CO Preferential Oxidation Reaction Research Articles

Superior performance of gold supported on doped CeO2 catalysts for the preferential CO oxidation (PROX)

Herein, the preferential oxidation of CO in excess hydrogen (PROX reaction) was studied over Au catalysts supported on ceria and Y or Nb doped ceria. Both supports and catalysts have been extensively characterized by a number of advanced techniques; XRD, N2-adsortion, Raman spectroscopy, XPS, and H2-TPR. The catalytic results showed that when an ideal mixture of H2 and CO is used for the PROX reaction the gold supported on pure ceria behaves better than the others samples. However, when a typical reformate gas composition containing CO2 and H2O is used, the gold supported on Nb doped sample behaves better than gold supported in pure ceria. It is suggested that niobium hampers the strong adsorption of CO2 and H2O in the active sites, thus improving the catalytic performance in real reformate gas.

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.

Could an efficient WGS catalyst be useful in the CO-PrOx reaction?

This work presents an evaluation of a high performance series of water gas shift (WGS) catalysts in the preferential CO oxidation reaction (PrOx) in order to examine the applicability of the same catalyst for both processes as a first step for coupling both reactions in a single process. Gold based catalysts are applied in an extensive study of the CO-PrOx reaction parameters, such as λ, WHSV, CO concentration and [H2O]/[CO2] ratio in order to obtain the best activity/selectivity balance. CO and H2 oxidation reactions were treated separately in order to establish the degree of CO/H2 oxidation competition. Additionally the catalysts behavior in the CO-PrOx parallel reactions such a WGS and RWGS have been also carried out to analyze their effect on product composition.

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.

고순도 수소 생산을 위한 CO 선택적 산화 반응용 Pt 촉매 연구

To develop preferential CO oxidation reaction (PROX) catalyst for small scale hydrogen generation system, supported Pt catalysts have been applied for the target reaction. The supports were systematically changed to optimize supported Pt catalysts. Pt/Al2O3 catalyst showed the highest CO conversion among the catalysts tested in this study. This is due to easier reducibility, the highest dispersion, and smallest particle diameter of Pt/Al2O3. It has been found that the catalytic performance of supported Pt catalysts for PROX depends strongly on the reduction property and depends partly on the Pt dispersion of supported Pt catalysts. Thus, Pt/Al2O3 can be a promising catalyst for PROX for small scale hydrogen generation system.

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.

Spectroscopic characterization of Mn–Co–Ce mixed oxides, active catalysts for COPROX reaction

Mn–Co–Ce mixed oxides are active and selective catalysts for the CO preferential oxidation (COPROX), which is a promising process for the purification of hydrogen streams. In this work, we report a careful spectroscopic characterization of the said system, with the aim of relating its physical chemistry properties to the catalytic behavior. In all the Co–Mn–Ce samples, we detected the formation of partially developed (Mn,Co)3O4 mixed spinels. The presence of these species, which can be reduced during the TPR experiments at an intermediate temperature range (300–600 °C), was also suggested by XRD and LRS. XPS results show that in all cases the catalytic surface is enriched in Mn, while the opposite occurs for Co. As regards the catalytic activity, we observed that the best formulations were those containing intermediate Mn/Co ratios (1/4 and 1/1), which can be ascribed to the promoting effect of Mn in improving the redox properties of Co active sites and provoking an increase in surface area. The best catalyst, which has a Mn/Co ratio of 1/4, was very stable after 75 h of time-on-stream with CO2 included in the feed.

Study of the synthesis of CeO2 nanoparticles for their use in CO preferential oxidation (COPrOx)

CeO2 nanoparticles were synthesized by the controlled precipitation method from a Ce(NO3)3 solution. To this end, two additives were used alternatively: ethylene glycol (EG) and tetramethylammonium hydroxide (TMAH). Their function was to reduce the particle size obtained after the synthesis. After precipitation and drying, nitrate and organic residuals must be removed, and the method employed for this step could affect the structure and size of the particles. This is an important issue for achieving contaminant-free measurements in catalytic tests. In order to optimize the residuals removing process, a thorough study of the species present and/or eliminated was carried out. Our findings show that a calcination temperature of at least 500°C is necessary in order to accomplish the complete removal of solvent and precursors such as NO3-. Among the catalysts studied, the one prepared with EG showed the best activity for CO preferential oxidation. In order to study the effect of the residuals upon the catalytic activity, samples prepared using EG were calcined at different temperatures and tested for the COPrOx reaction. CO conversions for all the samples were between 80% and 93% at different temperatures. The best activity was obtained with the sample calcined at 500°C, which is in agreement with the minimum temperature necessary for the total elimination of residuals.

ChemInform Abstract: Activation of Solid Surface as Catalyst

AbstractReview: 27 refs.

Copper oxide shape effect in CeO<SUB align="right">2/Cu<SUB align="right">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.

Catalisadores cerâmicos à base de CuO/CeO2 aplicados na reação de oxidação preferencial do CO

A oxidação preferencial do CO (PROX) é o método mais adequado para a purificação de fluxos gasosos ricos em H2. Catalisadores de CuO/CeO2 têm sido desenvolvidos e apresentados como uma alternativa bastante promissora para a reação de oxidação preferencial do CO-PROX-CO. O objetivo deste trabalho é sintetizar catalisadores cerâmicos a base de CuO/CeO2 por meio do método de síntese Pechini, caracterizar e analisar as suas estruturas e avaliar a performance catalítica destes materiais aplicados na reação de PROX-CO. Foram desenvolvidas duas amostras de catalisadores cerâmicos à base CuO/CeO2, uma contendo 0,1 mol de CuO e outra contendo 0,5 mol do mesmo óxido. De acordo com os resultados, ambas as amostras sintetizadas mostraram-se aptas a serem utilizadas em processos de conversão de CO para CO2. No entanto, a amostra que continha 0,1 mol de CuO mostrou-se mais ativa cataliticamente do que a amostra que continha 0,5 mol da mesma espécie ativa catalítica.

Activation of solid surface as catalyst

The original surface of a solid is not always active as a catalyst, but the surface becomes active during reaction. Activation of surfaces may be classified as follows; (i) originally active surfaces, (ii) intermediates produced by reaction with surface atoms, (iii) formation of active sites with functional groups, (iv) formation of active surface compounds, (v) cooperation of multiple catalytic processes. In this review, we discuss two important environmental reactions, one is NO+H2→1/2N2+H2O catalyzed by single crystal Pt–Rh-ally and Pt/Rh or Rh/Pt bimetals, and the other is the preferential oxidation (PROX) reaction of CO in H2 by heavily FeOx-loaded Pt/TiO2 catalyst and Pt-supported carbon with Ni–MgO. The specific activity of the Pt–Rh catalyst arises from the formation of special ordered bimetallic surface layers composed of (RhO) on Pt-layer. Formation of an active over-layer compound was confirmed on Pt0.25Rh0.75(100) alloy, Pt/Rh(100), Rh/Pt(100), Pt/Rh(110) and Rh/Pt(110) bimetal surfaces. The PROX reaction of CO in H2 was attained on two new catalysts, one being FeOx/Pt/TiO2 (ca. 100wt.% FeOx) and the other Pt supported on carbon with Ni–MgO. The mechanism of the PROX reaction of CO was deduced by in situ DRIFT spectroscopy, which indicates a coupled reaction of CO+OH−→HCOO− and HCOO+OH→CO2+H2O.

Study of CuO/CeO2 catalyst with for preferential CO oxidation reaction in hydrogen-rich feed (PROX-CO)

The CuO/CeO2 system was investigated as a catalyst for preferential CO oxidation reaction in hydrogen-rich feed (PROX-CO). The catalysts were prepared by deposition–precipitation (DEP) and co-precipitation (COP) methods and the catalytic performance reveals that the preparation method influences the properties of solids prepared, where a direct consequence is the difference in behavior of the catalysts in the PROX-CO reaction. A high specific area and a better dispersion of the metallic phase were obtained in the catalyst prepared by co-precipitation. The redox properties during the reaction were reported by measures of temperature programmed reduction (TPR), OSC measurements and X-ray absorption near edge structure (XANES-TPR) in situ showed the relationship between the preparation method, the physico-chemical characteristics and redox properties in the PROX-CO reaction. By this means, the good dispersion of CuO and the best oxygen capacity are the response of the high performance of CuO/CeO2-COP catalysts for the PROX-CO reaction.

Energy and exergy analysis of a fuel cell based micro combined heat and power cogeneration system

A fuel cell based micro combined heat and power (CHP) cogeneration system is a cost-effective means of meeting residential energy needs if capital cost targets can be met. The cogeneration system mainly consists of a fuel processing unit, a power generation unit and an auxiliary unit. The fuel-processing unit under investigation includes an autothermal reformer, high and low temperature shift reactors and a CO preferential oxidation reactor. Energy and exergy analysis of the system is useful to investigate the effects of key operating parameters on the system performance. A micro-CHP system that produces approximately 1kW of electricity is simulated with Aspen Plus. A typical case is analyzed and system energy and exergy loss break-down is studied. It is found that for the typical case, energy carried by unuseful streams accounts for the majority of the energy and exergy losses. Among all the components, proton exchange membrane fuel cell posses the least energy efficiency and exergy efficiency. Effects of steam to carbon ratio, air to carbon ratio, hydrogen utilization efficiency, power generation efficiency, and process methane feed variation on system performances are parametrically studied.

CO preferential oxidation on cordierite monoliths coated with Co/CeO2 catalysts

Cordierite monoliths washcoated with Co/CeO2 catalysts prepared from different methods were studied for the CO preferential oxidation reaction. Powder catalysts were also studied for the sake of comparison and in order to select the best formulations to prepare the catalytic coatings. High –Co loaded catalysts resulted in good CO conversions and they showed Co3O4 as the main cobalt containing phase. Consequently, three cordierite – washcoated catalysts were prepared with high Co loadings (ca. 10 wt. % of Co in the catalytic layer). C1 and C2 were obtained by CeO2 washcoating followed by cobalt impregnation. In the first case, Ce oxide particles were obtained from a nitrate solution and in the second, a Nyacol suspension was used. A third sample was prepared (C3) using a slurry of a co-precipitated Co10(CP) catalyst. Monolith C3 showed the best CO conversion, although the difference with the other catalysts was not so evident as the one observed for the powder formulations. The mechanical stability, measured by ultrasound tests, was good for all monolithic catalysts and monolith C1 showed no-deactivation after 100 h of time-on-stream at 190 °C. The structured catalysts prepared were characterized by XRD, TPR, LRS, SEM and XPS, showing that their physical-chemistry features depend on the preparation method and Co loading.

Effect of nature of ceria support in CuO/CeO2 catalyst for PROX-CO reaction

In order to understand the effect of CeO2 on the preferential CO oxidation reaction (PROX-CO), the support cerium oxide was prepared by hydrothermal (CeO2-HT) and precipitation (CeO2-PP) methods. The catalyst supported on CeO2-HT exhibited higher activity than CuO/CeO2-PP. Characterization revealed that CuO was better dispersed on the CuO/CeO2-HT surface favoring the PROX-CO reaction, compared to CuO/CeO2-PP. Also, the nature of ceria was important for enhancing the metal-support interaction, which affects the catalytic activity. The CuO/CeO2-HT catalyst was less sensitive to presence of CO2 and H2O, remaining stable in a 24h run.

Mesoporous ceria-zirconia supported cobalt oxide catalysts for CO preferential oxidation reaction in excess H2

Mesoporous Co3O4/CexZr1−xO2 (x=0.75, 0.85, 0.95, 1) catalysts were synthesized by surfactant-assisted co-precipitation with subsequent incipient wetness impregnation (SACP-IWI) method. The prepared mesoporous ceria-zirconia supported cobalt oxide catalysts were used to catalyze CO preferential oxidation (PROX) reaction to eliminate the trace CO from H2-rich gases. The effects of structure-directing agent (SDA) type, atomic ratio of Ce/(Ce+Zr), cobalt oxide loading and reaction parameters on the catalytic properties for CO PROX reaction in excess H2 were investigated. Moreover, the various characterization techniques like N2 adsorption/desorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD), Fourier-Transform infrared spectroscopy (FT-IR) were employed to study the relationship between catalyst nature and catalytic properties. The results of N2 adsorption/desorption and X-ray diffraction patterns indicate that catalysts prepared by using cationic surfactant cetyltrimethylammonium bromide (CTAB) as SDA possess an ordered mesoporous architecture and exhibit much better catalytic activity compared with those prepared by using anionic surfactant ammonium dodecylbenzenesulfonate (ADBS) as SDA. The residual sulfur from ADBS was demonstrated to be the main reason for the much worse catalytic performance by the characterization results of FT-IR and NH3-TPD. Results show that the developed Co3O4/meso-Ce0.85Zr0.15O2 catalysts by SACP-IWI method with CTAB as SDA show an outstanding catalytic performance for CO PROX reaction, which mainly depends on the redox behavior of catalyst and cobalt oxide dispersion affected by the ceria-zirconia support feature, atomic ratio of Ce/(Ce+Zr) of support and cobalt oxide loading.

Mechanism of highly selective low temperature PROX reaction of CO in H 2: Oxidation of CO via HCOO with OH

Oxidation of CO is markedly enhanced by H 2 and/or H 2O on FeO x loaded Pt/TiO 2 (FeO x /Pt/TiO 2) catalyst. Similarly, oxidation of CO on the Pt/CNT and Pt/CNF was enhanced by H 2 and/or H 2O. As a result, highly selective preferential oxidation (PROX) of CO is established at low temperature on these catalysts. The oxidation of CO on these catalysts has a hydrogen isotope effect by H 2O/D 2O and H 2/D 2, which suggests the intermediate at the rate determining step involves hydrogen atom. Dynamics of in situ DRIFT spectroscopy on FeO x /Pt/TiO 2 suggests that the rate determining step of the PROX reaction of CO is the oxidation of HCOO with OH. TEM image proves that Pt particles are on the outer wall of the CNT but Ni–MgO and FeO x are localized at the end of CNT and CNF. If Ni–MgO and Fe in CNT and CNF were removed (CNT-p and CNF-p), the Pt lost the activity for low temperature PROX reaction of CO. Characteristic feature of the PROX reaction suggests a dual functional catalysis involving ionic process of CO + OH − → HCOO −, which is responsible for the low temperature PROX reaction of CO.

Ligand Fluorination to Optimize Preferential Oxidation of Carbon Monoxide by Water-Soluble Rhodium Porphyrins

Catalytic, low temperature preferential oxidation (PROX) of carbon monoxide by aqueous [5,10,15,20-tetrakis(4-sulfonatophenyl)-2,3,7,8,12,13,17,18-octafluoroporphyrinato]rhodium(III) tetrasodium salt, (1[Rh(III)]) and [5,10,15,20-tetrakis(3-sulfonato-2,6-difluorophenyl)-2,3,7,8,12,13,17,18-octafluoroporphyrinato]rhodium(III) tetrasodium salt, (2[Rh(III)]) is reported. The PROX reaction occurs at ambient temperature in buffered (4 ≤ pH ≤ 13) aqueous solutions. Fluorination on the porphyrin periphery is shown to increase the CO PROX reaction rate, shift the metal centered redox potentials, and acidify ligated water molecules. Most importantly, β-fluorination increases the acidity of the rhodium hydride complex (pK(a) = 2.2 ± 0.2 for 2[Rh-D]); the dramatically increased acidity of the Rh(III) hydride complex precludes proton reduction and hydrogen activation near neutral pH, thereby permitting oxidation of CO to be unaffected by the presence of H(2). This new fluorinated water-soluble rhodium porphyrin-based homogenous catalyst system permits preferential oxidation of carbon monoxide in hydrogen gas streams at 308 °K using dioxygen or a sacrificial electron acceptor (indigo carmine) as the terminal oxidant.