Selective Oxidation Of Carbon Monoxide Research Articles

Effect of the Pore Structure of Nanosilicas Decorated with Cobalt and Cerium Oxides on Catalytic Activity in the Selective Oxidation of Carbon Monoxide

Effect of the Pore Structure of Nanosilicas Decorated with Cobalt and Cerium Oxides on Catalytic Activity in the Selective Oxidation of Carbon Monoxide

Effect of the Pore Structure of Nanosilicas Decorated with Cobalt and Cerium Oxides on Catalytic Activity in the Selective Oxidation of Carbon Monoxide

Two types of nanosilicas with different pore structures are synthesized and decorated via impregnation with cobalt and cerium oxides. Meso–microporous spherical silica particles with thin walls of SiO2 nanochannels having specific surface area and pore volume of up to 1400 m2/g and 0.8 cm3/g, respectively, are used. Macroporous three-dimensionally ordered structures based on SiO2 (so-called synthetic opals) consisting of close-packed submicron spherical silica particles with respective porosity characteristics of 11 m2/g and 0.2 cm3/g are also used. The synthesized materials are characterized via low-temperature nitrogen adsorption, X-ray diffraction, SEM, XPS, and Fourier transform IR spectroscopy, and tested as catalysts for the selective oxidation of CO in excess H2 (CO-PROX). The effect of silica, the ratio of introduced oxides, and the order of their introduction on the structure and catalytic properties of Co–Ce/SiO2 are revealed. The catalytic behavior of the synthesized materials is determined from the specificity of interactions among the metal oxides and with the silica surface.

Effect of the support material of IrRu catalysts on CO-assisted NOx reduction

Aluminum oxide (Al2O3)- and titanium dioxide (TiO2)-supported iridium–ruthenium (IrRu) catalysts were synthesized and the effect that their metal particle size and metal–support interactions have on their catalytic performance toward carbon monoxide (CO)-assisted nitric oxide (NO) reduction was investigated. A series of spectroscopic analyses revealed that IrRu bimetallic particles were well-alloyed on both the Al2O3 and TiO2 supports, but that the latter exhibited a smaller size due to the strong interactions between the metal and support. Despite the large metal particle size of IrRu/Al2O3, the selective conversion of NOx to N2 assisted by of CO oxidation was more efficient than that of IrRu/TiO2. Mechanistic and microkinetics analyses suggested that the defect-free flat surface structure of the IrRu alloy was beneficial for selective NOx reduction and CO oxidation due to the moderate binding strength of the intermediates of desired reactions. The metal–support interfaces were found to be inactive regardless of their interaction strength. This analysis provides an explanation for the superior performance of IrRu/Al2O3 compared to its TiO2-supported counterpart due to its few defects, large metal size, and small proportion of metal–support interfaces.

Selective Oxidation of H2 and CO by NiIr Catalyst in Aqueous Solution: A DFT Mechanistic Study.

One of the challenges in utilizing hydrogen gas (H2) as a sustainable fossil fuel alternative is the inhibition of H2 oxidation by carbon monoxide (CO), which is involved in the industrial production of H2 sources. To solve this problem, a catalyst that selectively oxidizes either CO or H2 or one that co-oxidizes H2 and CO is needed. Recently, a NiIr catalyst [NiIICl(X)IrIIICl(η5-C5Me5)], (X = N,N'-dimethyl-3,7-diazanonane-1,9-dithiolate), which efficiently and selectively oxidizes either H2 or CO depending on the pH, has been developed (Angew. Chem. Int. Ed. 2017, 56, 9723-9726). In the present work, density functional theory (DFT) calculations are employed to elucidate the pH-dependent reaction mechanisms of H2 and CO oxidation catalyzed by this NiIr catalyst. During H2 oxidation, our calculations suggest that dihydrogen binds to the Ir center and generates an Ir(III)-dihydrogen complex, followed by subsequent isomerization to an Ir(V)-dihydride species. Then, a proton is abstracted by a buffer base, CH3COO-, resulting in the formation of a hydride complex. The catalytic cycle completes with electron transfer from the hydride complex to a protonated 2,6-dichlorobenzeneindophenol (DCIP) and a proton transfer from the oxidized hydride complex to a buffer base. The CO oxidation mechanism involves three distinct steps, i.e., (1) formation of a metal carbonyl complex, (2) formation of a metallocarboxylic acid, and (3) conversion of the metallocarboxylic acid to a hydride complex. The formation of the metallocarboxylic acid involves nucleophilic attack of OH- to the carbonyl-C followed by a large structural change with concomitant cleavage of the Ir-S bond and rotation of the COOH group along the NiIr axis. During the conversion of the metallocarboxylic acid to the hydride complex, intramolecular proton transfer followed by removal of CO2 leads to the formation of the hydride complexes. In addition, the barrier heights for the binding of small molecules (H2, OH-, H2O, and CO) to Ir were calculated, and the results indicated that dissociation from Ir is a faster process than the binding of H2O and H2. These calculations indicate that H2 oxidation is inhibited by CO and OH- and thus prefers acidic conditions. In contrast, the CO oxidation reactions occur more favorably under basic conditions, as the formation of the metallocarboxylic acid involves OH- attack to a carbonyl-C and the binding of OH- to Ni largely stabilizes the triplet spin state of the complex. Taken together, these calculations provide a rationale for the experimentally observed pH-dependent, selective oxidations of H2 and CO.

Effect of various metal oxides phases present in CuMnOx catalyst for selective CO oxidation

Hopcalite (CuMnOx) is a highly efficient catalyst for low temperature oxidation of Carbon monoxide (CO). As synthesized by Co-precipitation method, it shows the high activity for CO oxidation. The coordination between CuO and MnOx in CuMnOx catalyst improves the catalytic activity for CO oxidation. In this research work, we investigate the individual catalytic activity of CuO and MnOx and compare with the multiphase CuMnOx catalyst. The performance of multiphase catalysts CuO and MnO2 were numerous times higher as compared to single phase CuMnOx. The activity order of catalysts for CO oxidation was as follows: CuMnOx> MnOx > CuOx. The success of CuMnOx catalyst has prompted a great deal of research work into each component and nature of active sites. In CuMnOx catalyst, the MnOx acts as an oxygen donor and CuO acts as an oxygen acceptor. The presence of MnOx is possible to assist in the reduction of CuO, due to the coordination between CuO and MnOx. The calcination strategies of precursors highly affect the physicochemical and catalytic properties of the catalysts for CO oxidation. The reactive calcination (RC) conditions (4.5% CO in air) for prepared catalysts showed the best activity result for CO oxidation, as compared to the traditional method of calcination.

Porous Materials as a Platform for Highly Uniform Single-Atom Catalysts: Tuning the Electronic Structure for the Low-Temperature Oxidation of Carbon Monoxide

The selective oxidation of carbon monoxide (CO) remains a challenge in many research areas. Here we propose using porous hybrid organic–inorganic frameworks as tunable single-metal site catalysts which can be utilized for the oxidation reaction. Low-valent zinc ions were embedded on ZSM-5 zeolite and metal organic framework (MOF) supports to be used as nonprecious metal catalysts. Unlike the case with ionic compensation between the metal and zeolite, linker-functionalized MOFs exhibit a delocalized electron of the metal residing on both the organic linker and the metal atom. This electron delocalization plays a crucial role in the catalytic activity by assisting charge transfer of the metal site to break the O–O bond. By adding electron-donating groups to the linker, we found the activation energy to be dramatically decreased to ∼4 kcal/mol compared with 18 kcal/mol for the zeolite. This is essential for oxidation at low temperature. Moreover, the donating groups result in a more stable Zn active site on ...

Recent advances in gold-metal oxide core-shell nanoparticles: Synthesis, characterization, and their application for heterogeneous catalysis

Heterogeneous catalysis with core-shell structures has been a large area of focus for many years. This paper reviews the most recent work and research in coreshell catalysts utilizing noble metals, specifically gold, as the core within a metal oxide shell. The advantage of the core-shell structure lies in its capacity to retain catalytic activity under thermal and mechanical stress, which is a pivotal consideration when synthesizing any catalyst. This framework is particularly useful for gold nanoparticles in protecting them from sintering so that they retain their size, structure, and most importantly their catalytic efficiency. The different methods of synthesizing such a structure have been compiled into three categories: seed-mediated growth, post selective oxidation treatment, and one-pot chemical synthesis. The selective oxidation of carbon monoxide and reduction of nitrogen containing compounds, such as nitrophenol and nitrostyrene, have been studied over the past few years to evaluate the functionality and stability of the core-shell catalysts. Different factors that could influence the catalyst’s performance are the size, structure, choice of metal oxide shell and noble metal core and thereby the interfacial synergy and lattice mismatch between the core and shell. In addition, the morphology of the shell also plays a critical role, including its porosity, density, and thickness. This review covers the synthesis and characterization of gold-metal oxide core-shell structures, as well as how they are utilized as catalysts for carbon monoxide (CO) oxidation and selective reduction of nitrogen-containing compounds.

Synthesis and Characterization of CoO-ZnO Catalyst System for Selective CO Oxidation

Carbon monoxide (CO) is one of the most common and widely distributed poisonous air pollutants. Oxidation of it to CO2 is an important process. Mixed metal oxides, cobalt oxide and zinc oxide with varying mole ratios were synthesized by co-precepitation technique. The synthesized materials were characterized by powder X-ray diffraction (XRD) for detection of crystalline phases, Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-EmmettTeller (BET) technique, Scanning electron microscopy (SEM) for morphology, diffuse reflectance ultraviolet-visible (DRS-UV-vis) to understand the oxidation state and coordination number of metal ions in solid samples. The XRD patterns carried the peaks pertaining to Co3O4 phase along with the crystalline wurtzite phase of ZnO in the mixed oxide catalyst. The CO oxidation performance of the synthesized catalyst was tested and the results revealed that the catalyst containing equal mole ratio of both the metal oxides exhibited high activity at low temperature of 70° C, while others showed the maximum conversion at 120 ° C. Presence of zinc oxide lowers the oxidation temperature. Hence cobalt oxide- zinc oxide catalyst is considered as one of the better choice of catalyst system for CO oxidation.

Energy analysis of an electrolytic-based selective CO oxidation system for on-board pure hydrogen production

Carbon monoxide (CO) in the hydrogen (H2) stream diminishes the performance of a low temperature polymer electrolyte membrane (PEM) fuel cell significantly. The existing technologies for on-board/site production of pure hydrogen with low CO concentrations operate at high temperatures and pressures and need on-board oxygen or air supply for CO oxidation. This study offers an alternative solution to on-board/site production of hydrogen suitable for low temperature PEM fuel cell applications. A thorough energy analysis and parametric study have been carried out to investigate the effect of different operating parameters on the performance of an electrolytic-based selective CO oxidation system operating at room temperature. Such a system electrochemically removes the CO molecules in a fuel stream where they are adsorbed onto the catalyst surface at the anode side of an electrolyzer, and produces additional hydrogen at the cathode side through an electrochemical water gas shift reaction. This additional hydrogen thus offsets the energy required to drive the electrolysis, making it an attractive solution for on-board/site applications. The breakthrough curves are measured for the adsorber (50 cm2 area PEM reactor) fed with different CO concentrations (100, 300 and 500 ppm CO) present in the wet hydrogen stream at different flow rates (40, 80, 120, 160 and 200 ml min−1), under the room temperature and atmospheric pressure. The electrolytic process (regeneration) parameters are optimized with an attempt of completely removing the adsorbed CO molecules. Furthermore, a thermodynamic-electrochemical model is developed to simulate the energy balance of the electrolyzer indicating that this process offsets the actual energy consumption as it produces extra hydrogen. Thermodynamically, removing CO by electricity is more efficient than by heat which leads to high energy efficiencies (>80%). The study has demonstrated that the electrolytic-based selective CO oxidation system is a promising system for on-board/site pure hydrogen production.

Effect of nickel oxide additive on properties of catalysts used in the reaction of selective oxidation of carbon monoxide

Effect of nickel oxide additives on the oxidation selectivity of carbon monoxide in the presence of hydrogen was studied for the widely recognized system constituted by copper and cerium oxides. It was shown that a significant positive effect is observed upon introduction of the nickel-containing additive (≤0.3%) due to the electron-donor effect of nickel oxide. It was demonstrated that the catalyst of composition NiO/CuO/CeO2/Al2O3 shows high selectivity in the reaction of CO oxidation.

Influence of NiO on the performance of CoO-based catalysts for the selective oxidation of CO in H2-rich gas

Abstract The catalytic properties of Ni, Co, and Co-Ni supported activated carbon (AC) catalysts for oxidation for the removal of carbon monoxide (CO) in H 2 -rich gas are investigated. Results show that Co x O y /AC and CoO–NiO/AC exhibit higher catalytic activity than NiO/AC and that CoO–NiO/AC gives high CO conversion of above 99.5% at a wide reaction temperature region of 413–463 K. The addition of nickel oxide (NiO) can lead to enriched CoO species on the surface of CoO-NiO/AC. The higher catalytic activity and selectivity of CoO-NiO/AC compared with Co x O y /AC can be attributed to NiO playing an important role.

Selective oxidation of carbon monoxide in hydrogen-containing gas on CuO-CeO2/Al2O3 catalysts prepared by surface self-propagating thermal synthesis

The CuO-CeO2/Al2O3 catalysts for the selective oxidation of CO in hydrogen-containing mixtures were prepared by surface self-propagating thermal synthesis (SSTS) with the use of cerium nitrate Ce(NO3)3, the ammonia complex of copper acetate [Cu(NH3)4](CH3COO)2, and citric acid C6H8O7 as a fuel additive. The effect of the C6H8O7/Ce(NO3)3 molar ratio on the catalyst activity and selectivity for oxygen was studied. The catalyst samples were studied by X-ray diffraction (XRD) analysis, temperature-programmed reduction (TPR-H2), IR spectroscopy of adsorbed CO, and transmission electron microscopy (TEM). It was found that an increase in the C6H8O7/Ce(NO3)3 ratio resulted in an increase in the degree of dispersion of the resulting CeO2 phase. The greatest amount of dispersed CuO particles, which are responsible for catalytic activity in the oxidation of CO, was formed at C6H8O7/Ce(NO3)3 = 1.

Catalytic activity of gold supported on ZnO tetrapods for the preferential oxidation of carbon monoxide under hydrogen rich conditions

It is reported that 3 nm gold nanoparticles deposited on ZnO tetrapods show high activity for the selective oxidation of carbon monoxide in hydrogen rich streams; the catalytic activity of this system is at least twice as high as the values hither to observed on any conventional support for this reaction.

Supported gold nanocatalyst for low temperature CO oxidation and combustion of volatile organic compounds (VOC)

Carbon monoxide (CO) and volatile organic compounds (VOC), such as butadiene and isoprene, are air pollutants emitted by many industrial sources, such as burning of wood and fuel with poor ventilation, and by natural sources including forest fires or volcanic eruptions. It was found that these compounds are also significantly abundant in many industrial processes. Therefore, low-temperature catalytic oxidation of CO and combustion of VOC is one of the most important problems in catalysis, since even small exposures to CO or VOC (ppm) can be lethal. Catalytic oxidation is one effective method of removing CO. Nanoparticle catalysts are characterized by a large surface area, high dispersion and strong metal-support interaction. It is therefore expected that nanoparticle catalysts would show high catalytic activity for the low temperature oxidation of CO. Our results demonstrate the application of the vapor phase synthesis to synthesize supported and unsupported nanoparticle catalysts for CO oxidation. The method is based on the laser vaporization/controlled condensation (LVCC) technique of gold (Au) and copper (Cu) nanoparticles supported on a variety of oxide supports such as CeO2, TiO2, CuO and MgO. Our results indicate that Au nanoparticles supported on CeO2 exhibit higher catalytic activity than Au supported on other oxides. This high activity is attributed to the strong interaction of Au with CeO2. The results also indicate that 5 % Au loading on CeO2 has higher activity than 2% Au or 10% Au. The effect of preparation method on the catalytic activity is investigated. It was found that the catalytic activity for 5%Au/CeO2 prepared by the chemical (deposition-precipitation) method is higher than the catalytic activity of Au/CeO2 prepared by physical (LVCC). In any combustion system, there are significant amounts of other toxic gases,besides CO, such as nitric oxide, butadiene, and isoprene. We investigated the catalytic activity of the Au/CeO2 nanoparticle catalyst in the presence of 1000 ppm of butadiene and in the presence of 1000 ppm of isoprene. Our results indicate the combustion of butadiene and isoprene to CO2 and H2O, as supported by the mass spectrum and the CO conversion curve. Finally, the Au/CeO2 nanoparticle catalyst can be an active catalyst for selective CO oxidation at temperatures below 300oC even in the presence of VOC. Furthermore, this catalyst shows great promise for the low temperature combustion of VOC such as butadiene and isoprene.

Structure and chemical activity of transition metal and metal oxide catalysts: An insight from theoretical DFT studies

The present theoretical DFT study discusses the structure and chemical activity of transition metal and metal oxide catalysts within the well-known cluster approach. Selective oxidation of carbon monoxide on gold supported on titania (Au/TiO2 (110)) as well as some key points in understanding the effect of non-metal doping on TiO2 with the aim to increase its photocatalytic functionality have been briefly discussed. It was shown that Au (with formal oxidation state equal to plus one) stabilized on water-assisted and vacancy containing TiO2 (110) can explain selective oxidation of CO. Here binding of O2 with the vacancy site is energetically preferable than its adsorption on an Au site. Conversely, CO adsorbs on an Au center of Au/TiO2 (110) which is energetically much more profitable than its interaction with the oxygen vacancy site. Also, carbon and nitrogen doping on TiO2 (110) leads to two different structures. Energetically most profitable is that carbon occupies an interstitial position in deep bulk while nitrogen replaces the protruded oxygen atom and forms a surface N-H group.

Evaluation of NiFe<sub>2</sub>O<sub>4</sub> Spinel, Synthesized by Combustion Reaction, as a Catalyst for Selective CO Oxidation

The selective reaction of CO oxidation (PROX) was named as the most attractive way to reduce the CO concentration, thereby purifying the hydrogen. The aim of this work is to make the structural and morphologic characterization of the NiFe2O4 spinel synthesized by combustion reaction, using glycine as fuel, and to evaluate as catalyst in the reaction of selective oxidation of carbon monoxide in the presence of hydrogen, oxygen and carbon monoxide. The powder was prepared by using a vitreous silica crucible on a hot plate at 480°C and according to stoichiometry established by theory of propellants and explosive. The powder was characterized by X-ray diffraction (XRD), FTIR, textural analyses, transmission electron microscopy (TEM) and catalytic measurements. The results from XRD show characteristic peaks of spinel phase without presence of secondary phases. The morphologic results show surface area of 3.1 m2/g and particle size calculated by TEM of 21.72 nm. The catalyst was active and selective for O2, reaching 100% of conversion.

Poison control

A combined theoretical and experimental approach has been used to improve catalysts for the selective oxidation of carbon monoxide in hydrogen feedstocks.

Performance of CuO/Al2O3 Catalysts Promoted by SnO2 and ZrO2 in the Selective Oxidation of Carbon Monoxide

The effect of added SnO2 and ZrO2 to CuO/Al2O3 catalysts was investigated with reference to the oxygen spillover phenomena in the selective oxidation of carbon monoxide. The TPR and TPO analyses indicated that SnO2 and ZrO2 addition caused oxygen migration and induced the formation of high concentrations of active oxygen species on the SnO2 and ZrO2 surface. The catalytic activities of SnO2 and ZrO2 supported CuO/Al2O3 catalysts were superior to that for CuO/Al2O3 catalysts in the selective oxidation of carbon monoxide. Oxygen, when absorbed to the SnO2 and ZrO2 surface can spill over to the CuO phase and easily react with carbon monoxide. Consequently, the addition of SnO2 and ZrO2 led to significantly improved activities. This can be attributed to the enhanced migration of oxygen to the catalyst surface.

Sequestration and selective oxidation of carbon monoxide on graphene edges

The versatility of carbon nanostructures makes them attractive as possible catalyticmaterials, as they can be synthesized in various shapes and chemically modified by doping,functionalization, and the creation of defects in the nanostructure. Recent research hasshown how the properties of carbon nanostructures can be exploited to enhance the yield ofchemical reactions such as the thermal decomposition of water (Kostov et al 2005 Phys.Rev. Lett. 95) and the dissociation of methane into carbon and hydrogen (Huang et al 2008J. Chem. Phys. at press). In this work, we consider the carbon-mediated partialsequestration and selective oxidation of carbon monoxide (CO), both in the presence andabsence of hydrogen. Using first-principles calculations we study several reactions of COwith carbon nanostructures, where the active sites can be regenerated by thedeposition of carbon decomposed from the reactant (CO) to make the reactionsself-sustained. Using statistical mechanics, we also study the conditions underwhich the conversion of CO to graphene and carbon dioxide is thermodynamicallyfavorable, both in the presence and in the absence of hydrogen. These resultsare a first step toward the development of processes for the carbon-mediatedpartial sequestration and selective oxidation of CO in a hydrogen atmosphere.

The effect of copper on the selective carbon monoxide oxidation over alumina supported gold catalysts

The selective oxidation of CO in the presence of H 2 was investigated on Au catalysts promoted with different amounts of Cu. Au catalysts were prepared by the deposition–precipitation method and exhibited a satisfactory activity at low temperature with adequate selectivity. A considerable improvement in CO conversion was achieved when the O 2/CO ratio was increased from the value of 0.5–1.0. The addition of Cu to Au/Al 2O 3 catalysts caused an increase in the selectivity to CO oxidation due to an interaction between Au and Cu on the surface of the catalysts. However, this beneficial effect was limited to an optimal content of Cu. The catalysts were characterized by temperature programmed reduction and DRS UV–vis spectroscopy, indicating the formation of small bimetallic Au–Cu particles. The presence of water vapor in the feed stream played a positive effect in the CO conversion and selectivity while the CO 2 presence diminished the CO conversion and selectivity. In the case of a realistic reformate, when both H 2O and CO 2 are present, the positive effect of H 2O was able to compensate the negative effect of CO 2 depending on the temperature of reaction.