Supported metal catalysts are of great importance in energy and environmental applications. Atmospheric-pressure (AP) cold plasma, generally generated by dielectric barrier discharge and cold plasma jet, has been proved to be a fast, facile, and energy efficient method for fabricating supported metal catalysts. In this review, the recent progress, challenges, and perspectives of AP cold plasma for synthesizing supported metal catalysts are discussed. Focus is placed on recent work demonstrating the discharge types of AP cold plasma, and the characteristics of the synthesized supported metal catalysts. The reduction mechanism of AP cold plasma is also discussed in light of several possible mechanisms that have been proposed in previous work. K E Y W O R D Satmospheric-pressure (AP) cold plasma, cold plasma jet, dielectric barrier discharge (DBD), hydrogen-containing species, supported metal catalysts Plasma Process Polym. 2018;15:e1700234.www.plasma-polymers.com

A high performance Pd/C catalyst (Pd/C-PC) was successfully prepared by simple incipient wetness impregnation followed by the process of dry plasma reduction and calcination. Oxygen-containing group surface-fuctionalized activated carbon was used to absorb the palladium precursor PdCl 4 2À , and small sized (1.92 AE 0.75 nm) Pd nanoparticles were formed in Pd/C-PC, which were smaller than those prepared by low pressure cold plasma (4.0-4.5 nm). The results of XRD, XPS, TPR and TEM showed that dry plasma with calcination could completely remove the residual Cl À ions and obtain predominantly metallic Pd nanoparticles without aggregation. The dry plasma prepared Pd/C-PC catalyst gave excellent catalytic activity for CO oxidation, and the TOF value for 5 wt% Pd/C-PC was about 6.1 times as that for 6 wt% Pd/graphene prepared by the conventional impregnation and hydrogen reduction method. The high performance was attributed to the smaller size and predominantly metallic Pd nanoparticles.

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Surface dielectric barrier discharge (DBD) was used for atmospheric-pressure plasma CVD of TiO2 films from TiCl4 and O2 for the first time. Under this experiment, the deposition rate was estimated at 22 nm min−1 by scanning electron microscope observation and the as-deposited TiO2 films were amorphous as evidenced by Raman analysis. The photocatalytic application of TiO2 films in removing HCHO from simulated air was examined in a continuous flow reactor. The TiO2 films after calcination at 350 or 450 °C were notably photocatalytically active for complete oxidation of formaldehyde to an innocuous product (CO2), which was consistent with the results of Raman analysis. Using the TiO2 films, an extremely harmful by-product, CO, was not detected from photocatalytic oxidation of HCHO in a simulated air stream.

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Catalytic materials play important roles in chemical, energy, and environmental fields. The exhaustion of fossil fuels and the resulting deteriorative environment have become worldwide problems to be solved urgently. Therefore, treatment of catalytic materials by a green process is required for a sustainable future, and the atom efficiency of the catalytic materials should be improved at the same time. Cold plasma is rich in high-energy electrons and active species, and the gas temperature can be close to room temperature. It has been proved to be a fast, facile, and environmentally friendly novel method for treating catalytic materials, and has aroused increasing research interests. First, plasma treatment can achieve the reduction, deposition, combination, and decomposition of active components during the preparation of catalytic materials. The fast, low-temperature plasma process with a strong electric field in it leads to different types of nucleation and crystal growth compared to conventional thermal methods. Correspondingly, the synthesized catalytic materials generally possess smaller particle sizes and controlled structure depending on the plasma processing parameters and the materials to be treated, which can enhance their activity and stability. Second, plasma treatment can achieve the modification, doping, etching, and exfoliation of the catalytic materials, which can tune the surface properties and electronic structures of the catalytic materials to expose more active sites. Third, plasma treatment can regenerate deactivated catalytic materials by removing the carbon deposits or other poisons, and reconstruction of the destroyed structure. This work reviews the current status of research on cold plasma treatment of catalytic materials. The focus is on physical and chemical processes during plasma processing, the processing mechanism of the catalytic materials, as well as the future challenges in this filed.