Highly selective CuO/γ–Al2O3 catalyst promoted with hematite for efficient methanol dehydration to dimethyl ether

A recent alternative for replacing traditional hydrocarbons like gasoline, diesel, and natural gas, is the use of dimethyl ether (DME), which is more environmentally friendly. One of the ongoing challenges is to catalyze methanol dehydration for selectively producing the DME (2CH₃OH → CH₃OCH₃ + H₂O). It is established that the CuO catalyst over alumina performs the methanol dehydration, but the formation of by-products is the main drawback. For these reasons, we synthesized a CuO/γ–Al₂O₃ catalyst promoted with hematite aiming to enhance the activity toward DME at atmospheric conditions. The resulting bimetallic catalyst (CuO-Fe₂O₃/Al₂O₃) performed a 70% conversion at 290 °C, which is similar to other catalysts recently reported in the literature but done in harsh conditions. In addition, this bimetallic catalyst exhibited a 100% in selectivity toward the DME production. XPS spectra of the fresh and used catalyst suggested that the chemical oxidation states of Cu and Fe remain without change. After regenerating the catalyst at 600 °C for 2 h in air, it performed at a similar catalytic conversion, confirming the reusability of the as-synthesized material and reducing the environmental impact.     

Facile preparation of ultra-low Pt loading graphene-immobilized electrode for methanol oxidation reaction

Pulse current electrodeposition (PCE) technique was used to prepare graphene-supported platinum nanoparticles (GN-PtNPs) electrodes for the methanol electro-oxidation reaction in acidic media. The influences of the PCE parameters (applied current density, concentration of the Pt precursor, and duty cycle) upon the as-prepared GN-PtNPs electrodes for the methanol oxidation reaction (MOR) in terms of catalytic activity and tolerance against poisoning were studied using the Taguchi design of experiment (DOE). The analysis of variance (ANOVA) and signal-to-noise (S/N) ratio analysis provided prediction of optimal electrodeposition conditions to yield GN-PtNPs electrode which give the best MOR performance. The values of confirmatory experiment were demonstrated close to the values predicted using the Taguchi method. Transmission electron microscopy images showed that the Pt crystallites in flower-like structure were deposited evenly on the surface of graphene sheet. The Pt crystallites were predominantly in a zero-valent, metallic Pt state based on the X-ray photoelectron spectroscopy analysis.     

Homogeneous polymer/filler composite membrane by spraying method for enhanced direct methanol fuel cell performance

In this work, composite membranes for a direct methanol fuel cell (DMFC) were prepared using a spraying method to improve cell performance especially at a high methanol concentration. Nafion polymer and mordenite as a filler were used for the composite membrane preparation using a spraying method and a conventional solution casting method and the membranes from the two methods were compared. SEM images showed that a more homogeneous composite membrane could be obtained using the spraying method. The effect of mordenite content was also studied. The membranes were consequently characterized and tested in DMFC operation. The results were compared to those prepared using the solution casting method at 30, 50, and 70 °C with methanol concentrations of 2, 4, and 8 M. It was found that the membrane with 5 wt.% mordenite from the spraying method showed a vast improvement in DMFC performance. When the cell was operated at 70 °C, the maximum power density of 5 wt.% mordenite from the spraying method was higher than that of commercial membrane and 5 wt.% from the solution casting method. Power densities from the 5 wt.% sprayed membrane were higher by around 29%, 40%, and 60% at 2, 4, and 8 M methanol concentration, respectively.     

Catalytic hydrogenation of CO2 from 600 MW supercritical coal power plant to produce methanol: A techno-economic analysis

Electricity and water from renewable hydropower plant are used as input for electrolysis unit to generate hydrogen, while CO₂ is captured from 600 MW supercritical coal power plant using post-combustion chemical solvent based technology. The captured CO₂ and H₂ generated through electrolysis are used to synthesize methanol through catalytic thermo-chemical reaction. The methanol synthesis plant is designed, modeled and simulated using commercial software Aspen Plus^®. The reactor is analyzed for two widely adopted kinetic models known as Graaf model and Vanden-Bossche (VB) model to predict the methanol yield and CO₂ conversion. The results show that the methanol reactor based on Graaf kinetic model produced 0.66 tonne of methanol per tonne of CO₂ utilized which is higher than that of the VB kinetic model where 0.6 tonne of methanol is produced per tonne of CO₂ utilized. The economic analysis reveals that 1.2 billion USD annually is required at the present cost of both H₂ production and CO₂ abatement to utilize continuous emission of 3.2 million tonne of CO₂ annually from 600 MW supercritical coal power unit to synthesize methanol. However, sensitivity analysis indicates that methanol production becomes feasible by adopting anyone of the route such as by increasing methanol production rate, by reducing levelised cost of hydrogen production, by reducing CO₂ mitigation cost or by increasing the current market selling price of methanol and oxygen.     

Numerical study of flow distribution uniformity for the optimization of gradient porosity configuration of porous copper fiber sintered felt for hydrogen production through methanol steam reforming micro-reactor

A macroscopic numerical method is proposed to study the flow distribution uniformity of a novel porous copper fiber sintered felt (PCFSF), which has gradient porosities and was developed as the methanol steam reforming micro-reactor catalyst support for hydrogen production for fuel cell applications. The macroscopic porous media developed by the ANSYS/FLUENT software is used to represent the PCFSF. Our results indicate that the gradient porosity can reshape the flow distribution of PCFSFs greatly, thus producing significant influence on their performance. It is further revealed that, for a PCFSF with a determined gradient porosity configuration but different reactant feed directions, the velocity uniformity can be used as a quantitative criterion to evaluate the performance of hydrogen production. Furthermore, new gradient PCFSFs are produced according to the flow distribution of original gradient PCFSFs. The preliminary experimental results of the new gradient PCFSFs of 0.8-0.9-0.7 and 0.7-0.9-0.8 exhibit better methanol conversion and H₂ flow rate. This indicates that the numerical method can be used for the optimization of PCFSFs' gradient porosity configuration, which consists of the shape and position of the interfaces between different porosity portions, the number of interfaces and the porosity distribution in different portions.     

Porous Ni2P nanoflower supported on nickel foam as an efficient three-dimensional electrode for urea electro-oxidation in alkaline medium

Porous Ni₂P nanoflower supported on nickel foam (Ni₂P@Ni foam) electrodes are synthesized via a simple hydrothermal growth strategy accompanied with further phosphating treatment. The prepared electrodes are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). Electro-catalytic performances towards urea electro-oxidation are tested by cyclic voltammetry (CV), chronoamperometry (CA) coupled with electrochemical impedance spectroscopy (EIS). By phosphating Ni(OH)₂ precursor, the final obtained Ni₂P@Ni foam electrode presents a porous Ni₂P nanoflower structure within abundant porosity, and so exposes a large amount of electro-catalytic active sites and electronic transmission channels to accelerate the interfacial reaction. Compared with Ni(OH)₂@Ni foam precursor, the Ni₂P@Ni foam catalyst exhibits more excellent electro-catalytic activity as well as lower onset oxidation potential. Remarkably, the Ni₂P@Ni foam catalyst reaches a peak current density of 750 mA cm^?2 with an onset oxidation potential of 0.24 V (vs. Ag/AgCl) accompanied by an excellent stability in 0.60 M urea with 5.00 M KOH solutions. Benefiting from the unique porous nanosheet structure, the as-synthesized Ni₂P@Ni foam catalyst performs a highly enhanced catalytic behavior for alkaline urea electro-oxidation, indicating that the material can be hopefully applied in direct urea fuel cells.     

Pt supported on boron,nitrogen co-doped carbon nanotubes (BNC NTs) for effective methanol electrooxidation

The research for electrocatalyst with high electroactivity and great CO-resistance ability for direct methanol fuel cells (DMFCs) is still a huge challenge. In this report, we develop Boron, Nitrogen co-doped carbon nanotubes (BNC NTs) as a support for Pt. Owing to the doping of boron, the catalyst not only provides extremely active sites for methanol oxidation reactions (MOR) but also protects Pt nanoparticles from agglutinating, performing superior electroactivity and excellent ability to anti CO poisoning. The X-ray photoelectron spectroscopy (XPS) results demonstrate the strong electron effect between Pt and B. Notably, the Pt/BNC NTs catalyst exhibits higher catalytic activity towards MOR and more superior durability in comparison with Pt/NC NTs and commercial JM Pt/C catalyst. The accelerated durability test (ADT) illustrates that Pt/BNC NTs catalyst can improve the issue of electrochemical surface area (ECSA) conservation, with only 30% diminish in comparison with the initial ECSA after 5000 cycles. The experiment result demonstrate that boron doping is the key step to improve the catalytic activities and CO-resistance ability due to the combination effects, involving firm B–C and N–C bonds, the stronger electron transfer in the nanotube structure among Pt, B and N, the stronger adsorption intensity of oxygen species from doped B.     

Investigation of the versatility of SPES membranes customized with sulfonated molybdenum disulfide nanosheets for DMFC applications

Sulfonated poly(ether sulfone) (SPES) based proton exchange membranes (PEMs) are fabricated using sulfonated molybdenum disulfide (S-MoS₂) nanosheets via facile solution casting method. SPES (DS = 30%) and S-MoS₂ are synthesized and sulfonation is evidently observed in FTIR and XRD analysis. The anchoring of sulfonic acid group on exfoliated molybdenum disulfide (E-MoS₂) and elemental composition of S-MoS₂ are confirmed by XPS spectrum. Physico-chemical characteristics such as ion-exchange capacity (IEC), water uptake, swelling ratio and oxidation stability are found to be increases after the addition of S-MoS₂ into SPES matrix. Increment in S-MoS₂ content in SPES matrix decreases the surface contact angle due to the increase in hydrophilicity. Further, the dispersing ability of S-MoS₂ in SPES matrix is evidently shown by an increase in surface roughness, tensile strength and thermal stability of the SPES/S-MoS₂ nanocomposite membranes. On the whole, SPES/S-MoS₂-1 membrane showed the highest proton conductivity of 5.98 × 10⁻³ Scm⁻¹, selectivity of 19.6 × 10⁴ Scm⁻³s, peak power density of 28.28 mWcm⁻² and lesser methanol permeability of 3.05 × 10⁻⁸ cm²s⁻¹. The strong interfacial interaction between SPES and S-MoS₂ in nanocomposite membranes create strong hydrogen bond network to facilitate the proton conduction pathway via both vehicle and Grotthuss type mechanisms. Overall results suggested that the SPES/S-MoS₂ nanocomposite membranes are superior and appropriate alternative for commercially high-cost Nafion® membranes for use in renewable direct methanol fuel cell (DMFC) devices.     

Technical assessment of liquefied natural gas,ammonia and methanol for overseas energy transport based on energy and exergy analyses

Transporting energy in liquefied forms results in reduction in volume, which enables energy to be transported economically over long overseas distances. In this study, liquefied natural gas, liquid ammonia and methanol are proposed to transport the energy of natural gas in different forms to overseas. Due to temperature difference between the energy storage medium and the ambient, a portion of liquefied energy carriers mass is lost as boil-off gas (BOG). Therefore, a technical assessment based on energy and exergy analyses is conducted in this work to assess the total required energy and losses due to BOG for each energy carrier. To make a fair comparison among the energy carriers, the ship volume capacity is the fixed factor. The results show that the total daily energetic BOGs for LNG, ammonia, and methanol are calculated as 0.610%, 0.098%, 0.034% while the exergetic BOGs are 0.491%, 0.068%, 0.032%, respectively. Ammonia and methanol generate significantly less daily BOG, respectively, compared to LNG during the full supply chain, which make them alternative for efficient energy carrier transport.     

Boosting cell performance and fuel utilization efficiency in a solar assisted methanol microfluidic fuel cell

Solar generated hydrogen from an optimized P25 thin film of 3.2 mg/cm² with 0.25% of platinum as co-catalyst improves the peak power output of a methanol microfluidic fuel cell operated with a methanol to water ratio of 1:1 almost ninefold, from 22 mW/cm² to 213 mW/cm². Different methanol to water ratios in the fuel tank generate similar amounts of hydrogen, but the cell performance has large variations due to the different oxidation kinetics of hydrogen and methanol in the fuel breathing anode, resulting in a mixed-potential anodic performance. The trade-off between power output and fuel utilization diminishes in this system. The methanol utilization efficiency at peak power operation increases from 50% (for 0.2 V) to 78% (for 0.5 V) for methanol to water ratio of 1:1. The result indicates that in-situ generation of hydrogen by solar light can be applied to both portable and large-scale stationary fuel cells.