Increase in atmospheric CO2 concentration due to the combustion of fossil fuels has been linked to the presently observed global warming phenomenon. In order to mitigate excessive emissions, efforts ...are underway to capture CO2 from various emission sources and sequester it underground. In parallel, utilization of the captured CO2 to produce value added products and fuels has also been advocated. Among these products, methanol, which can be used as a fuel and fuel additive, is of particular interest. Methanol can be synthesized by hydrogenation of CO2 and could therefore lead to a carbon neutral cycle in the frame of a methanol economy, as proposed by the late professor George Olah. In this review, we reflect upon the recent advances in homogeneous reduction of CO2 to methanol using molecular H2. This research area has seen significant progress over the last five years and the recent studies for this challenging transformation are discussed herein. Catalyst activity, selectivity, reaction mechanism and other aspects are analyzed. We also comment on future prospects awaiting exploration to improve the catalytic systems for this reduction. We hope that this review will provide the reader with an overview of the current state of the art on homogeneous CO2 hydrogenation to methanol in a concise manner and provide potential directions in which further investigations can be undertaken in order to eventually make this process economically viable.
In this work, we report that organocatalyst 1-Bcat-2-PPh2–C6H4 ((1); cat = catechol) acts as an ambiphilic metal-free system for the reduction of carbon dioxide in presence of hydroboranes (HBR2 = ...HBcat (catecholborane), HBpin (pinacolborane), 9-BBN (9-borabicyclo3.3.1nonane), BH3·SMe2 and BH3·THF) to generate CH3OBR2 or (CH3OBO)3, products that can be readily hydrolyzed to methanol. The yields can be as high as 99% with exclusive formation of CH3OBR2 or (CH3OBO)3 with TON (turnover numbers) and TOF (turnover frequencies) reaching >2950 and 853 h–1, respectively. Furthermore, the catalyst exhibits “living” behavior: once the first loading is consumed, it resumes its activity on adding another loading of reagents.
In the present work, three kinds of sulfonated poly(arylene ether ketones) (SPAEKs) with different structures are introduced into Nafion as blending modifiers to enhance the properties of Nafion, ...especially methanol resistance. Characterizations such as transmission electron microscope (TEM), proton conductivity, methanol crossover, and single cell performance, are carried out to evaluate these composite membranes (SPAEK@Nafion) as prepared. Besides, recast Nafion membrane is prepared and characterized for comparison via the same method. By investigating the microstructure of SPAEK@Nafion membranes, p-BPAF@Nafion membrane is found to have the most homogeneous distribution and Nafion-like phase separation among these membranes. The pendent sulfobutyl side-chain and fluorinated main chain of p-BPAF make it most similar structure with Nafion among three modifiers, and such Nafion-liked structure provides p-BPAF a good compatibility with Nafion, which can facilitate its enhancement for Nafion. Consequently, p-BPAF@Nafion-7.5 exhibits higher proton conductivity (0.256 S cm−1), lower methanol permeability (1.87 × 10−6 cm2 s−1), and better selectivity (13.69 × 104 S s cm−3) than those of recast Nafion. Therefore, owing to high proton conductivity and good methanol resistance, p-BPAF@Nafion-7.5 possesses a good DMFC performance with an open circuit voltage of 0.836 V and a peak power density of 111.53 mW cm−2, when fed with 2 M methanol at 80 °C.
•Three kinds of SPAEKs are synthesized and used as blending modifiers to enhance the properties of Nafion.•The microstructure of SPAEK@Nafion composite membranes is investigated by TEM.•Composite membranes exhibit DMFC performance than pristine Nafion.•Modifier with Nafion-liked structure (p-BPAF) enhances Nafion-based PEM more significantly.
Palladium (Pd) nanostructures are highly active non‐platinum anodic electrocatalysts in alkaline direct methanol fuel cells (ADMFCs) and their electrocatalytic performance relies highly on their ...morphology and composition. Herein, a facile high‐temperature pyrolysis method to synthesize high‐quality Pd‐palladium oxide (PdO) porous nanotubes (PNTs) by using Pd(II)‐dimethylglyoxime complex (Pd(II)‐DMG) nanorods as a self‐template is reported. The chemical component of pyrolysis products highly correlates with pyrolysis temperature. The electrochemical measurements and density functional theory calculations show the existence of PdO enhances the electroactivity of metallic Pd for both methanol oxidation reaction (MOR) and carbon monoxide oxidation reaction in alkaline media. Benefiting from its one‐dimensionally porous architecture and evident synergistic effect between PdO and Pd (e.g., electronic effect and bifunctional mechanism), Pd‐PdO PNTs achieve a 3.7‐fold mass activity enhancement and improved durability for MOR compared to commercial Pd nanocrystals. Considering the simple synthesis, excellent activity, and long‐term stability, Pd‐PdO PNTs may be highly promising anodic electrocatalysts in ADMFCs.
High‐quality porous palladium (Pd)‐palladium oxide (PdO) nanotubes are synthesized via a facial Pd(II)‐dimethylglyoxime complex nanorods‐induced self‐template method. Benefiting from the one‐dimensionally porous architecture and evident synergistic effect between PdO and Pd, the Pd‐PdO nanotubes achieve a 3.7‐fold mass activity enhancement and improved durability for methanol oxidation reaction compared to commercial Pd nanocrystals, revealing a highly promising robust anodic electrocatalyst in alkaline direct methanol fuel cells.
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In this study, a comparative study was conducted on the three reactor types (the adiabatic, water-cooled and gas-cooled reactor) employed for the traditional syngas to methanol (STM) ...process to investigate their potential applications to the STM process with the CO2-rich feed gas or the CO2 hydrogenation to methanol (CTM) process. The temperature profiles in the axial and radial directions particularly the hot-spot temperatures, operating conditions and methanol yields for the reactors have been investigated using the thermodynamic analysis, the CFD method and the pseudo-homogeneous model. The capital costs for CTM process with the three reactor types have also been evaluated. Compared with the traditional STM process, the STM process with the CO2-rich feed gas and CTM process exhibited reduced hot-spot temperatures. The simulation results showed that the single-bed adiabatic (without internal cooling) reactor and the gas-cooled reactor exhibited potentials for the CTM process, where the hot-spot temperatures the hot-spot temperatures in the reactors can be within the typical operating temperature range (e.g., 220–280 °C) for the catalyst. Regarding the comparison of the three reactor types for the CTM process, the water-cooled reactor showed advantages in terms of efficient heat removal, low hot-spot temperature and relatively wide range of inlet temperature for control. The adiabatic reactor and the gas-cooled reactor demonstrated a relatively low and medium performance, and also a relatively low and medium capital cost, respectively, which indicates the potentials of the two reactor types in a small-scale CTM process.
Sn-based electrocatalysts have recently been applied for CO.sub.2 reduction to generate fuels. Here, tin oxide crossed architectures (SnO) and petal-like Sn.sub.3O.sub.4 semiconductors were ...synthesized using the microwave-assisted hydrothermal method. The synthesized materials were applied in electrochemical reduction of CO.sub.2 and promoted the formation of methanol, ethanol and acetone. The best condition (greatest amount of products) was obtained with - 0.5 V vs Ag/AgCl for both electrocatalysts. For the first time, acetone formation was observed using both SnO and Sn.sub.3O.sub.4 materials. The SnO electrocatalyst exhibited the best electrochemical activity for CO.sub.2 reduction, ascribed to higher charge transfer corroborated by the higher current densities and lower resistance in the Nyquist diagram. Differences in methanol concentration obtained by the samples were ascribed to the different morphology and charge transfer over the films. The results showed that Sn-based electrocatalysts can be applied to generate important products, such as methanol and ethanol, aside from promoting acetone formation.
Direct methanol fuel cells (DMFCs) offer great advantages for the supply of power with high efficiency and large energy density. The search for a cost‐effective, active, stable and methanol‐tolerant ...catalyst for the oxygen reduction reaction (ORR) is still a great challenge. In this work, platinum group metal‐free (PGM‐free) catalysts based on Fe‐N‐C are investigated in acidic medium. Post‐treatment of the catalyst improves the ORR activity compared with previously published PGM‐free formulations and shows an excellent tolerance to the presence of methanol. The feasibility for application in DMFC under a wide range of operating conditions is demonstrated, with a maximum power density of approximately 50 mW cm−2 and a negligible methanol crossover effect on the performance. A review of the most recent PGM‐free cathode formulations for DMFC indicates that this formulation leads to the highest performance at a low membrane–electrode assembly (MEA) cost. Moreover, a 100 h durability test in DMFC shows suitable applicability, with a similar performance–time behavior compared to common MEAs based on Pt cathodes.
No nobles here! Platinum group metal‐free materials based on Fe‐N‐C are investigated as cost‐effective, active, stable and methanol‐tolerant catalysts for the oxygen reduction reaction (ORR) in direct methanol fuel cells (DMFCs). Outstanding performance of DMFCs is observed, even at high methanol concentration (10 m), owing to improved ORR activity and high tolerance to the alcohol.
Developing a laboratory scale or pilot scale chemical process into industrial scale is not trivial. The direct conversion of CO
2
to methanol, and concomitant production of hydrogen from water ...electrolysis on large scale, are no exception. However, when successful, there are certain benefits to this process over the conventional process for producing methanol, both economic and environmental. In this article, we highlight some aspects that are unique to the process of converting pure CO
2
to methanol. Starting from pure CO
2
and a separate pure source of H
2
, rather than a mixture of CO, CO
2
, and H
2
as is the case with syngas, simplifies the chemistry, and therefore also changes the reaction and purification processes from conventional methanol producing industrial plants. At the core of the advantages is that the reaction impurities are essentially limited to only water and dissolved CO
2
in the crude methanol. In this paper we focus on several aspects of the process that direct conversion of CO
2
to methanol enjoys over existing methods from conventional syngas. In particular, we discuss processes for removing CO
2
from a methanol synthesis intermediate product stream by way of a stripper unit in an overhead stream of a distillation column, as well as aspects of a split tower design for the distillation column with an integrated vapo-condenser and optionally also featuring mechanical vapor re-compression. Lastly, we highlight some differences in reactor design for the present system over those used in conventional plants.
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•Two options of CO2 utilized gas-to-methanol (CGTM) process are proposed.•CO2 is converted via CO2/Steam-mixed reforming and CO2 hydrogenation.•Process simulation and conceptual ...design are implemented using Aspen Plus.•Techno-economic analysis is implemented to evaluate the economic feasibility.•Both options are economically feasible in the plant scale range of 2500–5000TPD.
Conceptual design for two options of carbon-dioxide-utilized gas-to-methanol process (CGTM) was implemented by using process simulation software Aspen Plus. The overall mass and energy stream results as well as the thermal and carbon efficiency were obtained from the developed process models. Before the following economic evaluation and sensitivity analysis, total capital investment (TCI) and total product cost (TPC) of both CGTM options were determined. Then, economic evaluation were conducted to assess the economic profitability of the base cases for both CGTM options, using the economic evaluation indicators such as net present value (NPV), internal rate of return (IRR), and discounted payback period (DPBP). Furthermore, sensitivity analysis as well as break-even analysis were also applied to investigate the economic performance of both CGTM options under different circumstances, by changing parameters such as methanol and NG prices, plant scale, and carbon tax. It was shown that the methanol price, CAPEX, and NG price are the most sensitive factors, and the two CGTM options were economically feasible in the plant scale range of 2500–5000 ton per day, according to the economic evaluation indicators NPV, IRR, and DPBP, and were more economically competitive in the case of higher plant scale and carbon tax.
A two‐dimensional (2D) carbon nanofilm with uniform artificial nanopores is an ideal material to ultimately suppress the fuel permeation in the proton exchange membrane fuel cells. Graphdiyne has ...great mechanical strength, high dimensional stability, and controllable nanopores, and has good prospects to play this crucial role. It is found that graphdiyne nanofilm with amino groups and natural nanopores can be easily prepared with high integrity. The aminated graphdiyne has good compatibility with the Nafion matrix owing to the acid–base interaction between them. The excellent comprehensive properties of graphdiyne in selectivity, dimensional stability, and integrity effectively improve the power performance and stability of fuel cells at wide temperature. Our results can be developed into a universal method that can easily realize the selective separation of ions and small molecules, and open a new way for the emerging applications in green energy.
A 2D aminated graphdiyne nanofilm with well‐ordered structure is prepared. Its intrinsic in‐plane selectivity is beneficial for suppressing methanol crossover. The performance and durability of the direct methanol fuel cell are thus greatly improved.
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