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

In Situ X-ray Diffraction as a Basic Tool to Study Oxide and Metal Oxide Catalysts

X-ray diffraction (XRD) is a standard technique that is widely applied in heterogeneous catalysis to determine phase composition, atomic structure, and size of crystallites. This review is focused on the application of in situ XRD for studying the catalysts during their “lifetime” (under synthesis, activation, operation, and deactivation conditions), limiting the objects of research to oxide and metal oxide catalysts. Also included is a brief overview of modern techniques and instruments and the latest works illustrating different aspects of this technique in catalyst research. The main conclusion is that the field of heterogeneous catalysis research would benefit substantially from the application of in situ XRD for the structural, phase, and morphological characterization of solid catalysts. Even more useful information can be obtained if XRD is combined with other techniques that are more sensitive at length scales different from that of XRD

Effect of Ni–Mo Carbide Catalyst Formation on Furfural Hydrogenation

High-loading Ni⁻Mo carbide catalysts were prepared by the modified gel-combustion method under various thermal treatment conditions. All samples were studied by X-ray diffraction (XRD) analysis, which showed that the catalysts could contain cubic and hexagonal molybdenum carbides, nickel, nickel oxide and Ni⁻Mo solid solutions, depending on the thermal treatment conditions. Study of catalyst activity and selectivity in the hydrogenation of furfural was carried out in a batch reactor at 150 °C and hydrogen pressure 6.0 MPa. Analysis of the reaction products showed that the highest yields of 2-methylfuran (2-MF) and furfuryl alcohol (FA) were achieved using catalysts synthesized by calcination of the nickel-molybdenum-carbon precursor at 400 °С with the following reduction in a stream of hydrogen at 600 °C. The best results for production of FA with a yield of 80 mol % and 2-MF with a yield of 29 mol % were observed using Ni6MoC⁻SiO2 (400/600) and Ni1MoC⁻SiO2 (400/600) catalysts, respectively. It has been shown that the addition of nickel to the carbide molybdenum catalyst significantly increases the activity of the catalytic systems. In addition, nickel also contributes to the formation of products formed by hydrogenation of the aromatic ring tetrahydrofurfuryl alcohol (THFA) and 2-methyltetrahydrofuran (2-MTHF)

CuFeAl Nanocomposite Catalysts for Coal Combustion in Fluidized Bed

A method of oil-drop granulation was suggested for the preparation of spherical CuFeAl nanocomposite catalysts. The catalysts were characterized by a set of physicochemical methods (X-ray diffraction, temperature-programmed reduction by H2, low-temperature nitrogen adsorption, crushing strength) and tested in the oxidation of CO and burning of brown coal in a fluidized bed. It was found that the catalysts have high mechanical strength (16.2 MPa), and their catalytic properties in the oxidation of CO are comparable to the characteristics of industrial Cr-containing catalysts. It was shown that the addition of pseudoboehmite at the stage of drop formation contributes to the production of uniform spherical high-strength granules and facilitates the stabilization of the phase state of the active component. The use of CuFeAl nanocomposite catalysts for the burning of brown coal provides a low emission of CO (600 ppm) and NOx (220 ppm) and a high degree of coal burnout (95%), which are close to those of the industrial Cr-containing catalysts (emission of CO is 700 ppm, NOx—230 ppm, and degree of coal burnout is 95%)

Solvent-Free Method for Nanoparticles Synthesis by Solid-State Combustion Using Tetra(Imidazole)Copper(II) Nitrate

The development of solvent-free techniques for nanoparticles synthesis is one of the challenges of Green chemistry. In this work, the principled opportunity to obtain copper-containing nanosized particles without use of any solvents was shown. The copper complexes were prepared as precursors by the melting-assisted solvent-free synthesis. The formation of tetra(imidazole)copper(II) nitrate complex was confirmed by XRD, elemental analysis, FTIR spectroscopy, and thermal analysis. It was noted that their thermal decomposition occurs in two stages: (I) the low-temperature step may be related to redox interaction between organic ligands and nitrate-anions; (II) the high-temperature step may be related to the oxidation of the products of incomplete imidazole decomposition. TEM and XRD studies of solid products of complex combustion have shown that they are oxides with particle size less than 40 nm. Thus, the combustion of [Cu(Im)4](NO3)2 complex under air can be considered as a new approach to prepare nanosized particles of copper oxides without the use of solvents

Highly Active CuFeAl-containing Catalysts for Selective Hydrogenation of Furfural to Furfuryl Alcohol

CuFe-containing catalysts with different copper oxide content were prepared by fusion of metal salts. The obtained catalyst showed high activity in the hydrogenation of furfural to furfuryl alcohol (FA) in the batch reactor in the presence of isopropanol as a solvent at a temperature of 100 °C and a hydrogen pressure of 6.0 MPa. The yield of FA and furfural conversion are 97% and 98%, respectively. In the solvent-free reaction in the flow-type reactor; the most active catalyst Cu20Fe66Al14 leads to the 96% formation of FA with 100% conversion of furfural at liquid hourly space velocity (LHSV) = 1 h−1; 160 °C and a hydrogen pressure of 5.0 MPa during 30 h. According to the X-ray diffraction (XRD) method, the active component of the spent and fresh Cu20Fe66Al14 catalyst is the same and is represented by metallic copper and Fe3O4-type spinel. Using different methods, the formation of active sites was investigated

Solvent-Free Method for Nanoparticles Synthesis by Solid-State Combustion Using Tetra(Imidazole)Copper(II) Nitrate

The development of solvent-free techniques for nanoparticles synthesis is one of the challenges of Green chemistry. In this work, the principled opportunity to obtain copper-containing nanosized particles without use of any solvents was shown. The copper complexes were prepared as precursors by the melting-assisted solvent-free synthesis. The formation of tetra(imidazole)copper(II) nitrate complex was confirmed by XRD, elemental analysis, FTIR spectroscopy, and thermal analysis. It was noted that their thermal decomposition occurs in two stages: (I) the low-temperature step may be related to redox interaction between organic ligands and nitrate-anions; (II) the high-temperature step may be related to the oxidation of the products of incomplete imidazole decomposition. TEM and XRD studies of solid products of complex combustion have shown that they are oxides with particle size less than 40 nm. Thus, the combustion of [Cu(Im)4](NO3)2 complex under air can be considered as a new approach to prepare nanosized particles of copper oxides without the use of solvents

Magnetically Recovered Co and Co@Pt Catalysts Prepared by Galvanic Replacement on Aluminum Powder for Hydrolysis of Sodium Borohydride

Magnetically recovered Co and Co@Pt catalysts for H2 generation during NaBH4 hydrolysis were successfully synthesized by optimizing the conditions of galvanic replacement method. Commercial aluminum particles with an average size of 80 µm were used as a template for the synthesis of hollow shells of metallic cobalt. Prepared Co0 was also subjected to galvanic replacement reaction to deposit a Pt layer. X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, and elemental analysis were used to investigate catalysts at each stage of their synthesis and after catalytic tests. It was established that Co0 hollow microshells show a high hydrogen-generation rate of 1560 mL·min−1·gcat−1 at 40 °C, comparable to that of many magnetic cobalt nanocatalysts. The modification of their surface by platinum (up to 19 at% Pt) linearly increases the catalytic activity up to 5.2 times. The catalysts prepared by the galvanic replacement method are highly stable during cycling. Thus, after recycling and washing off the resulting borate layer, the Co@Pt catalyst with a minimum Pt loading (0.2 at%) exhibits an increase in activity of 34% compared to the initial value. The study shows the activation of the catalyst in the reaction medium with the formation of cobalt–boron-containing active phases

High-Loaded Nickel Based Sol–Gel Catalysts for Methylcyclohexane Dehydrogenation

Application of liquid organic hydrogen carriers, such as “methylcyclohexane (MCH)–toluene” chemical couple, is one of the promising approaches for hydrogen storage and transportation. In the present study, copper-modified nickel catalysts with high metal loading of 75 wt% were synthesized via heterophase sol–gel technique, and investigated in the dehydrogenation of MCH. Two approaches towards the copper introduction were applied. The catalyst samples prepared via wetness impregnation of the nickel sol–gel catalyst are characterized by more effective Ni-Cu interaction compared to those where two metals were introduced simultaneously by the mixing of their solid precursors. As a result, the “impregnated” catalysts revealed higher selectivity towards toluene. The addition of copper up to 30 wt% of total metal content was shown to increase significantly toluene selectivity and yield without a noticeable decrease in MCH conversion. The catalyst with the active component including 80 wt% of Ni and 20 wt% of Cu demonstrated 96% and 89% toluene selectivity at 40% and 80% MCH conversion, respectively. Based on the obtained data, this non-noble catalytic system appears quite promising for the MCH dehydrogenation