Differences in Deterioration Behaviors of Cu/ZnO/Al2O3 Catalysts with Different Cu Contents toward Hydrogenation of CO and CO2
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ABSTRACT:
SUBMITTER: Kamsuwan T
PROVIDER: S-EPMC9330176 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Cu-ZnO-Al2O3 catalysts are used as the industrial catalysts for water gas shift (WGS) and CO hydrogenation to methanol reactions. Herein, via a comprehensive experimental and theoretical calculation study of a series of ZnO/Cu nanocrystals inverse catalysts with well-defined Cu structures, we report that the ZnO-Cu catalysts undergo Cu structure-dependent and reaction-sensitive in situ restructuring during WGS and CO hydrogenation reactions under typical reaction conditions, forming the active sites of CuCu(100)-hydroxylated ZnO ensemble and CuCu(611)Zn alloy, respectively. These results provide insights into the active sites of Cu-ZnO catalysts for the WGS and CO hydrogenation reactions and reveal the Cu structural effects, and offer the feasible guideline for optimizing the structures of Cu-ZnO-Al2O3 catalysts.
| S-EPMC8282834 | biostudies-literature
Project description:The thermo-catalytic synthesis of hydrocarbons from CO2 and H2 is of great interest for the conversion of CO2 into valuable chemicals and fuels. In this work, we aim to contribute to the fundamental understanding of the effect of alloying on the reaction yield and selectivity to a specific product. For this purpose, Fe-Co alloy nanoparticles (nanoalloys) with 30, 50 and 76 wt% Co content are synthesized via the Inert Gas Condensation method. The nanoalloys show a uniform composition and a size distribution between 10 and 25 nm, determined by means of X-ray diffraction and electron microscopy. The catalytic activity for CO2 hydrogenation is investigated in a plug flow reactor coupled with a mass spectrometer, carrying out the reaction as a function of temperature (393-823 K) at ambient pressure. The Fe-Co nanoalloys prove to be more active and more selective to CO than elemental Fe and Co nanoparticles prepared by the same method. Furthermore, the Fe-Co nanoalloys catalyze the formation of C2-C5 hydrocarbon products, while Co and Fe nanoparticles yield only CH4 and CO, respectively. We explain this synergistic effect by the simultaneous variation in CO2 binding energy and decomposition barrier as the Fe/Co ratio in the nanoalloy changes. With increasing Fe content, increased activation temperatures for the formation of CH4 (from 440 K to 560 K) and C2-C5 hydrocarbons (from 460 K to 560 K) are observed.
| S-EPMC7408123 | biostudies-literature
Project description:The synergistic interaction among different components in complex catalysts is one of the crucial factors in determining catalytic performance. Here we report the interactions among the three components in controlling the catalytic performance of Cu-ZnO-ZrO2 (CZZ) catalyst for CO2 hydrogenation to methanol. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements under the activity test pressure (3 MPa) reveal that the CO2 hydrogenation to methanol on the CZZ catalysts follows the formate pathway. Density functional theory (DFT) calculations agree with the in situ DRIFTS measurements, showing that the ZnO-ZrO2 interfaces are the active sites for CO2 adsorption and conversion, while the presence of metallic Cu is also necessary to facilitate H2 dissociation and to provide hydrogen resource. The combined experiment and DFT results reveal that tuning the interaction between ZnO and ZrO2 can be considered as another important factor for designing high performance catalysts for methanol generation from CO2.
| S-EPMC6411953 | biostudies-literature
Project description:Noble metals such as Au, Ag, and Cu supported over semiconducting ZnO are well-known heterogeneous oxidation catalysts. All of them have been utilized for the oxidation of diesel soot with varied success. However, Au-supported ZnO is seen to be superior among them. Here, we present a comparative study of all these three catalysts for diesel soot oxidation to explain why Au/ZnO is the best among them, demonstrating the contribution of electronic states of metals in composite catalysts. The electronic states of Cu, Ag, and Au determined by X-ray photoelectron spectroscopy on 1 wt % Cu/ZnO, 1 wt % Ag/ZnO, and 1 wt % Au/ZnO catalysts were correlated with their diesel soot oxidation activities. Although all three catalysts present reasonable diesel soot oxidation activities at relatively low temperature, 1% Cu/ZnO and 1% Ag/ZnO oxidize only about 60% of the deposited diesel soot around 250 °C and 1% Au/ZnO oxidizes 100% of the deposited diesel soot, at a temperature as low as 230 °C. The activity of the catalysts is attributed to the formation of stable M0-Mδ+ bifunctional catalytic sites at the metal-ZnO interface, which enhances the contact efficiency of solid diesel soot on Mδ+ and generates the superoxide species on M0 moieties. The stability of the bifunctional M0-Mδ+ sites is controlled by the electronic interactions between the metal (M) and n-type semiconductor ZnO at their interface. Very high activity of 1% Au/ZnO is attributed to the presence of Au3+ at the catalyst surface, which generates a stronger Coulombic force with diesel soot electrons. We demonstrate a direct relation between the diesel soot oxidation activity of these three metals and their electronic states at the catalyst surface.
| S-EPMC6648296 | biostudies-literature
Project description:The nature of the Cu-Zn interaction and especially the role of Zn in Cu/ZnO catalysts used for methanol synthesis from CO2 hydrogenation are still debated. Migration of Zn onto the Cu surface during reaction results in a Cu-ZnO interface, which is crucial for the catalytic activity. However, whether a Cu-Zn alloy or a Cu-ZnO structure is formed and the transformation of this interface under working conditions demand further investigation. Here, ZnO/Cu2O core-shell cubic nanoparticles with various ZnO shell thicknesses, supported on SiO2 or ZrO2 were prepared to create an intimate contact between Cu and ZnO. The evolution of the catalyst's structure and composition during and after the CO2 hydrogenation reaction were investigated by means of operando spectroscopy, diffraction, and ex situ microscopy methods. The Zn loading has a direct effect on the oxidation state of Zn, which, in turn, affects the catalytic performance. High Zn loadings, resulting in a stable ZnO catalyst shell, lead to increased methanol production when compared to Zn-free particles. Low Zn loadings, in contrast, leading to the presence of metallic Zn species during reaction, showed no significant improvement over the bare Cu particles. Therefore, our work highlights that there is a minimum content of Zn (or optimum ZnO shell thickness) needed to activate the Cu catalyst. Furthermore, in order to minimize catalyst deactivation, the Zn species must be present as ZnOx and not metallic Zn or Cu-Zn alloy, which is undesirably formed during the reaction when the precatalyst ZnO overlayer is too thin.
| S-EPMC10979448 | biostudies-literature
Project description:The design and exploitation of high-performance catalysts have gained considerable attention in selective hydrogenation reactions, but remain a huge challenge. Herein, we report a RuNi single atom alloy (SAA) in which Ru single atoms are anchored onto Ni nanoparticle surface via Ru-Ni coordination accompanied with electron transfer from sub-surface Ni to Ru. The optimal catalyst 0.4% RuNi SAA exhibits simultaneously improved activity (TOF value: 4293 h-1) and chemoselectivity toward selective hydrogenation of 4-nitrostyrene to 4-aminostyrene (yield: >99%), which is, to the best of our knowledge, the highest level compared with reported heterogeneous catalysts. In situ experiments and theoretical calculations reveal that the Ru-Ni interfacial sites as intrinsic active centers facilitate the preferential cleavage of N-O bond with a decreased energy barrier by 0.28 eV. In addition, the Ru-Ni synergistic catalysis promotes the formation of intermediates (C8H7NO* and C8H7NOH*) and accelerates the rate-determining step (hydrogenation of C8H7NOH*).
| S-EPMC9178046 | biostudies-literature
Project description:We studied the initial stages of Ga interaction with the Cu(001) surface and environment-induced surface transformations in an attempt to elucidate the surface chemistry of the Cu-Ga catalysts recently proposed for CO2 hydrogenation to methanol. The results show that Ga readily intermixes with Cu upon deposition in vacuum. However, even traces of oxygen in the gas ambient cause Ga oxidation and the formation of two-dimensional ("monolayer") Ga oxide islands uniformly covering the Cu surface. The surface morphology and the oxidized state of Ga remain in H2 as well as in a CO2 + H2 reaction mixture at elevated pressures and temperatures (0.2 mbar, 700 K). The results indicate that the Ga-doped Cu surface under reaction conditions exposes a variety of structures including GaO x /Cu interfacial sites, which must be taken into account for elucidating the reaction mechanism.
| S-EPMC7830109 | biostudies-literature
Project description:The hydrogenation of CO2 to CH3OH is an important reaction for future renewable energy scenarios. Herein, we compare Cu/ZnO, Cu/CeO2, and Cu/ZnO-CeO2 catalysts prepared by flame spray pyrolysis. The Cu loading and support composition were varied to understand the role of Cu-ZnO and Cu-CeO2 interactions. CeO2 addition improves Cu dispersion with respect to ZnO, owing to stronger Cu-CeO2 interactions. The ternary Cu/ZnO-CeO2 catalysts displayed a substantially higher CH3OH selectivity than binary Cu/CeO2 and Cu/ZnO catalysts. The high CH3OH selectivity in comparison with a commercial Cu-ZnO catalyst is also confirmed for Cu/ZnO-CeO2 catalyst prepared with high Cu loading (∼40 wt %). In situ IR spectroscopy was used to probe metal-support interactions in the reduced catalysts and to gain insight into CO2 hydrogenation over the Cu-Zn-Ce oxide catalysts. The higher CH3OH selectivity can be explained by synergistic Cu-CeO2 and Cu-ZnO interactions. Cu-ZnO interactions promote CO2 hydrogenation to CH3OH by Zn-decorated Cu active sites. Cu-CeO2 interactions inhibit the reverse water-gas shift reaction due to a high formate coverage of Cu and a high rate of hydrogenation of the CO intermediate to CH3OH. These insights emphasize the potential of fine-tuning metal-support interactions to develop improved Cu-based catalysts for CO2 hydrogenation to CH3OH.
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Project description:Metal-support interaction has been one of the main topics of research on supported catalysts all the time. However, many other factors including the particle size, shape and chemical composition can have significant influences on the catalytic performance when considering the role of metal-support interaction. Herein, we have designed a series of CuxO/ZnO catalysts as examples to quantitatively investigate how the metal-support interaction influences the catalytic performance. The electronic metal-support interactions between CuxO and ZnO were regulated successfully without altering the structure of CuxO/ZnO catalyst. Due to the lower work function of ZnO, electrons would transfer from ZnO to CuO, which is favorable for the formation of higher active Cu species. Combined experimental and theoretical calculations revealed that electron-rich interface result from interaction was favorable for the adsorption of oxygen and CO oxidation reaction. Such strategy represents a new direction to boost the catalytic activity of supported catalysts in various applications.
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