High CO Oxidation Activity Research Articles

The effect of support pretreatment on activity of Ag/SiO2 catalysts in low-temperature CO oxidation

Silver supported on silica, prepared by impregnation method, was investigated using TEM, XRD, UV–vis spectroscopy, TPO, H2 TPR and CO TPR methods, and tested in low-temperature CO oxidation. To reveal the role of metal-support interaction, the Ag catalysts based on silica, pre-treated at 500 (SiO2-500) and 900°C (SiO2-900), were compared. Highly dispersed silver particles (1–4nm) were observed for both Ag/SiO2-500 and Ag/SiO2-900 catalysts. The highest amount of active oxidative species was determined for Ag/SiO2-900 catalysts using TPx methods. The high temperature (900°C) pretreatment of silica support is found favorable for formation of silver species active in O2 and CO activation and leads to increasing of catalytic activity in CO oxidation. The defect structure of Ag nanoparticles is a possible reason for high activity in low-temperature CO oxidation.

Temperature regulated-chemical vapor deposition for incorporating NiO nanoparticles into mesoporous media

We have developed a novel strategy for incorporating NiO nanoparticles into mesoporous Al2O3 with a mean pore size of ∼12nm and particle size of ∼1mm. Ni-precursor vapor and ambient atmosphere were filled in a closed chamber with mesoporous Al2O3, and the chamber was initially heated at ∼100°C, at which no chemical reaction between the inorganic precursor, oxygen, water vapor in the atmosphere, and the surface of Al2O3 took place. Next, the temperature of the system was increased to 260°C for deposition of NiO. We found that NiO nanoparticles were not only deposited on the surface, but were also incorporated in a 50μm-deep region of the mesoporous Al2O3 gel. We also demonstrated high CO oxidation activity and reusability of the deactivated NiO/Al2O3 catalysts prepared by the aforementioned method. These results suggest that our strategy could be widely applicable to the incorporation of various nanoparticles into mesoporous supports.

Formation of Ru Shell on Co/Al2O3 by Galvanic Deposition Method and Its High Catalytic Performance for Three-Way Conversion

Abstract A supported Ru catalyst was prepared by a galvanic deposition (GD) of Ru on Co particles supported on Al2O3 (Ru/Co-GD). The structure and chemical state of Ru/Co-GD was characterized by using a pulsed CO chemisorption technique, STEM-EDS, XAFS, XPS, CO adsorption FT-IR spectroscopy, and temperature-programed reduction (TPR) method. It is indicated that Ru/Co-GD forms Ru shell on Co nanoparticles. Such a unique structure was not formed on Ru/Co/Al2O3 prepared by a conventional sequential impregnation method (Ru/Co-seq). The Ru shell of Ru/Co-GD showed higher reducibility than Ru species of Ru/Co-seq as well as higher than Ru/Al2O3. Owing to the Ru shell having high reducibility, Ru/Co-GD showed enhanced catalytic activity for NO–C3H6 reaction. In addition, Co oxide on Ru/Co-GD exhibited high catalytic activity for CO and C3H6 oxidation. As a result, Ru/Co-GD showed superior performance for NO–C3H6–CO–O2 reaction compared to the conventional catalysts. The Ru shell structure also contributed to the suppression of Ru vaporization.

Atmospheric-Pressure DBD Cold Plasma for Preparation of High Active Au/P25 Catalysts for Low-Temperature CO Oxidation**supported by National Natural Science Foundation of China (Nos. 11505019, 21173028), the Science and Technology Research Project of Liaoning Provincial Education Department (No. L2013464), the Scientific Research Foundation for the Doctor of Liaoning Province (No. 20131004), and the Dalian Jinzhou New District Science and Technology Plan

Cold plasma generated by dielectric barrier discharge (DBD) at atmospheric pressure was adopted for preparation of commercial TiO2 Degussa P25 supported Au catalysts (Au/P25-P) with the assistance of the deposition-precipitation procedure. The influences of the plasma reduction time and calcination on the performance of the Au/P25-P catalysts were investigated. CO oxidation was performed to investigate the catalytic activity of the Au/P25 catalysts. The results show that DBD cold plasma for the fabrication of Au/P25-P catalysts is a fast process, and Au/P25-P (4 min) exhibited the highest CO oxidation activity due to the complete reduction of Au compounds and less consumption of oxygen vacancies. In order to form more oxygen vacancies active species, Au/P25-P was calcined to obtain Au/P25-PC catalysts. Interestingly, Au/P25-PC exhibited the highest activity for CO oxidation among the Au/P25 samples. The results of transmission electron microscopy (TEM) indicated that the smaller size and high distribution of Au nanoparticles are the mean reasons for a high performance of Au/P25-PC. Atmospheric-pressure DBD cold plasma was proved to be of great efficiency in preparing high performance supported Au catalysts.

Controlling activity and selectivity using water in the Au-catalysed preferential oxidation of CO in H2.

Industrial hydrogen production through methane steam reforming exceeds 50 million tons annually and accounts for 2-5% of global energy consumption. The hydrogen product, even after processing by the water-gas shift, still typically contains ∼1% CO, which must be removed for many applications. Methanation (CO + 3H2 → CH4 + H2O) is an effective solution to this problem, but consumes 5-15% of the generated hydrogen. The preferential oxidation (PROX) of CO with O2 in hydrogen represents a more-efficient solution. Supported gold nanoparticles, with their high CO-oxidation activity and notoriously low hydrogenation activity, have long been examined as PROX catalysts, but have shown disappointingly low activity and selectivity. Here we show that, under the proper conditions, a commercial Au/Al2O3 catalyst can remove CO to below 10 ppm and still maintain an O2-to-CO2 selectivity of 80-90%. The key to maximizing the catalyst activity and selectivity is to carefully control the feed-flow rate and maintain one to two monolayers of water (a key CO-oxidation co-catalyst) on the catalyst surface.

Effect of aging on the CO oxidation properties of copper manganese oxides prepared by hydrolysis–coprecipitation using tetramethyl ammonium hydroxide

Copper manganese mixed oxides were prepared by a hydrolysis-coprecipitation method using tetramethyl ammonium hydroxide and calcined at 573–873 K. The effect of aging treatment after the coprecipitation process on the catalytic properties of the calcined mixed oxides for CO oxidation was investigated. XRD and EXAFS studies showed that spinel phases were mainly formed in the aged catalysts and the degree of disorder in the Cu–Mn spinel oxide phases increased. The aging treatment suppressed the formation of crystallites of mixed oxides, but the treatment promoted the crystallization of impurity CuO phase. The aged catalyst exhibited higher activity for CO oxidation than the unaged catalysts. The optimum calcination temperature for obtaining the highest activity was changed by aging treatment. Refluxing during the aging treatment led to the detrimental effect on the CO oxidation activities.

Insights into the dominant factors of porous gold for CO oxidation.

Three different porous Au catalysts that exhibit high catalytic activity for CO oxidation were prepared by the leaching of Al from an intermetallic compound, Al2Au, with 10 wt. %-NaOH, HNO3, or HCl aqueous solutions. The catalysts were investigated using Brunauer-Emmett-Teller measurements, synchrotron X-ray powder diffraction, hard X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy (TEM). Broad diffraction peaks generated during the leaching process correlated with high activity for all the porous Au catalysts. CO oxidation catalyzed by porous Au leached with NaOH and HNO3 is considered to be dominated by different mechanisms at low (< 320 K) and high (> 370 K) temperatures. Activity in the low-temperature region is mainly attributed to the perimeter interface between residual Al species (AlOx) and porous Au, whereas activity in the high-temperature region results from a high density of lattice defects such as twins and dislocations, which were evident from diffraction peak broadening and were observed with high-resolution TEM in the porous Au leached with NaOH. It is proposed that atoms located at lattice defects on the surfaces of porous Au are the active sites for catalytic reactions.

Room temperature CO oxidation catalyzed by NiO particles on mesoporous SiO2 prepared via atomic layer deposition: Influence of pre-annealing temperature on catalytic activity

We prepared NiO nanoparticles on mesoporous SiO2 using atomic layer deposition and additionally annealed the prepared samples at four different temperatures (300–750°C) under dry air. NiO nanoparticles had lateral sizes less than ∼2nm up to 600°C, whereas annealing at a higher temperature (750°C) resulted in a significant agglomeration of NiO, with the formation of 30nm-sized particles. Annealing at a higher temperature resulted in a reduction in carbon impurities in the annealing temperature range of 300–600°C. Among the four samples annealed at different temperatures, the 450°C-annealed sample showed the highest CO oxidation activity at room temperature. CO oxidation reactivity of this sample initially decreased with reaction time; however, the deactivation became less pronounced over time, with maintenance of 60% of the initial activity of this catalyst after 680min. Furthermore, 450°C-annealing of used catalyst resulted in full recovery of the initial CO oxidation reactivity. These results suggest that ALD followed by annealing is a promising strategy for the fabrication of highly efficient and stable catalysts consisting of nanoparticles incorporated in the mesopores of a high-surface area support.

Theoretical investigations of non-noble metal single-atom catalysis: Ni1/FeOx for CO oxidation

The single-atom catalyst Ni1/FeOx has a high activity for CO oxidation and the oxygen vacancy on the surface of this catalyst can be created at room temperature.

Mild activation of CeO2-supported gold nanoclusters and insight into the catalytic behavior in CO oxidation.

We report a new activation method and insight into the catalytic behavior of a CeO2-supported, atomically precise Au144(SR)60 nanocluster catalyst (where thiolate -SR = -SCH2CH2Ph) for CO oxidation. An important finding is that the activation of the catalyst is closely related to the production of active oxygen species on CeO2, rather than ligand removal of the Au144(SR)60 clusters. A mild O2 pretreatment (at 80 °C) can activate the catalyst, and the addition of reductive gases (CO or H2) can enhance the activation effects of O2 pretreatment via a redox cycle in which CO could reduce the surface of CeO2 to produce oxygen vacancies-which then adsorb and activate O2 to produce more active oxygen species. The CO/O2 pulse experiments confirm that CO is adsorbed on the cluster catalyst even with ligands on, and active oxygen species present on the surface of the pretreated catalyst reacts with CO pulses to generate CO2. The Au144(SR)60/CeO2 exhibits high CO oxidation activity at 80 °C without the removal of thiolate ligands. The surface lattice-oxygen of the support CeO2 possibly participates in the oxidation of CO over the Au144(SR)60/CeO2 catalyst.

Enhanced preferential CO oxidation on Zn2SnO4 supported Au nanoparticles: support and H2 effects

Although reducible-oxide-supported gold nanostructures exhibit the highest CO oxidation activity at low temperatures, they are not suitable for preferential oxidation (PROX) reactions owing to their limited selectivity towards CO in the presence of H2.

High catalytic activity for CO oxidation on single Fe atom stabilized in graphene vacancies

The geometric, electronic and catalytic characters of Fe atom embedded graphene (including monovacancy and divacancy) are investigated using the first-principles method, which gives a reference on designing graphene-based catalysts for CO oxidation.

Au/BiPO4 nanorod catalysts: synthesis, characterization and their catalytic performance for CO oxidation

Au/BiPO4 catalysts exhibit high catalytic activity in low temperature CO oxidation.

High-surface-area activated red mud supported Co3O4 catalysts for efficient catalytic oxidation of CO

Red mud is activated and employed as the support of Co3O4 catalysts, exhibiting high catalytic activity for low-temperature CO oxidation.

CO Oxidation over Bimetallic Au–Pd Supported on Ceria–Zirconia Catalysts: Effects of Oxidation Temperature and Au:Pd Molar Ratio

Au–Pd supported on ceria–zirconia catalysts, with Au:Pd molar ratios in the 1:1–10:1 range, have been prepared using deposition precipitation of Au followed by impregnation with Pd. The resulting Au–Pd supported catalysts were activated by oxidation at 350, 450 and 700 °C. The oxidation at 700 °C led to the formation of large Au–Pd alloy nanoparticles showing lower catalytic activity for CO oxidation. The Au–Pd/Ce0.62Zr0.38O2 catalyst with the highest Au:Pd ratio, 10:1, exhibited the highest CO oxidation activity.

Highly active Au1/Co3O4 single-atom catalyst for CO oxidation at room temperature

CO oxidation is of great importance in both fundamental studies and practical applications. Oxide-supported noble metal catalysts are well known to be excellent CO oxidation catalysts. However, the high cost and limited supply of these noble metals pose significant challenges for sustainable applications. Maximizing the atom efficiency of supported noble metal catalysts is therefore highly desirable. In this work, a Co3O4 supported Au single-atom catalyst with very low Au (0.05 wt%) loading has been developed. This catalyst showed extremely high activity for CO oxidation and exhibited total conversion of CO at room temperature. The high activity originates from the isolated Au atoms distributed on the Co3O4 nanocrystallites, although the exact catalytic mechanism is still under investigation. The catalyst deactivation observed during the CO oxidation was attributed to the accumulation of CO2 rather than sintering of the single Au atoms. This extremely low loading of Au coupled to high activity is critical to reducing the cost of noble metal catalysts and making them more practical and attractive.

Highly Ordered Mesoporous Cobalt-Containing Oxides: Structure, Catalytic Properties, and Active Sites in Oxidation of Carbon Monoxide.

Co3O4 with a spinel structure is a very active oxide catalyst for the oxidation of CO. In such catalysts, octahedrally coordinated Co(3+) is considered to be the active site, while tetrahedrally coordinated Co(2+) is assumed to be basically inactive. In this study, a highly ordered mesoporous CoO has been prepared by H2 reduction of nanocast Co3O4 at low temperature (250 °C). The as-prepared CoO material, which has a rock-salt structure with a single Co(2+) octahedrally coordinated by lattice oxygen in Fm3̅m symmetry, exhibited unexpectedly high activity for CO oxidation. Careful investigation of the catalytic behavior of mesoporous CoO catalyst led to the conclusion that the oxidation of surface Co(2+) to Co(3+) causes the high activity. Other mesoporous spinels (CuCo2O4, CoCr2O4, and CoFe2O4) with different Co species substituted with non/low-active metal ions were also synthesized to investigate the catalytically active site of cobalt-based catalysts. The results show that not only is the octahedrally coordinated Co(3+) highly active but also the octahedrally coordinated Co(2+) species in CoFe2O4 with an inverse spinel structure shows some activity. These results suggest that the octahedrally coordinated Co(2+) species is easily oxidized and shows high catalytic activity for CO oxidation.

CO oxidation catalyzed by NiO supported on mesoporous Al2O3 at room temperature

A small amount of NiO was deposited on mesoporous Al2O3 using atomic layer deposition and was subsequently annealed at different temperatures. We show that all of the samples prepared here show substantially high catalytic activity for CO oxidation near room temperature. Furthermore, as the pre-annealing temperature increased, an enhanced resistance toward poisoning during CO oxidation was observed. Particularly, the samples pre-annealed at 525 and 600°C showed almost no change in the CO oxidation reactivity for 12h at 30°C, and they are structurally stable at the temperature higher than 500°C.

Screen Printed Porous La0.20Sr0.25Ca0.45TiO3 Fuel Electrode Scaffold Microstructures: Optimisation of Interaction with Impregnated Catalysts for More Durable Performance

Solid Oxide Fuel Cells (SOFC) offer an efficient method of electricity and heat production through electrochemical conversion of hydrocarbon fuels (e.g. methane) rather than direct combustion in conventional boiler units. The current industrial standard SOFC anode material is the Ni-based cermet. Although it shows high electrocatalytic activity for H2 and CO oxidation, it suffers from redox instability, Ni-grain agglomeration, gas feed sulfur intolerance and severe coking in the presence of hydrocarbon fuels. This deactivates the catalyst over time, hence a suitable replacement anode material is highly desired. La0.20Sr0.25Ca0.45TiO3 (LSCTA-) is a promising candidate for this role, acting as a ‘backbone’ structure into which electrocatalytic particles (NiO and CeO2) may be impregnated. This material has previously been used as an anode material in short-stack and full-scale testing at Hexis AG. Short-stack (5 cells) tests showed initial good performance (running at 200 mA cm-2) at 900 °C, however degradation was observed between 50 – 100 hours of operation. 1 Whilst in 1kW (nominal) Hexis Galileo 1000 N micro combined heat and power unit tests, an initial power output of ~700 W was obtained, decreasing to 250 W after 600 hours. 1 Post-test analysis revealed that non-optimal anode backbone microstructures and a small layer thickness led to poor current distribution and the generation of localised temperature ‘hotspots’ within the cells, leading to degradation of stack performance over time 1 (despite the initial comparability to the Ni-CGO standard at Hexis). Current research is focussing on the optimisation of the interaction between the backbone microstructure and impregnated electrocatalytic particles in order to improve electrochemical performance whilst minimising degradation. This paper will discuss initial research into optimisation of screen printed anode structures and the interaction with impregnated particles, including: NiO, CuO, CeO2 and lanthanum strontium chromium manganite (LSCrM). Reference: 1. Verbraeken, M. C. et al. Short stack and full system test using a ceramic A-site deficient strontium titanate anode in 11th European SOFC and SOE Forum, 1–13, (2014).

Easy Access to Metallic Copper Nanoparticles with High Activity and Stability for CO Oxidation.

Copper catalysts are very promising, affordable alternatives for noble metals in CO oxidation; however, the nature of the active species remains unclear and differs throughout previous reports. Here, we report the preparation of 8 nm copper nanoparticles (Cu NPs), with high metallic content, directly deposited onto the surface of silica nanopowders by magnetron sputtering deposition. The as-prepared Cu/SiO2 contains 85% Cu0 and 15% Cu2+ and was enriched in the Cu0 phase by H2 soft pretreatment (96% Cu0 and 4% Cu2+) or further oxidized after treatment with O2 (33% Cu0 and 67% Cu2+). These catalysts were studied in the catalytic oxidation of CO under dry and humid conditions. Higher activity was observed for the sample previously reduced with H2, suggesting that the presence of Cu-metal species enhances CO oxidation performance. Inversely, a poorer performance was observed for the sample previously oxidized with O2. The presence of water vapor caused only a small increase in the temperature require for the reaction to reach 100% conversion. Under dry conditions, the Cu NP catalyst was able to maintain full conversion for up to 45 h at 350 °C, but it deactivated with time on stream in the presence of water vapor.