From hydrogen sulfide waste to sustainable hydrogen and sulfur
In a collaborative project of the University of Amsterdam's Van 't Hoff Institute for Molecular Sciences (HIMS) with the State Key Laboratory of Fine Chemicals in Dalian (China), researchers have succeeded in the sustainable conversion of hydrogen sulfide. Using a light-driven process they are able to convert this chemical waste product into molecular hydrogen and solid sulfur. Their results have been published as a VIP paper in Angewandte Chemie.
To facilitate the transition to a society based on sustainable energy, scientists are searching for technologies to convert solar energy into fuels. These so-called solar fuels are important, amongst others, to help overcome the fluctuations in production and demand of alternative energy. In particular the direct solar-driven conversion of water to hydrogen and oxygen gets a lot of attention.
Although hydrogen sulfide - with the chemical formula H2S - is chemically related to water, it has hardly been studied in the context of solar fuels. Hydrogen sulfide is currently a waste product in the mining of oil and gas, and has little economic value. The light-driven conversion to moleculer hydrogen and solid sulfur as valuable products therefore is interesting both from a sustainability and an economic point of view.
Since 2016 HIMS professor Joost Reek, who also heads the university's research priority area Sustainable Chemistry, has been working with the State Key Laboratory of Fine Chemicals in Dalian (China) on the conversion of hydrogen sulfide. The VIP paper now published in Angewandte Chemie is the first tangible result of this cooperation, which takes place in the context of a '111 project' funded by the Chinese government. These 111 projects are aimed at strengthening the country's knowledge position.
The researchers have developed a supramolecular cage capable of binding organic dyes that absorb (sun) light. Adding to this, the vertices of their cage consist of nickel complexes that are catalytically active in proton reduction catalysis to efficiently form hydrogen.
The system, inspired by the reactive cavity of enzymes, thus combines in one and the same process the photocatalytic formation of hydrogen with the oxidation of sulfur. The pre-organization of the dye and the catalyst in the molecular cage proves to be crucial, as it ensures efficient light-driven hydrogen formation on the reductive side but is also important for the selective oxidation of sulfide to yield solid sulfur rather than polysulfide.
Detailed experiments show that the pre-organization in the cage affects the light-driven process. Instead of direct reaction with the sulfide present in solution, the light-activated dye reacts with the nickel. The oxidized dye then reacts with the sulfide to form solid sulfur. In addition, the cage ensures a great stability of the overall conversion system. The researchers have already proposed how to use their system in an industrial process.
Jing, X., Yang, Y., He, C., Chang, Z., Reek, J. N. H. and Duan, C. (2017), Control of Redox Events by Dye Encapsulation Applied to Light-Driven Splitting of Hydrogen Sulfide. Angew. Chem. Int. Ed.. DOI:10.1002/anie.201704327