CO In Excess Hydrogen Research Articles

Preferential oxidation of CO in excess hydrogen over a nanostructured CuO–CeO2 catalyst with high surface areas

CuO–CeO 2 is prepared by coprecipitation and ethanol washing and characterized using BET, HR-TEM, XRD and TPR techniques. The results show that CuO–CeO 2 is nanosized ( r TEM = 6.5 nm) and possesses high surface area ( S BET = 138 m 2 g −1 ). Furthermore, some lattice defects in the surface of CuO–CeO 2 are found, which are beneficial to enhance catalytic performance of CuO–CeO 2 in preferential oxidation of CO in excess hydrogen (PROX). Consequently, the nanostructured CuO–CeO 2 exhibits perfect catalytic performance in PROX. Namely, CO content can be lowered to less than 100 ppm at 150 °C with 100% selectivity of O 2 in the presence of 8% CO 2 and 20% H 2 O at 120 , 000 ml g cat - 1 h - 1 .

Selective removal of CO from hydrogen-rich stream over CuO/Ce xSn 1−xO 2–Al 2O 3 catalysts

The solid solutions of Ce x Sn 1− x O 2 incorporated with alumina to form Ce x Sn 1− x O 2–Al 2O 3 mixed oxides, by the suspension/co-precipitation method, were used to prepare CuO/Ce x Sn 1− x O 2–Al 2O 3 catalysts for the selective oxidation of CO in excess hydrogen. Incorporating Al 2O 3 increased the dispersion of Ce x Sn 1− x O 2, but did not change their main structures and did not weaken their redox properties. Doping Sn 4+ into CeO 2 increased the mobility of lattice oxygen and enhanced the activity of the 7%CuO/Ce x Sn 1− x O 2–Al 2O 3 catalyst in the selective oxidation of CO. The selective oxidation of CO was weakened as the doped fraction of Sn 4+ exceeded 0.5. Incorporating appropriate amounts of Sn 4+ and Al 2O 3 could obtain good candidates 7%CuO/Ce x Sn 1− x O 2–Al 2O 3(20%), 1– x=0.1–0.5, for a preferential oxidation (PROX) unit in a polymer electrolyte membrane fuel cell system for removing CO. Its activity was comparable with, and its selectivity was much larger than, that of the noble catalyst 5%Pt/Al 2O 3.

Influence of Ethanol Washing in Precursor on CuO–CeO2 Catalysts in Preferential Oxidation of CO in Excess Hydrogen

In this study, influence of ethanol washing in precursor on CuO–CeO2 catalysts in preferential oxidation of CO in excess hydrogen (PROX) was investigated. BET, FTIR and TPR techniques were used. The results showed that ethanol washing was beneficial to improve the catalytic performance of CuO–CeO2 catalysts in the PROX. The CO conversion over CuO–CeO2 catalysts without ethanol washing was only 85% at 190 °C, while the highest CO conversion over CuO–CeO2 catalysts with 200 mL ethanol washing was beyond 99% at 120 °C. XRD and TPR results showed that ethanol washing depressed the growth of CuO–CeO2 catalysts and improved the reducibility of CuO–CeO2 catalysts. The FTIR measurement proved that the absorption water was decreased by the way of ethanol washing, indicating that the amount of the H–O–H bridge between adsorption water and precursor of CuO–CeO2 catalysts was decreased and depressed the growth of CuO–CeO2 catalysts.

Influence of residual [formula omitted] on the catalytic performance of [formula omitted] catalysts in preferential oxidation of CO in excess hydrogen

Influence of residual K + on the preferential oxidation of CO in excess hydrogen (PROX) over CuO – CeO 2 catalysts was investigated. CuO – CeO 2 catalysts were characterized by BET, ICP, XRD, UV-Raman and TPR techniques. The results showed that the existence of residual K + made α peak in TPR of CuO – CeO 2 catalysts shift to higher temperatures and depressed the PROX in the absence of CO 2 and H 2 O in the feed over CuO – CeO 2 catalysts. However, small amount of residual K + was beneficial to the catalytic performance of CuO – CeO 2 catalysts in the PROX in the presence of CO 2 and H 2 O in the feed. Consequently, residual K + with an appropriate content was beneficial to improve the catalytic performance of CuO – CeO 2 catalysts in the presence of CO 2 and H 2 O .

Selective oxidation of CO in excess hydrogen over [formula omitted] catalysts

Alumina was incorporated with the solid solutions of Ce x Zr 1 - x O 2 to form Ce x Zr 1 - x O 2 – Al 2 O 3 mixed oxides, by the suspension/co-precipitation method, to be used as supports of CuO / Ce x Zr 1 - x O 2 – Al 2 O 3 catalysts. They were characterized, and the effects of Al 2 O 3 on the selective oxidation of CO in excess hydrogen were examined. Incorporating Al 2 O 3 increased the dispersion of Ce x Zr 1 - x O 2 , but did not change their main structures and did not weaken their redox properties. Doping zirconium into CeO 2 increased the mobility of lattice oxygen and enhanced the activity of the 7 % CuO / Ce 0.9 Zr 0.1 O 2 – Al 2 O 3 catalyst in the selective oxidation of CO in the H 2 -rich feed. The promotion of CO oxidation became weaker as the fraction of Zr 4 + dopant increased above 0.1. A small amount of Zr 4 + dopant and an appropriate amount of incorporated Al 2 O 3 could obtain a good candidate such as 7 % CuO / Ce 0.9 Zr 0.1 O 2 – Al 2 O 3 ( 20 % ) for a preferential oxidation (PROX) unit in a polymer electrolyte membrane fuel cell system for removing CO. Its activity was comparable with, and its selectivity was much larger than, that of the noble catalyst 5 % Pt / Al 2 O 3 .

Partial pressure dependent in situ spectroscopic study on the preferential CO oxidation in hydrogen (PROX) over Pt/ceria catalysts

Platinum supported on ceria can oxidize CO in excess hydrogen selectively (PROX process). In situ DRIFTS and high-pressure (∼1 mbar) XPS experiments were performed to study the mechanism of the PROX reaction on Pt/ceria catalysts. The partial pressure of O2 and/or CO was varied and correlated with induced changes in activity and selectivity as well as with the surface state and species under reaction conditions. Pt-carbonyl species changed rather insignificantly, especially relative to the wide variations of the product pattern with changing feed composition. Furthermore, the interconversion of formate and carbonate species was observed. Therefore, the changes in the evolution of surface species detected by in situ DRIFTS cannot explain the variation observed in CO oxidation activity. On the other hand, high-pressure XPS showed significant modification of the surface state with changing feed composition. Most significantly, oxygen vacancy formation seemed to correlate with enhanced CO oxidation activity. At higher vacancy density, water desorption was hindered. Highly hydrated ceria with significant vacancy density was found to be beneficial for the PROX process; here surface water blocked Hads oxidation sites. Moreover, lower apparent activation energy of CO oxidation was measured in the PROX reaction on catalysts with more vacancies. The results given here reinforce the view of catalysts being adaptive to a certain reaction rather than having active sites as prepared. Whereas IR-detectable surface species may only be indicators and/or consequences of this surface change, formation of the beneficial surface/near-surface state may be the rate-limiting factor in several catalytic processes.

Preferential Oxidation of CO in Excess Hydrogen over CuO-CeO 2 Catalyst Prepared by Chelating Method

Abstract The CuO-CeO 2 catalyst prepared by chelating method has a superior catalytic performance for the preferential oxidation of CO in rich hydrogen, compared with the CuO-CeO 2 catalyst prepared by coprecipitation method. The CO conversions over these catalysts, at 120 °C and 120000 ml/(g·h) in the absence of CO 2 and H 2O, are 99.6% and 88.6%, respectively, and the selectivity of O 2 over these catalysts is very close (i.e. 51.3% and 55.8%, respectively). The influence of certain factors such as hydrogen concentration, carbon monoxide concentration, H 2O, O 2/CO ratios, and space velocity on the catalytic performance of CuO-CeO 2 catalyst prepared by chelating method is also studied. The results show that the addition of hydrogen and H 2O has a negative effect on the catalytic performance of CuO-CeO 2 catalyst, however, the variation of space velocity and the O 2/CO ratio causes a comparatively slight influence.

Comparative study of different methods of preparing CuO-CeO 2 catalysts for preferential oxidation of CO in excess hydrogen

Influence of preparation methods (i.e. co-precipitation, chelating, citric acid and critical phase) on the preferential oxidation of CO in excess hydrogen over CuO-CeO 2 catalysts has been investigated. CuO-CeO 2 catalysts are characterized by using BET, X-ray powder diffraction (XRD), UV Raman and temperature-programmed reduction (TPR) techniques. The catalyst prepared by chelating is most active for the preferential oxidation of CO. In addition, XRD, UV Raman and TPR show that the chelating method enhances the formation of defects of ceria and produces a synergic effect between the cycle of Cu 1+/Cu 2+ and that of Ce 3+/Ce 4+, which is beneficial to the improvement of the performance of CuO-CeO 2 catalysts.

Silver catalysts supported over activated carbons for the selective oxidation of CO in excess hydrogen: effects of different treatments on the supports

Commercial activated carbon (AC) was used as a support either in its original form or after various modifications, giving diverse textural and surface chemical characteristics. The changes of these properties were monitored by N2 adsorption–desorption isotherms, temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Ag catalysts were prepared over the AC supports by a conventional wet impregnation method. The catalytic performances of supported Ag/AC catalysts in the selective oxidation of CO in excess H2 were tested. The results indicate the textural and surface chemical characteristics are responsible for the different catalytic performances.

Carbon-Supported Silver Catalysts for CO Selective Oxidation in Excess Hydrogen

Carbon materials were used as supports for Ag catalysts that are prepared using the conventional wet impregnation method, and their catalytic properties for CO selective oxidation in excess hydrogen at temperatures below 483 K were tested. A variety of techniques, e.g. N 2 adsorption, XPS, TPD, UV-Vis DRS, TEM and SEM, were used to determine the influence of physical and chemical properties of the carbon on the properties of Ag catalyst. It was found that defects on the carbon surface served as nucleation sites for silver ions, while functional groups on carbon surface induced their reduction to the metallic form. The formation of silver particles on carbon was governed by homogeneous and/or heterogeneous nucleation during the impregnation and subsequent activation processes. The best catalytic performance was obtained with a Ag/carbon black catalyst with a uniform size distribution of silver nanoparticles (about 12 nm), moderate BET surface area (with a mesoporous structure), and a limited amount of carbon-oxygen groups. The research indicates that carbon materials are potentially good supports for silver catalysts for preferential oxidation of CO in excess hydrogen.

Artificial neural network-aided design of Co/SrCO 3 catalyst for preferential oxidation of CO in excess hydrogen

Preferential oxidation (PROX) of 0.7–1 vol.% CO using the stoichiometric amount of O 2 was investigated in excess hydrogen. Cobalt loading and preparation conditions of Co/SrCO 3 was optimized by using a full factorial design of experiment, an artificial neural network and a grid search. The optimum catalyst was 3.2 mol% Co/SrCO 3 pretreated at 345 °C and 97% CO conversion was achieved at 240 °C under dry and CO 2 free conditions. However CO 2 and H 2O vapor inhibited the activity, and the new additive to the Co/SrCO 3 catalyst was investigated in the next step for the high tolerance towards CO 2 and H 2O. Representative 10 elements (B, K, Sc, Mn, Zn, Nb, Ag, Nd, Re, and Tl) were selected to represent the physicochemical properties of all elements. Based on the relation between the physicochemical properties of element X and the catalytic performance of Co–X/SrCO 3, the elements such as Bi, Ga, and In were predicted to be promising additives. Finally, the catalytic performance of these additives was experimentally verified. Sixty-four percent CO conversion and 70% selectivity for PROX at 240 °C was achieved in the presence of excess carbon dioxide and steam by Co 3.2–Bi 0.3 mol%/SrCO 3 pretreated at 345 °C.

Artificial neural network aided virtual screening of additives to a Co/SrCO 3 catalyst for preferential oxidation of CO in excess hydrogen

Preferential oxidation (PROX) of 0.7–1 vol% CO was investigated using the stoichiometric amount of O 2 in excess hydrogen. Cobalt supported on SrCO 3 showed high selectivity to PROX of CO, and the new additive to the Co/SrCO 3 catalyst was investigated for the high tolerance towards CO 2 and H 2O. Representative 10 elements (B, K, Sc, Mn, Zn, Nb, Ag, Nd, Re, and Tl) were selected to represent the physicochemical properties of all elements suitable for additives of solid catalyst. A supported cobalt catalyst with one kind of the above additive was prepared for CO PROX reaction. The activities at 240 °C and the physicochemical properties of the 10 elements were used as training data of a radial basis function network (RBFN), a kind of artificial neural network. After the training, the RBFN predicted the catalytic performance of the supported catalyst containing various element X as Co–X/SrCO 3. The elements such as Bi, Ga, and In were predicted to be promising additives. Finally, the catalytic performance of these additives was experimentally verified. Sixty four percent of CO conversion and 70% selectivity for PROX at 240 °C was achieved in the presence of excess carbon dioxide and steam by Co 3.2–Bi 0.3 mol%/SrCO 3 pretreated at 345 °C.

The preferential oxidation of CO in excess hydrogen: A study of the influence of KOH/K 2CO 3 on CuO–CeO 2− x catalysts

The preferential oxidation of CO in rich hydrogen has been studied for CuO–CeO 2− x catalysts. The catalysts were prepared by co-precipitation with K 2CO 3 + KOH as precipitators and characterized using N 2 physisorption isotherms, high resolution transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results indicate that nano-structured CuO–CeO 2− x catalysts are obtained, and that the ratio of KOH/K 2CO 3 has a beneficial influence on the properties of CuO–CeO 2− x catalysts, i.e., with the addition of KOH, the particle sizes grow smaller, CuO–CeO 2− x catalysts have larger surface areas, CuO species in CuO–CeO 2− x are more easily reduced and achieve higher catalytic performance in the preferential oxidation of CO in rich hydrogen. CO conversion higher than 99% with O 2 selectivity of 100% is obtained for CuO–CeO 2− x catalysts with KOH/K 2CO 3 equal to 4:0 at a temperature of 90–110 °C and a space velocity of 30,000–120,000 ml g −1 h −1.

Selective oxidation of CO in excess hydrogen over CuO/Ce xSn 1− xO 2 catalysts

Ce x Sn 1− x O 2 (1 − x = 0.1–0.5) mixed oxides were prepared as supports of CuO/Ce x Sn 1− x O 2 catalysts. They were characterized and used in the selective oxidation of CO in excess hydrogen. Incorporating Sn 4+ into CeO 2 not only increased the mobility of lattice oxygen but also promoted the activity of the selective CO oxidation. These promoting effects were attributed to the redox behaviors of Ce 4+/Ce 3+ and Sn 4+/Sn 2+ in Ce x Sn 1− x O 2 mixed oxides and to the interfacial interaction between fine clusters of CuO and Ce x Sn 1− x O 2. Of these CuO/Ce x Sn 1− x O 2 catalysts, 7% CuO/Ce 0.9Sn 0.1O 2 catalyst was the most active one; it was and more active than the 7% CuO/CeO 2 catalyst, with a T 100 temperature (80–85 °C) for complete conversion that was about 15 °C less than that of 7% CuO/CeO 2 (95–100 °C). The selective oxidation of CO was still promoted as the incorporated amount of Sn 4+ exceeded 10%, which is different from the result of incorporating Zr 4+ in Ce x Zr 1− x O 2 (1 − x > 0.1). Such incorporation of Zr 4+ in Ce x Zr 1− x O 2 weakened the selective oxidation. The 7% CuO/Ce 0.9Sn 0.1O 2 catalyst was almost inactive in H 2 oxidation below 110 °C, and it achieved a selectivity of approximately 100%. The activity of the 7% CuO/Ce 0.9Sn 0.1O 2 catalyst was weakened in the feed in the presence of CO 2 and H 2O, but the stability of the catalyst was maintained. The 7% CuO/Ce 0.9Sn 0.1O 2 catalyst exhibited a good activity that was comparable with that of the noble metal catalyst of 5% Pt/Al 2O 3 and a good selectivity of much greater than 5% Pt/Al 2O 3.

Preferential CO oxidation in hydrogen (PROX) on ceria-supported catalysts, part I: Oxidation state and surface species on Pt/CeO 2 under reaction conditions

The CO content of hydrogen feed to proton-exchange membrane fuel cells (PEMFCs) must be kept under 1–100 ppm for their proper operation. This can be achieved by using catalysts able to selectively oxidize CO in the presence of excess hydrogen (PROX). The present study reports on the mechanism of the PROX reaction on Pt/CeO 2 catalyst, using catalytic tests, in situ DRIFTS, high-pressure XPS, HRTEM, and TDS techniques. Bulk metallic, pronounced adsorbate-induced surface Pt, and a small amount of oxidized Pt sites were detected by in situ high-pressure XPS under PROX conditions. The preoxidized ceria surface was strongly reduced in pure H 2 but significantly reoxidized under PROX conditions (i.e., O 2 + CO in excess hydrogen) at T = 358 K . The remaining small amount of Ce 3+ decreased with increasing temperature. HRTEM found well-crystallized CeO 2 particles (8–10 nm) in the case of activated (pre-oxidized) sample that transformed in a large extent to an oxygen deficient ceria supercell structure after PROX reaction. Metallic Pt particles (2–3 nm) and small (0.5–0.6 nm) Pt clusters were found by HRTEM. These findings were in accordance with the variations in relative intensity of the corresponding Pt CO bands (DRIFTS). Different types of carbonate and formate species were detected (XPS and DRIFTS). Their possible role in the reaction mechanism is discussed. Resolved OH bands could not be found by DRIFTS in the PROX reaction mixture indicating significant amount of adsorbed water in a hydrogen-bonded structure. Its presence seems to suppress hydrogen oxidation while CO oxidation still takes place, as the metallic particles are covered by CO (DRIFTS). The direct contribution of surface water in a low-temperature water–gas shift-type reaction in the PROX mixture is proposed.

Artificial neural network-aided development of supported Co catalyst for preferential oxidation of CO in excess hydrogen

Preferential oxidation (PROX) of 1 vol% CO was investigated using the stoichiometric amount of O 2 in excess hydrogen. Cobalt supported on alkali earth metal carbonate, especially Co/SrCO 3, showed high selectivity to PROX of CO while the assistance of methanation of CO was necessary to achieve over 99% conversion of CO. Cobalt loading and preparation conditions of Co/SrCO 3 was optimized by using a full factorial design of experiment, an artificial neural network and a grid search. Over 99% O 2 conversion and 78% selectivity for PROX at 200 °C was achieved by 3.2 mol% Co/SrCO 3 pretreated at 345 °C.

Selective oxidation of CO in hydrogen-rich stream over Cu–Ce catalyst promoted with transition metals

Cu–Ce/ γ-Al 2O 3 catalysts promoted with Co were tested for the low temperature selective oxidation of CO in excess hydrogen. The effects of Cu–Ce composition, Co as a dopant, stoichiometric ratio ( λ=2O 2/CO), water vapor and CO 2 on the selective oxidation of CO to CO 2, O 2 consumption and selectivity of O 2 to CO oxidation as a function of temperature are presented. Also, the catalytic properties of the catalysts were investigated by using X-ray diffraction, CO-/H 2-temperature programmed reduction, temperature programmed oxidation, CO-/CO 2-/H 2O-temperature programmed desorption (TPD). Small addition (0.2 wt) of Co onto the Cu–Ce/ γ-Al 2O 3 brought large increase in selective CO oxidation activity. In the presence of either CO 2 (13 vol%) or H 2O (10 vol%) in the reformed gas feed, both Cu–Ce/ γ-Al 2O 3 and Cu–Ce-Co/ γ-Al 2O 3 showed decreased activity in CO oxidation at low temperatures, especially, under 200°C. Compared with the Cu–Ce/ γ-Al 2O 3, however, the Cu–Ce-Co/ γ-Al 2O 3 gives higher resistivity for the CO 2 and H 2O. From the CO 2/H 2O-TPD results, it could be explained that the main cause for the decrease in catalytic activity with CO 2 and H 2O in the feed may be attributed to the competitive adsorption of CO and CO 2 as well as the blockage of the active sites by water vapor at low reaction temperatures.

Activity and characterization of the Co-promoted CuO–CeO 2/γ-Al 2O 3 catalyst for the selective oxidation of CO in excess hydrogen

For the selective oxidation of CO in excess hydrogen, γ-Al 2O 3-supported CuO–CeO 2-based catalysts were investigated. Effects of the composition of Cu and Ce metals and the addition of Co as a promoter to the catalyst on the catalytic activity and the selectivity for the CO oxidation against H 2 were determined as a function of temperature. The effects of the feeding ratio of O 2 to CO and the presence of H 2O and/or CO 2 in the feeding reactant were also examined. Among the catalysts tested, CuO–CeO 2/γ-Al 2O 3 incorporating Co by 0.2 wt.% was the most active to show the CO conversion >99% in the wide temperature window of 150–220 °C with the CO oxidation selectivity of 94–50%. It was found from the catalyst characterization using temperature-programmed reduction/oxidation that the Co-promoted CuO–CeO 2/γ-Al 2O 3, as compared with the catalyst without Co addition, had an increased number of CO oxidation-active sites capable of being easily reduced or oxidized at relatively low temperatures. However, the presence of CO 2 and H 2O in the feed decreased the low-temperature activity of the catalyst, and shifted the temperature window of CO conversion >99% to higher temperature region, i.e. 205–230 °C. Irrespective of the presence of both CO 2 and H 2O in the feed, the Co-incorporated catalyst was found to have the temperature window of CO conversion >99.9% within 210–224 °C, whereas no such temperature window existed for the CuO–CeO 2/γ-Al 2O 3 catalyst. Temperature-programmed desorption of CO, CO 2, or H 2O was also conducted for understanding the catalytic reaction behavior in the presence of CO 2 and/or H 2O in the reactants.

Selective oxidation of CO in excess hydrogen on copper—cerium-containing catalysts

Selective oxidation of CO that is in mixtures enriched in H2 was studied to investigate catalytic properties of the 0.5—80% CuO/Ce0.7Zr0.3O2 system. The catalysts were prepared by the combined decomposition of copper, cerium, and zirconyl nitrates at 300 °C. The systems studied are active and stable under mild conditions of the process (80—160 °C) and at high space velocities (to 100000 h–1) of the reaction mixture (2% CO, 1% O2, 40—50% H2). With an increase in the CuO content in the catalysts up to 20%, the degree of CO removal achieves 60% (120 °C and V = 35000 h–1) and further does not change appreciably. The contribution of oxygen participation into CO oxidation is virtually independent of the copper concentration in the sample and ranges from 65 to 75%. The dependences of the Arrhenius equation parameters for CO and H2 oxidation on the catalyst composition were determined, which makes it possible to calculate the conversion of reactants and selectivity of CO conversion under the specified conditions of the process. The addition of CO2 and H2O (12—15%) to the reaction mixture decreases the catalyst activity and simultaneously increases the selectivity of CO oxidation to 100%. It is shown by the TPR and X-ray diffraction methods that the combined decomposition of the starting Cu2+, Ce3+, and ZrO2+ nitrates produces solid solutions of oxides with a high content of CuO. The reductive pre-treatment of fresh samples of the studied catalysts results in the destruction of the solid solution and formation of highly dispersed Cu particles on the surface of Ce—Zr—O. These particles are active in CO oxidation.

Selective oxidation of carbon monoxide in excess hydrogen over Pt-, Ru- and Pd-supported catalysts

Selective oxidation of CO in excess hydrogen has been studied over Pt-, Ru- and Pd-supported on Sibunit (porous carbonaceous material) catalysts. The Ru and Pt catalysts were found to be the most active and selective among the studied catalysts. They provided single-step removal of CO from hydrogen-rich stream both in the absence and presence of CO 2 and H 2O to a PEMFC tolerant level.