Water gas shift reaction is an important process for producing high-purity hydrogen from fossil fuels in industry, but it still faces problems such as high reaction temperature, high energy consumption and separation. Electrochemical water gas shift combines the electro-oxidation of carbon monoxide with hydrogen evolution reaction, and achieves the goal of room temperature reaction for the first time. However, the use of more precious metals and alkaline electrolytes increases the reaction cost. Therefore, some researchers have proposed the coupling electrothermal co-catalysis process of palladium single-atom catalyst. The oxidation of carbon monoxide is realized by room temperature thermochemical process, and H2 is generated by proton reduction. The water-gas shift reaction under room temperature acidic electrolyte with low noble metal consumption is realized to obtain high-purity hydrogen.
Through coprecipitation, the researcher synthesized palladium single-atom catalyst based on silicomolybdate (Pd1/CsSMA) in one step, and determined the structure of the catalyst and the form of elements by means of high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, nitric oxide diffuse reflection Fourier transform infrared spectroscopy, synchrotron radiation X-ray absorption spectroscopy, and proved that the palladium single-atom catalyst was successfully synthesized.
According to the basis of the previous work and the experimental results of the kettle reactor, the researchers verified that Pd1/CsSMA has a good oxidation ability of carbon monoxide at room temperature. The redox medium phosphomolybdic acid is used to store the electrons/protons from carbon monoxide. At the same time, the researchers established the reaction kinetics equations of thermochemical carbon monoxide oxidation and electrochemical phosphomolybdic acid regeneration, and determined the effect of reduction degree on the reaction rate in the reaction process.
Subsequently, the researcher continuously operated the electrothermal co-catalytic water-gas shift system. The reaction results showed that the production rate of hydrogen and carbon dioxide was highly correlated, in line with the stoichiometric ratio of the total water-gas shift reaction, and the reaction rate was related to the concentration of oxidation-reduction medium. The researchers further clarified the relationship between the concentration of oxidation-reduction medium and its reduction degree in continuous reaction by means of stepwise research, and understood the effect of reduction degree on the rate of thermal and electro-catalytic reaction. The turnover frequency (TOF) of the catalyst is 1.2 s-1, and the purity of hydrogen produced is more than 99.99%.
The researchers synthesized palladium single-atom catalyst based on silicomolybdate in one step, which has excellent oxidation activity for carbon monoxide at room temperature. The redox medium can store/release the electrons/protons in the reaction process reversibly. Electrothermal co-catalysis provides a new way to realize chemical process. The process has the advantages of good controllability, mild operability and simplified product separation.
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Reference
- Electrothermal Water–Gas Shift Reaction at Room Temperature with a Silicomolybdate based Pd Single-Atom Catalyst
Jinquan Chang, Max J. Hülsey, Sikai Wang, Maoshuai Li, Xinbin Ma, Ning Yan
