Complete CO Conversion Research Articles

EFFECT OF PREPARATION METHOD OF IRON-, COPPER- CONTAINING OXIDE CATALYSTS ON THEIR ACTIVITY IN THE REACTION OF OXIDATION OF CARBON MONOXIDE TO CARBON DIOXIDE

Iron- and copper-containing oxide catalysts have been synthesized by sol-gel technology with autocombustion using organic reagents - citric acid, glycine, urea as a complexing agent and "fuel"; studied their activity in the oxidation of carbon monoxide to dioxide. The obtained samples were characterized by the methods of X-ray powder diffraction, infrared spectroscopy and electronic paramagnetic resonance, the texture characteristics of these samples was determined by measuring the specific surface area. It is shown that, regardless of the preparation method, all synthesized samples are mixtures of iron oxides Fe 2O3, copper CuO, and copper ferrite CuFe2O4. It was found that the nature of the organic reagent affects the catalytic activity of the synthesized catalysts. On a catalyst with a Cu:Fe=1:1 ratio, prepared by the sol-gel method with autocombustion using urea, the complete conversion of CO is achieved at 130°C. The same catalyst, synthesized with citric acid, is active at 250°C and on a catalyst prepared using glycine, complete conversion of CO occurs at a higher temperature of 350°C. It is assumed that the different nature of combustion leads to the formation of different surface morphology and texture, which ultimately determines the catalytic activity. Thus, the most catalytically active sample was obtained using urea as a "fuel" has a higher specific surface area (25 m2 / g) than the other two samples (for the samples obtained with citric acid and glycine, the specific surface area is 9 m2 / g and 5.8 m2 / g, respectively).

Total oxidation of carbon monoxide, VOC and reduction of NO2 with catalytic ceramic filter media

This paper deals with the effect of catalyst loading on the activity and selectivity of CuOx−MnOy catalysts on alumina-silicate supports (fiber material-Al2O3(44)/SiO2(56)). A special focus lies on the oxidation of CO, on mixtures of VOC from 1-butene, isobutane, n-butane, propane, ethene, and ethane, as well as on CO oxidation in the presence of NO2. The catalysts are prepared through wet impregnation of the filter section with an aqueous solution of copper and manganese nitrate. The rate of CO oxidation for small carbon monoxide concentrations of up to 1 vol.% is independent of catalyst loading in the filter material. In contrast, at a carbon monoxide concentration of around 3 vol.%, it is found that the rate of CO oxidation increased rapidly with increasing catalyst loading of the filter material. The highest catalytic activity of over 93% CO elimination is achieved at 290 °C for 1 vol.% CO and smaller catalyst loading and for 3 vol.% CO with higher catalyst loading. In long-term stability tests, complete CO conversion is measured without deactivating the catalyst at 390 °C for at least 100 h. The highest catalytic activity for VOC elimination of 90% is achieved in the temperature range of 350–420 °C. During the CONO2 reaction with and without O2, a constant decrease in the CO oxidation rate is observed, while the NO2 reduction rate remained constant at a temperature below 300 °C.

Polyol-pretreated SBA-16 supported Ni-Fe bimetallic catalyst applied in CO methanation at low temperature

• Polyols were used to pretreat the mesoporous silica molecular sieve SBA-16 to adjust the surface groups. • Bimetallic Ni-Fe catalysts with polyol-pretreated support were obtained. • The mechanism of how the polyols influence the surface SiOH groups and thus the metal particles distribution was figured out. • Catalysts with polyol-pretreated support lowered the minimum temperature for CO complete conversion to 230 °C from 290 °C. Polyols were used to pretreat the mesoporous silica molecular sieve SBA-16 and thus supported bimetallic Ni-Fe catalyst was prepared in order to address the low activity of CO methanation at lower temperature. The characterization of the pretreated support and catalysts indicated that the residual polyols release heat during combustion, which could provide energy for the decomposition of metal precursors, lowering the decomposition temperature and reducing the metal particle size. More importantly, the pretreatment of support with polyols could increase the isolated silicon hydroxyl, and strengthen the metal-support interaction, thus obtaining smaller metal particles. The smaller metal particles promoted the dissociation of reactant gas, as a result, Ni-Fe bimetallic catalyst with polyol-pretreated support could lower the minimum temperature for CO complete conversion from 290 °C to 230 °C while keeping CH 4 selectivity above 90%. Catalysts with polyol-pretreated support provide a new possibility for low-temperature CO methanation technology.

Enhanced Activity for CO Preferential Oxidation over CuO Catalysts Supported on Nanosized CeO2 with High Surface Area and Defects

Nanosizedceria (n-CeO2) was synthesized by a facile method in 2-methylimidazolesolution. The characterization results of XRD, N2 adsorption-desorption, Raman and TEM indicate that n-CeO2 shows a regular size of 10 ± 1 nm, a high surface area of 130 m2·g−1 and oxygen vacancies on the surface. A series of CuO/n-CeO2 catalysts (CuCeOX) with different copper loading were prepared for the preferential oxidation of CO in H2-rich gases (CO-PROX). All CuCeOX catalysts exhibit a high catalytic activity due to the excellent structural properties of n-CeO2, over which the 100% conversion of CO is obtained at 120 °C. The catalytic activity of CuCeOX catalysts increases in the order of CuCeO12 < CuCeO3 < CuCeO6 < CuCeO9. It is in good agreement with the order of the amount of active Cu+ species, Ce3+ species and oxygen vacancies on these catalysts, suggesting that the strength of interaction between highly dispersed CuO species and n-CeO2 is the decisive factor for the activity. The stronger interaction results in the formation of more readily reducible copper species on CuCeO9, which shows the highest activity with high stability and the broadest temperature “window” for complete CO conversion (120–180 °C).

Process modelling for the production of hydrogen-rich gas from gasification of coal using oxygen, CO2 and steam reactants

This process modelling studied the effect of different reactants on syngas composition and gasifier heat duty (heat energy required to carry out the operation) and the downstream treatment of CO rich syngas to maximise hydrogen yield. The process modelling was validated against experimental data obtained from a large bench-scale entrained flow gasifier. Results show that considering the H2/CO ratio, the steam-O2 reactant favours the most compared to those of the pure oxygen and oxygen-CO2 reactants. Under comparable operating conditions, the highest H2/CO ratio of 0.74 was determined using steam-O2 reactant compared to that of 0.31 and 0.33 using steam-CO2 and pure oxygen reactant. The catalytic water-gas shift reaction (WGSR) favours the yield of H2 with complete CO conversion at a temperature of 400 °C using the steam/coal ratio of 1.2. Supplying steam in the gasifier requires more heat energy to be supplied to drive endothermic gasification reaction and maintain the gasifier temperature. Under complete carbon conversion, steam-CO2 and steam-oxygen reactants require 5–65 kW more energy than pure oxygen.

Enhanced catalytic performance of Ce-MCM-41-supported Rh for CO oxidation

1wt%Rh/Ce-MCM-41 catalysts were prepared by the incipient wet impregnation method using mesoporous Ce-MCM-41 materials as supports where the Si/Ce molar ratios varied from 10 to 50. The structural properties and physicochemical features of the catalysts were characterized with a variety of techniques such as N2 physisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The CO adsorption–desorption behaviors on the catalysts were explored with in situ Fourier-transform infrared (FTIR) spectroscopic technique. The light-off curves of CO oxidation achieved on the Rh/Ce-MCM-41 catalysts significantly shifted toward lower temperature range compared to that achieved with the Rh/CeO2 and Rh/MCM-41 reference catalysts. The Rh/Ce-MCM-41 catalysts exhibited high activity with complete CO conversion at temperatures near 440 K. The in situ CO-FTIR spectra confirmed that several forms of Rh−O, Rh2−CO, Rh3−CO and Rh−(CO)2 carbonyl species with linear, bridged, hollow and gem-dicarbonyl bonds were formed. CO preferentially adsorbs on highly dispersed Rh clusters to form gem-dicarbonyl species. A reaction mechanism was proposed based primarily on the formation of intermediary species of CO adsorbed over Rh3+ clusters and the active O···OH oxygen species present on the surface in combination with the incorporation of Ce4+ ion into the framework of MCM-41 material. These findings suggest that the deposition of the Rh phase on the ceria-modified mesoporous supports could remarkably promote CO oxidation at low temperatures.

Facile synthesis of multi-shelled MnO2–Co3O4 hollow spheres with superior catalytic activity for CO oxidation

Nano-oxide hollow structures have a wide range of applications in catalysis, but the preparation of multi-shelled composite oxide hollow structures still presents a major challenge. Herein, well-dispersed multi-shelled MnO2–Co3O4 hollow spheres have been successfully prepared via a facile “Kirkendall effect” method employing carbon spheres as sacrifice templates. The shell of the hollow spheres was constructed by interconnected Co3O4 nanosheets and catkin-like MnO2 nanorods. The interdiffusion of Carbon chain and MnO4− during synthesis could be the possible formation mechanism for the special morphology. Benefiting from the hierarchical porous structure, high surface area and strong synergistic effect between Co3O4 and MnO2 was obtained, the as-prepared Co–Mn composite hollow spheres showed reliably high activity and recycle stability for CO oxidation, achieving the complete CO conversion at 137 °C without significant decrease in activity after five cycles and 10h constant-temperature reaction. We believe that this work will provide a new method for the preparation of multi-shell composite hollow spheres.

Influence of preparation method on catalytic performance of three-dimensionally ordered macroporous NiO–CuO for CO oxidation

A series of three-dimensionally ordered macroporous (3DOM) nickel−copper mixed oxides (with the NiO/CuO molar ratios of 3 : 3, 3 : 2, and 3 : 1) calcined at various temperatures (450, 550, and 650 ​°C) were prepared using the dual-templating (Pluronic P123 and polymethyl methacrylate (PMMA)) method in a mixed solution of ethylene glycol and methanol with different volumetric ratios (1 : 2, 1 : 1.5, and 1 : 1). The sample obtained after the use of P123 and PMMA exhibited a much higher catalytic activity for CO oxidation, over which a complete CO conversion was achieved at 138 ​°C, CO/O2 volumetric ratio ​= ​2 : 5, and space velocity ​= ​60,000 mL/(g h), and this catalyst possessed good stability in the presence of water vapor in the feed stream. The large surface area, high oxygen adspecies concentration, good low-temperature reducibility, and unique nanovoid 3DOM structure were accountable for the superior catalytic performance of the sample prepared by the dual P123- and PMMA-templating method.

Rh/CeO2 composites prepared by combining dealloying with calcination as an efficient catalyst for CO oxidation and CH4 combustion

In this paper, a series of Rh/CeO2 catalysts with three-dimensional porous nanorod frameworks and large specific surface area were prepared by chemical dealloying Al–Ce–Rh precursor alloys and then calcining in pure O2. The effects of the Rh content and calcination temperature on CO oxidation and CH4 combustion were studied, and the results reveal that the Rh/CeO2 catalysts produced by dealloying melt-spun Al91.3Ce8Rh0.7 alloy ribbons and then calcining at 500 °C exhibit the best catalytic activity, the reaction temperatures for the complete conversion of CO and CH4 are as low as 90 and 400 °C, respectively. Furthermore, after 150 h of continuous testing at high concentrations of H2O and CO2, the nature of the catalyst is not irreversibly destroyed and can still return to its initial level of activity. This excellent catalytic activity is attributed to a portion of Rh being uniformly distributed on the CeO2 nanorod surface in the form of nanoparticles, forming strong Rh–CeO2 interfacial synergy. Another portion of Rh permeated into the CeO2 lattice, which results in a significant increase in the number of oxygen vacancies in CeO2, thus allowing more surface active oxygen to be adsorbed and converted from the gas phase. Moreover, the catalytic reaction can proceed even in an oxygen-free environment due to the excellent oxygen storage performance of the Rh/CeO2 catalyst.

Solid-state synthesis method for the preparation of cobalt doped Ni–Al2O3 mesoporous catalysts for CO2 methanation

In this study, a simple solid-state synthesis method was employed for the preparation of the Ni–Co–Al2O3 catalysts with various Co loadings, and the prepared catalysts were used in CO2 methanation reaction. The results demonstrated that the incorporation of cobalt in nickel-based catalysts enhanced the activity of the catalyst. The results showed that the 15 wt%Ni-12.5 wt%Co–Al2O3 sample with a specific surface area of 129.96 m2/g possessed the highest catalytic performance in CO2 methanation (76.2% CO2 conversion and 96.39% CH4 selectivity at 400 °C) and this catalyst presented high stability over 10 h time-on-stream. Also, CO methanation was investigated and the results showed a complete CO conversion at 300 °C.

Flexible Co3O4/TiO2 monolithic catalysts for low‐temperature and long‐term stable CO oxidation

AbstractThe development of efficient monolithic catalysts and their fabrication methods for low‐temperature and long‐term stable CO oxidation always remains a challenge for both fundamental research and technological application. In this work, an innovative synthetic strategy to in‐situ integrate Co3O4/TiO2 monolithic catalysts on flexible Ti mesh substrate through multi‐step processes was demonstrated. The in‐situ grown catalysts show strong substrate adhesion, large surface areas and a complete CO conversion temperature of 105°C, which is superior or comparative to most noble metal catalysts. The in‐situ grown Co3O4/TiO2 catalysts on Ti mesh also exhibit excellent long‐term stability that is critically important for industrial application. It is expected that the in‐situ synthesis strategy of well‐defined Co3O4/TiO2 monolithic catalysts on flexible mesh substrate can be extended to the development of a variety of oxide‐based monolithic catalysts towards diverse catalysis applications.

Methanation of CO on Ru/graphitized-carbon catalysts: Effects of the preparation method and the carbon support structure

Two kinds of Ru/C catalysts prepared by two different methods and supported on two graphitized carbons differing in their surface area were studied in CO methanation in the H2-rich gas. The textural parameters of the support materials were characterized by means of N2 physisorption. XRPD, XPS, TEM and CO- chemisorption studies indicate that the application of wet impregnation leads to more homogeneous composition of the Ru/carbon system and higher Ru dispersion than dry impregnation for both supports. The activity of the Ru/carbon samples in CO methanation in a H2-rich gas stream depends on the structure and average size of the active phase crystallites. The combination of wet impregnation and the use of graphitized carbon of appropriate structure in the preparation of the Ru/C catalyst lead to a complete conversion of CO at 240 °C.

Golden Bristlegrass-Like Hierarchical Graphene Nanofibers Entangled with N-Doped CNTs Containing CoSe2 Nanocrystals at Each Node as Anodes for High-Rate Sodium-Ion Batteries.

Golden bristlegrass-like unique nanostructures comprising reduced graphene oxide (rGO) matrixed nanofibers entangled with bamboo-like N-doped carbon nanotubes (CNTs) containing CoSe2 nanocrystals at each node (denoted as N-CNT/rGO/CoSe2 NF) are designed as anodes for high-rate sodium-ion batteries (SIBs). Bamboo-like N-doped CNTs (N-CNTs) are successfully generated on the rGO matrixed nanofiber surface, between rGO sheets and mesopores, and interconnected chemically with homogeneously distributed rGO sheets. The defects in the N-CNTs formed by a simple etching process allow the complete phase conversion of Co into CoSe2 through the efficient penetration of H2 Se gas inside the CNT walls. The N-CNTs bridge the vertical defects for electron transfer in the rGO sheet layers and increase the distance between the rGO sheets during cycles. The discharge capacity of N-CNT/rGO/CoSe2 NF after the 10 000th cycle at an extremely high current density of 10 A g-1 is 264 mA h g-1 , and the capacity retention measured at the 100th cycle is 89%. N-CNT/rGO/CoSe2 NF has final discharge capacities of 395, 363, 328, 304, 283, 263, 246, 223, 197, 171, and 151 mA h g-1 at current densities of 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 A g-1 , respectively.

Highly dispersed boron-nitride/CuOx-supported Au nanoparticles for catalytic CO oxidation at low temperatures

Supported-Au catalysts show excellent activity in CO oxidation, where the nature of the support has a significant impact on catalytic activity. In this work, a hexagonal boron nitride (BN) support with a high surface area and adequately exposed edges was obtained by the ball-milling technique. Thereafter, impregnation of the BN support with Cu(NO3)2 followed by calcination under air at 400 °C yielded a CuO-modified support. After Au loading, the obtained Au-CuOx/BN catalyst exhibited high CO oxidation activity at low temperatures with a 50% CO conversion temperature (T50%) of 25 °C and a complete CO conversion temperature (T100%) of 80 °C, well within the operational temperature range of proton exchange membrane fuel cells. However, the CO oxidation activity of Au/BN, prepared without CuOx for comparison, was found to be relatively low. Our study reveals that BN alone disperses both Cu and Au nanoparticles well. However, Au nanoparticles on the surface of BN in the absence of CuO species tend to aggregate upon CO oxidation reactions. Conversely, Au nanoparticles supported on the surface of CuO-modified BN remain small with an average size of ∼2.0 nm before and after CO oxidation. Moreover, electron transfer between Au and Cu species possibly favors the stabilization of highly dispersed Au nanoparticles on the BN surface and also enhances CO adsorption. Thus, our results demonstrate that thermally stable and conductive CuO-modified BN is an excellent support for the preparation of highly dispersed and stable Au catalysts.

A highly dispersed mesoporous zeolite@TiO2 – supported Pt for enhanced sulfur-resistance catalytic CO oxidation

A novel mesoporous zeolite Beta@TiOx with core-shell structure and highly dispersed Pt species was designed and synthesized by a facile photochemical reduction route. The obtained Pt/m-Beta@TiO2 catalyst exhibited oxygen vacancy defects and showed excellent catalytic activity for CO oxidation. Especially, the optimal sample Pt/m-Beta@TiO2-3 exhibited an improved sulfur-resistance, where CO complete conversion at as low as 105 °C in the presence of H2O and SO2 was achieved due to the highly dispersed Pt species and the protective TiO2-shell.

Synthesis and Description of Small Gold and Palladium Nanoparticles on CeO2 Substrate: FT- IR Spectroscopy Data

Palladium (Pd/CeO2), gold (Au/CeO2), and bimetallic (PdAu/CeO2) nanoparticles obtained via impregnation of the surface of cerium dioxide with tetraethylene pentamine and subsequent reduction in a H2/Ar flow are synthesized and described. The particles possess a high degree of dispersion, but their small size complicates their analysis with conventional methods (transmission electron microscopy and X-ray powder diffraction). Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) combined with CO sample molecules is used to study the size and morphology of the nanoparticles and the substrate. The intensity ratios of the bands assigned to bridge and linear carbonyls at palladium centers indicate that there are finely divided nanoparticles in the case of a monometallic sample and larger nanoparticles in the case of a bimetallic one. The resulting materials have high catalytic activity and stability: the complete conversion of CO for Pd/CeO2 is achieved at about 50°C. We find that the catalytic activity of the samples decreases in the series Pd/CeO2–Au/CeO2–PdAu/CeO2, which indicates that there is no synergistic effect in the case of a bimetallic sample.

Toward a Full One-Pass Conversion for the Fischer–Tropsch Synthesis over a Highly Selective Cobalt Catalyst

The Fischer–Tropsch synthesis (FTS) has been studied for decades; however, it is very difficult to simultaneously obtain a high one-pass CO conversion and a high selectivity of long-chain (C5+) hydrocarbons. A layered CoMn/TiO2 catalyst is fabricated and used as an efficient catalyst in FTS. The unique layered structure of the CoMn/TiO2 catalyst effectively inhibits the agglomeration of Co nanoparticles and enhances the diffusion of the reactants and products in FTS. The catalyst exhibits superior activity, high C5+ selectivity, and excellent stability due to its unique multiple mesopores structure as well as high cobalt dispersion. Even at a nearly complete one-pass CO conversion (>95%), which is considered to be a very harsh condition in the FTS reaction, CoMn/TiO2 still exhibits a high C5+ hydrocarbon selectivity of around 93% and a very low selectivity of undesired C1 products (CH4 and CO2) of below 4.5%.

3D ordered honeycomb-shaped CuO⋅Mn2O3: Highly active catalysts for CO oxidation

Highly 3D ordered honeycomb-shaped xCuO⋅Mn2O3 (CuO content (x) = 10, 20, and 30 wt%) catalysts with various CuO contents were synthesized by adopting a colloidal crystal template method with poly(methyl methacrylate) (PMMA) as template, and the as-prepared catalysts were used in oxidation of CO. The catalysts possessed a macro-mesoporous structure. The catalytic performance at low temperatures improved significantly with a rise in CuO content. The light-off temperature (10 % conversion) and the temperature for CO complete conversion were 71 and 98 oC over 30 wt% CuO⋅Mn2O3, respectively. Good stability of the 30 wt% CuO⋅Mn2O3 catalyst was also observed under the dry and wet (in the presence of water vapor) conditions. It is concluded that high catalytic activity of 30 wt.% CuO.Mn2O3 was related to its unique pore structure, high oxygen adspecies concentration, and oxygen vacancy.

N-Coordinated Dual-Metal Single-Site Catalyst for Low-Temperature CO Oxidation

Catalysts for CO oxidation reaction are mainly based on oxide/hydroxide materials with multicomponent active sites. Here, we report a nonoxide/hydroxide material, atomically dispersed dual-metal single sites (Fe–Co sites) on N-doped carbon support, as a highly active catalyst for CO oxidation. It can greatly lower the temperature for complete CO conversion as low as −73 °C with a turnover frequency of 0.096 s–1. X-ray absorption near-edge structure spectra, pulse-adsorption microcalorimetry, and density functional theory studies show that the Fe–Co sites synergistically catalyze CO oxidation facilely following the Langmuir–Hinshelwood (L-H) mechanism with CO preferentially adsorbing at the Co sites and O2 adsorbing at the Fe sites. These results, for the first time, reveal that the dual-metal single site on N-doped carbon can efficiency catalyze low-temperature CO oxidation reaction without the involvement of supports, such as oxygen vacancies and surface hydroxyl groups.

Polyol Synthesis of Ag/BN Nanohybrids and their Catalytic Stability in CO Oxidation Reaction

AbstractPolyol method provides variety of options for microstructure control of a synthesized material. The present study aims to demonstrate that in case of Ag/h‐BN nanohybrid fabrication the synthesis time requires precise tuning. Nonlinear correlation between synthesis time and Ag nanoparticles (AgNPs) formation and deposition is found and discussed. Catalytic stability of the studied system toward carbon monoxide oxidation is investigated for the first time. Two stages of catalytic activity decrease are found and associated with the sintering of AgNPs of the certain size. Correlations between Ag content, particle size distribution and temperature of complete CO conversion allow us to conclude that AgNPs, which size is below the critical value (3 nm), have a decisive role in Ag/BN nanohybrid catalytic performance. Density functional theory (DFT) calculations uncover the mechanism behind the increased catalytic activity of smaller AgNPs and highlight an importance of the Ag/BN interfacial regions.