Search

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. [ABSTRACT FROM AUTHOR]

Novel bimetallic Pd-Co catalysts supported on the carbon material Sibunit were synthesized by an incipient wetness impregnation method and used for ethylene production by selective acetylene hydrogenation. It has been established that an increase in the Pd:Co molar ratio from 1:0 to 1:2 in 0.5%Pd-Co/C catalysts, treated in hydrogen at 500 °C, leads to an increase in the ethylene selectivity from 60 to 67% (T = 45 °C). The selectivity does not change with a further increase in the modifier concentration. The catalysts were investigated by TPR-H2, XRD, TEM HR, EDS, and XPS methods. It was shown that palladium and cobalt in the 0.5%Pd-Co/C samples form Pd(1−x)Cox phases of solid solutions with different compositions depending on the Pd:Co ratio. The cobalt concentration in the Pd-Co particles increases with an increase in the Pd:Co ratio up to 1:2 and then remains at a constant level. In addition, monometallic Co particles were present in the samples with the Pd:Co ratio higher then 1:2. The optimal combination of catalytic properties (the ethylene yield is 62–63%) is typical for catalysts with a Pd:Co molar ratio of 1:2–1:4. which is mainly due to the presence of bimetallic particles containing ~41–43% by at. of cobalt. [ABSTRACT FROM AUTHOR]

Structural features of bimetallic Pd−Zn catalysts supported on Sibunit carbon material were studied by EXAFS, TEM, XRD and XPS methods, depending on the heat treatment conditions in hydrogen. It was found that supported particles of PdZn intermetallic compound of tetragonal structure are formed in all samples. An increase in the duration of catalyst reduction in H2 at 500 °C from 1 to 20 hours leads to an increase in the amount of PdZn intermetallic particles (dav=2–3 nm), which is confirmed by the increasing of the Pd−Zn coordination number from 2.4 to 4.3 and by the decreasing of the surface Pd0/PdZn ratio from 0.63 to 0.18. The observed changes in the nature and structure of active sites provide an increase in the ethylene selectivity of Pd−Zn/C catalysts in liquid‐phase acetylene hydrogenation. [ABSTRACT FROM AUTHOR]

Changes in the structural and textural properties of NiAl-layered double hydroxides (LDHs) (with 2–4 molar ratios of metals) and state of nickel that occur in different steps of the synthesis of nickel catalysts were studied using XRD, thermal analysis, TPR, low-temperature nitrogen adsorption, XANES, EXAFS, and electron microscopy methods. Relations between nickel content, catalyst reduction conditions, state of nickel, and its catalytic properties were revealed. It was shown that the use of NiAl LDH as the catalyst precursor even at a high content of active metal allows for the obtaining of the dispersed particles of supported nickel that are active in the aqueous-phase hydrogenation of furfural. The catalyst activity and conversion of furfural were found to increase with elevation of the catalyst reduction temperature and the corresponding growth of the fraction of reduced nickel. However, a lower reduction temperature (500 °C) makes it possible to form smaller nickel particles with the size of 4–6 nm, and a high Ni content (Ni:Al = 4) can be used to obtain the active Ni@NiAlOx catalyst. Under mild reaction conditions (90 °C, 2.0 MPa), the furfural conversion reached 93%, and furfuryl alcohol was formed with the selectivity of 70%. Under more severe reaction conditions (150 °C, 3.0 MPa), complete conversion of furfural was achieved, and cyclopentanol and tetrahydrofurfuryl alcohol were the main hydrogenation products. [ABSTRACT FROM AUTHOR]

The reusability of metal catalysts is a key issue for the potential application of new catalysts in research and industrial practice. The most common procedure for testing catalyst reusability in liquid‐phase heterogeneous reactions is based on separating a catalyst from a reaction mixture followed by the next run. An alternative procedure called "fresh start" consists of the addition of a new portion of reagents to the reaction mixture without any isolation operation. In this work, we compare both procedures in a model Pd/C‐catalyzed hydrogenation with different heteroatoms, e. g., O‐, S‐, and N‐vinyl derivatives. It was shown that regardless of whether the catalyst is stable or potentially poisoned during the reaction, both procedures lead to comparable results. It appears that a much easier implementation of a fresh start procedure may be an option of choice. The possibilities of using both procedures to rationalize the experimental protocol for assessing Pd/C catalyst reusability in liquid‐phase hydrogenations are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

[Display omitted] • The formation of Pd x Co (1-x) nanoalloys supported on Sibunit was studied in detail. • Pd x Co (1- x) supported particles are formed during treatment in H 2 at T ≥ 500 °C. • Increasing the reduction temperature to 700 °C leads to the Co-enrichment of PdCo. • Pd-Co/Sibunit catalysts are promising in C 2 H 4 production by acetylene hydrogenation. • The Pd x Co (1- x) (x = 0.45–0.5) particles provide the highest ethylene yield of 66–68 % The research is devoted to the study of active component formation in the novel Pd-Co catalysts supported on carbon material Sibunit. It was shown that 0.5 %Pd–0.5 %Co/C samples exhibit high ethylene yield in the acetylene hydrogenation process due to the presence of fcc Pd x Co (1-x) particles. According to in situ XRD-TPR analysis, solid solution formation begins during the reduction of samples in H 2 at T ≥ 500 °C. Using the EXAFS, XRD and EDX it was established that H 2 -treatment at 500 °C leads to the formation of ∼Pd 0.6 Co 0.4 particles and an increase in the reduction temperature to 600 and 700 °C is accompanied by the enrichment of the Pd-Co-phase with cobalt to ∼Pd 0.5 Co 0.5 and ∼Pd 0.45 Co 0.55 compositions, respectively. The ethylene yield on Pd-Co/C catalysts reduced at 500, 600 and 700 °C is 56, 66 and 68 %, respectively, which significantly exceeds the ethylene quantity obtained on monometallic Pd/C samples (∼52 %). It is assumed that the excellent selectivity of Pd-Co/C samples treated in H 2 at 600 and 700 °C is due to an increase in the amount of palladium atoms surrounded by cobalt and a change in the palladium electronic state (XPS). [ABSTRACT FROM AUTHOR]

In the present research, the process of the formation of the active components of Pd-Zn catalysts supported on carbonaceous material Sibunit prepared by the joint impregnation (Pd:Zn = 1) is studied. It was shown by means of TPR and EXAFS techniques that the interaction between palladium and zinc begins already at T > 200 °C. During the reduction in hydrogen at temperatures of 200–300 °C the surface of particles being formed is enriched with oxidized zinc. In the temperature range of 400–500 °C zinc is completely reduced, and the crystal lattice of a substitutional solid solution based on fcc lattice of palladium is restructured in tetragonal lattice of PdZn. However, an increase of the calcination temperature in H 2 atmosphere (500 °C) significantly rises up the probability of partial destruction of bimetallic phase due to the partial migration of zinc atoms from the surface into the bulk of particles. Unlabelled Image • Pd/Sibunit catalysts were doped with zinc. • The structure of the Pd-Zn/Sibunit catalysts was studied at increasing of reduction temperature in a hydrogen. • The interaction between palladium and zinc begins at T > 200 °C and completed at T = 400–500 °C. • For Pd-Zn/Sibunit catalysts, an increasing of the active component dispersion was found. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pd-Ga/Al 2 O 3 catalysts are promising in liquid-phase acetylene hydrogenation process. • Co-deposition of Pd(NO 3) 2 and Ga(NO 3) 3 prevents the γ-Ga 2 O 3 -Al 2 O 3 phase formation. • Ga changes the electronic state of Pd at Pd:Ga = 1:0.5 and C 2 H 4 selectivity is 66%. • Selectivity of C 2 H 4 increases to 70% at Pd:Ga = 1:2 due to the Pd 2 Ga phase formation. • The catalyst treated in H 2 at 500 °C has the highest ethylene selectivity of 75%. The structural properties of Pd-Ga/γ-Al 2 O 3 samples prepared from joint Pd(NO 3) 2 and Ga(NO 3) 3 solution and their catalytic properties in liquid-phase acetylene hydrogenation have been studied. Using temperature programmed reduction (TPR-H 2), transmission electron microscopy (TEM), diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO (CO-DRIFTS) and X-ray photoelectron spectroscopy (XPS) it was found that an increase in the ethylene selectivity to ∼ 66–70% is explained by the modification of the electronic properties of palladium by gallium at a Ga:Pd molar ratio of 0.5 and by the formation of bimetallic Pd 2 Ga particles in the case of Ga:Pd = 2. [ABSTRACT FROM AUTHOR]