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•A highly efficient photo-reactor configuration for CO2 abatement is presented.•A broad absorption Ni catalyst is used in the photocatalytic conversion of CO2.•Thermal and non-thermal ...effects allow a high conversion and selectivity to CH4.•The performance of the photoreactor is ≈ 10 times higher than previous reports.
Methane can be obtained from the direct hydrogenation of CO2 via the Sabatier reaction. This reaction is usually performed at high temperatures and/or pressures but it has been recently reported that in the presence of certain nanostructured catalysts, CO2 methanation can proceed at lower temperatures in solar photo-assisted processes. In this study, an inexpensive and commercially available nickel-based catalyst (Ni/Al2O3·SiO2) has been selected to perform the continuous CO2 hydrogenation in a fixed bed photocatalytic reactor using high-radiance/low consumption light emitting diodes (LEDs). These illumination conditions allowed us to attain the reaction temperatures required without the need of additional heating sources. Different LED excitation wavelengths and irradiances were evaluated. Under selected irradiation conditions (460 nm wavelength) not only the photothermal but also the photo-catalytic conversion of CO2 into CH4 takes place, with high selectivity. Conversion levels above 70% with production rates of ca. 35 mmol CH4 g−1 h-1 were obtained, outperforming the results obtained by conventional heating methods or with other irradiation wavelengths.
Hydrogenation of carbon dioxide (CO2) to formic acid by the enzyme formate dehydrogenase (FDH) is a promising technology for reducing CO2 concentrations in an environmentally friendly manner. ...However, the easy separation of FDH with enhanced stability and reusability is essential to the practical and economical implementation of the process. To achieve this, the enzyme must be used in an immobilized form. However, conventional immobilization by physical adsorption is prone to leaching, resulting in low stability. Although other immobilization methods (such as chemical adsorption) enhance stability, they generally result in low activity. In addition, mass transfer limitations are a major problem with most conventional immobilized enzymes. In this review paper, the effectiveness of metal organic frameworks (MOFs) is assessed as a promising alternative support for FDH immobilization. Kinetic mechanisms and stability of wild FDH from various sources were assessed and compared to those of cloned and genetically modified FDH. Various techniques for the synthesis of MOFs and different immobilization strategies are presented, with special emphasis on in situ and post synthetic immobilization of FDH in MOFs for CO2 hydrogenation.
•Conversion of CO2 to valuable products is preferable over sequestration.•Formate dehydrogenase can be used to convert CO2 to formic acid.•Enzyme recovery and reuse can be effectively achieved by immobilization in metal organic frameworks.•Recent progress of Formate dehydrogenase immobilization in MOFs are presented.
Formaldehyde (HCHO) is a crucial C1 building block for daily‐life commodities in a wide range of industrial processes. Industrial production of HCHO today is based on energy‐ and cost‐intensive ...gas‐phase catalytic oxidation of methanol, which calls for exploring other and more sustainable ways of carrying out this process. Utilization of carbon dioxide (CO2) as precursor presents a promising strategy to simultaneously mitigate the carbon footprint and alleviate environmental issues. This Minireview summarizes recent progress in CO2‐to‐HCHO conversion using hydrogenation, hydroboration/hydrosilylation as well as photochemical, electrochemical, photoelectrochemical, and enzymatic approaches. The active species, reaction intermediates, and mechanistic pathways are discussed to deepen the understanding of HCHO selectivity issues. Finally, shortcomings and prospects of the various strategies for sustainable reduction of CO2 to HCHO are discussed.
This Minireview summarizes recent progress in the production of HCHO from CO2, including chemical catalysis (hydrogenation using H2 and hydroboration/hydrosilylation), photo/electrocatalysis, and biocatalysis (enzymatic reduction). From analysis of advantages and deficits of each methodology, we present viewpoints and potential strategies for optimizing the CO2‐to‐HCHO conversion.
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•Fluorinated hydrotalcites are synthesized by incorporation of (AlF6)3− into layers.•The incorporation of fluorine greatly improved the fraction of strongly basic site.•CH3OH ...selectivity first increases obviously and then decreases with increased F/Al.•The introduction of suitable amount of (AlF6)3− can enhance CH3OH yield markedly.
A series of fluorinated Cu/Zn/Al/Zr hydrotalcite-like compounds are synthesized by incorporation of different amount of (AlF6)3− into hydrotalcite-like sheets. The fluorine-modified Cu/ZnO/Al2O3/ZrO2 catalysts are then obtained by calcination and reduction of fluorinated precursors. With increasing of F/Al atomic ratios, the Cu particle size increases continuously and the Cu surface area and dispersion decrease gradually, as well as the amount of moderately and strongly basic sites first increases significantly and then decreases. The catalytic performance for the methanol synthesis from CO2 hydrogenation is examined. The change of CO2 conversion is small when F/Al≤0.8, while the CO2 conversion decreases remarkably with further increase of fluorine content. It is also found that the CH3OH selectivity is closely related to the distribution of basic sites and the selectivity of CH3OH takes a volcanic trend with increased fluorine content. The introduction of suitable amount of (AlF6)3− into the hydrotalcite-like structure can enhance the methanol yield markedly and the fluorine-modified catalysts with F/Al=0.83 affords the substantial stability and the best catalytic performance.
•Concept design of a novel biomass-solar system for methanol production.•Four indicators are defined to build a framework for developing the system.•Time-dependent performance of a large-scale solar ...power plant is investigated.•Various scenarios are evaluated for the electricity to the water electrolysis.
One solution to achieving a large scale distribution, transportation and storage of renewable energy is methanol production from renewable-based power plants integrated with hydrogenation. In this study, a novel non-combustion heat-carrier biomass gasifier system is proposed, coupled with a large-scale solar power plant and alkaline water electrolysis system, for methanol production from syngas, water and carbon dioxide. Aspen Plus, MATLAB and TRNSYS are used to simulate and assess the performance of each component of the proposed system, under different climatic conditions of Toronto, Canada, and Crotone, Italy. In both localities, the best energy performance that minimizes the grid energy interaction factor is obtained with a photovoltaic station of 50.4 MW coupled to biomass gasification, which leads to 0.60 kWh and 0.57 kWh, respectively, in Toronto and Crotone, of electricity sent to or drawn from the grid for each kWh required by the electrolyser. However, higher profitability may be achieved in both localities with a single biomass gasification system which brings an enhanced benefit of 0.56 M€ in Toronto and 0.44 M€ in Crotone for each kW installed. It is expected that the developed modelling approach and these four newly formulated dimensionless indicators, i.e., the satisfied load fraction, utilization factor, grid energy interaction factor, and grid economic interaction value can be used to evaluate large-scale integrated renewable-based power systems.
The main objective of the present study is to synthesize iron oxide catalysts with engineered crystal defects and to clarify their crucial impact on the final catalytic activity in the CO2 ...hydrogenation process. The method used to engineer the desired crystal defects is based on changing the precipitation reaction conditions, such as the addition rate and the order of the precipitant during the primary phase of the synthesis of iron oxide catalysts. The catalyst synthesis process is based on the formation of iron oxalates in the first step, followed by thermal decomposition into iron oxides in the second step, which were subsequently tested as catalysts in CO2 hydrogenation. The reversed double-beam photoacoustic spectroscopy used for advanced characterization of the prepared catalysts demonstrated that the observed change in catalytic activity is related to the energy and density of electron traps connected with the defects in the crystal lattice of the catalysts. These defects occur during the precipitation of oxalates, and their formation is significantly affected by changes in the precipitation conditions, i.e., the course of nucleation and growth of iron oxalate crystals. The results of the presented study thus affirmed the cardinal importance of defect engineering in heterogeneous catalysis.
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•Changes in the rate and order of reactant mixing significantly affect the catalytic activity of the resulting catalysts.•Using reversed double-beam photoacoustic spectroscopy to evaluate the energy and density of electron traps.•Confirmation of the link between the catalytic activity of the iron catalysts and the energy and density of electron traps.
The total entropy generation rate, internal exergy loss and exergy efficiency of the membrane reactor of methanol synthesis via carbon dioxide hydrogenation are compared, and the results show that ...the total entropy generation rate minimization is equivalent to the internal exergy loss minimization and the exergy efficiency maximization under the fixed inlet exergy. Therefore, this paper optimizes the membrane reactor with total entropy generation rate minimization as an optimization objective under a fixed methanol production rate. The optimal temperatures curves of exterior walls for three optimal membrane reactors with different boundary conditions are obtained by using optimal control theory and nonlinear programming. The influences of other geometric and operating parameters on optimization results of optimal membrane reactors are analyzed. The results indicate that when inlet temperatures of the reaction mixture and mixture in the permeable tube are unfixed, the optimizing curve of exterior wall temperature makes the total entropy generation rate of membrane reactor reduce by 12.39% compared with the total entropy generation rate of a reference membrane reactor with a linear exterior wall temperature. Decreasing the inlet molar flow rate of sweep gas and gas hourly space velocity and increasing inlet pressure of reaction mixture, the inlet pressure of mixture in the permeable tube and heat transfer coefficients are favorable for decreasing the total entropy generation rate in the membrane reactor. As the porosity of catalyst bed and reactor length increases, the minimum total entropy generation rate decreases first and then increases. From the perspective of engineering application, this paper establishes two membrane reactors (membrane reactor heated by three-stage furnaces of the same length and membrane reactor heated by three-stage furnaces of different lengths), respectively. The minimum total entropy generation rates of the two reactors are reduced by 11.67% and 11.79% compared with the total entropy generation rate in the reference membrane reactor, respectively. The obtained results are beneficial to the optimal design of energy-efficient membrane reactors.
In this paper, the optimization of the methanol production process is investigated. For this purpose, the parameters affecting methanol production including catalyst type (4 cases), temperature, ...pressure, and GHSV have been investigated and then by selecting the appropriate catalyst and process conditions, possible process changes such as hydrogen injection as make up, applying two reactors and inert gases, the use of dry hydrogen, and adding recycle stream on methanol yield have been studied.
Then, by selecting the appropriate process, simulating, and validating the simulation results, the selected catalyst is used for the process. The process is simulated in 8 cases with changes in the studied parameters and the amount of recycle flow. Then, the key parameters of the optimized process were compared with the baseline. The results showed that, the investment costs (smaller dimensions of process equipment such as compressors, reactors, and distillation columns, etc. due to recycling flow reduction) and current costs (including electricity and steam consumption), significantly improved.
In general, the use of CuZnOAl2O3 catalyst in the methanol production process reduced the reactor temperature, decreased the recycle flow by about 38% and reduced the electrical energy consumption and steam consumption relative to the baseline by about 5% and 67%, respectively. Finally by the process optimization conducted in this work, in addition to reducing the recycle flow and reducing energy consumption, it is possible to annually reduce the GHG emissions of 7526.35 ton CO2eq and 19.43 tons of air pollutants (per 100 kton/y of methanol production).
•The process parameters affecting methanol production were optimized.•The recycle flow and energy consumption were reduced by 38% and 17%, respectively.•The GHG and air pollutants were decreased by about 16.9% relative to the baseline.
A facile one‐step method to shape covalent triazine frameworks (CTFs) for catalytic applications is reported. Phase inversion of the CTF powder by using a polyimide as a binder in a microfluidic ...device results in the formation of composite spheres with accessible CTF porosity and a high mechanical and thermal stability. The fabricated spheres can be used to host organometallic complexes. The obtained shaped catalysts, Ir@CTF spheres, are active and fully recyclable in the direct hydrogenation of carbon dioxide into formic acid under mild reaction conditions (20 bar and 50–90 °C) and in the dehydrogenation of formic acid.
Shaping covalent triazine frameworks: A facile one‐step method to shape covalent triazine frameworks (CTFs) into composite spheres with accessible porosity, and high mechanical and thermal stability is reported. The fabricated spheres were used to host organometallic complexes and the obtained catalyst Ir@CTF spheres is active and fully recyclable in the direct hydrogenation of carbon dioxide into formic acid.
An optimization model is established for the reaction process of CO2 hydrogenation to light olefins in a fixed-bed tubular reactor based on finite time thermodynamics or entropy generation ...minimization theory. In the present study, the specific generation rate (entropy generation rate averaged by the production rate of the target product) is proposed as an optimization objective function and the optimal design parameters which minimize the objective function have been investigated. The model is developed based on the reversible kenetic models and their cooresponding kinetic parameters, which are obtained by fitting the experimental data. The irreversibilities due to heat transfer, chemical reactions and viscous flow are considered and the local entropy generation rate of each term is calculated according to the irreversible thermodynamics. The analyses of the performance characteristics are conducted as well. The results show that the CO2 hydrogenation to light olefins accords with a two-step reaction mechanism, and Fischer-Tropsch reaction is the rate-controlling step. The irreversibility mainly located in the front of the reactor, which most contributions are caused by chemical reactions. The reductions of the specific entropy generation up to 24.78% and 10.04% can be achieved for optimal reactor inner diameter and optimal catalyst bed density, respectively.
•Reaction process of CO2 hydrogenation to light olefins is studied.•Finite time thermodynamics is applied.•A one-dimensional mathematical model of industrial reactor is established.•Entropy generation rate is minimized.•It considers heat transfer, chemical reaction and viscous flow processes.
