediates.

In-depth characterization and computations show that the catalyst triggers the CO₂ molecules to a greater level than gold nanoparticles, more strongly captures the stimulated *CO intermediates, reduces the energy barrier for binding hydrogen ions, and steadies the *CH₃ intermediate. This enables CH₄ to be the preferred product and reduces the emission of CO.

Journal Reference

Si, S., et al. (2022) Low-Coordination Single Au Atoms on Ultrathin ZnIn2S4 Nanosheets for Selective Photocatalytic CO₂ Reduction towards CH₄. Angewandte Chemie. doi.org/10.1002/anie.202209446.