Enhanced Methanol Production over Non-promoted CuMgOAl2O3 Materials with Ex-solved 2 nm Cu Particles: Insights from an Operando Spectroscopic Study (original) (raw)
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ACS Catalysis, 2022
Enhanced methanol production is obtained over a non-promoted Cu−MgO−Al 2 O 3 mixed oxide catalyst derived from a Cu−Mg−Al hydrotalcite precursor (HT) containing narrowly distributed small Cu NPs (2 nm). Conversions close to the equilibrium (∼20%) with a methanol selectivity of 67% are achieved at 230°C, 20 bar, and a space velocity of 571 mL•g cat −1 •h −1. Based on operando spectroscopic studies, the striking activity of this Cu-based catalyst is ascribed to the stabilization of Cu + ions favored under reaction conditions due to lattice reorganization associated with the "HT-memory effect" promoted by water. Temperature-resolved infrared−mass spectrometry experiments have enabled the discernment of monodentate formate species, stabilized on Cu + as the intermediate in methanol synthesis, in line with the results of density functional theory calculations. These monodentate formate species are much more reactive than bridge formate species, the latter ones behaving as intermediates in methane and CO formation. Moreover, poisoning of the Cu 0 surface by strongly adsorbed species behaving as spectators is observed under reaction conditions. This work presents a detailed spectroscopic study highlighting the influence of the reaction pressure on the stabilization of active surface sites, and the possibility of enhancing methanol production on usually less active non-promoted nano-sized copper catalysts, provided that the proper support is selected, allowing the stabilization of doped Cu +. Thus, a methanol formation rate of 2.6 × 10 −3 mol MeOH •g cat −1 •h −1 at 230°C, 20 bar, and WHSV = 28 500 mL•g cat −1 •h −1 is obtained on the Cu−MgO−Al 2 O 3 HTderived catalyst with 71% methanol selectivity, compared to 2.2 × 10 −4 mol MeOH •g cat −1 •h −1 with 54% methanol selectivity obtained on a reference Cu/(Al 2 O 3 /MgO) catalyst not derived from a HT structure.
Catalysis Research
A precursor CuO/ZnO/Al2O3 catalyst for methanol synthesis has been prepared at room temperature by introducing a ternary salt solution into the excess of sodium carbonate solution following the reverse co-precipitation method. The catalyst was tested for the synthesis of methanol from synthesis gas. The composition (vol. %) has been presented: CO, 22; CO2, 5.8; N2, 5.5; H2, balance. The methanol productivity was recorded to be 2.7 kg kgcat–1 h–1 at a temperature of 260 °С, a pressure of 3 MPa, and a space velocity of 61,700 l (kgcat)–1 h–1. The possibility of regenerating the activity of a catalyst subjected to conditions of artificial aging (overheating in a syngas environment) has been tested: approximately 92% of the initial activity could be restored. Physicochemical studies were conducted using the thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), the scanning electron microscopy (SEM), and the X-ray diffraction (XRD) techniques using the Cu, Zn,...
On the role of adsorbed atomic oxygen and CO2 in copper based methanol synthesis catalysts
Catalysis Letters, 1994
The role of adsorbed atomic oxygen in methanol synthesis is investigated by a series of transient experiments of the interaction of CO and CO2 with a ternary Cu/ZnO/A1203 catalyst under methanol synthesis conditions. In particular, the response of adding CO and CO2 aspulses and as steps to the reaction gas mixture is studied. Hereby it is possible to study both the formation of CO2 from the reaction of adsorbed atomic oxygen (O-*) with CO, and the dissociation of CO2 in situ, i.e., while the catalyst is producing methanol. The experiments show no evidence of a significant coverage of O-* under methanol synthesis conditions. In addition, it is shown that COz is the main carbon source in methanol synthesis under the given conditions.
ACS Catalysis, 2020
Dispersion of metallic Cu nanoparticles on a metal oxide support increases the number of exposed metallic Cu sites and/or Cu-support interfacial sites, resulting in good catalytic performance for CO 2-to-methanol hydrogenation. However, the formation of highly dispersed Cu nanoparticles is challenging because they are easily sintered. Here, we studied Cu nanoparticle formation by a simple deposition−reduction technique using Cu-doped MgAl 2 O 4 (Mg 1−x Cu x Al 2 O 4). Mg 1−x Cu x Al 2 O 4 possessed the following three types of Cu 2+ species: short O−Cu octahedrally coordinated [CuO 6 ] s , elongated O−Cu octahedrally coordinated [CuO 6 ] el , and tetrahedrally coordinated [CuO 4 ] t. The former two are found in the inverse-spinel-type Mg 1−x Cu x Al 2 O 4 , while the other is found in the normal-spinel-type Mg 1−x Cu x Al 2 O 4. Additionally, by focusing on the difference in the reducibility of the Cu 2+ species, we clarified that their fraction is related to Cu loading. For low Cu loading (x < 0.3), Mg 1−x Cu x Al 2 O 4 mainly contained the [CuO 6 ] s species. On the other hand, for high Cu loading (x ≥ 0.3), the fraction of the [CuO 6 ] el and [CuO 4 ] t species increased. Notably, among the prepared catalysts, H 2-reduced Mg 0.8 Cu 0.2 Al 2 O 4 (x = 0.2) had the largest number of exposed metallic Cu sites, resulting in its good catalytic performance. Hence, the H 2 reduction of [CuO 6 ] s is essential for forming metallic Cu nanoparticles on metal oxides.
Catalysts
Renewable methanol, obtained from CO2 and hydrogen provided from renewable energy, was proposed to close the CO2 loop. In industry, methanol synthesis using the catalyst CuO/ZnO/Al2O3 occurs at a high pressure. We intend to make certain modification on the traditional catalyst to work at lower pressure, maintaining high selectivity. Therefore, three heterogeneous catalysts were synthesized by coprecipitation to improve the activity and the selectivity to methanol under mild conditions of temperature and pressure. Certain modifications on the traditional catalyst Cu/Zn/Al2O3 were employed such as the modification of the synthesis time and the addition of Pd as a dopant agent. The most efficient catalyst among those tested was a palladium-doped catalyst, 5% Pd/Cu/Zn/Al2O3. This had a selectivity of 64% at 210 °C and 5 bar.
Reaction Kinetics, Mechanisms and Catalysis, 2013
This paper demonstrates the benefit of using a ternary Cu-Cr-Al system as a support for palladium catalysts in the methanol synthesis reaction (MS) obtained from CO hydrogenation. The influence of ternary oxide composition and palladium addition on the physicochemical and catalytic properties of Pd/Cu-Cr-Al catalysts in methanol synthesis is discussed. The physicochemical properties of the studied systems were examined by XRD, TPR and BET methods. The promotion effect of palladium on the catalytic activity and reduction of ternary oxide was proven. It was found that palladium promoted catalysts prepared from palladium nitrate precursor showed higher yield in methanol formation.