H2-rich Stream Research Articles

Selective oxidation of CO in H2-rich stream over ZSM5 zeolites supported Ru catalysts: An investigation on the role of the support and the Ru particle size

Selective oxidation of CO in H2-rich stream was studied over ZSM5 zeolite supported Ru catalysts and the results were compared with those obtained over Ru samples supported on alumina, silica and ceria. ZSM5 zeolite supported Ru catalysts exhibited higher yields to CO2 than Ru samples on other supports. The SiO2/Al2O3 ratio of the zeolite was found to strongly affect the performance of the Ru/ZSM5 system, the Ru sample supported on the H-ZSM5 with the highest SiO2/Al2O3 ratio (280) being the most efficient towards the CO selective oxidation. The form of the zeolite (H- or Na-) had instead a lower influence. On the basis of characterization data (TEM, XPS, H2-TPR, NH3-TPD) it was pointed out that the performance of the Ru/ZSM5 samples are strongly dependent on the Lewis acidity of the zeolite and/or the Ru particle size, a lower number of Lewis acid sites and bigger Ru particles resulting in higher CO2 yields.

Effect of carbon dioxide and water on the performances of an iron-promoted copper/ceria catalyst for CO preferential oxidation in H2-rich streams

The catalytic behavior of an iron-promoted copper/ceria catalyst towards CO-PROX reaction under feed mixtures containing variable concentrations of CO2 (0–15 vol.%) and H2O (0–10 vol.%) was compared to that of an unpromoted sample with the same copper loading. At low temperature both species inhibit CO conversion on Fe-promoted catalyst more than on the reference Cu/CeO2 catalyst, although the performance is restored more rapidly to that corresponding to CO2-free conditions by increasing the temperature. CO2 temperature programmed desorption tests were carried out and experimental curves modeled to evaluate quantitatively the active sites for CO and H2 oxidation. Iron addition significantly reduced the amount of H2 oxidation sites, likely promoting copper dispersion, leading to the observed better selectivity under CO2-free conditions. The inhibiting effect of CO2 was ascribed to the formation of quite stable CO2 adsorbed species blocking copper active sites. The different dependence on the temperature of CO2 desorption results in a higher inhibition at low temperature for the Fe-promoted catalyst, but also in an easier CO2 desorption at higher temperature restoring the performance under CO2-free conditions for this sample.

A novel and facile method to rapidly synthesize Ce0.8Zr0.2O2 nanoparticles for CO preferential oxidation in H2-rich stream.

A novel urea grind combustion (UGC) route was reported in this paper to rapidly prepare the ceria-zirconia nanoparticles (Ce0.8Zr0.2O2). For comparison, the conventional surfactant-assisted (SA) and sol-gel (SG) methods were also employed to prepare Ce0.8Zr0.2O2 nanoparticles. CO preferential oxidation in H2-rich stream (CO-PROX) was chosen as probe reaction to investigate the catalytic performance of these Ce0.8Zr0.2O2 catalysts prepared with different methods to highlight the superiority of UGC. It was found that Ce0.8Zr0.2O2-UGC showed the better reducibility and oxygen mobility than the Ce0.8Zr0.2O2 prepared by SA and SG, because the UGC route favored the more incorporation of zirconia into CeO2, leading to more serious distortion of the structure, and more defective sites in the Ce0.8Zr0.2O2. As a result, Ce0.8Zr0.2O2-UGC exhibited the higher CO conversion, better O2 selectivity, and excellent catalytic stability without any deactivation during 72-h reaction on stream. More importantly, the UGC method, as compared to the relatively complex and time-consuming SA and SG method, is simple, facile, low-cost, time-saving (within 30 minutes) and scalable, thereby, might be very promising for the application in many fields.

Characterization and catalytic properties of CuO/CeO2/MgAl2O4 for preferential oxidation of CO in H2-rich streams

Catalysts of copper (1wt.%) supported on a CeO2/MgAl2O4 mixed support have been prepared by using different pH values (pH∼4, 8 and 10) in the impregnating solution of copper with the aim of favoring different situations of interaction between copper and the two support components. The catalysts have been characterized in detail by XRD, SBET measurement, HREM and associated techniques, XPS, H2-TPR and EPR which allows establishing a model of structural characteristics of the catalysts. The characterization results have been correlated with analysis of the catalytic properties of the samples for preferential oxidation of CO in a H2-rich stream (CO-PROX) complemented by operando-DRIFTS. Important structural/chemical/catalytic differences as a function of the pH of the impregnating solution are revealed. These are explained on the basis of the characteristics of the interfaces formed between the different components present in each catalyst which basically determine the catalytic properties in each case.

Freeze-dried Co3O4–CeO2 catalysts for the preferential oxidation of CO with the presence of CO2 and H2O in the feed

A synthesis method in two steps was used to obtain Co3O4–CeO2 (COCE) catalysts. Firstly, freeze-drying precursors to obtain a submicrometric ceria powders support were calcined at a temperature as low as 400°C. Then, the support was impregnated with a Co(II) acetate solution by incipient wetness impregnation, varying the loading of Co between 5 and 20wt%, and calcined again at 400°C. xCOCE samples were tested for the preferential oxidation of CO in a H2-rich stream (CO-PROX). All samples showed catalytic activity and high selectivity towards CO2 at low reaction temperatures, being 15COCE the most active catalyst. Moreover, simulating a CO-PROX unit operation, the influence of the presence of CO2 and H2O in the feed was tested, showing a high activity and selectivity mainly to CO2.

Pd/zeolite-based catalysts for the preferential CO oxidation reaction: ion-exchange, Si/Al and structure effect

A screening of Pd/zeolite-based catalysts in the PrOx-CO reaction in H2-rich streams was performed using zeolites with different cations (H+, Na+ and Cs+) prepared by ion exchange and framework type (MFI and FAU).

Highly active subnano Rh/Fe(OH)x catalyst for preferential oxidation of CO in H2-rich stream

A novel catalyst formulation of 3.1wt.% Rh/Fe(OH)x was prepared via a co-precipitation method and investigated for CO preferential oxidation in H2-rich stream. This catalyst exhibited a wider temperature range of 20–70°C for CO total removal and better resistance to CO2 and H2O compared with the standard gold catalyst, standing out as the best Rh-based catalyst ever. The Rh species were highly dispersed in a subnano scale of ∼1nm and improved the reducibility of Fe(OH)x support. The adsorption of O2 was thus promoted over the reduced support, together with the weakened CO adsorption over the Rh clusters, permitting a non-competitive Langmuir–Hinshelwood mechanism through the elementary reaction of CO(ad)+O(ad). The reaction rate equation of r=k[CO]0.73[O2]0.64 and small apparent activation energy of 24kJmol−1 were then derived from the kinetic studies.

A systematic approach to the modeling and simulation of a Sorption Enhanced Water Gas Shift (SEWGS) process for CO2 capture

Dynamic operation of a multi-train Sorption Enhanced Water Gas Shift (SEWGS) system, based on a Pressure Swing Adsorption (PSA) process, is investigated by a detailed dynamic modeling and simulation. The multi-train SEWGS system, which consists of eight reactors in each train, operating in parallel, treats the feed syngas being produced continuously in a gasifier of an Integrated Gasification Combined Cycle (IGCC). Syngas is converted to a H2-rich product and a separate CO2-rich stream is also produced. The SEWGS system is designed for pre-combustion CO2 capture in the IGCC power plant. Therefore dynamic characteristic of the system at different loads of feed syngas is interesting for investigation of the performance of IGCC power plant at different Gas Turbine (GT) load levels. Simulation results reveal performance of the system in terms of components breakthrough curves and steam consumption of the system with a CO2 recovery rate of 95% and 99% purity of the recovered CO2. The H2-rich product purity achieved is around 81%. It is found that changing the rinse and purge steam amount affects the CO2 purity and recovery rate. However, the H2-rich product purity remains almost unchanged. Simulation results at different loads of feed syngas shows that to maintain the CO2 recovery and purity of the design case as the target performance, in addition to changing the rinse and purge steam loads, duration of the feed step and thus the cycle time should be varied as well. The H2-rich stream flow rate is found to undergo a periodic fluctuation of around ±33%, which should be minimized due to the GT requirements. It is tried to reduce the fluctuations by scheduling operation of the trains with time lags. Operation of the SEWGS system under two different scheduled operation scheme is investigated. H2-rich stream flow rate fluctuations are decreased from ∼±33% in the basic operation scheme to ∼±14% and ∼±11% in the first and second scheme. However, compared to the basic scheme, the H2-rich stream overall production rate drops around 5.5% and 6.2% on average, respectively.

Anchoring High-Concentration Oxygen Vacancies at Interfaces of CeO2–x/Cu toward Enhanced Activity for Preferential CO Oxidation

Catalysts are urgently needed to remove the residual CO in hydrogen feeds through selective oxidation for large-scale applications of hydrogen proton exchange membrane fuel cells. We herein propose a new methodology that anchors high concentration oxygen vacancies at interface by designing a CeO2-x/Cu hybrid catalyst with enhanced preferential CO oxidation activity. This hybrid catalyst, with more than 6.1% oxygen vacancies fixed at the favorable interfacial sites, displays nearly 100% CO conversion efficiency in H2-rich streams over a broad temperature window from 120 to 210 °C, strikingly 5-fold wider than that of conventional CeO2/Cu (i.e., CeO2 supported on Cu) catalyst. Moreover, the catalyst exhibits a highest cycling stability ever reported, showing no deterioration after five cycling tests, and a super long-time stability beyond 100 h in the simulated operation environment that involves CO2 and H2O. On the basis of an arsenal of characterization techniques, we clearly show that the anchored oxygen vacancies are generated as a consequence of electron donation from metal copper atoms to CeO2 acceptor and the subsequent reverse spillover of oxygen induced by electron transfer in well controlled nanoheterojunction. The anchored oxygen vacancies play a bridging role in electron capture or transfer and drive molecule oxygen into active oxygen species to interact with the CO molecules adsorbed at interfaces, thus leading to an excellent preferential CO oxidation performance. This study opens a window to design a vast number of high-performance metal-oxide hybrid catalysts via the concept of anchoring oxygen vacancies at interfaces.

Multishell hollow CeO2/CuO microbox catalysts for preferential CO oxidation in H2-rich stream

Multishell hollow CuO microbox was synthesized by a template method and the Ce(IV) nitrate solution was impregnated into the hollow cavity of the CuO support. The as-prepared catalysts were characterized by FESEM, TEM, XRD, N2 physisorption and H2-TPR. It is found that the alternate CuO and CeO2 multishell structure reduces the agglomeration of CuO species and improves the dispersion of CeO2. The special structure ensures even distribution of the two species in the material matrix and the optimum ratio of CeO2 to CuO provides two-component active sites with high concentration. Thus, the wider full CO conversion window and higher CO2 selectivity are achieved over the 30CeO2/CuO microbox catalyst.

Highly Efficient Catalysis of Preferential Oxidation of CO in H2-Rich Stream by Gold Single-Atom Catalysts

Preferential oxidation of CO (PROX) in H2-rich stream is critical to the production of clean H2 for the H2-based fuel cells, which provide clean and efficient energy conversion. Development of highly active and selective PROX catalysts is highly desirable but proved to be extremely challenging. Here we report that CeO2-supported Au single atoms (Au1/CeO2) are highly active, selective, and extremely stable for PROX at the PEMFC working temperature (∼80 °C) with >99.5% CO conversion over a wide temperature window, 70–120 °C (or 50–100 °C, depending on the Au loading). The high CO conversion realized at high temperatures is attributed to the unique property of single-atom catalysts that is unable to dissociatively adsorb H2 and thus has a low reactivity toward H2 oxidation. This strategy is proven in general and can be extended to other oxide-supported Au atoms (e.g., Au1/FeOx), which may open a new window for the efficient catalysis of the PROX reaction.

CO preferential oxidation under H2-rich streams on copper oxide supported on Fe promoted CeO2

In this work the effect of Fe addition to copper/ceria catalysts on the catalytic activity toward CO-PROX reaction has been studied and related to the modification of textural and redox properties induced by iron. Catalysts have been characterized by the use of BET surface area measure, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and TPR with different reducing mixtures (CO/N2 and/or H2/N2). Results show that iron promotes a superficial enrichment of highly dispersed copper sites improving catalyst reducibility, especially under CO-containing mixture, thus resulting in an enhanced selectivity of CO-PROX reaction.

Activity of Au/Fe2O3–TiO2 catalyst for preferential CO oxidation

A series of Au supported on Fe2O3–TiO2 catalysts were prepared, characterized and investigated the catalytic activity in the preferential CO oxidation (PROX) under a H2-rich stream. The effects of the different metal support ratio, the calcination temperature, the gold loading, and the pre-treatment condition were studied on both the characteristics and catalytic activity of the catalysts. The results obviously showed that 1% Au/Fe2O3–TiO2 (1:4) exhibited higher CO conversion than the 1% Au/TiO2 and 1% Au/Fe2O3 catalysts, especially temperature lower than 100 °C, which due to the formation of reducible gold species at lower temperature. TPR results suggested the improvement of Au–Au and metal–metal (in support) interaction. Additionally, XPS spectra suggested the Au0 could be the predominant active site. The effect of O2 pretreatment showed a negative effect in both activity and selectivity which suggested the formation of adsorbed oxygen species on the surface of the catalyst. Moreover, the deactivation was affected by injection H2O, CO2 or the combination of CO2–H2O into the typical feed.

Optimization of the preparation method of CuO/CeO2 structured catalytic monolith for CO preferential oxidation in H2-rich streams

Copper/ceria washcoated monoliths were prepared by a modified dip coating procedure and operated under CO-PROX conditions. Slurry preparation was suitably modified with respect to more conventional procedure in order to improve the washcoat adhesion onto the cordierite walls. Wet instead of dry milling of the powder ceria used to prepare slurry and colloidal ceria addition to the slurry significantly improved washcoat adhesion, due to partial penetration of the washcoat into the cordierite macropores. Moreover, ceria specific surface area and pore size distribution were affected by both preparation and composition of slurry. Samples prepared by modified slurries showed also improved copper dispersion with a consequent higher selectivity to CO2.

Ethanol steam reforming over bimetallic coated ceramic foams: Effect of reactor configuration and catalytic support

In recent years, hydrogen production from renewable feed-stocks attracts particular attention. Specifically, the steam reforming of biomass-derived bioethanol could provide H2-rich effluent streams, representing an interesting research field. This study focuses on the development of bimetallic structured catalysts (containing Ni and Pt as active species and supported on ceria and ceria-zirconia) active in Ethanol Steam Reforming (ESR) reaction at low-temperature (300–600 °C) and characterized by improved heat transfer properties. ESR reaction was carried out on ceramic foams and, as a comparison, on powders catalysts. In particular, catalytic tests were carried out on two reactor configurations: catalytic powders were tested in both a tubular and annular reactor; in addition, the tubular configuration was also employed for the structured catalysts. Unsatisfactory results were observed for powders in the tubular reactor while the better thermal management of the annular configuration ensured significantly higher conversions. Moreover, the enhanced thermal conductivity of SiC foams catalysts, tested in the tubular reactor, allowed overcoming heat transfer limitations in an easy reactor geometry, resulting in very good performances. The catalytic behaviour of bimetallic CeO2 and CeO2–ZrO2 based catalysts was also compared and the effect of catalytic support on ethanol conversion and H2 yield at different space velocities (100,000–400,000 h−1) was investigated. Finally, Pt–Ni/CeO2–ZrO2 catalysts, which displayed a more interesting catalytic activity with respect to CeO2 based samples, were employed for stability tests at 100,000 h−1 and 450 °C: products gas distribution was not affected during TOS and total ethanol conversion was recorded for almost 5 h.

Selective CO methanation in H2-rich stream over Ni–, Co– and Fe/CeO2: Effect of metal and precursor nature

Selective CO methanation in the realistic H2-rich gas mixture containing 10 vol.% H2O and 20 vol.% CO2 was investigated over 10 wt.% Ni–, Co– and Fe/CeO2 catalysts, prepared from nitrate and chloride precursors. BET, XRD, HRTEM, EDX and CO chemisorption techniques were used for catalyst characterization. Among the catalysts studied, the Ni/CeO2 catalyst, prepared from NiCl2 precursor, showed the best catalytic performance. This phenomenon can be associated with inhibition of CO2 hydrogenation activity by the presence of chlorine on the catalyst surface.

The preferential oxidation of CO in hydrogen rich streams over platinum doped nickel oxide catalysts

NiO/Al2O3, Pt/Al2O3 and Pt/NiO/Al2O3 catalysts were prepared by the incipient wetness technique with a Ni loading of 25wt% and Pt loading of 0.5wt%. These catalysts were characterized by ICP-OES, XRD, BET, TPR, N2 adsorption–desorption isotherms, CO chemisorption, FTIR-CO, XPS, SEM-EDX and TEM. XRD and XPS results of the catalysts showed the presence of NiO and PtO phases on the respective supports and in situ redox reactions showed that the catalysts underwent reversible phase changes (oxide and metallic) that were stable. FTIR-CO studies showed that the Pt containing samples exhibited both linear and bridged CO adsorption with higher intensities observed for the Pt/NiO/Al2O3 catalyst. The catalysts were tested for the oxidation of CO in H2 rich streams (preferential oxidation-PROX) in a continuous flow fixed bed stainless steel reactor. The NiO/Al2O3 catalyst produced very low conversions of CO in the stipulated PROX temperature range and showed highest conversion of 11% with a selectivity of 25% toward CO2. The Pt/Al2O3 catalyst showed improved activity within the PROX temperature range with highest CO conversion of 56% and selectivity toward CO2 of 68% at 200°C. The Pt/NiO/Al2O3 catalyst revealed synergistic effects, obtaining much higher CO conversions within the PROX temperature ranges compared to both the mono-metallic catalysts. The highest CO conversion, of 99.9%, for this catalyst was at 200°C, with a selectivity of 72.8% toward CO2 using a C:O2 ratio of 1:2.

Elimination of acetaldehyde from hydrogen rich streams employing Ni/ZrO2

The elimination of acetaldehyde from H2 streams was studied employing the TPSR of acetaldehyde decomposition, thermodesorption of acetaldehyde followed by FTIR and catalytic tests employing Ni/ZrO2 catalyst and also Ni/SiO2 catalyst, being the latter a reference. The results show that Ni/ZrO2 is a very promising catalytic system for the CO and acetaldehyde simultaneous elimination from H2 rich streams. Indeed, the outstanding performance of Ni/ZrO2 when compared with Ni/SiO2 might be related to two factors: its high activity toward acetaldehyde and CO elimination and its large number of active sites located on the metal and mainly on the support.

CuO/CeO2 based monoliths for CO preferential oxidation in H2-rich streams

Copper/ceria washcoated monoliths were prepared by means of a modified dip coating procedure and operated under CO-PROX conditions. The effect of the substrate properties (cell density and wall thermal conductivity) was studied. The significant role of the temperature profile on the performances (CO conversion and selectivity to CO2) was found by testing monoliths with different cell density and wall thermal conductivity. High cell density monoliths with substrate showing the higher thermal conductivity (SiC) appear the best option, providing the best thermal management of the process.

NO oxidation to NO2 over manganese-cerium mixed oxides

There is a recognized need for lowering greenhouse gas emissions from mobile sources in order to address concerns regarding global climate change. Diesel engines offer superior fuel efficiency and greenhouse gas reduction potential; however, the highly loaded Pt for converting NO to NO2 in diesel aftertreatment catalysts is one of the major hurdles in the broad implementation of highly fuel efficient diesel engine vehicles. Here, we reported that manganese-cerium mixed oxides coated on monolith substrates demonstrated a superior NO oxidation to NO2 activity, showing a promise for PGM thriftting for diesel or lean burn engines emission control catalysts. The mixed oxide (MnOx-CeO2) shows a much higher NO oxidation to NO2 rate and is nearly 3 and 10 times active of that MnOx and CeO2 at 200°C, respectively. Significantly lower reduction temperature of the mixed oxide (MnOx-CeO2) compared with MnOx and higher Mn4+ to Mn3+ reduction peak intensity suggest that ceria helps stabilize higher oxidation state of Mn. The MnOx-CeO2 mixed oxide shows higher activity for NO oxidation due to the enhanced rate of nitrites decomposition to NO2. The structure of the MnOx-CeO2 mixed oxide maintained during a cyclic treatment of oxidative/reductive gas conditions at 650°C. Furthermore, the incorporation of ZrO2 into MnOx-CeO2 mixed oxide not only increased NO oxidation activity but also the sulfur tolerance. About 70% of the activity of the MnOx-CeO2-ZrO2 was recovered via regeneration in a H2 rich stream.