CO and CO2 methanation over Ni catalysts supported on alumina with different crystalline phases

Synthesis and Characterization of the Metal–Organic Framework CIM-80 for Organic Compounds Adsorption

Metal–organic frameworks (MOF) are a new type of porous materials that have great potential for adsorption of voltaic organic compounds (VOCs). These types of materials composed of metal ions and organic ligands are easy to synthesize, have high surface areas, their surface chemistry can be adjusted to the desired application, and they can also have good chemical and thermal stability. Therefore, this work focuses on the synthesis of a highly hydrophobic MOF material called CIM-80, a porous material that is made up of the Al³⁺ cation and the mesaconate linker. This MOF has a B.E.T. of approximately 800 m²/g and has potential applications for the adsorption of hydrophobic organic compounds. However, its synthesis is expensive and very dirty. Therefore, we have studied the synthesis conditions necessary to achieve high synthesis yields (85%) and materials with high crystallinity and accessible porosity. To achieve these results, we have used urea as a mild deprotonation reagent and modulator as an alternative to NaOH, which is traditionally used for the synthesis of this MOF. Once the synthesis of this material was controlled, its adsorption/desorption behavior of water and organic compounds such as toluene, cyclohexane and m-xylene was studied by means of vapor adsorption isotherms. The results show the hydrophobic character of the material and the greater affinity the material has toward aliphatic compounds than toward aromatic ones, with toluene being the most adsorbed compound, followed by cyclohexane and m-xylene.

Catalytic activity of Cu/η-Al2O3 catalysts prepared from aluminum scraps in the NH3-SCO and in the NH3-SCR of NO

Copper-loaded η-alumina catalysts with different copper contents were prepared by impregnation/evaporation method. The catalysts were characterized by XRD, FTIR, BET, UV-Vis, and H₂-TPR and evaluated, for the first time, in the selective catalytic reduction of NO by NH₃ and in the selective catalytic oxidation of NH₃. The characterization techniques showed that the impregnation/evaporation method permits to obtain highly dispersed copper oxide species on the η-alumina surface when a low amount of copper is used (1wt. % and 2 wt.%). The wet impregnation method made it possible to reach a well dispersion of the copper species on the surface of the alumina for the low copper contents Cu(1)-Al₂O₃ and Cu(2)-Al₂O₃. The latter justifies the similar behavior of Cu(1)-Al₂O₃) and Cu(2)-Al₂O₃ in the selective catalytic oxidation of NH₃ where these catalysts exhibit a conversion of NH₃ to N₂ of the order of 100% at T> 500 °C.

Promising Catalytic Systems for CO2 Hydrogenation into CH4: A Review of Recent Studies

The increasing utilization of renewable sources for electricity production turns CO2 methanation into a key process in the future energy context, as this reaction allows storing the temporary renewable electricity surplus in the natural gas network (Power-to-Gas). This kind of chemical reaction requires the use of a catalyst and thus it has gained the attention of many researchers thriving to achieve active, selective and stable materials in a remarkable number of studies. The existing papers published in literature in the past few years about CO2 methanation tackled the catalysts composition and their related performances and mechanisms, which served as a basis for researchers to further extend their in-depth investigations in the reported systems. In summary, the focus was mainly in the enhancement of the synthesized materials that involved the active metal phase (i.e., boosting its dispersion), the different types of solid supports, and the frequent addition of a second metal oxide (usually behaving as a promoter). The current manuscript aims in recapping a huge number of trials and is divided based on the support nature: SiO2, Al2O3, CeO2, ZrO2, MgO, hydrotalcites, carbons and zeolites, and proposes the main properties to be kept for obtaining highly efficient carbon dioxide methanation catalysts.

COx co-methanation over coal combustion fly ash supported Ni-Re bimetallic catalyst: Transformation from hazardous to high value-added products

The hazardous industrial waste, coal combustion fly ash (CCFA), was creatively applied as Ni-Re bimetallic catalyst support. The expected catalyst was facilely prepared by co-impregnation method and further tested for CO_x co-methanation in a continuous fixed-bed reactor. The physico-chemical properties of the catalyst were examined by a series of techniques including XRF, ICP, XRD, N₂ isothermal adsorption, H₂-TPR, SEM and TEM. The results showed that compared to non-promoted monometallic Ni catalyst, the addition of Re promoter forming Ni-Re bimetallic catalyst was able to facilitate NiO reduction and increase Ni dispersion as well as inhibit carbon deposition and Ni sintering during reaction. The performance tests revealed that Ni₁₅Re_1.0 presented superior CO_x co-methanation activity over Ni₁₅Re_0, Ni₁₅Re_0.5 and Ni₁₅Re_1.5 due to its better anti-coking and anti-sintering ability. Based on in-situ DRIFTS analysis, a possible cycle reaction mechanism of CO_x co-methanation was reasonably proposed in the end. The reaction pathway for CO and CO₂ methanation differed from each other, where CO was linearly adsorbed on Ni metals followed by stepwise hydrogenation while CO₂ was first immobilized by the surface hydroxyl group and then gradually reacted with H₂ to form CH₄.

Direct Optical and Ultrasensitive Probing of Nonequilibrium Dynamics of Carbon Monoxide in an Aqueous Phase during Biochemical Reactions

Detection of trace carbon monoxide (CO) dissolved in an aqueous phase is key for monitoring and optimizing biological and chemical gas conversions. So far, irrespective of the nonequilibrium nature of these conversion processes, because of low water solubility of CO, such detection has been performed indirectly, under the assumption of thermodynamic equilibrium, by the combination of chromatographic measurement of relatively abundant CO in a gas phase and Henry's law. Direct and sensitive detection of dissolved CO under nonequilibrium has not been explored yet. Here, we report the direct, ultrasensitive, and real-time monitoring of nonequilibrium dynamics of CO in an aqueous phase during biochemical conversions by devising miniaturized fluidic reactors with built-in CO-specific optical probes via surface-enhanced Raman spectroscopy. As the sensitive and selective probes, we fabricate ligand-free Au@Pd core-shell nanoparticle monolayers to maximize the Raman signal of single CO in the aqueous phase. We confirm that under equilibrium conditions, aqueous and gaseous CO concentrations estimated by our method are in good agreement with those measured directly and indirectly by gas chromatography (GC). We show that our probe can detect the aqueous CO concentrations as low as ca. 0.01% with high signal reproducibility, which is 200-fold more sensitive than that achieved by infrared spectroscopy. Finally, we successfully observe the nonequilibrium dynamics of the aqueous CO during biochemical reactions, which cannot be sensed by other detection methods including even indirect measurement by GC. We anticipate that our method can be widely applied not only for monitoring of biochemical gas reactions on multiple scales from a large reactor to a single-molecule level but also for molecular imaging of biological systems.

Promising Utilization of CO2 for Syngas Production over Mg2+- and Ce2+-Promoted Ni/γ-Al2O3 Assisted by Nonthermal Plasma

Dry reforming of methane is conducted in a catalyst packed-bed dielectric barrier discharge (DBD) reactor aiming to improve the reaction efficiency. The MgO- and CeO₂-promoted Ni/γ-Al₂O₃ catalyst is tested to carry out the reaction. An interesting observation is that Ni/MgO_Al₂O₃ integration provides ∼35 and 13% conversion of CH₄ and CO₂, respectively. The highest syngas ratio of 0.94 is obtained with Ni/MgO_Al₂O₃, whereas the ratio is only 0.57 with Ni/CeO₂_Al₂O₃ and 0.64 with bare DBD. In addition, Ni/CeO₂_Al₂O₃ offers the highest selectivity (68%) of CO due to the oxygen buffer property of CeO₂. Finally, the optimal acid/base property is highly desirable for the dry reforming reaction.

CO2 Methanation over Ni/Al@MAl2O4 (M = Zn, Mg, or Mn) Catalysts

In this study, unique core-shell aluminate spinel supports, Al@MAl2O4 (M = Zn, Mg, or Mn), were obtained by simple hydrothermal surface oxidation and were applied to the preparation of supported Ni catalysts for CO2 methanation. For comparison, CO methanation was also evaluated using the same catalysts. The prepared catalysts were characterized with a variety of techniques, including N2 physisorption, CO2 chemisorption, H2 chemisorption, temperature-programmed reduction with H2, temperature-programmed desorption of CO2, X-ray diffraction, high-resolution transmission electron microscopy, and in-situ diffuse reflectance infrared Fourier transform spectroscopy. The combination of supports with core-shell spinel structures and Ni doping with a deposition–precipitation method created outstanding catalytic performance of the Ni catalysts supported on Al@MgAl2O4 and Al@MnAl2O4 due to improved dispersion of Ni nanoparticles and creation of moderate basic sites with suitable strength. Good stability of Ni/Al@MnAl2O4 catalyst was also confirmed in the study.