The effect of sodium on the structure–activity relationships of cobalt-modified Cu/ZnO/Al2O3 catalysts applied in the hydrogenation of carbon monoxide to higher alcohols

Oxygen Vacancies Enrichment in Citric Acid-Assisted Synthesis of Zirconia Supported Ni Catalyst for Highly Selective Hydrogenolysis of 5-Hydroxymethylfurfural

2, 5-Dimethylfuran (DMF), which is a promising new-generation liquid biofuel, has attracted widespread attention owing to the sustainability of biomass-derived energy sources. In this study, a highly dispersed zirconia-supported nickel catalyst (CA-Ni/ZrO2) was prepared via citric acid-assisted wetness impregnation for the selective hydrogenolysis of 5-hydroxymethylfurfural (HMF) to produce DMF. The characterization results confirmed the presence of Zr3+ species in the mesoporous CA-Ni/ZrO2 catalyst and the formation of oxygen vacancies during its preparation, which led to the formation of a large number of catalytically active sites for the adsorption and activation of the C=O/C-O groups. Under appropriate reaction parameters, an excellent DMF selectivity of 99.1 % and an HMF conversion of 98.4 % were achieved. A suitable kinetic model revealed that DMF was preferentially formed via the 2,5-dihydroxymethylfuran intermediate route, although a 5-methylfurfural route was also observed. Additionally, the interaction between Ni and ZrO2 significantly affected the stability of the catalyst. This study will provide guidelines for optimizing the catalytic conversion of furan derivatives over heterogeneous catalysts.

Potassium regulating electronic state of zirconia supported palladium catalyst and hydrogen spillover for improved acetylene hydrogenation

High-selectivity acetylene hydrogenation to produce ethylene is an important issue of removing acetylene impurity in ethylene for industrial polyethylene production. Developing high-efficiency catalyst with excellent ethylene selectivity and catalytic durability is desirable but still challenging. In this work, potassium doped palladium catalysts supported on zirconia with different K contents (Pd/ZrO2-xK) have been developed to catalyze acetylene hydrogenation, the Pd/ZrO2-16K exhibits impressive catalytic performance with acetylene conversion of 100 %, ethylene selectivity of 81 % and high catalytic durability. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) and density functional theory (DFT) calculations reveal that K doping effectively weakens the adsorption of ethylene by regulating the electronic state of catalyst to improve ethylene selectivity and substantially lowers the barriers of hydrogen activation and transfer reactions to favor hydrogen spillover, thus conferring a remarkably improved durability on the Pd/ZrO2-16K catalysts.

A Review of Theoretical Studies on Carbon Monoxide Hydrogenation via Fischer-Tropsch Synthesis over Transition Metals

The increasing demand for clean fuels and sustainable products has attracted much interest in the development of active and selective catalysts for CO conversion to desirable products. This review maps the theoretical progress of the different facets of most commercial catalysts, including Co, Fe, Ni, Rh, and Ru. All relevant elementary steps involving CO dissociation and hydrogenation and their dependence on surface structure, surface coverage, temperature, and pressure are considered. The dominant Fischer-Tropsch synthesis mechanism is also explored, including the sensitivity to the structure of H-assisted CO dissociation and direct CO dissociation. Low-coordinated step sites are shown to enhance catalytic activity and suppress methane formation. The hydrogen adsorption and CO dissociation mechanisms are highly dependent on the surface coverage, in which hydrogen adsorption increases, and the CO insertion mechanism becomes more favorable at high coverages. It is revealed that the chain-growth probability and product selectivity are affected by the type of catalyst and its structure as well as the applied temperature and pressure.

Direct synthesis of higher alcohols from syngas over modified Mo2C catalysts under mild reaction conditions

The RhK/Mo2C catalyst exhibited remarkable selectivity for higher alcohols synthesis from syngas under mild reaction conditions owing to the interface sites between Rh and Mo2C promoted by K, which greatly facilitated CO insertion.

CuCo alloy nanonets derived from CuCo2O4 spinel oxides for higher alcohols synthesis from syngas

Porous CuCo alloy nanonets were used as superior catalysts for higher alcohol synthesis from syngas. The catalyst was fabricated via structural topological transformation of CuCo2O4 spinel precursor.

Unravelling the Structural Modification (Meso-Nano-) of Cu/ZnO-Al2O3 Catalysts for Methanol Synthesis by the Residual NaNO3 in Hydroxycarbonate Precursors

The effects of residual NaNO3 on the modification of Cu/ZnO-Al2O3 catalysts have been extensively documented, but the modification mechanism is so far unclear. This work studies in detail the influence of the residual sodium nitrate present in the hydroxycarbonate precursors on their decomposition during calcination and how it affects to the formation and configuration of the final active sites of the Cu/ZnO-Al2O3 catalysts. Different samples with varying sodium content after washing (from 0.01 to 7.3 wt%) were prepared and studied in detail after calcination and reduction steps. The results of this work demonstrated that NaNO3 affects the decomposition mechanism of the hydroxycarbonate precursors during calcination and produces its decarbonation at low temperature. The enhancement of the decarbonation by NaNO3 leads to segregation and crystallization of CuO and ZnO with loss of mesostructure and surface area in the calcined catalysts. The loss of mesostructure in calcined catalysts affects the subsequent reduction step, decreasing the reducibility and damaging the nanostructure of the reduced catalysts forming large Cu particles in poor contact with ZnOx that results in a significant decrease in the intrinsic activity of the copper active sites for methanol synthesis.

Chemical Batteries with CO2

Efforts to obtain raw materials from CO₂ by catalytic reduction as a means of combating greenhouse gas emissions are pushing the boundaries of the chemical industry. The dimensions of modern energy regimes, on the one hand, and the necessary transport and trade of globally produced renewable energy, on the other, will require the use of chemical batteries in conjunction with the local production of renewable electricity. The synthesis of methanol is an important option for chemical batteries and will, for that reason, be described here in detail. It is also shown that the necessary, robust, and fundamental understanding of processes and the material science of catalysts for the hydrogenation of CO₂ does not yet exist.

The Support Effects on the Direct Conversion of Syngas to Higher Alcohol Synthesis over Copper-Based Catalysts

The types of supports employed profoundly influence the physicochemical properties and performances of as-prepared catalysts in almost all catalytic systems. Herein, Cu catalysts, with different supports (SiO2, Al2O3), were prepared by a facile impregnation method and used for the direct synthesis of higher alcohols from CO hydrogenation. The prepared catalysts were characterized using multiple techniques, such as X-ray diffraction (XRD), N2 sorption, H2-temperature-programmed reduction (H2-TPR), temperature-programmed desorption of ammonia (NH3-TPD), X-ray photoelectron spectroscopy (XPS) and in situ Fourier-transform infrared spectroscopy (FTIR), etc. Compared to the Cu/Al2O3 catalyst, the Cu/SiO2 catalyst easily promoted the formation of a higher amount of C1 oxygenate species on the surface, which is closely related to the formation of higher alcohols. Simultaneously, the Cu/Al2O3 and Cu/SiO2 catalysts showed obvious differences in the CO conversion, alcohol distribution, and CO2 selectivity, which were probably originated from differences in the structural and physicochemical properties, such as the types of copper species, the reduction behaviors, acidity, and electronic properties. Besides, it was also found that the gap in performances in two kinds of catalysts with the different supports could be narrowed by the addition of potassium because of its neutralization to surface acidy of Al2O3 and the creation of new basic sites, as well as the alteration of electronic properties.

Synergetic catalysis of bimetallic copper–cobalt nanosheets for direct synthesis of ethanol and higher alcohols from syngas

The reaction scheme of CO hydrogenation to ethanol under the synergetic catalysis of uniformly dispersed bimetallic copper–cobalt nanosheets.

Investigation of copper precursors in the synthesis of higher alcohols from syngas over CuZnAl catalysts without promoters

The catalytic performances of different CuZnAl catalysts prepared using copper nitrate, copper acetate and copper citrate for CO hydrogenation to higher alcohols (C₂₊OH) were studied in a slurry bed reactor.

Bimetallic Ni–Co catalysts supported on Mn–Al oxide for selective catalytic CO hydrogenation to higher alcohols

A sol–gel synthesis provides a facile method for preparing Ni–Co catalysts which contributed to the high selectivity for higher alcohols.

Defect-rich Ni–Ti layered double hydroxide as a highly efficient support for Au nanoparticles in base-free and solvent-free selective oxidation of benzyl alcohol

Defect-rich Ni–Ti layered double hydroxide supported Au nanoparticles exhibited greatly enhanced activity in the oxidation of benzyl alcohol.

The formation mechanism of the initial C-C chain in ethanol synthesis on γ-AlOOH(100)

An in-depth understanding of the reaction mechanism at the molecular level is the key to guide the synthesis of ethanol over the CuZnAl catalyst, which is one of the major challenges for ethanol application in energy. Reported herein is a density functional theory study of ethanol synthesis from mixed methanol and syngas on the γ-AlOOH(100) surface. The possible elementary reactions are unambiguously identified and for the first time we confirm the high reactivity of the γ-AlOOH(100) surface for the initial C-C chain formation via CO insertion into CH₃, which has a 62.8 kJ mol^-1 (0.65 eV) activation barrier that is significantly lower than the barriers previously reported. And its corresponding reaction energy is -288.2 kJ mol^-1 (-2.99 eV). Bader charge analyses indicate that it is advantageous for the nucleophilic attack of CO to the neighboring CH₃ on the γ-AlOOH(100) surface. Our calculations show that ethanol synthesis starts with CH₃OH dissociation, goes through CH₃O dissociation to yield CH₃, subsequently, CO inserts into CH₃ to form CH₃CO, which is further hydrogenated to yield CH₃CHO and eventually obtain C₂H₅OH. And the formation of intermediate CH₃ is the rate-determining step of the overall reaction. The results not only provide new mechanistic insights into the role of γ-AlOOH but also may be useful for the rational designing and optimizing of the CuZnAl catalyst for ethanol synthesis.

Tuning the catalytic CO hydrogenation to straight- and long-chain aldehydes/alcohols and olefins/paraffins

The catalytic CO hydrogenation is one of the most versatile large-scale chemical syntheses leading to variable chemical feedstock. While traditionally mainly methanol and long-chain hydrocarbons are produced by CO hydrogenation, here we show that the same reaction can be tuned to produce long-chain n-aldehydes, 1-alcohols and olefins, as well as n-paraffins over potassium-promoted CoMn catalysts. The sum selectivity of aldehydes and alcohols is usually >50 wt% whereof up to ∼97% can be n-aldehydes. While the product slate contains ∼60% n-aldehydes at /p_CO=0.5, a 65/35% slate of paraffins/alcohols is obtained at a ratio of 9. A linear Anderson–Schulz–Flory behaviour, independent of the /p_CO ratio, is found for the sum of C₄₊ products. We advocate a synergistic interaction between a Mn₅O₈ oxide and a bulk Co₂C phase, promoted by the presence of potassium, to be responsible for the unique product spectra in our studies.

The catalytic CO hydrogenation traditionally produces mainly methanol and long-chain hydrocarbons. Here, the authors show that the same reaction can be tuned to produce long-chain n-aldehydes, 1-alcohols and olefins, as well as n-paraffins over potassium-promoted CoMn catalysts.