Oxidation Of Dimethyl Ether Research Articles

(Invited) High Temperature Membrane Electrode Assemblies for Intermediate Temperature Fuel Cells: Past, Present, and Future

Fuel cells that operate between approximately 150 oC and 250 oC accrue certain advantages, most notably facilitated operation with low grade / low cost hydrogen sourced from carbon feedstocks, robust cathode performance in the presence of air contaminants, absence of balance of plant components for stack water management, high quality heat, and readily sourced materials of construction. Fuel cells running at these intermediate temperatures with phosphoric acid as the electrolyte currently hold the record for a commercial lifetime warrantee (1). Yet, lower temperature polymer electrolyte fuel cells (PEFC) operating at under 100 oC and comprised of a conductive membrane, electrodes, and gas diffusion layers offer the potential for low cost assembly at high volumes, especially if these components are made in roll-to-roll processes. The better of these two technologies would be a hybrid high temperature Membrane Electrode Assembly (MEA) based on phosphoric acid electrolyte. The first hybrid high temperature (HT) MEA made use of polybenzimidazole (PBI) as a membrane matrix for phosphoric acid and originated from the Case Western Reserve University team of Litt, Savinell and Wainright in the early 1990s as part of a research proposal to the Defense Advanced Research Projects Agency (DARPA). Their initial motivation was to develop a system that could overcome the limitations of direct methanol oxidation at under 100 oC (2). Although ultimately not viable for direct methanol oxidation, hydrogen oxidation with 1-2 % CO proved good enough to license the technology to PEMEAS, the company that developed the first commercial PBI HT MEA based on pre-formed membranes of PBI. However, using a preformed PBI membrane posed some limitations on acid content, and through the efforts of Calundann and Benicewicz, a second generation PBI membrane was invented (3). This new process identified a technique to polymerize PBI in the presence of polyphosphoric acid (PPA), and then hydrolyze the cast film to phosphoric acid (PA). The change of solvent from PPA to PA also radically changed the morphology of the PBI from a viscous solution into a tough second generation PBI plastic that held over 90 % by weight PA. This development also radically simplified the construction of HT MEAs by eliminating the acid soaking step. Due to the nature of these materials, new gas diffusion electrode architectures were developed and optimized to accommodate a membrane-electrode interface substantially different than that found in LT MEA assemblies. This electrode effort on roll coaters was awarded a Department of Energy Manufacturing R&D award (4). Ultimately, BASF purchased PEMEAS, as well as the electrode team at PEMEAS. In parallel to the development of the polybenzimidazole (PBI) system, Advent Technologies identified and developed a pyridine polymer based TPS® system also using PA imbibed into the membrane matrix. Advent’s TPS membranes operate over a wide temperature range from ~120 °C to greater than 200 °C. In 2014, Advent became the licensee of BASF’s PBI MEA and gas diffusion electrode technology. Advent develops, manufactures, and markets both the PBI and TPS MEAs. This presentation will present an overview of the commercial and technical history of developing HT MEAs, including some of the latest membrane advances like the third generation PBI MEAs, and cross-linked TPS MEAs operating at 210 oC, and conclude with future directions such as the application of HT MEAs in facilitating direct oxidation of dimethyl ether (DME). http://www.doosanfuelcell.com/en/main.doRobert F. Savinell and Jesse Wainright, "Overture: The Early History of PBI/Phosphoric acid membranes," in High Temperature Polymer Electrolyte Membrane Fuel Cells: Approaches, Status and Perspectives, edited by Qingfeng Li, David Aili, Hans Aage Hjuler and Jens Oluf Jensen, Spring International Publishing, 2016.For example, G. Calundann et al. US Patent 7,820,314.US Department of Energy Annual Merit Review, 2013.

Catalytic combustion of dimethyl ether over α-MnO2 nanostructures with different morphologies

Herein, α-MnO2 catalysts with three well-defined morphologies (nanorod, ultra-long nanowire and microsphere) were rational designed and prepared by the hydrothermal route, and their catalytic activities were evaluated for the dimethyl ether (DME) combustion. These nanostructured α-MnO2 catalysts were characterized in detail by various analytical techniques: XRD, FESEM, TEM, BET, XPS and H2-TPR. As a result, the α-MnO2 nanorod exhibited the higher catalytic activity (T10=170°C and T90=238°C at WHSV=30,000mLg−1h−1) than the other two α-MnO2 samples due to its larger specific surface area, higher average oxidation state of Mn, more abundant surface lattice oxygen (Olatt) species and higher reducibility, and there was no obvious decrease after the α-MnO2 nanorod was run for 50h. Moreover, the transient response technique revealed that the Olatt species of the α-MnO2 nanorod should be the crucial role in the deep oxidation of DME.

Quantification of the Keto-Hydroperoxide (HOOCH2OCHO) and Other Elusive Intermediates during Low-Temperature Oxidation of Dimethyl Ether.

This work provides new temperature-dependent mole fractions of elusive intermediates relevant to the low-temperature oxidation of dimethyl ether (DME). It extends the previous study of Moshammer et al. [ J. Phys. Chem. A 2015 , 119 , 7361 - 7374 ] in which a combination of a jet-stirred reactor and molecular beam mass spectrometry with single-photon ionization via tunable synchrotron-generated vacuum-ultraviolet radiation was used to identify (but not quantify) several highly oxygenated species. Here, temperature-dependent concentration profiles of 17 components were determined in the range of 450-1000 K and compared to up-to-date kinetic modeling results. Special emphasis is paid toward the validation and application of a theoretical method for predicting photoionization cross sections that are hard to obtain experimentally but essential to turn mass spectral data into mole fraction profiles. The presented approach enabled the quantification of the hydroperoxymethyl formate (HOOCH2OCH2O), which is a key intermediate in the low-temperature oxidation of DME. The quantification of this keto-hydroperoxide together with the temperature-dependent concentration profiles of other intermediates including H2O2, HCOOH, CH3OCHO, and CH3OOH reveals new opportunities for the development of a next-generation DME combustion chemistry mechanism.

Kinetic studies of ozone assisted low temperature oxidation of dimethyl ether in a flow reactor using molecular-beam mass spectrometry

The ozone assisted low temperature oxidation chemistry of dimethyl ether (DME) from 400K to 750K has been investigated in the mixture of DME/O3/O2/He/Ar in an atmospheric-pressure flow reactor coupled with the molecular beam mass spectrometry (MBMS) sampling technique. The mole fraction of ozone was varied from 0 to 0.146% in the mixture to study its enhanced kinetic effect on DME oxidation. The mole fractions of DME, O2, O3, CH2O, H2O2, CO, CO2, and CH3OCHO were quantified as functions of temperature at a fixed total volumetric flow rate. The experimental results revealed that the presence of ozone dramatically enhances the low temperature DME oxidation. Numerical simulations using the existing kinetic models (Kurimoto's model (KM) (Kurimoto et al., 2015), Burke's model (BM) (Burke et al., 2015), and Wang's model (WM) (Wang et al., 2015)) with an ozone sub-mechanism over-predicted the DME oxidation significantly. The observed large discrepancies between models and experiments for DME, CH2O, O2 and CH3OCHO mole fractions suggested that there were large uncertainties in the branching ratios of two competing chain-propagation and chain-branching reaction pairs involving CH3OCH2O2 and CH2OCH2O2H radicals at low temperature.

Facilitated Direct Dimethyl Ether Fuel Cells through High Temperature Membrane Electrode Assemblies

In searching for an exemplary carbon neutral fuel, dimethyl ether (DME) may be the most appealing. This simplest of the ethers can be readily produced from renewably sourced hydrogen and CO2, making it essentially a hydrogen carrier (1). Both nontoxic and easy to liquefy under moderate pressure, DME closely matches diesel and has been run in trucks (2). The ubiquitous propane grill tanks can store DME without modification. Recently, Los Alamos National Laboratory (LANL) demonstrated the potential for direct oxidation of DME in a fuel cell.The breakthrough of our work is LANL’s highly active catalyst for direct oxidation of DME that in the early phase of development shows similar performance to direct methanol when using typical low-temperature membranes. However, the output is not sufficient to approach commercial acceptance targets for higher power applications or precious metal cost. High-temperature membrane electrode assemblies (HT-MEAs), based on phosphoric-acid-imbibed membranes, operate at 160 °C to 180 °C without additional water and are highly tolerant to carbon monoxide – an intermediate of DME oxidation. This work exploits a novel ternary LANL anode catalyst with the features of high-temperature operation to produce high-power, low-cost direct DME MEAs.In support of direct DME oxidation, scientists at LANL have recently shown a direct liquid fuel cell operating with DME as part of a program to develop technology for direct methanol (MeOH), ethanol (EtOH), and DME fuel cells (3). In this work, it has been shown that DME can be directly oxidized via a PtRuPd ternary catalyst that not only activates the ether bonds but facilitates the removal of CO as a reaction by product (Figure 1). Even at this early stage, the team led by LANL has shown results that approach a highly developed DMFC system with regards to performance and precious metal loading (3). One highly relevant aspect of this work is the sharp temperature dependency of the current-voltage behavior, with an increase in the cell temperature from 80 °C to 90 °C leading to an increase in the current density at 0.5 V by ca. 50%, from 140 mA cm-2 to 220 mA cm- 2 High-temperature PEM MEAs developed by BASF for the polybenzylimide (PBI) system or pyridine polymer based TPS®system of Advent Technologies, Inc. have demonstrated utility and robustness when operating with highly impure reformates of around 1-3% CO (4). Similarly, cathode sensitivity to air contaminants is also ameliorated. The electrolyte in both systems is phosphoric acid imbibed into a stable and inert polymer matrix. Phosphoric acid is notable in that it does not need water to conduct protons, and can do so over a wide temperature range from ~120 °C to more than 200 °C. Advent is a licensee of BASF’s MEA and gas-diffusion-electrode technology.This presentation will summarize our on-going efforts at facilitating direct oxidation of DME by using high temperature PEM MEAs with both PBI and TPS combined with the LANL catalyst operating at 160 oC to 180 oC. Olah, G.A., Goeppert, A. and Prakash, G.K. Surya in J. Org. Chem., 2009, 74, 487-498. Hutchinson, H., 2013 in ASME web article www.asme.org/engineering-topics/articles/transportation/diesel-alternative-hits-the-road. Advanced Materials and Concepts for Portable Power Fuel Cells, 2014 Hydrogen and Fuel Cells Program AMR presentation. Technical Brochure, 2014 Advent Technologies, Inc. at www.Advent-Energy.com. Figure 1

Transient plasma effects on the autoignition of DME/O2/Ar and C3H8/O2/Ar mixtures

The effects of transient plasma discharge on the autoignition characteristics of dimethyl ether and propane mixtures with oxygen and argon were investigated computationally in a zero-dimensional constant pressure environment. A simple model of hydrocarbon decomposition by electron collisions was superimposed on detailed chemical kinetic models that describe the low temperature oxidation of dimethyl ether and propane. The results suggest that the effectiveness of plasma discharges in promoting autoignition is very high at low temperatures. However, in the negative temperature coefficient region, the plasma discharge was determined to be less effective in promoting autoignition, as a result of complexity of the neutral state chemistry. The degree of effectiveness was quantified and was determined to differ significantly for different mixtures. An explanation for these differences is presented based on what is currently known about low temperature hydrocarbon kinetics.

Review of Acetic Acid Synthesis from Various Feedstocks Through Different Catalytic Processes

Acetic acid (AA) has been largely used with a wide range of applications such as a raw material for a synthesis of vinyl acetate monomer, cellulose acetate or acetate anhydrate, acetate ester and a solvent for a synthesis of terephthalic acid and so on. The present paper briefly summarizes the commercialized chemical processes with their Rh or Ir-based catalytic systems in a liquid-phase carbonylation reaction such as Monsanto, Cativa and Acetica processes. In addition, some alternative catalytic systems such as heterogeneous catalysts to produce AA by direct oxidation or indirect carbonylation of dimethyl ether through BP-SaaBre process in a gas-phase reaction to solve some problems such as a difficult separation of homogeneous catalysts in a corrosive reaction medium. Some home-made heterogeneous catalysts such as a rhodium incorporated graphitic carbon nitride (Rh-g-C3N4) and some heterogenized homogeneous catalysts using the supports of tungsten carbide, iron oxide or graphitic carbon nitride containing rhodium complexes were also introduced for the synthesis of AA through a liquid-phase methanol carbonylation reaction to effectively solve the leaching problem of active rhodium metal as well as to mitigate the separation problem of homogeneous catalysts.

Catalytic oxidation of dimethyl ether

The total count number concentration of particles from 10 to 1000 nm, particle size distribution, and PM2.5 (aerodynamic diameter ≤ 2.5 μm) mass concentration were measured on a parking apron next to the runway at Tianjin International Airport in China. The data were collected 250, 270, 300, 350, and 400 m from the runway. Wind direction and wind speed played important roles in determining the characteristics of the atmospheric particles. An inverted U-shaped relationship was observed between the measured particle number concentration and wind speed, with an average peak concentration of 2.2 × 105 particles/cm3 at wind speeds of approximately 4–5 m/s. The atmospheric particle number concentration was affected mainly by aircraft takeoffs and landings, and the PM2.5 mass concentration was affected mainly by the relative humidity (RH) of the atmosphere. Ultrafine particles (UFPs, diameter < 100 nm), with the highest number concentration at a particle size of approximately 16 nm, dominated the measured particle size distributions. The calculated particle emission index values for aircraft takeoff and landing were nearly the same, with mean values of 7.5 × 1015 particles/(kg fuel) and 7.6 × 1015 particles/(kg fuel), respectively. The particle emission rate for one aircraft during takeoff is two orders of magnitude higher than for all gasoline-powered passenger vehicles in Tianjin combined. The particle number concentrations remained much higher than the background concentrations even beyond 400 m from the runway.

Kinetics of dimethyl ether oxidation over Pt/ZSM-5 catalyst

A kinetic study of dimethyl ether (DME) combustion over Pt/ZSM-5 was performed below 423 K. Power law model and Langmuir-Hinshelwood model were established to predict the reaction rate. Reaction orders for DME and O2 were 0.28 and 2.30, respectively. Activation energies for the two models were 99.35 and 109.30 kJ/mol. The reaction orders and adsorption constants suggested DME was more strongly adsorbed on Pt/ZSM-5 than O2 at low temperatures. The reliability of the models was confirmed by the comparison between the predicted and experimental conversions of DME.

A detailed combined experimental and theoretical study on dimethyl ether/propane blended oxidation

In this paper, a binary fuel model for dimethyl ether (DME) and propane is developed, with a focus on engine-relevant conditions (10–50atm and 550–2000K). New rapid compression machine (RCM) data are obtained for the purpose of further validating the binary fuel model, identifying reactions important to low-temperature propane and DME oxidation, and understanding the ignition-promoting effect of DME on propane. It is found that the simulated RCM data for DME/propane mixtures is very sensitive to the rates of C3H8+OH, which acts as a radical sink relative to DME oxidation, especially at high relative DME concentrations. New rate evaluations are conducted for the reactions of C3H8+OH=products as well as the self-reaction of methoxymethyl peroxy (in competition with RO2=QOOH isomerization) of 2CH3OCH2O2=products. Accurate phenomenological rate constants, k(T, P), are computed by RRKM/ME methods (with energies obtained at the CCSD(T)-F12a/cc-pVTZ-F12 level of theory) for several radical intermediates relevant to DME. The model developed in this paper (120 species and 711 reactions) performs well against the experimental targets tested here and is suitable for use over a wide range of conditions. In addition, the reaction mechanism generator software RMG is used to explore cross-reactions between propane and DME radical intermediates. These cross-reactions did not have a significant effect on simulations of the conditions modeled in this paper, suggesting that kinetic models for high- and low-reactivity binary fuel mixtures may be assembled from addition of their corresponding submodels and a small molecule foundation model.

Interactions of Metal Oxo Species with Platinum-Based Catalysts Toward More Efficient Electrooxidation of Dimethyl Ether: Comparison to Methanol

Methanol is so far the most commonly considered fuel as an alternative to hydrogen. However, the practical performance is limited by several factors, which include the slow kinetics of methanol oxidation and crossover of methanol from the anode to the cathode side of the cell. More recently, there has been growing interest in dimethyl ether (CH3OCH3), a gas commonly used in aerosol propellants, solvents and coolants, as a possible alternative fuel for low temperature fuel cells. Dimethyl ether (DME) is non-toxic, non-teratogenic, non-mutagenic and non-carcinogenic gas. When oxidized to CO2, a CH3OCH3 molecule releases 12 electrons. The fuel has several advantages over typical organic fuels. Unlike ethanol (CH3CH2OH), the CH3OCH3 ether does not require breaking of the C-C bond. A fairly low CH3OCH3 dipole moment results in the lower ether crossover (through the membrane) in comparison to methanol. Dimethyl ether is much less toxic than methanol and can be readily stored and transported using existing technologies. In addition, the CH3OCH3 ether has potentially higher energy density relative to methanol (namely, 8.2 vs. 6.1 kWh kg-1). Platinum is one of the typical catalysts for the oxidation of organic molecules. It is quite active toward the dehydrogenation step, but suffers from the CO oxidation step. The bimetalic catalysts (e.g. PtRu, PtSn) can lower the onset potential of DME oxidation peak from 0.5 V for Pt/C to 0.4 V vs. Normal Hydrogen Electrode (NHE), but the maximum current densities are obtained on Pt/C. We propose here to study the electrooxidation of DME at Pt and PtRu nanoparticles that have been deposited onto nanostructured zirconium(IV) oxide matrix (thin film on electrode surface). Zirconia is known to act as a catalytic component capable of enhancing the reactivity of the electrocatalytic system by increasing the overall acidity at the reaction interface. When combined (as a support) with Pt or PtRu centers, the existence of large population of hydroxyl groups on ZrO2 surface is believed to facilitate desorption of CO adsorbates from Pt and to induce their oxidation to CO2. In the presence of nanostructured zirconia (existing in the vicinity of the catalytic metal), the transport of protons at the electrocatalytic interface is also favored. Synergistic interactions between ruthenium and zirconia components are also feasible. In the present report, we will not limit our results to DME, but similar effects have been observed during oxidation of methanol. We are also going to consider combination of Pt or PtRu with the other metal (Pd) or metal (W, Mo) oxo nanostructures. The support from National Research Center (NCN), Poland under the MAESTRO Project No 2012/04/A/ST4/00287 is highly appreciated.

Low-Temperature Oxidation of Dimethyl Ether to Polyoxymethylene Dimethyl Ethers over CNT-Supported Rhenium Catalyst

Due to its excellent conductivity, good thermal stability and large specific surface area, carbon nano-tubes (CNTs) were selected as support to prepare a Re-based catalyst for dimethyl ether (DME) direct oxidation to polyoxymethylene dimethyl ethers (DMMx). The catalyst performance was tested in a continuous flow type fixed-bed reactor. H3PW12O40 (PW12) was used to modify Re/CNTs to improve its activity and selectivity. The effects of PW12 content, reaction temperature, gas hourly space velocity (GHSV) and reaction time on DME oxidation to DMMx were investigated. The results showed that modification of CNT-supported Re with 30% PW12 significantly increased the selectivity of DMM and DMM2 up to 59.0% from 6.6% with a DME conversion of 8.9%; besides that, there was no COx production observed in the reaction under the optimum conditions of 513 K and 1800 h−1. The techniques of XRD, BET, NH3-TPD, H2-TPR, XPS, TEM and SEM were used to characterize the structure, surface properties and morphology of the catalysts. The optimum amount of weak acid sites and redox sites promotes the synthesis of DMM and DMM2 from DME direct oxidation.

Effects of tetrahedral molybdenum oxide species and MoOx domains on the selective oxidation of dimethyl ether under mild conditions

A new preparation method for MoO3–SnO2 catalysts precipitated by HNO3 was developed to selectively synthesize industrially useful chemicals formaldehyde and methyl formate via oxidation of dimethyl ether.

Application of modified CNTs with Ti(SO4)2 in selective oxidation of dimethyl ether

The possible reaction pathway of DME oxidation to DMM2 over Ti(SO4)2/CNTs.

New Insight into Competition between Decomposition Pathways of Hydroperoxymethyl Formate in Low Temperature DME Oxidation

Hydroperoxymethyl formate is a crucial intermediate formed during the low-temperature oxidation of dimethyl ether. The decomposition pathways of HOOCH2OCHO were calculated at QCISD(T)/CBS//B3LYP/6-311++G(d,p) level. The temperature- and pressure-dependent rate constants are computed using microcanonical variational transition state theory coupled with the RRKM/master equation calculations. The calculations show that a pathway leads to the formation of formic acid and a Criegee intermediate does exist, besides the direct dissociation channel to OH and OCH2OCHO radicals. However, formation of the Criegee intermediate has never been considered as an intermediate in dimethyl ether combustion before. The computed rate constants indicate that the newly confirmed pathway is competitive to the direct dissociation route and it is promising to reduce the low-temperature oxidation reactivity. Also electronic effect of groups, e.g. -CHO and O atom, is taken into account. Moreover, Hirshfeld atomic charge and natural bond order analysis are performed to explain this phenomenon from a perspective of chemical nature.

A microreactor with metallic catalyst support for hydrogen production by partial oxidation of dimethyl ether

A microreactor system with porous metallic catalyst support was prepared and its catalytic efficiency and long term stability were compared with those of a conventional pack bed reactor using partial oxidation of DME for production of hydrogen. The microreactor system had a thin layer of γ-Al2O3 on FeCrAl metal foam as catalyst support. The pack bed reactor had γ-Al2O3 balls densely packed in a quartz tube. With enough catalyst materials (0.5wt% Rh), both of the reactors showed good hydrogen yield higher than 90% at reaction temperature up to 750°C. However, with decreasing Rh content, the pack bed reactor showed deteriorating reaction efficiency while the microreactor maintained the efficiency. In the end, in order to maintain similar reaction efficiency for long term hydrogen production, 10 times more Rh content was necessary for the pack bed reactor than that needed for the microreactor. The pack bed reactor maintained hydrogen production only up to about 120h, while the microreactor maintained hydrogen production up to 1200h, 10 times longer than that of pack bed reactors. This comparison shows superior reaction efficiency and stability of metallic support loaded microreactors over conventional ceramic support loaded pack bed reactors for exothermic and high temperature reactions.

Quantification of HO2 and other products of dimethyl ether oxidation (H2O2, H2O, and CH2O) in a jet-stirred reactor at elevated temperatures by low-pressure sampling and continuous-wave cavity ring-down spectroscopy

Measuring the formation of HO2 and H2O2 from the oxidation of fuels is challenging but extremely important for determining their tendency to follow chain-termination pathways from R + O2 compared to chain-branching leading to the production of OH radicals. Furthermore, such data are vital for improving existing detailed chemical kinetics models. Dimethyl ether (DME), a clean renewable fuel, is the simplest ether exhibiting cool flame oxidation chemistry, a key-process for auto-ignition in internal combustion engines. Although the oxidation of DME has been studied in the past, little information is available for the production of HO2 and H2O2. The oxidation of dimethyl ether was performed in a jet-stirred reactor at atmospheric pressure, over a range of temperatures (∼540–850 K) and equivalence ratios (φ = 0.5–2) and, for the first time, the concentrations of HO2 and H2O2 were measured using a newly developed experimental setup involving low-pressure sampling and near-infrared cw-cavity ring down spectroscopy. Concentrations of H2O and CH2O were also measured. These new experimental results extend the available kinetic database for the oxidation of dimethyl ether which is needed to assess the validity of combustion kinetics models, as shown here.

Cobalt-iron oxides made by CVD for low temperature catalytic application

Thin films of cobalt-iron oxides (CoFe2O4) with spinel-type structure were prepared by pulsed-spray evaporation chemical vapor deposition (PSE-CVD) using Fe(acac)3 and Co(acac)3 as precursors. The optimal depositions of CVD-type growth have been established and such growth can be achieved at 400 °C. The obtained films have been systematically characterized in terms of structure (XRD and Raman), surface, and bulk composition (XPS and EDS) as well as morphology (SEM). CoFe2O4 has been successfully tested as an active catalyst toward total oxidation of CO, C3H6, dimethyl ether (DME), and n-C4H8. The results indicate that both the lattice and adsorbed oxygen presented at the surface of the catalyst play determinant roles in the catalytic oxidation process.

High‐Activity PtRuPd/C Catalyst for Direct Dimethyl Ether Fuel Cells

Dimethyl ether (DME) has been considered as a promising alternative fuel for direct-feed fuel cells but lack of an efficient DME oxidation electrocatalyst has remained the challenge for the commercialization of the direct DME fuel cell. The commonly studied binary PtRu catalyst shows much lower activity in DME than methanol oxidation. In this work, guided by density functional theory (DFT) calculation, a ternary carbon-supported PtRuPd catalyst was designed and synthesized for DME electrooxidation. DFT calculations indicated that Pd in the ternary PtRuPd catalyst is capable of significantly decreasing the activation energy of the CO and CH bond scission during the oxidation process. As evidenced by both electrochemical measurements in an aqueous electrolyte and polymer-electrolyte fuel cell testing, the ternary catalyst shows much higher activity (two-fold enhancement at 0.5 V in fuel cells) than the state-of-the-art binary Pt50 Ru50 /C catalyst (HiSPEC 12100).

Experimental and Modeling Investigation of the Low-Temperature Oxidation of Dimethyl Ether.

The oxidation of dimethyl ether (DME) was studied using a jet-stirred reactor over a wide range of conditions: temperatures from 500 to 1100 K; equivalence ratios of 0.25, 1, and 2; residence time of 2 s; pressure of 106.7 kPa (close to the atmospheric pressure); and an inlet fuel mole fraction of 0.02 (with high dilution in helium). Reaction products were quantified using two analysis methods: gas chromatography and continuous wave cavity ring-down spectroscopy (cw-CRDS). cw-CRDS enabled the quantification of formaldehyde, which is one of the major products from DME oxidation, as well as that of hydrogen peroxide, which is an important branching agent in low-temperature oxidation chemistry. Experimental data were compared with data computed using models from the literature with important deviations being observed for the reactivity at low-temperature. A new detailed kinetic model for the oxidation of DME was developed in this study. Kinetic parameters used in this model were taken from literature or calculated in the present work using quantum calculations. This new model enables a better prediction of the reactivity in the low-temperature region. Under the present JSR conditions, error bars on predictions were given. Simulations were also successfully compared with experimental flow reactor, jet-stirred reactor, shock tube, rapid compression machine, and flame data from literature. The kinetic analysis of the model enabled the highlighting of some specificities of the oxidation chemistry of DME: (1) the early reactivity which is observed at very low-temperature (e.g., compared to propane) is explained by the absence of inhibiting reaction of the radical directly obtained from the fuel (by H atom abstraction) with oxygen yielding an olefin + HO2·; (2) the low-temperature reactivity is driven by the relative importance of the second addition to O2 (promoting the reactivity through branching chain) and the competitive decomposition reactions with an inhibiting effect.