CO2 Methanation: Solvent-Free Synthesis of Nickel-Containing Catalysts from Complexes with Ethylenediamine.

CO2 methanation was studied in the presence of nickel catalysts obtained by the solid-state combustion method. Complexes with a varying number of ethylenediamine molecules in the coordination sphere of nickel were chosen as the precursors of the active component of the catalysts. Their synthesis was carried out without the use of solvents, which made it possible to avoid the stages of their separation from the solution and the utilization of waste liquids. The composition and structure of the synthesized complexes were confirmed by elemental analysis, IR spectroscopy, powder XRD and XPS methods. It was determined that their thermal decomposition in the combustion wave proceeds in multiple stages with the formation of NiO and Ni(OH)2, which are reduced to Ni0. Higher ethylenediamine content in the complex leads to a higher content of metal in the solid products of combustion. However, different ratios of oxidized and reduced forms of nickel do not affect the initial activation temperature of nickel catalysts in the presence of CO2. It was noted that, after activation, the sample obtained from [Ni(C2H8N2)2](NO3)2 exhibited the highest activity in CO2 methanation. Thus, this complex is a promising precursor for CO2 methanation catalysts, and its synthesis requires only a small amount of ethylenediamine.

The Use of Hybrid Genetic Algorithm in the Kinetic Analysis of Thermal Decomposition of [Ni(C2H8N2)3](ClO4)2 with Overlapping Stages.

This work describes the mathematical modeling of the thermal decomposition of the complex compound [Ni(En)3](ClO4)2 (En = C2H8N2 = ethylenediamine) in an inert atmosphere under non-isothermal conditions. This process is characterized by several simultaneous and intense stages: elimination of ethylenediamine from the nickel coordination sphere, decomposition of perchlorate anions, and explosive-like oxidation of free or bound ethylenediamine. These stages overlap and merge into a one step on the differential thermogravimetric curve. Typically, this curve is modeled as a one-stage process during kinetic analysis. In this paper, for the first time, the data from the dynamic mass-spectral thermal analysis and thermogravimetric analysis were modeled using the hybrid genetic algorithm, and the results were compared. A two-stage scheme of [Ni(En)3](ClO4)2 thermolysis was proposed and the kinetic parameters for each stage were obtained. It was shown that the decomposition of [Ni(En)3](ClO4)2 begins with the elimination of one molecule of ethylenediamine (stage A), then the perchlorate anions quickly decompose with the evolution of oxygen (stage B). We believe that the resulting ClO4-x- (x = 1-3), as stronger oxidizing agents, instantly start an explosive-like exothermic process of ethylenediamine oxidation (stage B).

New Solvent-Free Melting-Assisted Preparation of Energetic Compound of Nickel with Imidazole for Combustion Synthesis of Ni-Based Materials.

In this work two approaches to the synthesis of energetic complex compound Ni(Im)6(NO3)2 from imidazole and nicklel (II) nitrate were applied: a traditional synthesis from solution and a solvent-free melting-assisted method. According to infrared spectroscopy, X-ray diffraction, elemental and thermal analysis data, it was shown that the solvent-free melt synthesis is a faster, simpler and environmentally friendly method of Ni(Im)6(NO3)2 preparation. The results show that this compound is a promising precursor for the production of nanocrystalline Ni-NiO materials by air-assisted combustion method. The combustion of this complex together with inorganic supports makes it possible to synthesize supported nickel catalysts for different catalytic processes.

Catalytic Behavior of Iron-Containing Cubic Spinel in the Hydrolysis and Hydrothermolysis of Ammonia Borane.

The paper presents a comparative study of the activity of magnetite (Fe3O4) and copper and cobalt ferrites with the structure of a cubic spinel synthesized by combustion of glycine-nitrate precursors in the reactions of ammonia borane (NH3BH3) hydrolysis and hydrothermolysis. It was shown that the use of copper ferrite in the studied reactions of NH3BH3 dehydrogenation has the advantages of a high catalytic activity and the absence of an induction period in the H2 generation curve due to the activating action of copper on the reduction of iron. Two methods have been proposed to improve catalytic activity of Fe3O4-based systems: (1) replacement of a portion of Fe2+ cations in the spinel by active cations including Cu2+ and (2) preparation of highly dispersed multiphase oxide systems, involving oxide of copper.

The Formation of Mn-Ce Oxide Catalysts for CO Oxidation by Oxalate Route: The Role of Manganese Content.

The Mn-Ce oxide catalysts active in the oxidation of CO were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), transition electron microscopy (TEM), energy dispersive X-Ray (EDX), and a differential dissolution technique. The Mn-Ce catalysts were prepared by thermal decomposition of oxalates by varying the Mn:Ce ratio. The nanocrystalline oxides with a fluorite structure and particle sizes of 4-6 nm were formed. The introduction of manganese led to a reduction of the oxide particle size, a decrease in the surface area, and the formation of a MnyCe1-yO2-δ solid solution. An increase in the manganese content resulted in the formation of manganese oxides such as Mn2O3, Mn3O4, and Mn5O8. The catalytic activity as a function of the manganese content had a volcano-like shape. The best catalytic performance was exhibited by the catalyst containing ca. 50 at.% Mn due to the high specific surface area, the formation of the solid solution, and the maximum content of the solid solution.

Invisible Surface Oxygen Vacancies in a Thin MgO Film: Impacts on the Chemical Activity and Secondary Electron Emission.

Today, Fs defects in MgO as isolated surface neutral oxygen vacancies are in the focus of surface science, catalysis research, and emission coating of microchannel plates. With the 10-4 atom % content at 750 K and under pO2 = 10-9 Torr, estimated by us from the known equilibrium T-x and p-T-x diagrams of MgO, Fs defects remain invisible or difficult-to-detect objects. The MgO(100) → MgO(100) + Fs + 1/2O2 phase transition was studied in MgO films deposited by the metal-organic chemical vapor deposition (MOCVD) procedure from the mixed-ligand Mg precursor on Si substrates at 725 K in the O2 flow where the nonstoichiometric phase (MgO/Fs) is formed in the gas medium containing simultaneous H2, CO, H2O, CO, and O2 species in unbalanced concentrations. Realization of the above transition was proven theoretically and experimentally through kinetic-thermodynamic analysis of the nonequilibrium system with revealing thermodynamic motive forces, i.e., the positive enthalpy and entropy, as well as through a new combination of diagnostic methods including the original differential dissolution method, due to which separate determination of the point and morphological defects was achieved. It was found that Fs defects occur when oxygen in the immediate vicinity to the substrate surface is replaced practically completely by the oxidized products of the precursor and the resulting oxygen pressure becomes enough for this process. The 90 mass % of the as-deposited MgO-film-involved (MgO/Fs) phase; its chemical activity is demonstrated through dissolution in hot water, while the electron donor activity is through 9 at 750 eV secondary electron yield. A good understanding of gas-phase reactions between the precursors and oxygen provides the fundamental basis of the MOCVD process to deposit MgO films that are dense, free from carbon, and of homogeneous texture. This makes the MOCVD process suitable also for use as coatings of microchannel plates.