Preferential Oxidation Reaction Research Articles

Hydrogen production by steam reforming of dimethyl ether and CO-PrOx in a metal foam micro-reactor

Abstract A bi-function catalyst containing CuZnAlCr and HZSM-5 was used to generate hydrogen by stream reforming of dimethyl ether (SRD) in a metal foam micro-reactor and a fix-bed reactor. Dimethyl ether conversion of 99% and hydrogen yield of >95% was reached with HZSM-5/CuZnAlCr (mass ratio of 1:1) in the micro-reactor. A suitable balance between the dimethyl ether hydrolysis and methanol reforming steps requires the proper acidity and the metal sites. The CuZnAlCr/HZSM-5 properties, effect of CuZnAlCr to HZSM-5 mass ratio were investigated in the metal foam micro-reactor. Moreover, CO was removed from hydrogen-rich gas by preferential oxidation reaction (CO-PrOx) with PtFe/γ-Al 2 O 3 catalyst in a similar metal foam micro-reactor follows the SRD stage. With the optimized O 2 /CO ratio and reaction temperature, the CO concentration dropped to

Coupled operation of a diesel steam reformer and an LT- and HT-PEFC

Polymer electrolyte fuel cells (PEFC) combined with diesel fuel processors offer a great potential for auxiliary power units (APU) in mobile applications. In a joint research project with partners from industry, Oel-Waerme-Institut GmbH is developing an integrated modular fuel cell system for mobile power generation in caravans and yachts. The system includes a steam reforming fuel processor that allows the operation of low-temperature (LT-) as well as high-temperature (HT-) PEFC.In the presented work the coupled operation of the fuel processor and LT-PEFC and HT-PEFC stacks is demonstrated using logistic diesel from a gas station. For LT-PEFC operation, a single-stage preferential oxidation reactor (PROX) was applied to achieve the required CO concentration. Long-term coupled operation was carried out at a reformer temperature of 780 °C using both diesel surrogate (sulfur content <2 wt. ppm) and logistic diesel from a gas station (sulfur content <10 wt. ppm). In contrast to diesel surrogate, an increase in residual hydrocarbon concentration in the reformate was measured using logistic diesel, which is related to the catalyst deactivation from sulfur. Consequently, during LT-PEFC operation cell voltage remained stable using the diesel surrogate, but decreased over operating time using logistic diesel due to deactivation of both reformer and fuel cell catalyst. At a reformer temperature of 800 °C, residual hydrocarbon concentration and cell voltage of the LT-PEFC remained stable during operation with logistic diesel. It was concluded that residual hydrocarbons deactivate the LT-PEFC catalyst more severely than sulfuric compounds.During HT-PEFC operation, cell voltage remained stable in spite of an increasing hydrocarbon concentration. The HT-PEFC showed no indication of anode catalyst deactivation during operation with reformate from steam reforming of logistic diesel and therefore has great potential for coupling with the fuel processor without the need for a PROX reactor.

Thermal Treatment Effect on Catalytic Activity of Au/TiO&lt;sub&gt;2&lt;/sub&gt; for CO Oxidation

A novel and well-organized study for the synthesis and enhanced catalytic activity of Au/TiO2catalysts has been developed. A momentous improvement in the catalytic activity of Au/TiO2in CO oxidation and preferential oxidation reaction by thermal treatment has been studied. Au/TiO2catalyst (Au (1 wt.%) supported on TiO2) was prepared by conventional deposition-precipitation method with NaOH followed by washing, drying and calcination in air at 400 °C for 4 h. Thermal treatment of Au/TiO2was performed at 450 °C under 0.05 mTorr. The activity of the catalysts has been examined in the reaction of CO oxidation and preferential oxidation (PROX) at 25-250 °C. The catalytic performance was found to be strongly affected by thermal treatment of the prepared catalyst prior to the reaction. Heat treatment after Au deposition has a positive effect on the CO oxidation performance. This is attributed to the introduction of a stronger interaction between the oxide and Au which improves the catalytic activity.

Synthesis of mesoporous Co–Ce oxides catalysts by glycine-nitrate combustion approach for CO preferential oxidation reaction in excess H2

Preferential oxidation of CO (CO-PrOx) is an important step to meet the need of the proton exchange membrane (PEM) fuel cell without the Pt anion poison. A glycine-nitrate approach was used for the synthesis of Co/CeO2 nanoparticle for preferential oxidation of CO, which a precursor solution was prepared by mixing glycine with an aqueous solution of blended nitrate in stoichiometric ratio. Then the glycine-mixed precursor solution was heated in a beaker for producing nanosized porous powders. Catalytic properties of the powders were investigated and results illustrate that the Co-loading of 30 wt.% catalysts exhibits excellent catalytic properties. Various characterization techniques like X-ray diffraction, SEM, BET, Raman and TPR were used to analyze the relationship between catalyst nature and catalytic performance. The X-ray diffraction patterns and SEM micrographs indicate that catalysts prepared by glycine-nitrate combustion own mesopore structure. The BET, Raman and TPR results showed that the high activity of the 30 wt.% Co-loading of Co/CeO2 catalysts is related to the high BET surface and the strongly interaction between fine-dispersed Co species and CeO2 support.

Ceria-based palladium zinc catalysts as promising materials for water gas shift reaction

The production of hydrogen for fuel cell applications requires several fuel processing steps, including CO removal by means of the water gas shift (WGS) and CO preferential oxidation reactions. In this work we investigate the behavior of palladium–zinc supported on CeO2, Ce0.5Zr0.5O2 and ZrO2 as a promising alternative to low temperature WGS catalysts for fuel processing. WGS activity is optimized when the PdZn alloy is formed. Ceria-containing materials show little deactivation during startup–shutdown cycles in reformate gas and for palladium–zinc supported on pure ceria the activity can be fully recovered by an in situ reduction treatment.

Gold supported on CuOx/CeO2 catalyst for the purification of hydrogen by the CO preferential oxidation reaction (PROX)

Hydrogen produced from the conversion of hydrocarbons or alcohols contains variable amounts of CO that should be removed for some applications such as feeding low-temperature polymer electrolyte membrane fuel cells (PEMFCs). The CO preferential oxidation reaction (PROX) is particularly well-suited for hydrogen purification for portable and on-board applications. In this work, the synthesis and characterization by XRF, BET, XRD, Raman spectroscopy and H2-TPR of a gold catalyst supported on a copper−cerium mixed oxide (AuCeCu) for the PROX reaction are presented. The comparison of this catalyst with the copper–cerium mixed oxide (CeCu) revealed that the experimental procedure used for the deposition of gold gave rise to the loss of reducible material by copper lixiviation. However, the AuCeCu solid was more active for CO oxidation at low temperature. A kinetic study has been carried over the AuCeCu catalyst for the PROX reaction and compared with that of the CeCu catalyst. The main difference between the models affected the contribution of the CO adsorption term. This fact may be related to the surface electronic activity produced by the interaction of the cationic species in the AuCeCu solid, able to create more active sites for the CO adsorption and activation in the presence of gold.

Coupling Experiment of Compact Integrated Fuel Processors with 75kW PEM Fuel Cells

A compact autothermal reformer suitable for liquid fuel for instance methanol et al. was developed. The fuel reformer was combined with polymer electrolyte membrane fuel cells (PEM FC) and a system test of the process chain was successfully performed. The fuel processor consists of a fuel evaporating step, two-stage reformer and a two-stage reactor of water gas shift (WGS, one for high temperature water gas shift and the other for low temperature water gas shifter) and a four-stage preferential oxidation (PROX) reactor and some internal heat exchanger in order to achieve optimized heat integration. The fuel processor is designed to provide enough hydrogen for 75kWel fuel cells. After the initial step of methanol ATR, CO WGS and CO PROX steps are used for 'clean-up' CO. The exhaust gas from FC anode feedback to the fuel processor to vaporizes the feedstock of methanol and water by a catalytic combusting-evaporator. The hydrogen source system can produce hydrogen 70.5 m3/hr and its specific gravity power and specific volume power reach 255W/kg and 450W/L respectively. During three hours coupling experiment, the fuel processing system and the fuel cells all has been running smoothly. The volume concentration of H2 and CO in product gas (dry basis) was kept in 53% and 20ppm respectively, completely meeting the requirements of PEM fuel cells. The conversion efficiency of the hydrogen producing system based on LHV of fuel and hydrogen can exceed 95.85%. The fuel cells stacks put up strong resistance to CO and its maximum electronic load to the fuel cells reaches 75.5kW. It indicates that it is feasible technically for supplying hydrogen for Proton Exchange Membrane Fuel Cells by catalytic reforming of hydrogen-rich liquid fuel on-board or on-site.

Enhancement of catalytic activity of Au/TiO2 by thermal and plasma treatment

A significant enhancement in the catalytic activity of Au/TiO2 in CO oxidation and preferential oxidation reaction by creating the active sites on the catalyst surface by thermal treatment as well as by producing small gold particles by plasma treatment has been studied. Au/TiO2 catalyst (Au (1 wt%) supported on TiO2) was prepared by conventional deposition-precipitation method with NaOH (DP NaOH) followed by washing, drying and calcination in air at 400 °C for 4 h. Thermal treatment of Au/TiO2 was carried out at 550 °C under 0.05 mTorr. A small amount of Au/TiO2 catalyst was taken from the untreated and thermally treated Au/TiO2 and both kinds of catalysts were treated with plasma sputtering at room temperature. The activity of the catalysts has been examined in the reaction of CO oxidation and preferential oxidation (PROX) at 25–250 °C. Thermally treated Au/TiO2 showed better catalytic activity as compared to the untreated catalyst. There is also an additional enhancement in the catalytic activity due to plasma sputtering on the both kinds of catalysts. Thermally treated Au/TiO2 followed by plasma sputtering Au/TiO2 showed higher conversion rates for CO oxidation reaction compared with untreated, thermally treated and plasma sputtered Au/TiO2 catalysts. It may be concluded that the enhancement of catalytic activity of thermally treated Au/TiO2 followed by plasma sputtering is owing to the generation of active sites such as oxygen vacancies/defects in TiO2 support using thermal treatment as well as by producing small gold particles using plasma treatment.

Polymer electrolyte membrane fuel cell grade hydrogen production by methanol steam reforming: A comparative multiple reactor modeling study

Analysis of a fuel processor based on methanol steam reforming has been carried out to produce fuel cell grade H2. Six reactor configurations namely FBR1 (fixed bed reactor), MR1 (H2 selective membrane reactor with one reaction tube), MR2 (H2 selective membrane reactor with two reaction tubes), FBR2 (FBR1+preferential CO oxidation (PROX) reactor), MR3 (MR1+PROX), and MR4 (MR2+PROX) are evaluated by simulation to identify the suitable processing scheme. The yield of H2 is significantly affected by H2 selective membrane, residence time, temperature, and pressure conditions at complete methanol conversion. The enhancement in residence time in MR2 by using two identical reaction tubes provides H2 yield of 2.96 with 91.25mol% recovery at steam/methanol ratio of 1.5, pressure of 2bar and 560K temperature. The exit retentate gases from MR2 are further treated in PROX reactor of MR4 to reduce CO concentration to 4.1ppm to ensure the safe discharge to the environment. The risk of carbon deposition on reforming catalyst is highly reduced in MR4, and MR4 reactor configuration generates 7.4NLmin−1 of CO free H2 from 0.12molmin−1 of methanol which can provide 470W PEMFC feedstock requirement. Hence, process scheme in MR4 provides a compact and innovative fuel cell grade H2 generating unit.

Co/ZrO2, Co/CeO2 and MnCoCe structured catalysts for COPrOx

Cordierite monoliths washcoated with MnCoCe(CP), Co(I)/ZrO2 and Co(I)/CeO2 catalysts were prepared and studied for the CO preferential oxidation (COPrOx) reaction. Among them, the MnCoCe/M system presented the best CO conversion at low temperatures and the Co(I)/CeO2-M catalyst, the best selectivities toward CO2. In the three catalysts, Co3O4 was the main Co containing compound and it was the active species for the COPrOx reaction. Nevertheless, the Co(I)/CeO2-M and MnCoCe/M solids resulted more active than Co(I)/ZrO2-M, possibly due to the better redox properties of the ceria. In the MnCoCe/M catalyst prepared by co-precipitation, the addition of Mn represented an additional positive effect. The presence of Mn promoted the re-oxidation of Co2+ to Co3+ and, consequently, the activity increased at low temperature. It is also shown that homogeneous and mechanically stable coatings on the walls of the three monolithic catalysts were obtained, which in turn yielded promising results in the COPrOx reaction.

Improvement of catalytic performance of preferential oxidation of CO in H2-rich gases on three-dimensionally ordered macro- and meso-porous Pt–Au/CeO2 catalysts

Three-dimensionally ordered macro- and meso-porous (3DOM) M/CeO2 (M=Pt, Au and Pt–Au) catalysts supported with different noble metal nanoparticles of Pt, Au and Pt–Au alloy were synthesized by thermal decomposition of cerium nitrate precursor using the close packed structures of PS colloidal crystals as templates. The obtained 3DOM M/CeO2 catalysts possess well-defined 3DOM skeletons composed of ultrafine CeO2 nanoparticles. The macroporous CeO2 skeletons contain the mesoporous walls possessing the nanopores of ∼3–4nm and the noble metal nanoparticles of Pt, Au, and Pt–Au alloy with the grain sizes of ∼5.0nm homogenously dispersed. The catalytic performance of CO preferential oxidation (PROX) in H2-rich gases on 3DOM Pt/CeO2, Au/CeO2, and Pt–Au/CeO2 catalysts were systematically studied. The superior catalytic performance with 90% CO conversion and 83% CO2 selectivity are realized on 3DOM 1wt.% Pt1Au1/CeO2 catalyst at 80°C under the weight hourly space velocity of 30,000mLg−1h−1. Moreover, the 3DOM 1wt.% Pt1Au1/CeO2 catalyst exhibits excellent catalytic stability maintaining 90% CO conversion and 56% CO2 selectivity even after the test period of 260h under the same flow rate. The three-dimensionally ordered macro- and meso-porous skeletons, the synergistic effect due to the formation of Pt–Au alloy, and the strong interaction of Pt–Au alloy nanoparticles with CeO2 supports are identified to be beneficial to the improvement of catalytic activity and stability of CO PROX. The obtained 3DOM Pt–Au/CeO2 catalysts may be potential candidates with the improved catalytic performance of CO PROX reaction in H2-rich gases for polymer electrolyte membrane fuel cells (PEMFCs) applications.

Insight into the Mechanism of the Preferential Oxidation of Carbon Monoxide by Using Isotope-Modulated Excitation IR Spectroscopy

DRIFTing through time: Modulation excitation in situ diffuse-reflectance IR Fourier transform (DRIFT) spectroscopy with periodic isotopic perturbation (D2 and 13CO) has been applied to elucidate the pathway for the preferential oxidation of carbon monoxide (PROX) over a commercial Pt/alumina catalyst. The time- and phase-domain IR spectra suggest a water-assisted pathway for the preferential oxidation reaction.

PtCu Intermetallic Compound Supported on Alumina Active for Preferential Oxidation of CO in Hydrogen

Intermetallic compounds (IMCs) have unique geometric and electronic structure compared with their component pure metals. We already found that PtCu IMC supported on silica gel was more active than Pt/SiO2 for the preferential oxidation (PROX) of CO in excess hydrogen. In this study, we have tried to prepare these IMC particles on alumina by the liquid-phase reductive deposition (LRD) method, characterized them by X-ray diffraction (XRD), transmission electron micrograph (TEM), and Fourier transform infrared (FT-IR) spectroscopy, and carried out the PROX reaction with a continuous flow reactor. PtCu IMC was formed as single-phase particles on alumina with the particle size of 3–5 nm. PtCu/Al2O3 gave much higher activity for the PROX reaction than PtCu/SiO2 and Pt/Al2O3 prepared by the LRD method and Pt–Cu/Al2O3 prepared by the usual impregnation method, indicating the superiority of alumina support, IMC formation, and the LRD method. In situ FT-IR spectroscopy and transient reaction measurements suggest th...

Performance analysis of an integrated biomass gasification and PEMFC (proton exchange membrane fuel cell) system: Hydrogen and power generation

The PEMFC (proton exchange membrane fuel cell) is expected to play a significant role in next-generation energy systems. Because most hydrogen that is used as a fuel for PEMFCs is derived from the reforming of natural gas, the use of renewable energy sources such as biomass to produce this hydrogen offers a promising alternative. This study is focused on the performance analysis of an integrated biomass gasification and PEMFC system. The combined heat and power generation output of this integrated system is designed for residential applications, taking into account thermal and electrical demands. A flowsheet model of the integrated PEMFC system is developed and employed to analyze its performance with respect to various key operating parameters. A purification process consisting of a water–gas shift reactor and a preferential oxidation reactor is also necessary in order to reduce the concentration of CO in the synthesis gas to below 10 ppm for subsequent use in the PEMFC. The effect of load level on the performance of the PEMFC system is investigated. Based on an electrical load of 5 kW, it is found that the electrical efficiency of the PEMFC integrated system is 22%, and, when waste heat recovery is considered, the total efficiency of the PEMFC system is 51%.

A comparative study on energetic and exergetic assessment of hydrogen production from bioethanol via steam reforming, partial oxidation and auto-thermal reforming processes

Three known types of ethanol reforming processes, ethanol steam reforming (ESR), partial oxidation (POX) and auto-thermal reforming (ATR), are investigated. Favorable operating conditions are identified for each reaction system to maximize the production of hydrogen from bioethanol. Each process consists of three sections: the main reactor (ESR, POX or ATR), the CO clean-up section comprised of the water gas shift reactor and preferential CO oxidation reactor and finally, the purification section. The performances of these processes are evaluated through mass, energy and exergy analyses.The material balances show that the total amount of ethanol required to generate 1mol of hydrogen is 0.23mol for the ATR, 0.24mol for the POX and 0.25mol for the ESR. The ATR reforming process is shown to have the highest energetic efficiency, i.e., the lowest amount of energy is consumed to produce the same amount of hydrogen from ethanol. Moreover, the ATR process has the best exergetic performance, as it presents the highest ratio of exergy recovered in the hydrogen stream to the total exergy supplied to the system. For all three of the systems, the exergy destruction occurs mainly in the reformer due to the high irreversibility of the reaction.

ChemInform Abstract: Activation of Solid Surface as Catalyst

AbstractReview: 27 refs.

Copper oxide shape effect in CeO&lt;SUB align="right"&gt;2/Cu&lt;SUB align="right"&gt;2O catalysts for PROX reaction

Cubic and octahedral Cu2O nanocrystals were used as supports for ceria deposition. Ceria tended to deposit on the vertexes and edges of the nanocrystals more. Whisker type of ceria was deposited on Cu2O surface. The prepared CeO2/Cu2O composite materials were tested as catalysts for preferential oxidation (PROX) reaction of CO in the presence of abundant H2. As the amount of ceria became higher (e.g., 1 wt% vs. 10 wt%), CO conversion was higher. Cubic nanocrystals showed higher activity than octahedral nanocrystals, especially at lower temperature region. Also, the activity depended significantly on the oxidation state of copper oxide. When CeO2/Cu2O catalysts were oxidised first then used for PROX reaction, the activity was enhanced. Cu2O turned into CuO with a slight shape change after oxidation at 400oC. The activity degraded at higher reaction temperature because the copper oxide was reduced to metallic copper.

Mesostructured Co–Ce–Zr–Mn–O composite as a potential catalyst for efficient removal of carbon monoxide from hydrogen-rich stream

Mesostructured CoxCe0.85Zr0.15MnyOe composites were firstly prepared by a simple one-pot surfactant-assisted co-precipitation (SACP) method and then employed to catalyze the CO preferential oxidation (CO PROX) reaction in an H2-rich stream. Effects of the Co and Mn contents (x and y, respectively) in the formula, as well as the presence of H2O and CO2 in feed were investigated. The as-synthesized Co0.4Ce0.85Zr0.15Mn0.10Oe catalyst showed excellent catalytic performance in the CO PROX reaction: 100% CO conversion could be observed in a wide temperature range of 140–200 °C; even in the simulated syngas, the almost complete CO removal could still be achieved at 175–225 °C; no obvious change in both CO conversion and CO2 selectivity over the catalyst took place during the CO PROX process with simulated syngas as feed. N2 physisorption (BET), temperature-programmed reduction (TPR), X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopic (XPS) characterization techniques were employed to reveal the relationship between the catalyst nature and catalytic performance. The outstanding catalytic performance in CO PROX reaction was remarkably dependent on a larger specific surface area, more reducible Co3+ and the high dispersity of the Co3O4, affected by the Co and Mn contents through strong Co–Ce–Zr–Mn interactions. The mesostructured Co0.4Ce0.85Zr0.15Mn0.10Oe catalyst prepared by the simple one-pot SACP protocol can be a promising candidate for CO PROX reaction in excess H2.

Experimental investigation on a methane fuel processor for polymer electrolyte fuel cells

This study presents experimental study on a novel methane fuel processing system for hydrogen (H2) production. The unit includes into a single package the autothermal reformer, the CO shift converter, the preferential oxidation reactor and the internal heat exchangers. Effects of operative conditions, related to the H2 productivity, on the performances, were investigated experimentally, in order to evaluate the integration of the fuel processor with a Polymer Electrolyte Fuel Cell (PEFC) system for residential applications. The sensitivity analysis showed that the overall performance is strongly dependent upon the operative conditions considered.

Analysis of Biomass Gasification and PEMFC Integrated Systems for Power Generation: A Combined Heat and Power Approach

A proton exchange membrane fuel cell (PEMFC) is expected to play a significant role in the next energy generation system. The purpose of this study is to evaluate the performance and the feasibility of an alternative combined heat and power (CHP) system based on biomass gasification and PEMFC processes for residential applications satisfying thermal and electrical demands. A model of the integrated CHP system is employed to analyze its performance under different operating conditions. The system is designed for the electrical load of 5 kW. The simulation results show that the gasification process can produce the synthesis gas having the hydrogen content of around 25-35 mol.% and the high heating value of 4-10 MJ/Nm 3 . A purification process consisting of a water gas shift reactor and a preferential oxidation reactor is also necessary in order to reduce the concentration of CO in the synthesis gas to be lower than 10 ppm for PEMFC. The useful heat in the high-temperature synthesis gas derived from the gasifer is recovered and used in the purification step and thus the efficiency of the fuel processor is enhanced. Effect of a load level on the performance of PEMFC is investigated. The results of the system evaluation indicate that the total efficiency of the PEMFC-based cogeneration system is 92 % and the electrical efficiency is 22 %.