Ni(Mg)Al-layered hydroxides with molar ratios of (Ni + Mg)/Al = 2, 3, 4 and Ni/(Ni + Mg) = 0.1, 0.3, 0.5, 0.7 were synthesized by mechanochemical activation. It has been proven that the phase ...composition of the samples was presented by a single hydrotalcite phase up to Ni/(Ni + Mg) = 0.5. For the first time, catalysts based on Ni(Mg)Al-layered hydroxides prepared by a mechanochemical route have been studied in the reaction of furfural hydrogenation. The correlation between furfural conversion, the selectivity of the products, and the composition of the catalysts was established. The effect of phase composition, surface morphology, and microstructure on the activity of the catalysts was shown by XRD, SEM, and TEM. It was found that catalysts with Ni/(Ni + Mg) = 0.5 have the highest furfural conversion. Herewith, the product selectivity can be regulated by the (Ni + Mg)/Al ratio.
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Ni(Mg)Al-layered double hydroxides (LDH) were synthesized by coprecipitation. Structural properties of LDH and mixed oxides Ni(Mg)AlOx, obtained by LDH calcination, were studied by XRD and SEM. ...Textural properties of Ni(Mg)AlOx were studied by the nitrogen adsorption-desorption method. It was found that the formation of the single-phase LDH was occurred for any nickel content in the samples. The mixed oxides have a high specific surface area, the value of which decreases with increasing nickel content in the samples. Ni(Mg)AlOx are characterized by high activity in furfural hydrogenation. Selectivity of the formation of different reaction products depends on the nickel content in the catalysts. The full furfural conversion with the furfuryl alcohol selectivity no more than 65% was observed for the catalyst with a low nickel content. At the same time an increase in selectivity for furfuryl alcohol up to 84% occurs for the NiAl-catalyst with a furfural conversion not exceeding 43%.
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•Synthesis of single-phase Ni(Mg)Al-layered hydroxides by coprecipitation.•Structural and textural properties of the Ni(Mg)Al-layered hydroxides and their calcined forms.•High activity of the Ni(Mg)AlOx catalysts in the reaction of aqua-phase furfural hydrogenation.•Selectivity of products formation can vary by changing the nickel amount in the Ni(Mg)AlOx catalysts.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Catalysts based on CoCuMgAl mixed oxides were synthesized and studied in the hydrogenations of furfural and 5-hydroxymethylfurfural under different conditions. The changes in the structural ...properties of the catalysts at different stages of their preparation were studied using a set of physical methods (XRD, SEM, and TEM). It was shown that the fine regulation of the chemical compositions of the mixed oxides (i.e., changes in the Co/Cu ratio) made it possible to vary the structure, morphology, and catalytic properties of the samples. The phase composition of catalysts with Co/Cu = 1 did not change during the catalytic reaction, although the initial catalysts had a less-homogeneous morphology. 5-hydroxymethylfurfural conversion was higher for the samples with Co/Cu = 1. Furfural conversion increased when raising the Co/Cu ratio. The selectivity toward furfuryl alcohol for the catalyst with Co/Cu = 2 under mild conditions of furfural hydrogenation was more than 99%. The results obtained are important for the development of the scientific foundations of the preparation of hydrogenation catalysts with a fine-tunable composition in order to obtain the desired hydrogenation products.
Simulation of diffraction patterns for 1D disordered crystals was used to investigate the structure of the initial CO32− containing MgGa LDHs with a different Mg2+/(Mg2+ + Ga3+) ratio equal to 0.67, ...0.75, and 0.80; mixed oxides obtained by calcination of LDHs at a temperature of 550 °C; and the hydroxide obtained by hydration of MgGa oxide with the Mg2+ content of 0.80. The initial LDHs contain lamellar inclusions of manasseite structure (polytype 2H1) in the hydrotalcite structure (3R1). A loss of water at 200 °C leads to the formation of a metastable dehydrated phase where layers are packed, as in polytypes 3R2 and 1H, with turbostratic disorder. The structure of mixed oxides is also layered and consists of periclase-like octahedral layers and spinel-like octahedral-tetrahedral layers. Hydration of the oxides results in restoring the initial layered hydrotalcite structure (polytype 3R1) for Mg2+ mole fractions 0.67 and 0.75. For the Mg2+ content of 0.80, the phase composition is represented by the hydroxide with hydrotalcite structure and the layered mixed hydroxide with the alternation of hydrotalcite and brucite lamellar domains, which was also revealed by calculation of diffraction patterns using models of 1D disordered crystals.
Single phase CuCoMgAl-layered hydroxides were obtained by making fine adjustment to their composition through changing the (Co + Cu)/Mg = 0.5; 1; 2; 3 and Co/Cu = 0.5; 1; 2 ratios. The rise of Co/Cu ...in systems contributed to the increase in their thermal stability. CuCoMgAl-catalysts showed high selectivity of carbonyl group hydrogenation in furfural and 5-hydroxymethylfurfural. In furfural hydrogenation, the selectivity to furfuryl alcohol was more than 99%, and in 5-hydroxymethylfurfural hydrogenation, the selectivity to 2,5-hydroxymethyl furfural was 95%. The surface of the samples with different Co/Cu after calcination and reduction was the same and had a «core-shell» structure (TEM). «Core» consisted of Cu and Co metallic particles. «Shell» consisted of CuCoMgAlOx mixed no-stoichiometric spinel oxides. There was no sintering or change in size of the metallic particles after the reaction. For the sample with Co/Cu = 1, their phase composition after reaction remained unchangeable. The increase of Co/Cu led to the formation of an X-ray amorphous phase after the reaction. This suggests the decrease in structural stability of this sample. The obtained results prove the prospects of using bimetallic CoCu-systems for hydrogenation of furan aldehydes, and opens up new directions for further research and improvement.
Catalysts based on CuAl-, CoAl-, and CuCoAl-layered hydroxides with M2+/Al = 2 and Cu/Co = 1 molar ratio were obtained. The effect of amount of cobalt on the structural properties, morphology, ...surface cations distribution, oxide phase formation, thermal stability of the samples and reduction of metals from them was studied. The effect of reaction conditions (temperature, time, pressure, solvent) and conditions of preliminary treatment of catalysts on their catalytic properties in furfural hydrogenation was established. High selectivity to furfuryl alcohol was observed for all the samples irrespective of pretreatment and reaction conditions. The synergetic effect in furfural hydrogenation between Co and Cu in the CuCoAlOx catalysts was revealed when ethanol is used as a solvent.
The hydrogenation of unsaturated double bonds with molecular hydrogen is an efficient atom-economic approach to the production of a wide range of fine chemicals. In contrast to a number of reducing ...reagents typically involved in organic synthesis, hydrogenation with H2 is much more sustainable since it does not produce wastes (i.e., reducing reagent residues). However, its full sustainable potential may be achieved only in the case of easily separable catalysts and high reaction selectivity. In this work, various Pd/C catalysts were used for the liquid-phase hydrogenation of O-, S-, and N-vinyl derivatives with molecular hydrogen under mild reaction conditions (room temperature, pressure of 1 MPa). Complete conversion and high hydrogenation selectivity (>99%) were achieved by adjusting the type of Pd/C catalyst. Thus, the proposed procedure can be used as a sustainable method for vinyl group transformation by hydrogenation reactions. The discovery of the stability of active vinyl functional groups conjugated with heteroatoms (O, S, and N) under hydrogenation conditions over Pd/C catalysts opens the way for many useful transformations.
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•The solvent nature has a significant effect on the interaction of TNB and its radical anions with surface sites of oxides.•The increasing of Mg/Al ratio in MgAl double oxides lead to ...more intense TNB radical anions formation after its adsorption.•A convenient probe EPR technique for the study of oxide catalysts is to adsorb TNB from a solution in n-hexane.
In current work the features of 1,3,5-trinitrobenzene (TNB) transformation into paramagnetic products on the surface of aluminum/magnesium oxides calcined at 550°C, as well as MgAl double oxides, were investigated by EPR spectroscopy. It was shown that the increase of basicity (i.e. MgO content) leads to the increase in the concentration of formed radical anions, wherein the presence of acidic sites contributes to their stabilization on the surface. The effect of n-hexane and toluene used as solvents in the transformation of adsorbed TNB radical anions was established, and a new probe EPR technique for using TNB to determine the concentration of the basic sites in MgAl double oxides was proposed. The results of the proposed technique are in good agreement with the data on the basic sites concentration obtained from the adsorption capacity CO2 of the corresponding samples.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The catalytic properties of molybdenum-alumina systems depend on the synthesis conditions. Herein, we considered the effect of MoO3/Al2O3 catalyst pretreatment conditions on their activity in ...propylene and propane conversion. MoO3/Al2O3 catalysts were synthesized by wetness impregnation of the support with a solution of molybdenum citrate complex and activated in different atmospheres at 550–590 °С. The maximum conversion of propylene and yields of metathesis products were observed for the sample activated in an inert gas flow. This is caused by the formation of precursors of the metathesis active sites in this sample, i.e. isolated surface monomolybdate species. Activation of the catalyst in hydrogen leads to the reduction of Mo6+ to Mo5+/Mo4+, which ensure the increased activity and selectivity in propane dehydrogenation. Therefore, it was shown that make it possible to purposefully change the properties of the same molybdenum-alumina catalyst to suit the problems of the specific reaction (metathesis, oligomerization, dehydrogenation, aromatization, cracking).
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•Pretreatment conditions affect the formation of MoO3/Al2O3 active sites.•UV-Vis, Raman Spectroscopy and XPS were used to characterize the catalyst.•Isolated Мо6+ species are precursors of active sites for alkene metathesis.•Reduced Mo4+ and/or Mo5+ species are associated with dehydrogenation/aromatization.•Catalyst pretreatment conditions have an effect on surface acidity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Ni(Mg)Al-layered hydroxides with molar ratios of (Ni + Mg)/Al = 2, 3, 4 and Ni/(Ni + Mg) = 0.1, 0.3, 0.5, 0.7 were synthesized by mechanochemical activation. It has been proven that the phase ...composition of the samples was presented by a single hydrotalcite phase up to Ni/(Ni + Mg) = 0.5. For the first time, catalysts based on Ni(Mg)Al-layered hydroxides prepared by a mechanochemical route have been studied in the reaction of furfural hydrogenation. The correlation between furfural conversion, the selectivity of the products, and the composition of the catalysts was established. The effect of phase composition, surface morphology, and microstructure on the activity of the catalysts was shown by XRD, SEM, and TEM. It was found that catalysts with Ni/(Ni + Mg) = 0.5 have the highest furfural conversion. Herewith, the product selectivity can be regulated by the (Ni + Mg)/Al ratio.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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