Performance For CO Preferential Oxidation Research Articles

Mn-induced Cu/Ce catalysts with improved performance for CO preferential oxidation in H2/CO2-rich streams

A series of xMnCu/Ce catalysts with constant low Cu loading of 1 wt% were prepared by the simple impregnation method. The obtained catalysts were characterized by XRD, BET, H2-TPR and XPS, and the preferential oxidation of CO was evaluated in CO2/H2-rich atmospheres. It was shown that partial Mn and Cu could be incorporated into the Ceria lattice, forming surface ternary Cu–Mn–Ce oxide solid solutions. At Mn/Cu = 0.6, the catalyst presented strong interaction among Cu, Mn and Ce, had more Ce3+ and Mn4+ at the surface and showed the best catalytic performance, making CO conversion increase of 23.57% at 90 °C as compared with the Cu/Ce catalyst. For CO-Prox, the highest CO conversion was 94.7% with an oxidation selectivity of 78.9% at 125 °C. At this temperature, the catalyst revealed stable catalytic performance for a total TOS of 205 h. In addition, with CO/Ar as feed gas, CO conversion was 100%, confirming the negative effects of CO2/H2.

Promotional Effect of H2 Pretreatment on the CO PROX Performance of Pt1/Co3O4: A First-Principles-Based Microkinetic Analysis.

Atomic Pt studded on cobalt oxide is a promising catalyst for CO preferential oxidation (PROX) dependent on its surface treatment. In this work, the CO PROX reaction mechanism on Co3O4 supported single Pt atom is investigated by a comprehensive first-principles based microkinetic analysis. It is found that as synthesized Pt1/Co3O4 interface is poisoned by CO in a wide low temperature window, leading to its low reactivity. The CO poisoning effect can be effectively mitigated by a H2 prereduction treatment, that exposes Co ∼ Co dimer sites for a noncompetitive Langmuir-Hinshelhood mechanism. In addition, surface H atoms assist O2 dissociation via "twisting" mechanism, avoiding the high barriers associated with direct O2 dissociation path. Microkinetic analysis reveals that the promotion of H-assisted pathway on H2 treated sample helps improve the activity and selectivity at low temperatures.

Sn-induced CuO–CeO2 catalysts with improved performance for CO preferential oxidation in H2-rich streams

Sn modified CuO–CeO2 catalysts with different Sn loadings were prepared by a facile, green and solvent-free method. The effect of Sn/Ce ratio over Sn–Cu–Ce-x (x = 0, 1, 2.5, 5, 7.5) samples on CO activity and O2 selectivity was investigated. The samples were characterized by various techniques using N2-adsorption/desorption, XRD, H2-TPR, XPS, Raman and in-situ DRIFTS. It was revealed that stronger interaction between acitve sites and support, higher amounts of Sn2+ and Ce3+, associated with increased amount of oxygen vacancies, were observed on the catalyst of Sn–Cu–Ce-5. As a result, the optimized catalyst displayed an excellent catalytic performance even in the presence of CO2 and H2O. In this sense, probing the Sn modified CuO–CeO2 catalyst can elucidate some useful keys for the development of high CO2 and H2O-resistance catalyst during CO-preferential oxidation in H2-rich streams.

Highly dispersed Pt studded on CoOx nanoclusters for CO preferential oxidation in H2

Highly dispersed Pt studded on CoOx catalysts are designed and fabricated by selective atomic layer deposition method for enhanced CO preferential oxidation performance.

The catalytic performance of isolated-dispersed Au on nanosized CeO2 for CO preferential oxidation in H2-rich stream

Nanosized CeO2 and supported Au catalysts were synthesized and their catalytic performance for CO preferential oxidation in H2-rich streams was evaluated. Transmission electron microscope (TEM), N2 isothermal adsorption/desorption, X-ray diffraction (XRD), temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and in-situ DRIFTS techniques were adopted to characterize their structure property, redox property as well as dispersion and valence states of the active Au species. The results demonstrate the strong interaction between highly dispersed gold species (grain size <2 nm) and CeO2 in catalysts with low gold loading, which promotes the reduction of surface and sub-surface oxygen and the stabilization of high-valent Au3+ species. Meanwhile, it creates more lattice defects and benefits to the enhanced mobility of lattice oxygen and the activation of gas oxygen, thus contributing to the low-temperature CO preferential oxidation. However, over high Au content (≥0.6%) would lead to the agglomeration of gold nanoparticles and the formation of Au0 species, which weakens the gold-ceria interaction and decreases the active sites. On the other hand, the formation of Au0 species with large grain size would accelerate the dissociation of H2, which is the main reason for the decreasing of O2 selectivity toward CO over Au/CeO2 catalysts.

Tailoring catalytic performance of carbon nanotubes confined CuO[sbnd]CeO2 catalysts for CO preferential oxidation

Multi-wall carbon nanotubes confined CuOCeO2 binary oxide catalysts (CuxCe1-xO/CNTs, x = 0, 0.2, 0.4, 0.6 and 1.0) have been prepared by a special ultrasound-aided impregnation. The effects of CuCe molar ratios on the structure and catalytic performance for CO preferential oxidation have been systematically investigated. Judging from XRD patterns and Raman analysis, Cu2+ ions incorporate into CeO2 lattice to form ceria-base solid solution, accompanied by oxygen vacancies and an interaction produces between the catalyst particles and inner surface of carbon nanotubes. TEM microstructural analysis shows that CuO and CeO2 particles are uniformly dispersed in carbon nanotubes for the CuxCe1-xO/CNTs (x = 0.4) catalyst. Meanwhile, the reducibility of active copper species is enhanced markedly. In addition, the Cu0.4Ce0.6O/CNTs sample possesses more surface lattice oxygen and oxygen vacancies according to surface species characterization, which can provide more active oxygen species for CO oxidation and promote the mobility of lattice oxygen. The CuxCe1-xO/CNTs (x = 0.4) catalyst exhibits excellent activity, wide temperature span of full CO conversion (120–160 °C) and high selectivity especially above 110 °C (maintaining high selectivity until 140 °C).

Ru–Pd Bimetallic Catalysts Supported on CeO2-MnOX Oxides as Efficient Systems for H2 Purification through CO Preferential Oxidation

The catalytic performances of Ru/ceria-based catalysts in the CO preferential oxidation (CO-PROX) reaction are discussed here. Specifically, the effect of the addition of different oxides to Ru/CeO2 has been assessed. The Ru/CeO2-MnOx system showed the best performance in the 80–120 °C temperature range, advantageous for polymer-electrolyte membrane fuel cell (PEMFC) applications. Furthermore, the influence of the addition of different metals to this mixed oxide system has been evaluated. The bimetallic Ru–Pd/CeO2-MnOx catalyst exhibited the highest yield to CO2 (75%) at 120 °C whereas the monometallic Ru/CeO2-MnOx sample was that one with the highest CO2 yield (60%) at 100 °C. The characterization data (H2-temperature programmed reduction (H2-TPR), X-ray diffraction (XRD), N2 adsorption-desorption, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), X-ray photoelectron spectroscopy (XPS)) pointed out that the co-presence of manganese oxide and ruthenium enhances the mobility/reactivity of surface ceria oxygens accounting for the good CO-PROX performance of this system. Reducible oxides as CeO2 and MnOx, in fact, play two important functions, namely weakening the CO adsorption on the metal active sites and providing additional sites for adsorption/activation of O2, thus changing the mechanism from competitive Langmuir–Hinshelwood into non-competitive one-step dual site Langmuir–Hinshelwood/Mars–van Krevelen. As confirmed by H2-TPR and XPS measurements, these features are boosted by the simultaneous presence of ruthenium and palladium. The strong reciprocal interaction of these metals between them and with the CeO2-MnOx support was assumed to be responsible of the promoted reducibility/reactivity of CeO2 oxygens, thus resulting in the best CO-PROX efficiency at low temperature of the Ru-Pd/CeO2-MnOx catalyst. The higher selectivity to CO2 found on the Ru–Pd system, which reduces the undesired H2 consumption, represents a promising result of this research, being one of the key aims of the design of CO-PROX catalysts.

Enhanced catalytic performance for CO preferential oxidation over CuO catalysts supported on highly defective CeO2 nanocrystals

Herein, we synthesized CeO2 nanocrystals (Ce250) with a large number of surface lattice defects by calcining the superfine Ce(OH)3 nanowires at 250°C. They were then utilized as the support of the CuO catalysts for CO preferential oxidation (CO PROX). The strong interaction between CuO and CeO2 is the key factor to improve the catalytic activity, and our results show that the surface lattice defects on the CeO2 support can strengthen the interaction between CuO and CeO2 during the catalyst preparation procedure. With the increase of the calcination temperature, the surface areas of the CuO/CeO2 catalysts gradually drops, but the interaction between CuO and CeO2 is strengthened. Their catalytic activities present a “volcano” type, and the CuCe500 calcined at 500°C shows the highest catalytic activity.

Recent Advances in the Preferential Thermal-/Photo-Oxidation of Carbon Monoxide: Noble Versus Inexpensive Metals and Their Reaction Mechanisms

Preferential oxidation (PROX) of CO is applicable because of its low cost, ease of implementation, and low loss of H2 during purification. Mo–SiO2 and Cr–SiO2 photocatalysts utilized charge separation at metal=O bonds, and the PROX selectivity of CO was high. The CO PROX rates using semiconductor-based photocatalysts were comparable to those of photocatalysts (380 μmol h−1 g cat −1 ) and were also selective (100 %). These photocatalysts are advantageous because they do not activate H2 in comparison to noble metal catalysts. Below 473 K using noble metals, Ru, Rh, Pt, or Au supported on reducible metal oxides exhibited excellent CO thermal-PROX rates of ~4900 μmol h−1 g cat −1 ; however, the CO PROX selectivity of ~48 % was insufficient because of H2 activation on noble metals in nature. CO adsorbed onto TiO2 and O2 was stabilized at the interface between a Ti site and an Au atom. Weakly adsorbed water increased the effective number of active sites by stabilizing Au–OOH or Au–COOH. The PROX rates of CO using Au/TiO2-based catalysts under dark conditions increased under UV–visible light by the effect of charge separation and surface plasmon resonance and the promoted electron transfer to the adsorbed O2. In the case of CuO–CeO2 catalysts, CO adsorbed onto CuO and reacted with lattice O atoms at the boundary between CuO and CeO2 to form CO2 at an O vacancy, which was subsequently filled with an O2 molecule. The combination of Cu or Co with a reducible metal oxides also provided performance comparable to or higher than that of CuO–CeO2 owing to adequate standard reduction potential for Cu2+, Co3+, Mn3+/4+, and Ce4+. Finally, binary metal–organic framework consisting of oxyhydroxide Ti clusters interlinked by organic ligands and Cu oxyhydroxide ligands showed superior CO PROX performance (76 % conversion and 99 % selectivity) to that achieved using CuO–CeO2 owing to effective dispersion of Cu–O–Ti connection in microporous crystallites. Further progress is needed to alleviate the activity loss in the presence of moisture and/or CO2 based on suggestions that steric hindrance of some types of microporous crystallites would suppress the blocking of moisture or CO2.

A facile and rapid route to synthesize CuOx/Ce0.8Zr0.2O2 catalysts with high performance for CO preferential oxidation (CO-PROX)

CuO(10)–Ce0.8Zr0.2O2-UGC-300 (CuO–Ce0.8Zr0.2O2 prepared by urea grind combustion method, with 10 wt.% CuO loading and calcined at 300 °C) and CuO(10)–Ce0.8Zr0.2O2-IWI-300 (prepared by incipient wetness impregnation method) catalysts were tested for CO-PROX. It was noticed that both the CO conversion and the O2 selectivity of CuO(10)–Ce0.8Zr0.2O2-UGC-300 are higher than those of CuO(10)–Ce0.8Zr0.2O2-IWI-300. The high performance catalytic activities of CuO(10)–Ce0.8Zr0.2O2-UGC-300 have been attributed to the synergistic effects of highly dispersed Cu species together with the stronger interaction between CuO and the support. The effect of the CuO content and calcination temperature on the catalytic activity of the CuO–Ce0.8Zr0.2O2 catalysts were investigated in detail. The catalyst with 10 wt.% CuO loading and calcined at 300 °C exhibited the highest catalytic activity. CuO(10)–Ce0.8Zr0.2O2-UGC-300 catalyst exhibited excellent adaptability of space velocity from 12,000 h−1 to 36,000 h−1 and with good tolerance towards CO2 and H2O.

Variation of redox activity and synergistic effect for improving the preferential oxidation of CO in H2-rich gases in porous Pt/CeO2–Co3O4 catalysts

The porous Pt/CeO2–Co3O4 catalysts show superior catalytic performance for CO preferential oxidation in H2-rich gases.

Superior catalytic performance of non-stoichiometric solid solution Ce1 − xCuxO2 − δ supported copper catalysts used for CO preferential oxidation

A series of Ce1−xCuxO2−δ non-stoichiometric solid solutions and their supported copper catalysts CuO/Ce1−xCuxO2−δ (x=0, 0.005, 0.022, 0.043) were prepared by co-precipitation and deposition–precipitation, respectively. The CuO/Ce1−xCuxO2−δ catalysts show high performance for CO preferential oxidation (CO PROX). Multiple techniques of N2 sorption (BET), XRD, Laser Raman spectroscopy (LRS), HRTEM, H2-TPR, O2-TPO, N2O chemisorption and in-situ DRIFTS were used for catalyst characterization. The results of XRD, LRS and H2-TPR conformably indicate that a small amount of Cu2+ ions can be incorporated into the lattice of CeO2, forming non-stoichiometric solid solutions Ce1−xCuxO2−δ, which shows much better reducibility than pure CeO2. The supported CuO/Ce1−xCuxO2−δ catalysts exhibit remarkably enhanced activity for CO PROX as compared with CuO/CeO2, especially the catalyst CuO/Ce0.978Cu0.022O2−δ containing 15% Cu, which displays the best CO PROX performance, showing not only the lowest temperature (115°C) for CO total conversion, but also the 100% selectivity of O2 to CO2 at this temperature. Several aspects including the presence of more oxygen vacancies, the improved reducibility, and stronger capability for CO chemisorption of this catalyst account well for its superior performance for CO PROX. Based upon the in-situ DRIFTS study, it is revealed that Cu+ is the main active site for CO oxidation, while Cu0 is more active for H2 activation and oxidation.

Promotion effect of adsorbed water/OH on the catalytic performance of Ag/activated carbon catalysts for CO preferential oxidation in excess H2

Activated carbon (AC) supported silver catalysts were prepared by incipient wetness impregnation method and their catalytic performance for CO preferential oxidation (PROX) in excess H2 was evaluated. Ag/AC catalysts, after reduction in H2 at low temperatures (≤200 °C) following heat treatment in He at 200 °C (He200H200), exhibited the best catalytic properties. Temperature-programmed desorption (TPD), X-ray diffraction (XRD) and temperature-programmed reduction (TPR) results indicated that silver oxides were produced during heat treatment in He at 200 °C which were reduced to metal silver nanoparticles in H2 at low temperatures (≤200 °C), simultaneously generating the adsorbed water/OH. CO conversion was enhanced 40% after water treatment following heat treatment in He at 600 °C. These results imply that the metal silver nanoparticles are the active species and the adsorbed water/OH has noticeable promotion effects on CO oxidation. However, the promotion effect is still limited compared to gold catalysts under the similar conditions, which may be the reason of low selectivity to CO oxidation in PROX over silver catalysts. The reported Ag/AC-S-He catalyst after He200H200 treatment displayed similar PROX of CO reaction properties to Ag/SiO2. This means that Ag/AC catalyst is also an efficient low-temperature CO oxidation catalyst.

Three-dimensionally ordered macroporous Au/CeO2–Co3O4 catalysts with mesoporous walls for enhanced CO preferential oxidation in H2-rich gases

Three-dimensionally ordered macroporous (3DOM) Au/CeO2–Co3O4 catalysts with well-defined macroporous skeletons and mesoporous walls were created via a precursor thermal decomposition-assisted colloidal crystal templating method, and their catalytic performance for CO preferential oxidation in H2-rich gases was systematically investigated. The results showed that the 3DOM Au/CeO2–Co3O4 catalysts possessed well-defined 3DOM skeletons composed of well-crystallized CeO2 and Co3O4 nanoparticles and mesoporous walls with nanopores ∼3–4nm. Their catalytic performance was closely correlated to their compositions, phase structures, porous architectures, surface elemental compositions, and valence states. In comparison with the Au supported CeO2 or Ce3O4 catalysts previously reported, the 3DOM Au/CeO2–Co3O4 catalysts showed superior catalytic conversion, selectivity, and stability—in particular, longer-term stability—for CO preferential oxidation in H2-rich gases, making them potentially applicable in polymer electrolyte membrane fuel cells.

Effect of synthesis pH and Au loading on the CO preferential oxidation performance of Au/MnOx–CeO2 catalysts prepared with ultrasonic assistance

As a novel and rather convenient method, ultrasonic pretreatment was employed for the preparation of nanostructured Au/MnOx–CeO2 (Mn/Ce = 1:1) catalysts which were used for CO preferential oxidation. The effects of synthesis pH (7.0–11.0) and Au loading (0.5–5.0 wt.%) on the performance of these catalysts were systematically investigated. It is found that the Au(1.0)/MnOx–CeO2-10.0 with 1.0 wt.% Au prepared at pH = 10.0 exhibits the best catalytic performance, giving not only the highest CO conversion of 90.9% but also the highest oxygen to CO2 selectivity of 47.8% at 120 °C. The results of XRD, HR-TEM and XPS indicate that this catalyst possesses the highest dispersion of Au species and the largest amount of surface adsorbed oxygen species, which facilitates CO oxidation. The H2-TPR results reveal that the selectivity of oxygen to CO2 is mainly determined by the reducibility of Au species in the catalysts. The strong interaction between Au species and the supports in the catalyst Au(1.0)/MnOx–CeO2-10.0 decreases its capability for H2 dissociation, effectively inhibiting the hydrogen spillover, as a result, the selectivity of oxygen to CO2 is remarkably increased.

Influence of reduction energy match among CuO species in CuO-CeO 2 catalysts on the catalytic performance for CO preferential oxidation in excess hydrogen

Abstract In the present study, we have investigated the reducibility of CuO species on CuO-CeO 2 catalysts and the influence of CuO species on the catalytic performance for CO preferential oxidation (CO PROX) in excess hydrogen. It is revealed that the smaller the difference of reduction temperature (denoted as T) for two adjacent CuO species is, the higher the catalytic activity of CuO-CeO 2 for the PROX in excess hydrogen may be obtained. It means that if the reduction energy of Cu 0-Cu 2+ pairs matched better, the reduction-oxidation recycle of Cu 0-Cu 2+ pairs would go on more easily, then the transferring energy of Cu 0-Cu 2+ pairs would be lesser. Therefore, the CuO-CeO 2 catalysts will be largely improved in their catalytic performance if the different CuO species on the catalysts have matched the reduction energy, which would allows them to cooperate effectively.

Morphology effects of nanocrystalline CeO2 on the preferential CO oxidation in H2-rich gas over Au/CeO2 catalyst

Gold supported on CeO2 nanocrystals of rod, cubic and polyhedral shapes were used for CO preferential oxidation (CO-PROX) in H2-rich gas. The catalytic activity ranked by CeO2 nanocrystals as follows: rods > polyhedra > cubes. The results of X-ray photoelectron spectroscopy, temperature-programmed reduction/desorption and in situ Fourier transform infrared spectroscopy indicated that the surface gold species and also the adsorption/desorption properties for CO and oxygen species were closely related to the nature of exposed crystal planes of CeO2 nanocrystals. The gold catalyst on CeO2-rods with {1 0 0}/{1 1 0}-dominant surfaces showed the best CO-PROX performance.

Model-based analysis of reactor geometrical configuration on CO preferential oxidation performance

Abstract Modeling studies have been conducted on Preferential Oxidation (PROX) Reaction, covering chemical kinetics and heat/mass transfer phenomena that occur in a shell and tube system, to be used in a beta 5 kWe hydrogen generator for Polymer Electrolyte Fuel Cells (PEFCs). The critical issue in the PROX reactor design is to achieve temperature control along the catalyst bed, because poor selectivities primarily result from excess reactor temperature. Aim of the model is to investigate the effects of the reactor dimensions on process performance, in order to obtain high CO conversion and high selectivity with respect to the undesired H 2 oxidation. The CO removal from simulated reformate was examined, by evaluating the temperature and the gas concentration profiles along the reactor. The sensitivity analysis showed that the overall performance is strongly dependent upon the geometrical configurations examined.