Ethanol from hydrogen and carbon monoxide via methanol homologation

The carbonylation of methanol using a rhodium complex catalyst is a commercial route for the manufacture of acetic acid (Monsanto process). Using the same catalytic system Dumas [J. Organometall. Chem.177, 239 (1979)] has been able to direct the reaction towards ethanol formation using syngas mixtures very rich in hydrogen. Unfortunately the data reported by Dumas are not completely reliable. We have reinvestigated this interesting process and confirmed that the homologation of methanol may be a most promising process for the production of oxygenated C₂ chemicals.     

Kinetic interactions between hydrogen and carbon monoxide oxidation over platinum

The heterogeneous chemistry coupling of H₂ and CO over platinum was investigated experimentally and numerically for H₂/CO/O₂/N₂ mixtures with overall lean equivalence ratios φ = 0.13–0.26, H₂:CO molar ratios 1:5–3:1, and a pressure of 5 bar. Experiments were performed in an optically accessible channel-flow reactor at surface temperatures 510–827 K and involved in situ Raman measurements of major gas-phase species concentrations and thermocouple measurements of surface temperatures. Emphasis was placed on the low temperature range 510–600 K, whereby H₂ inhibited the CO oxidation, and which was of particular relevance to gas turbine idling and part-load operation. Comparisons of measurements with 2-D simulations attested the aptness of the employed kinetic scheme, not only for H₂/CO fuel mixtures but also for pure CO. Measured and predicted transition temperatures below which H₂ inhibited CO oxidation agreed well with each other, showing a main dependence on the overall equivalence ratio (550 ± 5 K at φ = 0.13 and 600 ± 5 K at φ = 0.26) and a weaker dependence on the H₂:CO ratio. Furthermore, this inhibition was non-monotonically dependent on the H₂:CO ratio, becoming higher at a value of 1:1. The inhibiting kinetic effect of H₂ was an outcome of the competition between H₂ and CO/O₂ for surface adsorption and, most importantly, of the competition between the adsorbed H(s) and CO(s) for surface-deficient O(s). Finally, transient simulations in practical catalytic channels revealed the interplay between kinetic and thermal effects. While at φ = 0.13 the H₂/CO reactive mixture exothermicity was insufficient to overtake the kinetic inhibition, at φ = 0.26 catalytic ignition could still be achieved at temperatures well-below the transition temperature. The effect of H₂:CO molar ratio on the light-off times was quite strong, suggesting care when designing syngas catalytic rectors with varying compositions.     

Effect of carbon monoxide on the electrooxidation of hydrogen by tungsten carbide

The effect of carbon monoxide (CO) on the anodic oxidation of hydrogen by tungsten carbide (WC) electrocatalysts is described. CO poisoning of these base electrocatalysts is small, with reductions of ≤6% of the hydrogen current. Tests of the anodic oxidation of CO alone on these catalysts show the reaction to be very slow. The low degree of poisoning is quite reversible and ascribed to weak adsorption of CO on WC surfaces. The experiments have been conducted on a variety of WCs synthesised from several different routes, all showing similar results.     

Metal oxide hydrogen,oxygen, and carbon monoxide sensors for hydrogen setups and cells

Use of hydrogen, oxygen, and carbon oxide semiconductor sensors made of metal oxides allows controlling electronically the content of these gases in operation of many hydrogen setups, cells and devices. Present review-paper gives a general idea of achievements in this field.     

Kinetic interplay between hydrogen and carbon monoxide in syngas-fueled catalytic micro-combustors

The combined oxidation of hydrogen and carbon monoxide over platinum in micro-combustors at catalytic surface temperatures below 600 K was studied numerically, using a two-dimensional computational fluid dynamics (CFD) model with detailed heterogeneous and homogeneous reaction mechanisms and multicomponent transport. Simulations were performed at different surface temperatures and feed compositions to study the kinetic interplay between hydrogen and carbon monoxide. A sensitivity analysis of the heterogeneous reaction mechanism was performed to identify the rate-controlling steps. Finally, possible mechanisms for the observed behavior were discussed. It was shown that there is significant kinetic interplay between hydrogen and carbon monoxide. Carbon monoxide significantly inhibits the catalytic oxidation of hydrogen. In contrast, the presence of hydrogen was found to promote the catalytic oxidation of carbon monoxide, with the largest effect shown for the small addition of hydrogen, then this effect progressively decreases with the further increase of hydrogen concentration. Accordingly, the apparent reaction order with respect to hydrogen changes from positive to negative, then to zero. The promoting effect of hydrogen can be attributed to the carboxyl pathway, which is crucial to describe the process.     

Periodically regenerating diesel particulate filter with a hydrogen/carbon monoxide mixture addition

This investigation analyses the effect of introducing a H₂/CO mixture, upstream of a diesel particulate filter (DPF), in an attempt to support the regeneration process. The introduction of the mixture was achieved via various periodic strategies in an attempt to reduce the volume of mixture required while still maintaining proficient regeneration qualities. In addition to this, the effect of space velocity and engine load on the regeneration process was also investigated. The experimental data showed that the mixture addition supported the regeneration process by increasing the filter temperature via an exothermic reaction. The most beneficial spraying strategy introduced the mixture to the DPF every 20 s, with each injection event lasting for a period of 10 s. This strategy required 50% less mixture volume than the constant spray strategy but still induced similar regeneration capabilities. In addition to this, it was noted that a decrease in space velocity reduced the rate of temperature increase but improved the peak filter temperature resulting in increased regeneration proficiency. It was also noted that a reduction in engine load reduced the mean filter temperature but overall had minimal effect on the regeneration process.     

Hydrogen production from ethanol with low carbon monoxide generation in a one-pot reaction with iron oxides as catalysts

Bulk γ-Fe₂O₃ (maghemite) and Fe₃O₄ (magnetite) were synthesized with Fe(III) hydroxyacetate as an intermediate during the preparation step. The fresh and used catalysts were characterized by X-ray diffraction, N₂ adsorption at 77 K, Mössbauer spectroscopy at 298 K, diffuse-reflectance spectroscopy, and thermogravimetric analysis. The solids were used as catalysts in the ethanol hydrotreatment within the range of 673–758 K. The catalysts showed a satisfactory selectivity for H₂ and an especially low CO production. These activities and selectivities were analyzed in conjunction with the structural properties of the oxides. Magnetite seemed to be a more appropriate catalyst than maghemite since the latter was converted into magnetite at reaction temperatures higher than 713 K because of the reducing atmosphere.     

Studies on influence of hydrogen and carbon monoxide concentration on reduction progression behavior of molybdenum oxide catalyst

Temperature programmed reduction (TPR) analysis was applied to investigate the chemical reduction progression behavior of molybdenum oxide (MoO₃) catalyst. The composition and morphology of the reduced phases were characterized by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM). The reduction progression of MoO₃ catalyst was attained with different reductant types and concentration (10% H₂/N₂, 10% and 20% CO/N₂ (%, v/v)). Two different modes of reduction process were applied. The first approach of reduction involved non-isothermal mode reduction up to 700 °C, while the second approach of reduction involved the isothermal mode reduction for 60 min at 700 °C. Hydrogen temperature programmed reduction (H₂-TPR) results showed the reduction progression of three-stage reduction of MoO₃ (Mo⁶⁺ → Mo⁵⁺ → Mo⁴⁺ → Mo⁰) with Mo⁵⁺ and Mo⁴⁺. XRD analysis confirmed the formation of Mo₄O₁₁ phase as an intermediate phase followed by MoO₂ phase. After 60 min of isothermal reduction, peaks of metallic molybdenum (Mo) appeared. Whereas, FESEM analysis showed porous crater-like structure on the surface cracks of MoO₂ layer which led to the growth of Mo phase. Meanwhile, the reduction of MoO₃ catalyst in 10% carbon monoxide (CO) showed the formation of unstable intermediate phase of Mo₉O₂₆ at the early stage of reduction. Furthermore, by increasing 20% CO led to the carburization of MoO₂ phase, resulted in the formation of Mo₂C rather than the formation of metallic Mo, as confirmed by XPS analysis. Therefore, the presented study shows that hydrogen gave better reducibility due to smaller molecular size, which contributed to high diffusion rate and achieved deeper penetration into the MoO₃ catalyst compared to carbon monoxide reductant. Hence, the reduction of MoO₃ in carbon monoxide atmosphere promoted the formation of Mo₂C which was in agreement with the thermodynamic assessment.     

Engine knock and combustion characteristics of a spark ignition engine operating with varying hydrogen and carbon monoxide proportions

Varying proportions of hydrogen and carbon monoxide (synthesis gas) have been investigated as a spark ignition (SI) engine fuel in this paper. It is important to understand how various synthesis gas compositions effect important SI combustion fundamentals, such as knock and burn duration, because in synthesis gas production applications, the compositions can vary significantly depending on the feedstock and production method.A single cylinder cooperative fuels research (CFR) engine was used to investigate the knock and combustion characteristics of three blends of synthesis gas (H₂/CO ratio); 1) 100/0, 2) 75/25, and 3) 50/50, by volume. These blends were tested at three compression ratios (6:1, 8:1, and 10:1), and three equivalence ratios (0.6, 0.7, and 0.8).It was revealed that the knock limited compression ratio (KLCR) of a H₂/CO mixture increases with increasing CO fraction, for a given spark timing. For a given equivalence ratio and spark timing, a 50%/50% H₂/CO mixture produced a KLCR of 8:1 compared to a 100% H₂ condition, which produced a KLCR of 6:1. The burn duration and ignition lag is also increased with increasing CO fraction. The results from this work are important for those considering using synthesis gas as a fuel in SI engines. It reveals that although CO is a slow burning fuel, higher CO fractions in synthesis gas can be beneficial, because of its increased resistance to knock, which gives it the potential of producing higher indicated efficiencies through the utilization of an engine with a higher compression ratio.     

Fuel-cell grade hydrogen production by coupling steam reforming of ethanol and carbon monoxide removal

Challenges of coupling steam reforming of ethanol (SRE) and carbon monoxide (CO) removal to continuous fuel-cell grade hydrogen (H₂) production were assessed. A SRE reactor, based on a previous optimized RhPt/CeO₂SiO₂ catalyst, was coupled to a CO removal reactor, based on AuCu/CeO₂ catalysts with different Au:Cu weight ratios. Fuel-cell grade H₂ was achieved with a Au_1.0Cu_1.0/CeO₂ catalyst at 210 °C on the CO removal reactor. AuCu/CeO₂ catalysts characterization suggests that Au favors CO conversion by the formation of possible Au⁰-CO_ad species, and Cu improves CO₂ yield by promoting oxygen vacancies on CeO₂. However, operando DRIFTS by 95 h showed that Au_1.0Cu_1.0/CeO₂ catalyst is susceptible to deactivation by the diminish on the CO_ad species and oxygen vacancies, and the formation of carbonate species. These results allowed us to propose a cyclic reduction treatment to prevent catalyst deactivation of Au_1.0Cu_1.0/CeO₂ (95 h of time-on-stream) while producing fuel-cell grade H₂.     

Design of fuel cell systems laboratory for hydrogen,carbon monoxide and hydrocarbon safety

As research and development efforts in the area of fuel cells and hydrogen based energy accelerate, a large number of accidents have occurred in research laboratories. In this context, a design methodology for a simple, scaleable, modular and human-independent system for hydrogen, carbon monoxide and hydrocarbon safety in research laboratories is valuable. We have designed, developed and operationalized such a system in a pre-existing generic laboratory space. In this paper, we provide details of the mechanical, electrical and control aspects of this laboratory. We use CFD analysis to design a ventilation system, and to locate gas detectors for optimum detection time. The gas detectors, actuators, a real-time controller and other electrical components are part of a safety monitoring system that continuously gathers information, processes this information and takes appropriate action to safeguard personnel and equipment in real time. This fully operational safety laboratory is now a University-level research hub for all fuel cell (and other energy related) research activities, and is also one of a kind in the region. We also expect that the experience gained in this endeavor will be useful to other researchers in building a safe workplace.     

Influence of hydrogen and various carbon monoxide concentrations on reduction behavior of iron oxide at low temperature

The aims of this study are to produce Fe₃O₄ from Fe₂O₃ using hydrogen (H₂) and carbon monoxide (CO) gases by focusing on the influence of these gases on reduction of Fe₂O₃ to Fe₃O₄ at low temperature (below 500 °C). Low reduction temperature behavior was investigated by using temperature programmed reduction (TPR) with the presence of 20% H₂/N₂, 10% CO/N₂, 20% CO/N₂ and 40% CO/N₂. The TPR results indicated that the first reduction peak of Fe₂O₃ at low temperature appeared faster in CO atmosphere compared to H₂. Furthermore, reducibility of first stage reduction could be improved when increasing CO concentration and reduction rate were followed the sequence as: 40% CO > 20% CO > 10% CO > 10% H₂. All reduction peaks were shifted to higher temperature when the CO concentration was reduced. Although, initial reduction by H₂ occurred slower (first peak appeared at higher temperature, 465 °C) compared to CO, however, it showed better reduction with Fe₂O₃ fully reduced to Fe at temperature below 800 °C. Meanwhile, complete reduction happened at temperature above 800 °C in 10% and 20% CO/N₂. Thermodynamic calculation revealed that CO acts as a better reducer than H₂ as the enthalpy change of reaction (ΔH_r) is more exothermic than H₂ and the change in Gibbs free energy (ΔG) at 500 °C is directed to more spontaneous reaction in converting Fe₂O₃ to Fe₃O₄. Therefore, formation of magnetite at low temperature was thermodynamically more favorable in CO compared to H₂ atmosphere. XRD analysis explained the formation of smaller crystallite size of magnetite by H₂ whereas reduction of CO concentration from 40, 20 to 10% enhanced the growth of highly crystalline magnetite (31.3, 35.5 and 39.9 nm respectively). All reductants were successfully transformed Fe₂O₃ → Fe₃O₄ at the first reduction peak except for 10% CO/N₂ as there was a weak crystalline peak due to remaining unreduced Fe₂O₃. Overall, less energy consumption needed in reducing Fe₂O₃ to Fe₃O₄ by CO. This proved that CO was enhanced the formation of magnetite, encouraged formation of highly crystalline magnetite in more concentrated CO, considered better reducing agent than H₂ and these are valid at lower temperature.     

Studies on reduction of chromium doped iron oxide catalyst using hydrogen and various concentration of carbon monoxide

Chemical reduction behaviour of 3% chromium doped (Cr–Fe₂O₃) and undoped iron oxides (Fe₂O₃) were investigated by using temperature programmed reduction (TPR). The reduced phases were characterized by X-ray diffraction spectroscopy (XRD). The reduction processes were achieved with 10% H₂ in nitrogen (%, v/v), 10% and 20% of carbon monoxide (CO) in nitrogen (%, v/v). In hydrogen atmosphere, the TPR results indicate that the reduction of Cr–Fe₂O₃ and Fe₂O₃ proceed in three steps (Fe₂O₃ → Fe₃O₄ → FeO → Fe) with Fe₃O₄ and FeO as intermediate states. A complete reduction to metallic iron for both samples occurred at 900 °C. As for CO reductant, the profiles show the reduction of Fe₂O₃ also proceeded in three steps with a complete reduction occurs at 900 °C in 10% CO with no sign of carbide formation. Nevertheless, a 20% CO was able to reduce the completely at lower temperature at 700 °C and there is a formation of iron carbide at 500 °C but the carbide disappeared as the reduction temperature increase. Meanwhile in 10% CO atmosphere, Cr–Fe₂O₃ shows a better reducibility compared to Fe₂O₃ with a complete reduction at 700 °C, which is 200 °C lower than Fe₂O₃. A Cr dopant in the Fe₂O₃ can lead to formation of various forms of iron carbides such as F₂C, Fe₅C₂, Fe₂₃C₆ and Fe₃C as the CO concentration was increased to 20%. The transformation profile of iron phases during carburization follows the following forms, Fe₂O₃ → Fe₃O₄ → iron carbides (Fe_xC). The XRD pattern shows the diffraction peaks of Cr–Fe₂O₃ are more intense with improved crystallinity for the characteristic peaks of Fe₂O₃ compare to undoped Fe₂O₃. No visible sign of chromium particles peaks in the XRD spectrum that indicates the Cr particles loaded onto the iron oxide are well dispersed. The uniform dispersion with no sign of sintering effects of the Cr dopant on the Fe₂O₃ was confirmed by FESEM. The study shows that Cr dopant gives a better reducibility of iron oxide but promotes the formation of carbides in an excess CO concentration.     

Development of a polyaniline nanofiber-based carbon monoxide sensor for hydrogen fuel cell application

The sensing of carbon monoxide (CO) impurity contained in hydrogen fuel is a challenging work in the field of low temperature proton exchange membrane fuel cell (PEMFC). In the present work a chemiresistive gas sensor based on polyaniline (PANI) nanofibers was developed to detect CO in hydrogen. The sensor was fabricated by a template-free electrochemical polymerization of aniline on an interdigitated electrode. The most distinctive feature of the fabricated sensor was the formation of a horizontally oriented, monolayered PANI nanofiber network on the insulating gap area. The gas sensing character of the PANI nanosensor was evaluated by measuring the change in electrical resistance when gas atmosphere was changed from pure hydrogen to mixtures of CO in hydrogen. The results demonstrated that the PANI nanosensor had an excellent responding ability on CO in hydrogen with a concentration as low as 1 ppm. The influences of parameters, such as nanostructure, doping level, dopants, and CO concentrations, on the sensing characters of the nanosensor were discussed. The responding mechanism was attributed to the different binding sites of CO and H₂ with PANI: H₂ with the protonated amine nitrogen atoms and CO with the unprotonated amine nitrogen atoms. In view of its novel sensing mechanism and high sensing performance, the fabricated sensor is very promising to be applied as a new type of CO sensor to prevent the catalysis poisoning of PEMFC.     

The inhibitory effect of carbon monoxide contained in hydrogen gas environment on hydrogen-accelerated fatigue crack growth and its loading frequency dependency

The effect of carbon monoxide (CO) contained in H₂ gas as an impurity on the hydrogen-accelerated fatigue crack growth of A333 pipe steel was studied in association with loading frequency dependency. The addition of CO to H₂ gas inhibited the accelerated fatigue crack growth due to the hydrogen. The inhibitory effect was affected by the CO content in the H₂ gas, loading frequency, and crack growth rate. Based on these results, it was revealed that the inhibitory effect of CO was governed by both competition between the rate of fresh surface creation by the crack growth and the rate of coverage of the surface by CO and time for hydrogen diffusion in the material to the crack tip with reduced hydrogen entry by CO.     

Counter-rotating dual-stage swirling combustion characteristics of hydrogen and carbon monoxide at constant fuel flow rate

In this paper, experimental and numerical methods were used to study the combustion characteristics of a counter-rotating double-stage swirling syngas combustor at constant fuel flow rate, and the effect on it of hydrogen content of syngas. In the experiment, the speed and temperature in the combustor were respectively obtained with PIV and temperature rake, while Reynolds stress equation model and the detailed chemical reaction mechanism of syngas were adopted in the numerical method. The calculation results were in good agreement with the experimental data. Research results indicated that in the working conditions of different hydrogen contents, the flow field structures in the combustor are almost the same, and the maximum temperatures at the outlet remain almost the same. However, as hydrogen content in the fuel increases, the axial velocity in the central area of flow field is increasing, and the outlet temperature distribution coefficient decreases first and then increases. In addition, it was also found in the study that the distribution structure of temperature on the central section of the combustor is almost impervious to the changes in hydrogen content, but with numerical differences, i.e. the higher hydrogen content in the fuel, the farther the stabilization position of flames in the central area is away from the head. It was also indicated in the study that the conventional combustor is no longer applicable to the combustion of syngas, especially the hydrogen-rich fuel. And the work provided the improvement scheme of hydrogen-containing fuel for gas turbine combustor.     

Preferential catalytic oxidation of carbon monoxide in presence of hydrogen over bimetallic AuPt supported on zeolite catalysts

A series of AuPt/A zeolite and Pt/A zeolite catalysts prepared by incipient wetness impregnation are investigated for the preferential oxidation (PROX) of carbon monoxide in the presence of hydrogen over the temperature range of 50–310 °C under atmospheric pressure. The results indicate that when a small amount of gold is added to the Pt/A zeolite catalyst, the CO selectivity is improved at low temperatures, and 1% AuPt/A zeolite (at a weight ratio of Au:Pt = 1:2) gives the best performance, which provides a high CO conversion in combination with a high CO selectivity. In more realistic simulated reformate gases containing 10% CO₂ and 10% H₂O, there is not much difference between those in the presence and the absence of CO₂ and H₂O. Transmission electron microscopic and X-ray diffraction studies show that the two metals, Au and Pt, appear to be severely phase separated, which is confirmed by energy dispersive investigations.     

Understanding on the effect of morphology towards the hydrogen and carbon monoxide sensing characteristics of tin oxide sensing elements

Though the gas sensing properties of atmospheric plasma sprayed tungsten oxide, zinc oxide, titanium oxide, tin oxide and copper oxide coatings were well investigated, reports comparing sensing characteristics of plasma sprayed sensor thick film coating with its bulk counterpart are hardly found in the literature. This work attempts to compare hydrogen and carbon monoxide sensing characteristics, namely gas response, response time, recovery time of plasma sprayed tin dioxide thick film with tin dioxide bulk sensor. Gas response in the presence of hydrogen gas (23–81%) was superior to that of carbon monoxide gas (19–79%). An attempt was made to understand plausible reason behind superior hydrogen gas response. Thus, gas response as a function of temperature was simulated using a gas diffusion equation for hydrogen and carbon monoxide gases. Estimated parameters, namely, activation energy of transduction and first order kinetics were correlated with sensor microstructure and experimental gas response values. For hydrogen sensing, shorter response time (30–138 s) and recovery time (118–161 s) of thick film as compared to response time (64–234 s) and recovery time (183–196 s) of bulk sensor was correlated with microstructure of sensory elements. It was observed that tin dioxide thick film, owing to its porous morphology with small-sized particulates exhibited superior hydrogen gas response, short response time and recovery time as compared to its bulk counterpart.     

Characterisation of the electrochemical water gas shift reactor (EWGSR) operated with hydrogen and carbon monoxide rich feed gas

Water gas shift units are used to raise the H₂ yield of reforming processes by converting CO to CO₂ and additional H₂. Additional subsequent processes are required to separate H₂ from the product gas stream to obtain pure H₂. This study investigates a novel electrochemical membrane reactor, where the water gas shift reaction occurs electrochemically. The reactor is operated at 393 K and 403 K with electrical energy to enable hydrogen purification in terms of electrochemical pumping, as well as a simultaneous electrochemical CO oxidation to increase the yield of purified H₂. The experimental results show the influence of several operation parameters upon its operation characteristics (e.g. cell voltage, electrochemical CO oxidation, the energy demand, etc.). The process yielded high overall exergy efficiencies of, e.g. 78.3%, whereas the anodic outlet stream contributed with 35%-units, and the purified hydrogen with 43.3%-units.