Methanation of carbon oxides on Ni/Ce/SBA-15 pretreated with dielectric barrier discharge plasma

A review of the advances in catalyst modification using nonthermal plasma: Process, Mechanism and Applications

With the continuous development of catalytic processes in chemistry, biology, organic synthesis, energy generation and many other fields, the design of catalysts with novel properties has become a new paradigm in both science and industry. Nonthermal plasma has aroused extensive interest in the synthesis and modification of catalysts. An increasing number of researchers are using plasma for the modification of target catalysts, such as modifying the dispersion of active sites, regulating electronic properties, enhancing metal-support interactions, and changing the morphology. Plasma provides an alternative choice for catalysts in the modification process of oxidation, reduction, etching, coating, and doping and is especially helpful for unfavourable thermodynamic processes or heat-sensitive reactions. This review focuses on the following points: (i) the fundamentals behind the nonthermal plasma modification of catalysts; (ii) the latest research progress on the application of plasma modified catalysts; and (iii) main challenges in the field and a vision for future development.

Ni-CeO2/SBA-15 Catalyst Prepared by Glycine-Assisted Impregnation Method for Low-Temperature Dry Reforming of Methane

Developing low-temperature nickel-based catalysts with good resistance to coking and sintering for dry reforming of methane (DRM) is of great significance. In this work, Ni (5 wt%) and CeO2 (5 wt%) were supported on SBA-15 porous material by glycine-assisted impregnation method to obtain Ni-CeO2/SBA-15-G catalyst. XRD and TEM results showed that the addition of glycine can effectively promote the dispersion of NiO and CeO2 in the pores of SBA-15. H2-TPR and XPS results confirmed the formation of stronger metal-support interaction. In addition, after the addition of glycine, the NixCe1−xOy solid solution content was increased significantly, meanwhile, the Ce3+ concentration was increased from 31% to 49%, accompanied by more oxygen vacancies and generation of active oxygen species. For the above reasons, Ni-CeO2/SBA-15-G had better catalytic performance in the low-temperature DRM test (20 h, 600 °C) with high GHSV (600,000 mL/gcat/h), its CH4 conversion after reaction of 20 h was 2 times that of Ni-CeO2/SBA-15-C catalyst prepared by a conventional impregnation method. TGA-DTA test also proved that Ni-CeO2/SBA-15-G almost completely eliminated carbon deposition. The above advantages of the Ni-CeO2/SBA-15-G catalyst may have originated from the complexation of glycine with metal cations and can prevent them from gathering.

Structural effect of Ni/TiO2 on CO methanation: improved activity and enhanced stability

CO methanation over a supported Ni catalyst has attracted increasing attention for its applications in synthetic natural gas production, CO removal for ammonia synthesis and fuel cells, among others. However, the deactivation of the Ni catalyst caused by sintering and carbon deposition hinders further application of the Ni catalyst. The activity of Ni catalysts needs further improvement as well. In this work, the structural effect of the Ni/TiO2 catalyst on CO methanation was investigated. A plasma decomposition, initiated at room temperature and operated around 150 °C, of the nickel precursor was applied to prepare the catalyst. Compared to the thermally decomposed Ni/TiO2 catalyst, the plasma-decomposed catalyst shows improved activity with enhanced stability. The catalyst characterization shows that the plasma-decomposed Ni/TiO2 catalyst possesses smaller Ni particle size and higher Ni dispersion, resulting in improved coke resistance and enhanced anti-sintering ability for CO methanation. The present study confirms that a catalyst with good activity for CO methanation possesses good activity for CO2 methanation as well, if the CO2 methanation takes the CO methanation pathway.

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.

Highly Dispersed Ni Nanocatalysts Derived from NiMnAl-Hydrotalcites as High-Performing Catalyst for Low-Temperature Syngas Methanation

Increasing the low-temperature performance of nickel-based catalysts in syngas methanation is critical but very challenging, because at low temperatures there is high concentration of CO on the catalyst surface, causing formation of nickel carbonyl with metallic Ni and further catalyst deactivation. Herein, we have prepared highly dispersed Ni nanocatalysts by in situ reduction of NiMnAl-layered double hydroxides (NiMnAl-LDHs) and applied them to syngas methanation. The synthesized Ni nanocatalysts maintained the nanosheet structure of the LDHs, in which Ni particles were decorated with MnOy species and embedded in the AlOx nanosheets. It was observed that the Ni nanocatalysts exhibited markedly better low-temperature performance than commercial catalysts in the syngas methanation. At 250 °C, 3.0 MPa and a high weight hourly space velocity (WHSV) of 30,000 mL·g−1·h−1, both the CO conversion and the CH4 selectivity reached 100% over the former, while those over the commercial catalyst were only 14% and 76%, respectively. Furthermore, this NiMnAl catalyst exhibited strong anti-carbon and anti-sintering properties at high temperatures. The enhanced low-temperature performance and high-temperature stability originated from the promotion effect of MnOy and the embedding effect of AlOx in the catalyst.

Developmental trends in CO2 methanation using various catalysts

Co₂ methanation-two edged sword to counter global warming and energy crisis.

Vacuum Thermal Treated Ni-CeO₂/SBA-15 Catalyst for CO₂ Methanation

Ni-CeO₂/SBA-15-V catalyst was prepared by the impregnation method with vacuum thermal treatment and used for CO₂ methanation reaction. Compared with Ni-CeO₂/SBA-15-air catalyst with thermal treatment in air, the reduced Ni-CeO₂/SBA-15-V catalyst with vacuum thermal treatment exhibited higher Ni dispersion and smaller Ni particle size. In CO₂ methanation reaction, the Ni-CeO₂/SBA-15-V catalyst was more active and selective than the Ni-CeO₂/SBA-15-air catalyst. The good activity and selectivity of Ni-CeO₂/SBA-15-V catalyst should be due to highly dispersed Ni in contact with small CeO₂ particles.