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Active and selective structured RuO/AlO catalysts for CO methanation using a flow simulating CO-rich reformate gases from WGS and PROX units (H excess, CO presence and 300 ppm CO concentration) were prepared. Both, the RuO/AlO powder and the slurry prepared from it for its structuration by washcoating of the metallic micromonolithic structure, were also active and selective. Both the slurry (S-RuAl) and micromonoliths (M-RuAl) were able to completely and selectively methanate CO at much lower temperatures than the parent RuAl powder. The optimal working temperature in which the CO conversion is maximum and the CO conversion is minimized was determined to be from 149 °C to 239 °C for S-RuAl and from 165 °C to 232 °C for M-RuAl, whilst it was from 217 °C to 226 °C for RuAl powder. TPR, XRD and TEM measurements confirmed that the changes in the activity and selectivity for CO methanation among the considered catalysts can be related with modifications in the surface particle size of ruthenium and its reducibility. These were ascribed to the metallic substrate, the presence of PVA and colloidal alumina in the slurry preparation, the aqueous and acidic media and the thermal treatment used, resulting in a more active and selective catalysts than the parent powder.

The cathode activity in a solid oxide fuel cell can be promoted by introducing various catalysts to reduce its polarization resistance towards oxygen reduction, and thus improve cell performance. In this work, the La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) cathode surface is modified by the infiltration of Pr6O11 and the power density at 0.8 V and 750 °C is improved by 21%. Moreover, by replacing the traditional barrier layer Gd0.2Ce0.8O1.9 with mixed conducting Pr0.1Gd0.1Ce0.8O1.9 (PGCO), the power density increases by 38%. The ohmic resistance is dramatically reduced by applying the PGCO interlayer. The distribution of relaxation time was used to analyze the mechanism for which the polarization resistance was decreased, attributing to the mixed conduction nature in PrOx. An increase of power density, ∼0.358 W/cm2 (71%) at 0.8 V, is achieved with the implementation of both surface modification and buffer layer engineering.

Nanocomposite Cu–Mn–O nano-particle (CuMnNP) and nano-sheet (CuMnNS) catalyst were successfully prepared using a one-step hydrothermal method in the absence of any templating reagent. Materials were characterised applying various structural techniques. SEM images showed that composite Cu–Mn oxide sheets were tailor-made synthesised by a one-pot urea-abetted protocol. Conversely, upon replacing carbamate by Na2CO3, oxidised metal Cu–Mn particles could be obtained. The formation of bulk mixed Cu–Mn phases resulted in an enhanced crystal lattice oxygen reactivity in CuMnNS. XPS, XRD and TPR measurements confirmed the presence of the Cu+ and Cu2+ species in nano-catalysts, and CuMnNS nanomaterials possessed more surface defects, thus causing a higher O2 adsorption/storage capacity. CuMnNS presented a superior catalytic activity as opposed to CuMnNP in the preferential oxidation (PROX) pathway of CO. With both CO2 and H2O in feed, a decrease in CO turnover was observed, due to a competitive interface binding of CO, CO2 and H2O. Compared to CuMnNP, CuMnNS also demonstrated a high time-on-stream conversion of methanol for the reforming for all operating conditions.

We obtain a characterization of the proximal normal cone to a prox-regular subset of a Riemannian manifold. Moreover, some properties of Bouligand tangent cones to prox-regular sets are described. We prove that for a prox-regular subset S of a Riemannian manifold, the metric projection P_S to S is locally Lipschitz on an open neighborhood of S and it is directionally differentiable at boundary points of S. Finally, a necessary condition for a curve to be a minimizing curve in a prox-regular set is derived.

A copper-chromium mixed oxide with Cu:Cr 1:2 ratio has been prepared by a microemulsion method and employed as support of CeO2 in different amounts from 5 to 80 wt%. The catalysts have been characterized by XRD, HRTEM/XEDS, H2-TPR and XPS. The characterization results have been examined in correlation with their catalytic properties for the CO-PROX process complemented by operando-DRIFTS. The catalysts are formed by composites of CuCr2O4 and CuO on which aggregates of CeO2 nanoparticles are dispersed. Incorporation of CeO2 onto the CuCr mixed oxide appreciably enhances the CO-PROX performance of the catalyst. This is related to a promotion of the generation and stabilization of active partially reduced copper sites during the course of the interaction of the catalysts with the reactant mixture and which are evidenced to be formed on both CuCr oxide and CeO2 components of the catalysts.

Pr-modified MnOx catalyst was synthesized through a facile co-precipitation process, and the results showed that MnPrOx catalyst exhibited much better selective catalytic reduction (SCR) activity and SO2 resistance performance than pristine MnOx catalyst. The addition of Pr in MnOx catalyst led to a complete NO conversion efficiency in 120–220 °C. Moreover, Pr-modified MnOx catalyst exhibited a superior resistance to H2O and SO2 compared with MnOx catalyst. After exposing to SO2 and H2O for 4 h, the NO conversion efficiency of MnPrOx catalyst could remain to 87.6%. The characterization techniques of XRD, BET, hydrogen-temperature programmed reduction (H2-TPR), ammonia-temperature programmed desorption (NH3-TPD), XPS, TG and in situ diffuse reflectance infrared spectroscopy (DRIFTS) were adopted to further explore the promoting effect of Pr doping in MnOx catalyst on SO2 resistance performance. The results showed that MnPrOx catalyst had larger specific surface area, stronger reducibility, and more L acid sites compared with MnOx catalyst. The relative percentage of Mn4+/Mnn+ on the MnPrOx-S catalyst surface was also much higher than those of MnOx catalyst. Importantly, when SO2 exists in feed gas, PrOx species in MnPrOx catalyst would preferentially react with SO2, thus protecting the Mn active sites. In addition, the introduction of Pr might promote the reaction between SO2 and NH3 rather than between SO2 and Mn active sites, which was also conductive to protect the Mn active sites to a great extent. Since the presence of SO2 in feed gas had little effect on NH3 adsorption on the MnPrOx catalyst surface, and the inhibiting effect of SO2 on NO adsorption was alleviated, SCR reactions could still proceed in a near-normal way through the Eley-Rideal (E-R) mechanism on Pr-modified MnOx catalyst, while SCR reactions through the Langmuir-Hinshelwood (L-H) mechanism were suppressed slightly.

We report on bimetallic FeRh clusters with a narrow size-distribution grown on graphene on Ir(111) as a carbon-supported model catalyst to promote low-temperature catalytic CO oxidation. By combining scanning tunneling microscopy with catalytic performance measurements, we reveal that Fe-Rh interfaces are active sites for oxygen activation and CO oxidation, especially at low temperatures. Rh core Fe shell clusters not only provide the active sites for the reaction, but also thermally stabilize surface Fe atoms towards coarsening compared with pure Fe clusters. Alternate isotope-labelled CO/O2 pulse experiments show opposite trends on preferential oxidation (PROX) performance as a result of surface hydroxyl species formation and competitive adsorption between CO and O2 . The present results introduce a general strategy to stabilize metallic clusters and to reveal the reaction mechanisms on bimetallic structures for low-temperature catalytic CO oxidation as well as preferential oxidation.

We have studied the alpha decay properties of actinides using seven different proximity potentials MP 77, MP 81, Bass 77, Prox 13, Ng80, DP00 and Prox 00. The values produced by the present work are compared with experiments. Decay chains of actinides are presented. The present work is useful in the study of decay modes of actinides.

Background: Port-wine stains (PWS) on proximal limbs respond better to pulsed dye laser (PDL) than PWS on distal limbs. Objective: To investigate whether the superiority of PDL efficacy on the prox...

Preferential oxidation (PROX) of CO in hydrogen is of great significance for proton exchange membrane fuel cells (PEMFCs) that need a CO-free hydrogen stream as fuel. The key technical problem is developing catalysts that can efficiently remove CO from the H2-rich stream within the working temperature range of PEMFCs. Herein, we design a Au/Bi2O3 interfacial catalyst for PROX with excellent catalytic performance, which can achieve 100% CO conversion in the PROX reaction over a wide temperature window (70-200 °C) and is perfectly compatible with the operating temperature window (80-180 °C) of PEMFCs. Moreover, the catalyst also demonstrates excellent high flow performance and long-term stability. Density functional theory (DFT) calculations reveal that the electrons transferring from Bi2O3 to Au and then to adsorbed perimeter CO and O2 molecules promote the activation of CO and O2, thus enhancing the catalytic performance of PROX.

Composite CuxCe1–xO2 nanorod catalysts with abundant Cu–Ce interface for CO preferential oxidation are synthesized via a one-pot co-precipitation method at ambient temperature, and then copper spec...

Global hydrogen production from catalytic reforming of hydrocarbons exceeds 50 million tons annually and accounts for 2–5% of global energy consumption. The hydrogen product generally contains 0.5–1 vol% of CO, which must be removed for certain industrial applications. Preferential oxidation (PROX) of CO is regarded as a promising and cost-effective method for hydrogen purification and potentially applicable to new generation fuel cell vehicles. In this work, bifunctionally faceted Pt/Ru nanoparticle catalysts are designed and fabricated via selective atomic layer deposition, which provides an unprecedented capability of tuning nanoparticles’ structure–property relationship for PROX in H2. Pt atomic layers are selectively deposited onto (0 0 1) facets of Ru, while leaving neighboring Ru surfaces exposed. By modulating the extent of electron donation with varied Pt coating configurations, it is demonstrated that the bifunctional catalyst with a single monolayer of Pt on Ru shows optimal activity and selectivity. The enhancement of PROX performance originates from the elimination of competitive CO adsorption on Pt, where a neighboring exposed Ru surface could readily provide highly active sites for O2 dissociation.

CuOx–CeO2 catalysts with different copper contents are synthesized via a coprecipitation method and thermally treated at 700 °C. Various characterization techniques including X-ray diffraction (XRD) Rietveld refinement, N2 adsorption–desorption isotherms, X-ray photoelectron spectra (XPS), UV-Raman, high-resolution transmission electron microscopy (HRTEM), temperature-programmed reduction (TPR) and in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) were adopted to investigate the structure/texture properties, oxygen vacancies, Cu–Ce interaction and redox properties of the catalysts. After the thermal treatment, the catalysts exhibited outstanding catalytic properties for the preferential oxidation (PROX) of CO (with the T50% of 62 °C and the widest operation temperature window of 85–140 °C), which provided a new strategy for the design of Cu–Ce based catalysts with high catalytic performance. The characterization results indicated that moderately elevating the copper content (below 5%) increases the amount of highly dispersed Cu species in the catalysts, including highly dispersed surface CuOx species and strongly bonded Cu–[Ox]–Ce species, strengthening the Cu–Ce interaction, increasing oxygen vacancies and promoting redox properties, but a further increase in copper content causes the agglomeration of crystalline CuO and decreases the highly dispersed Cu species. This work also provides evidence from the perspective that the catalytic performance of CuOx–CeO2 catalysts for CO-PROX at low and high reaction temperatures is dependent on the redox properties of highly dispersed CuOx species and strongly bonded Cu–[Ox]–Ce species, respectively.

A novel cyclic molecular designed dispersion (CMDD) method was employed to uniformly deposit 0.0–6.5 wt% Fe on CeO2. The gold catalysts (0.0–3.8 wt%) supported on Fe2O3-CeO2 were tested for CO preferential oxidation (PROX). As the CMDD method involved grafting of Fe (acac)3 onto the surface –OH groups, 2.7 surface –OH/nm2 was determined for the CeO2 by using the Grignard reagent. The performance of CMDD catalysts was compared with the corresponding catalysts prepared by impregnation. The catalysts were characterized by XPS, XRD, TPR, HRTEM-EDX, BET and ICP. The results suggested that Au/Fe2O3-CeO2 was significantly more active and selective than Au/CeO2. The CMDD-prepared catalysts with 1.4–2.5 wt% iron showed the highest activity and selectivity, especially at temperatures as low as 323 K. The formation of Ce-Fe solid solution for CMDD catalysts promoted the dispersion of both iron and gold. Highly dispersed gold nanoparticles mainly as small as 2.2 nm were observed in HRTEM.

It is shown that with the same quantitative composition of the copper-ceria-zirconia catalyst, varying only the structural and dimensional characteristics of the yttrium stabilized zirconia (YSZr), it is possible to improve the activity and selectivity of the catalyst and expand the «temperature window» of its effective operation. It has been established that the low surface area of YSZr support, due to the high degree of agglomeration of its nanoparticles, contributes to the formation of a larger number of interaction zones of copper and cerium oxides that are active sites of the process of selective oxidation of CO in hydrogen (PROX – Preferential CO oxidation).

The thermal stability of Au nanoparticles on ceria support of various morphology (nanocubes, nanooctahedra, and {111}-nanofacetted nanocubes) in oxidizing and reducing atmospheres was investigated by electron microscopy. A beneficial effect of the reconstruction of edges of ceria nanocubes into zigzagged {111}-nanofacetted structures on the inhibition of sintering of Au nanoparticles was shown. The influence of different morphology of Au particles on various ceria supports on the reducibility and catalytic activity in CO oxidation, and CO PROX of Au/ceria catalysts was also investigated and discussed. It was shown, that ceria nanocubes with flat {110} terminated edges are more suitable as a support for Au nanoparticles, used to catalyze CO oxidation, than zigzagged {111}- nanofacetted structures. Graphic Abstract

Copper and cobalt oxides supported on CeO2 were investigated for preferential oxidation of carbon monoxide (CO-PROX) in the presence of excess hydrogen and CO2. (CuO)1−x(Co3O4)x/3−(CeO2)2.5 (x = 0, 0.25, 0.50, 0.75, 0.85 and 1) catalysts were prepared by coprecipitation method. These mixed oxide catalysts were characterized by several physicochemical techniques, such as BET surface area (SBET), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). XRD studies show the peaks related to CuO and Co3O4 phases in copper and cobalt containing CeO2 catalysts. The average particle size of the CeO2 crystallites is in the range of 8–10 nm as evaluated from HRTEM studies. XPS studies demonstrate that Cu, Co and Ce in (CuO)1−x(Co3O4)x/3−(CeO2)2.5 catalysts are presented in +2 and +1, +3 and +2 and +4 and +3 oxidation states, respectively. The catalyst with x = 0.75 shows better activity and selectivity towards CO-PROX. Though the catalyst with only copper (CuO–CeO2, x = 0) shows good activity but reverse water gas shift (RWGS) reaction is noticed at high temperature. On the other hand, RWGS reaction is suppressed on the cobalt containing CuO–CeO2 catalyst. Cobalt on CeO2 with x = 1 shows hardly any activity for PROX reaction at low temperatures. No methanation activity is observed on CuO–CeO2 or Co3O4–CeO2 catalysts. In contrast, combination of copper and cobalt on CeO2 shows methanation of CO where enhanced activity is observed with increasing in cobalt content.

Comparative research about the total CO oxidation and CO-PROX reaction over Au-based materials supported on different oxides was carried out. CeO2, MnO2, TiO2 and SiO2 with nominal content of 1 wt.% of Au were prepared by a modified deposition–precipitation method. The samples were characterized by XRF, XRD, BET, H2-TPR and HR-TEM techniques. Catalytic results of the CO oxidation in the absence and presence of hydrogen showed that the supports and Au/SiO2 were inactive. For the Au/MnO2 and Au/TiO2 samples, CO conversion was lower in the presence of H2, while for Au/CeO2 the conversion of CO in the CO-PROX was higher compared to that in the total CO oxidation. These results show that the impact of H2 on CO oxidation over Au catalysts is dependent on the charactersitics of the materials that, in turn, are influenced by the nature of the support.

Gold-based nanocatalysts have proved to be an appropriate candidate for the selective preferential CO oxidation (PROX) in H2-containing atmosphere. Effectiveness of small gold nanoparticles in the presence of immobilized on GO–CeO2 nanocomposites was investigated by a range of ball milling conditions for the PROX reaction. First, GO–CeO2 nanocomposites were fabricated using the combination of ball milling and hydrothermal methods, and then, the gold nanocomposites were activated at 400 ± 2 °C for 4 h in Ar atmosphere. Next, Au/GO–CeO2 catalysts were synthesized, and after that, the gold nanocontents calcined at 400 ± 2 °C in Ar gas during 4 h. The catalytic activity and selectivity of activated gold catalysts (Au/GO–CeO2) were studied for the preferential CO oxidation at optimized conditions from the ambient temperature to 175 ± 2 °C. The gas and vapor phase components were analyzed by a Fourier Transform Infrared Spectroscopy. The effects of ball mill’s parameters, such as milling time, bead amounts, loading percentage, and milling temperatures, on the catalytic activity and selectivity of gold catalysts were investigated. Under relatively optimized conditions, the results showed the high conversion (C%: 97) and selectivity (S%: 92) for the gold nanocatalysts at 150 °C reaction time towards CO2 as the main product when the Au/GO–CeO2 nanocatalysts were synthesized by the use of 12% of GO solution with 90 zirconia oxide balls at 70 °C for 8 h of the ball milling condition.

The Al@γ-Al2O3 core-shell microstructures prepared from aluminum particles by hydrothermal surface oxidation were superior to the conventional alumina support owing to the facile heat flux through the metal-ceramic composite structures. The Ru catalysts supported on Al@γ-Al2O3 were used for the preferential CO oxidation (PROX) reaction, which is a highly exothermic reaction requiring high heat flux. For comparison, commercially available α-Al2O3 and γ-Al2O3 were also used as catalyst supports. The catalysts were characterized by N2-physisorption, X-ray diffraction, CO chemisorption, transmission electron microscopy (TEM), temperature-programmed desorption of ethanol (ethanol-TPD) and ammonia (NH3-TPD), and temperature-programmed oxidation (TPO). The Ru/α-Al2O3 catalyst with the lowest Ru dispersion showed the best PROX performance among the tested catalysts in the absence of CO2 and H2O. Even though Ru/Al@γ-Al2O3 and Ru/γ-Al2O3 had similar Ru dispersions, the former catalyst exhibited a much better PROX performance than the latter. This could be explained by the fact that the Ru metal deposited on Al@γ-Al2O3 was more resistant to surface oxidation as compared to that on γ-Al2O3, based on the TPO results. A lower desorption temperature of ethanol was observed over Al@γ-Al2O3 than over γ-Al2O3 during ethanol-TPD experiments, even though both supports had similar amounts of acid sites, as determined by NH3-TPD. Among the tested catalysts, Ru/Al@γ-Al2O3 also showed the best PROX performance in the presence of CO2 and H2O. A further enhancement in the PROX performance was achieved by increasing the Ru metal particle size from 1.4 to 2.6 nm by pretreating the Ru/Al@γ-Al2O3 catalyst with 1 mol% O2 in He at 150 ℃.

The method of electrochemical impedance is used to study the polarization conductivity of porous platinum electrodes in the Pt|YSZ|Pt cells over the temperature range from 500 to 700°C in air. Electrodes are impregnated with microquantities of praseodymium oxide PrOx (from 10–4 to 0.1 mg/cm2) by the impregnating them with praseodymium nitrate solution, with further thermal treatment: slow heating (50°С/h) up to 850°C. This processing resulted in the formation of the praseodymium oxide nanofilm on the electrolyte surface. The introducing of PrOx, even in an amount of 10–4 mg/cm2, is found to significantly increase the electrode polarization conductivity. Analysis of the electrochemical impedance spectra was performed by DRT (distribution of relaxation times) method, which revealed a change of the rate-determining stage of the electrode process in the concentration range of praseodymium oxide from 1 × 10–3 to 3.3 × 10–3 mg/cm2. The studied electrodes are discussed in terms of the island model of dense-oxide-PrOx-electrodes in which platinum plays the role of the current collector.

Rare earth metal oxides have been widely used as pseudocapacitor electrodes owing to their unique physical and electronic properties. The present paper reports the synthesis and pseudocapacitor applications of praseodymium oxides, owing to their unique physical properties. PrOx/unzipped carbonnanotubes were synthesized following a hydrothermal approach. Detailed morphological as well as electrochemical analyses were performed to elucidate how the unique properties of PrOx affect the charge storage ability. Special emphasis was given on the effect of anion intercalation due to the surface oxygen vacancies in PrOx which would contribute towards the pseudocapacitive energy storage. Oxygen intercalation was exploited for the first time in fluorite crystals for fast energy storage and a specific capacitance value as high as 1099 F/g was obtained with the electrodes. An asymmetric supercapacitor prototype was also fabricated with a V2O5/graphene counter electrode and the energy and power density values obtained are as high as 52.08 Wh/kg and 2.9 kW/kg, respectively.

The redox properties of ceria make it suitable as a catalyst or support in oxidation reactions. Ceria-supported transition metal nanoparticles or isolated single atoms provide a metal-support interface that reduces the energy cost to remove interfacial oxygen atoms, providing active oxygen species that can participate in Mars van Krevelen oxidation processes. CO oxidation is a key probe reaction to test the reducibility of ceria-supported catalysts and is also practically important in the elimination of CO at relatively low temperatures in various applications. Preferential oxidation of CO (PROX) in excess H2 controls the CO concentration to ultra-low levels to prevent poisoning of hydrogen oxidation electrocatalysts. The reactivity of catalysts in CO oxidation and selectivity towards CO over H2 in PROX is dependent on the type and dispersion of metal species, the structural and chemical properties of CeO2, and the synthetic preparation methods of the catalysts. In this review, we summarize recently published works on catalytic CO oxidation and PROX reactions on ceria-supported metal nanoparticles and single atoms. We summarize the reactivity on different supported metals, and on different CeO2 surfaces with the same metal. We summarize the most likely reaction mechanisms as suggested by density functional theory calculations. The factors contributing to selectivity towards CO oxidation in PROX reactions on various supported metals are also discussed.

Exploring highly active cathode materials with fast cathodic oxygen reduction has been considered as one of the most promising approaches to accelerate the commercialization process of intermediate temperature solid oxide fuel cells (IT -SOFCs). Herein, a highly active hybrid catalyst system with multiphase heterointerfaces consisting of (PrSr)Ni0.5Mn0.5O3-δ, PrOx nanoparticles and (PrSr)2(MnNi)O4-δ is self-assembly formed by substitution of Sr into Pr2Ni0.5Mn0.5O4-δ (S-PNM). Further using S-PNM as cathode materials for IT-SOFCs, S-PNM achieves a remarkable maximum power density of 960 mW cm−2 at 800 °C and an outstanding short-term stability with the discharge voltage of 0.68 V for 80 h. The excellent electrochemical performance by the preliminary experimental results is attributed to the coexistence of multiphase heterointerfaces of (PrSr)Ni0.5Mn0.5O3-δ, (PrSr)2(MnNi)O4-δ and PrOx nanoparticles, which can accelerate cathodic oxygen reduction.

Preferential oxidation of CO in hydrogen (PROX) is an effective process for purification of H2 gas streams containing CO. Conventional PROX catalysts are usually platinum group or Au-based. However...

Pt supported on TiO2 and ZrO2 catalysts were synthesized via wet impregnation and deposition precipitation methods. The catalysts were tested for CO removal from reformate gas following the water-gas shift reaction for on-board fuel processors. Tests included oxidation of CO to CO2, preferential oxidation of CO to CO2 in the presence of H2 (PROX), and hydrogenation of CO to CH4 (selective methanation, SMET). The Pt–ZrO2 catalysts showed better metal dispersions, particle sizes, lower degrees of reduction and higher oxygen storage capacities than the TiO2 supported catalysts. All catalysts showed low activity for the oxidation of CO in the PROX reaction, due to H2 and O2 spillover effects. ZrO2, with its high reducing properties and strong metal-support interactions, was found to be the best support for hydrogenation of CO. ZrO2 induced small well-dispersed Pt particles that were key parameters in this reaction. Both Pt–ZrO2 catalysts showed CO conversions over 99% above 350 °C with high CH4 selectivities (99%). The study shows advantageous effects of strong metal to support interactions, like participation of MOx (support) species in activating the CO molecule. The CO concentration was effectively reduced to the desired ppm levels (