Enhancement of methanation of carbon dioxide using dielectric barrier discharge on a ruthenium catalyst at atmospheric conditions

Unraveling Temperature-Dependent Plasma-Catalyzed CO2 Hydrogenation

Hydrogenation of carbon dioxide to value-added chemicals and fuels has recently gained increasing attention as a promising route for utilizing carbon dioxide to achieve a sustainable society. In this study, we investigated the hydrogenation of CO2 over M/SiO2 and M/Al2O3 (M = Co, Ni) catalysts in a dielectric barrier discharge system at different temperatures. We compared three different reaction modes: plasma alone, thermal catalysis, and plasma catalysis. The coupling of catalysts with plasma demonstrated synergy at different reaction temperatures, surpassing the thermal catalysis and plasma alone modes. The highest CO2 conversions under plasma-catalytic conditions at reaction temperatures of 350 and 500 °C were achieved with a Co/SiO2 catalyst (66%) and a Ni/Al2O3 catalyst (68%), respectively. Extensive characterizations were used to analyze the physiochemical characteristics of the catalysts. The results show that plasma power was more efficient than heating power at the same temperature for the CO2 hydrogenation. This demonstrates that the performance of CO2 hydrogenation can be significantly improved in the presence of plasma at lower temperatures.

Dielectric Barrier Discharge Plasma-Assisted Catalytic CO2 Hydrogenation: Synergy of Catalyst and Plasma

CO2 hydrogenation is an effective way to convert CO2 to value-added chemicals (e.g., CH4 and CH3OH). As a thermal catalytic process, it suffers from dissatisfactory catalytic performances (low conversion/selectivity and poor stability) and high energy input. By utilizing the dielectric barrier discharge (DBD) technology, the catalyst and plasma could generate a synergy, activating the whole process in a mild condition, and enhancing the conversion efficiency of CO2 and selectivity of targeted product. In this review, a comprehensive summary of the applications of DBD plasma in catalytic CO2 hydrogenation is provided in detail. Moreover, the state-of-the-art design of the reactor and optimization of reaction parameters are discussed. Furthermore, several mechanisms based on simulations and experiments are provided. In the end, the existing challenges of this hybrid system and corresponding solutions are proposed.

Experimental Study on CO2 Methanation over Ni/Al2O3, Ru/Al2O3, and Ru-Ni/Al2O3 Catalysts

CO2 methanation is recognized as one of the best technologies for storing intermittent renewable energy in the form of CH4. In this study, CO2 methanation performance is investigated using Ni/Al2O3, Ru/Al2O3, and Ru-Ni/Al2O3 as the catalysts under conditions of atmospheric pressure, a molar ratio of H2/CO2 = 5, and a space velocity of 5835 h−1. For reaction temperatures ranging from 250 to 550 °C, it was found that the optimum reaction temperature is 400 °C for all catalysts studied. At this temperature, the maximum values of CO2 conversion, H2 efficiency, and CH4 yield and lowest CO yield can be obtained. With temperatures higher than 400 °C, reverse CO2 methanation results in CO2 conversion and CH4 yield decreases with increased temperature, while CO is formed due to reverse water-gas shift reaction. The experimental results showed that CO2 methanation performance at low temperatures can be enhanced greatly using the bimetallic Ru-Ni catalyst compared with the monometallic Ru or Ni catalyst. Under ascending-descending temperature changes between 250 °C and 550 °C, good thermal stability is obtained from Ru-Ni/Al2O3 catalyst. About a 3% decrease in CO2 conversion is found after three continuous cycles (74 h) test.

A Facile Method for Preparing UiO-66 Encapsulated Ru Catalyst and its Application in Plasma-Assisted CO2 Methanation

With increasing applications of metal-organic frameworks (MOFs) in the field of gas separation and catalysis, the preparation and performance research of encapsulating metal nanoparticles (NPs) into MOFs (M@MOF) have attracted extensive attention recently. Herein, an Ru@UiO-66 catalyst is prepared by a one-step method. Ru NPs are encapsulated in situ in the UiO-66 skeleton structure during the synthesis of UiO-66 metal-organic framework via a solvothermal method, and its catalytic activity for CO₂ methanation with the synergy of cold plasma is studied. The crystallinity and structural integrity of UiO-66 is maintained after encapsulating Ru NPs according to the X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). As illustrated by X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), and mapping analysis, the Ru species of the hydration ruthenium trichloride precursor are reduced to metallic Ru NPs without additional reducing processes during the synthesis of Ru@UiO-66, and the Ru NPs are uniformly distributed inside the Ru@UiO-66. Thermogravimetric analysis (TGA) and N₂ sorption analysis show that the specific surface area and thermal stability of Ru@UiO-66 decrease slightly compared with that of UiO-66 and was ascribed to the encapsulation of Ru NPs in the UiO-66 skeleton. The results of plasma-assisted catalytic CO₂ methanation indicate that Ru@UiO-66 exhibits excellent catalytic activity. CO₂ conversion and CH₄ selectivity over Ru@UiO-66 reached 72.2% and 95.4% under 13.0 W of discharge power and a 30 mL·min^-1 gas flow rate ( V H 2 : V C O 2 = 4 : 1 ), respectively. Both values are significantly higher than pure UiO-66 with plasma and Ru/Al₂O₃ with plasma. The enhanced performance of Ru@UiO-66 is attributed to its unique framework structure and excellent dispersion of Ru NPs.

A Review of Recent Advances of Dielectric Barrier Discharge Plasma in Catalysis

Dielectric barrier discharge plasma is one of the most popular methods to generate nanthermal plasma, which is made up of a host of high-energy electrons, free radicals, chemically active ions and excited species, so it has the property of being prone to chemical reactions. Due to these unique advantages, the plasma technology has been widely used in the catalytic fields. Compared with the conventional method, the heterogeneous catalyst prepared by plasma technology has good dispersion and smaller particle size, and its catalytic activity, selectivity and stability are significantly improved. In addition, the interaction between plasma and catalyst can achieve synergistic effects, so the catalytic effect is further improved. The review mainly introduces the characteristics of dielectric barrier discharge plasma, development trend and its recent advances in catalysis; then, we sum up the advantages of using plasma technology to prepare catalysts. At the same time, the synergistic effect of plasma technology combined with catalyst on methanation, CH₄ reforming, NO_x decomposition, H₂O₂ synthesis, Fischer–Tropsch synthesis, volatile organic compounds removal, catalytic sterilization, wastewater treatment and degradation of pesticide residues are discussed. Finally, the properties of plasma in catalytic reaction are summarized, and the application prospect of plasma in the future catalytic field is prospected.