scholarly journals CO2 Hydrogenation to Methanol over La2O3-Promoted CuO/ZnO/Al2O3 Catalysts: A Kinetic and Mechanistic Study

Catalysts ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 183 ◽  
Author(s):  
Marios Kourtelesis ◽  
Kalliopi Kousi ◽  
Dimitris I. Kondarides
Keyword(s):  
Intermediate Formation ◽  
Reaction Rates ◽  
Catalytic Performance ◽  
High Specific Surface Area ◽  
Mechanistic Study ◽  
Partial Pressures ◽  
Surface Formate ◽  
Adsorption Of Co2 ◽  
In Situ Infrared Spectroscopy

The hydrogenation of CO2 to methanol has been investigated over CuO/ZnO/Al2O3 (CZA) catalysts, where a part of the Al2O3 (0, 25, 50, 75, or 100%) was substituted by La2O3. Results of catalytic performance tests obtained at atmospheric pressure showed that the addition of La2O3 generally resulted in a decrease of CO2 conversion and in an increase of methanol selectivity. Optimal results were obtained for the CZA-La50 catalyst, which exhibited a 30% higher yield of methanol, compared to the un-promoted sample. This was attributed to the relatively high specific surface area and porosity of this material, the creation of basic sites of moderate strength, which enhance adsorption of CO2 and intermediates that favor hydrogenation steps, and the ability of the catalyst to maintain a large part of the copper in its metallic form under reaction conditions. The reaction mechanism was studied with the use of in situ infrared spectroscopy (DRIFTS). It was found that the reaction proceeded with the intermediate formation of surface formate and methoxy species and that both methanol and CO were mainly produced via a common formate intermediate species. The kinetic behavior of the best performing CZA-La50 catalyst was investigated in the temperature range 190–230 °C as a function of the partial pressures of H2 (0.3–0.9 atm) and CO2 (0.05–0.20 atm), and a kinetic model was developed, which described the measured reaction rates satisfactorily.

scholarly journals Hydrotalcite-Type Materials Electrodeposited on Open-Cell Metallic Foams as Structured Catalysts

Inorganics ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 74 ◽  
Author(s):  
Phuoc Ho ◽  
Erika Scavetta ◽  
Domenica Tonelli ◽  
Giuseppe Fornasari ◽  
Angelo Vaccari ◽  
...  
Keyword(s):  
Catalytic Performance ◽  
H2 Production ◽  
High Specific Surface Area ◽  
Metallic Foams ◽  
Open Cell ◽  
Structured Catalysts ◽  
Fundamental Understanding ◽  
Acidic Sites ◽  
Coating Procedure

Structured catalysts based on hydrotalcite-derived coatings on open-cell metallic foams combine tailored basic/acidic sites, relatively high specific surface area and/or metal dispersion of the coating as well as low pressure drop and enhanced heat and mass transfer of the 3D metallic support. The properties of the resulting structured catalysts depend on the coating procedure. We have proposed the electro-base generation method for in situ and fast precipitation of Ni/Al and Rh/Mg/Al hydrotalcite-type materials on FeCrAlloy foams, which after calcination at high temperature give rise to structured catalysts for syngas (CO + H2) production through Steam Reforming and Catalytic Partial Oxidation of CH4. The fundamental understanding of the electrochemical-chemical reactions relevant for the electrodeposition and the influence of electrosynthesis parameters on the properties of the as-deposited coatings as well the resulting structured catalysts and, hence, on their catalytic performance, were summarized.

scholarly journals Ambient base-free glycerol oxidation over bimetallic PdFe/SiO2 by in situ generated active oxygen species

2021 ◽  
Author(s):  
Ricci Underhill ◽  
Mark Douthwaite ◽  
Richard J. Lewis ◽  
Peter J. Miedziak ◽  
Robert D. Armstrong ◽  
...  
Keyword(s):  
Heterogeneous Catalysts ◽  
Bimetallic Catalyst ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Active Oxygen Species ◽  
Catalytic Performance ◽  
Resonance Spectroscopy ◽  
Oxygen Species ◽  
Paramagnetic Resonance ◽  
Temperature Oxidation

AbstractLow temperature oxidation of alcohols over heterogeneous catalysts is exceptionally challenging, particularly under neutral conditions. Herein, we report on an efficient, base-free method to oxidise glycerol over a 0.5%Pd-0.5%Fe/SiO2 catalyst at ambient temperature in the presence of gaseous H2 and O2. The exceptional catalytic performance was attributed to the in situ formation of highly reactive surface-bound oxygenated species, which promote the dehydrogenation on the alcohol. The PdFe bimetallic catalyst was determined to be significantly more active than corresponding monometallic analogues, highlighting the important role both metals have in this oxidative transformation. Fe leaching was confirmed to occur over the course of the reaction but sequestering experiments, involving the addition of bare carbon to the reactions, confirmed that the reaction was predominantly heterogeneous in nature. Investigations with electron paramagnetic resonance spectroscopy suggested that the reactivity in the early stages was mediated by surface-bound reactive oxygen species; no homogeneous radical species were observed in solution. This theory was further evidenced by a direct H2O2 synthesis study, which confirmed that the presence of Fe in the bimetallic catalyst neither improved the synthesis of H2O2 nor promoted its decomposition over the PdFe/SiO2 catalyst.

In situ growth of ultrathin Ni–Fe LDH nanosheets for high performance oxygen evolution reaction

2017 ◽  
Vol 4 (7) ◽  
pp. 1173-1181 ◽  
Author(s):  
Haidong Yang ◽  
Sha Luo ◽  
Yun Bao ◽  
Yutong Luo ◽  
Jun Jin ◽  
...  
Keyword(s):  
Oxygen Evolution ◽  
Oxygen Evolution Reaction ◽  
High Performance ◽  
Copper Foil ◽  
Catalytic Performance ◽  
In Situ Growth ◽  
Ultrathin Nanosheet

The ultrathin Ni70Fe30LDH nanosheets were successfullyin situgrown on anodic polarized copper foil, denoted as u-Ni70Fe30LDHs/a-CF. Benefiting from the ultrathin nanosheet structure, the catalyst exhibits remarkable catalytic performance for OER in 1 M KOH solution.

scholarly journals Perborate Oxidation of Substituted 5-Oxoacids in Aqueous Acetic Acid Medium: A Kinetic and Mechanistic Study

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
S. Shree Devi ◽  
B. Muthukumaran ◽  
P. Krishnamoorthy
Keyword(s):  
Acetic Acid ◽  
Acid Medium ◽  
Reaction Rate ◽  
Reaction Medium ◽  
Activation Parameters ◽  
Reaction Rates ◽  
Mechanistic Study ◽  
Aqueous Acetic Acid ◽  
Sodium Perborate ◽  
Acetic Acid Medium

Kinetics and mechanism of oxidation of substituted 5-oxoacids by sodium perborate in aqueous acetic acid medium have been studied. The reaction exhibits first order both in [perborate] and [5-oxoacid] and second order in [H+]. Variation in ionic strength has no effect on the reaction rate, while the reaction rates are enhanced on lowering the dielectric constant of the reaction medium. Electron releasing substituents in the aromatic ring accelerate the reaction rate and electron withdrawing substituents retard the reaction. The order of reactivity among the studied 5-oxoacids is p-methoxy ≫ p-methyl > p-phenyl > –H > p-chloro > p-bromo > m-nitro. The oxidation is faster than H2O2 oxidation. The formation of H2BO3+ is the reactive species of perborate in the acid medium. Activation parameters have been evaluated using Arrhenius and Eyring’s plots. A mechanism consistent with the observed kinetic data has been proposed and discussed. Based on the mechanism a suitable rate law is derived.

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