Preferential Oxidation Of CO Research Articles

The exquisite inserting way: Pd and perovskite on the preferential oxidation of CO or H2

Preferential oxidation of CO is an important reaction for the application of membrane fuel cells, while preferential oxidation of H2 is the key process of coal-to-ethylene glycol technology in coal chemical industry. The pivot of the performance of catalysts used in preferential oxidation (PROX) is maximizing the selectivity to a single component while maintaining the high activity at the same time. Two types of catalysts with different interactions of Pd and perovskite support (LaMO3, M = Fe or Ni) were synthesized and applied in the preferential oxidation of CO or H2. The catalyst (PLFOsg) with Pd element inserted into the LaFeO3 support surface carries the best catalytic activity and the highest H2O selectivity, whereas the performance of PLNOsg (Pd element inserted into LaNiO3) is inferior. TOFs and activation energies under the reaction condition are calculated. The characterization results explain that the different Pd species and O species are the critical factors of the catalytic performance, and it explains the reason for the excellent performance of Pd-inserted PLFOsg sample.

Viability of Au/La2O3/HAP catalysts for the CO preferential oxidation reaction under reformate gas conditions

The viability of gold supported on lanthanum-modified HAP catalysts is investigated for CO preferential oxidation (PROX) in H2-rich stream. All samples comprise small nanoparticles (NPs) of Au (< 4 nm). Addition of La enhances the chemisorption of CO, whereas it lowers that of H2 and H2O. Moreover, lanthanum improves the reducibility of the catalysts and the mobility of oxygen. FTIR studies show that under CO oxidation conditions Au exists in two distinct forms on La-promoted samples, namely Auσ+ and Au+ species. The catalytic tests under different PROX conditions show an improvement of the performance with lanthanum addition. The observed improvement is linked to suitable chemical properties, whereas efficiency dependence on Au NP sizes is rather secondary. At 80 °C, La-rich catalysts completely eliminate CO and prove to be selective (66%) under realistic PROX conditions (in the presence of H2O and CO2). Moreover, they are exceptionally stable during an extended period (240 h).

Effect of one-dimensional ceria morphology on CuO/CeO2 catalysts for CO preferential oxidation

The one-dimensional CeO2 nanocrystals (nanorods, nanowires and nanotubes) were synthesized by hydrothermal methods and supported CuO for CO preferential oxidation (CO-PROX). The supports and catalysts were characterized by various techniques. The results show that the morphologies of support and the interaction between copper species and ceria greatly affect the activity of catalysts. Compared with CeO2-W and CeO2-R, CeO2-T presents higher activity at low-temperature. After loading CuO, the strong interaction between CuO and CeO2 nanocrystals makes the activity of CuCeO catalysts much higher than that of CeO2. Among the CuCeO catalysts, CuCeO-T displays the best catalytic activity for CO oxidation. The CO conversion over CuCeO-T can reach to 100% at 100 ​°C with O2 selectivity of 89%. The addition of copper species further enriches the surface defects, Ce3+ concentration and oxygen vacancies, which should be the main reason for the high activity of CuCeO-T catalyst.

Simulated solar light-driven photothermal preferential oxidation of carbon monoxide in H2-rich streams over fast-synthesized CuCeO2–x nanorods

Aiming for purification the trace amount of CO in H2-rich streams with reduced energy consumption and low cost, solar-driven photothermal preferential oxidation of carbon monoxide on the non-precious metal oxide catalyst is proposed in this work. Cu doped CuCeO2−x nanorods catalysts were synthesized with a fast and simple coprecipitation method at the room temperature, which shows high CO oxidation activity in photothermal preferential oxidation of CO (CO-PROX) under UV-Vis-IR light irradiation. Rely on the various characterization methods such as UV-Vis-IR diffuse reflection spectrum (UV-Vis-IR DRS), photoluminescence spectrum (PL), transient photocurrent test, HRTEM, XRD, XPS, UV-Raman and H2-TPR, the optical and chemical properties of the CuCeO2−x nanorods catalysts were uncovered. The photothermal catalytic activity of CuCeO2−x nanorods doped with 10 wt% Cu reaches to 90% CO conversion under Xe lamp illumination (2.5 suns), and the solar driven photothermal CO-PROX reaction on CuCeO2−x nanorods were proposed to be proceeded by the light-to-thermal conversion and subsequently to drive a thermal catalytic process. The catalytic performance of CuCeO2−x nanorods in photothermal CO-PROX is closely related to the photo-to-thermal conversion efficiency and Cu-Ce synergetic interaction of CuCeO2−x nanorods catalyst. The introduction of CuOx greatly broaden the optical absorption range and promotes the light absorption capacity of ceria nanorods, which induces the catalyst with high photo-to-thermal conversion capability. Moreover, the optimal copper dopant benefits to enhance the Cu-Ce synergetic interaction and accelerate the oxidation reaction taking place at low temperature. CuCeO2−x nanorods catalyst shows promising competitive activity and ultra-low cost compared with the noble-based catalyst for the purification of hydrogen streams by the clean and eco-friendly sunlight sources.

Preferential CO oxidation in hydrogen-rich gases over Ag catalysts supported on different supports

Preferential CO oxidation in hydrogen-rich gases over Ag catalysts supported on different supports

Optimization of nano-catalysts for application in compact reformers

• Demand for H 2 necessitated the development of a compact reformer. • Core unit process of compact reformer includes SRM, WGS, and PROX. • Scale-down of reformer decrease thermal efficiency and increase processing capacity. • This review introduces the studies about each core unit and provides a guide. • It especially focuses on the selection of appropriate materials in catalysts. Climate change triggered by the excessive use of fossil fuels has resulted in an increased focus on the use of hydrogen. In addition to its clean property, hydrogen exhibits a higher efficiency for fuel cell applications compared to heat engines. Although hydrogen is one of the most common elements on Earth, it is not readily available in its elemental form in nature, indicating that it is a secondary energy source that requires the processing of hydrocarbons or water. Currently, hydrogen is predominantly produced using fossil fuels (96%), and the large-scale production of hydrogen from natural gas has already been commercialized. However, the increasing demand for on-site/distributed power generation systems has necessitated the development of a small-scale hydrogen production process. This scale-down induces a decrease in thermal efficiency and an increase in processing capacity, which compels the development of an integrated and harmonized technology. Studies are being conducted on compact reformers in this regard. The core unit processes of compact reformer include steam reforming of methane (SRM), water–gas shift (WGS), and preferential CO oxidation (PROX), with each process requiring the development of customized catalysts. This review introduces the basic thermodynamics and kinetics of these core unit processes, details their various issues, and provides a guide regarding current research trends on the development of customized catalysts for the unit processes of SRM, WGS, and PROX in compact reformers. State of the art for compact reformers are also introduced, showing that there are only several types of commercial compact reformers yet compared to their importance.

High jolt-resistance monolithic CuO–CeO2/AlOOH/Al-fiber catalyst for CO-PROX: Influence of AlOOH/Al-fiber calcination on Cu–Ce interaction

Micro-reactors for the preferential oxidation of CO in H 2 -rich stream (CO-PROX) are attractive for PEMFCs employed in portable electronic devices and automobiles, but the jolt is inevitable, which makes micro-reactors necessitate high jolt resistance. The monolithic structured catalyst could effectively resolve these problems. Herein, we employed the thin-felt monolithic Al-fiber substrate to fabricate the CuO–CeO 2 /AlOOH/Al-fiber catalyst for the CO-PROX reaction. This catalyst was prepared via first growing AlOOH nanosheets onto the Al-fiber surface by steam oxidation method, followed by depositing CuO–CeO 2 onto the AlOOH/Al-fiber support. The preferred catalyst delivered 100% CO conversion and 81% O 2 selectivity at 140 °C with a gas hourly space velocity of 12,000 mL g −1 h −1 , and particularly, performed stably for 120 h at the changeable temperatures of 120–160 °C. This work provides a strategy to tailor a qualified monolithic catalyst that couples the promising jolt resistance and catalytic performance at 120–160 °C. • The monolithic CuO–CeO 2 /AlOOH/Al-fiber catalyst was fabricated for CO-PROX. • This catalyst exhibits both good performance and high jolt resistance. • As-grown AlOOH nanosheets on Al-fiber enable high Cu–Ce dispersion and interaction. • The calcination of AlOOH/Al-fiber leads to decreased activity and hydroxyl amount.

Molecular-Level Insights into the Notorious CO Poisoning of Platinum Catalyst.

Carbon monoxide (CO) is notorious for its strong adsorption to poison platinum group metal catalysts in the chemical industry. Here, we conceptually distinguish and quantify the effects of the occupancy and energy of d electrons, emerging as the two vital factors in d-band theory, for CO poisoning of Pt nanocatalysts. The stepwise defunctionalization of carbon support is adopted to fine-tune the 5d electronic structure of supported Pt nanoparticles. Excluding other promotional mechanisms, the increase of Pt 5d band energy strengthens the competitive adsorption of hydrogen against CO for the preferential oxidation of CO, affording the scaling relationship between Pt 5d band energy and CO/H2 adsorption energy difference. The decrease of Pt 5d band occupancy lowers CO site coverage to promote its association with oxygen for the total oxidation of CO, giving the scaling relationship between Pt 5d occupancy and activation energy. The above insights outline a molecular-level understanding of CO poisoning.

Molecular‐Level Insights into the Notorious CO Poisoning of Platinum Catalyst

AbstractCarbon monoxide (CO) is notorious for its strong adsorption to poison platinum group metal catalysts in the chemical industry. Here, we conceptually distinguish and quantify the effects of the occupancy and energy of d electrons, emerging as the two vital factors in d‐band theory, for CO poisoning of Pt nanocatalysts. The stepwise defunctionalization of carbon support is adopted to fine‐tune the 5d electronic structure of supported Pt nanoparticles. Excluding other promotional mechanisms, the increase of Pt 5d band energy strengthens the competitive adsorption of hydrogen against CO for the preferential oxidation of CO, affording the scaling relationship between Pt 5d band energy and CO/H2 adsorption energy difference. The decrease of Pt 5d band occupancy lowers CO site coverage to promote its association with oxygen for the total oxidation of CO, giving the scaling relationship between Pt 5d occupancy and activation energy. The above insights outline a molecular‐level understanding of CO poisoning.

Comparison study of preferential oxidation of CO over nanocrystalline Cu/CeO2 catalysts synthesized by different preparation methods

Preferential oxidation of carbon monoxide in presence of excess hydrogen is a promising alternative to restrict the CO deposition in the Pt-anode in the practical polymer electrolyte membrane fuel cell application. In the present work, nanocrystalline copper-ceria catalysts have been synthesized by hydrothermal method, wet impregnation method and urea nitrate combustion method. Their characterizations have been carried out by using X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy . It has been found that Cu 2+ replaced Ce 4+ in cerium oxide, creating oxygen vacancy. The formation of more nano-sized CeO 2 leads to more oxygen vacancies in CeO 2 through the formation of interfacial Cu 1+ ions, which also enhances the CO oxidation activity. Among the synthesized Cu-CeO 2 catalysts, the catalyst prepared by hydrothermal method have shown both CO conversion and CO 2 selectivity as 100% towards CO oxidation at 373 K in the presence of excess H 2 making this catalyst viable for practical fuel cell application.

Formation of Catalytically Active Nanoparticles under Thermolysis of Silver Chloroplatinate(II) and Chloroplatinate(IV).

The thermal behaviour of Ag2[PtCl4] and Ag2[PtCl6] complex salts in inert and reducing atmospheres has been studied. The thermolysis of compounds in a helium atmosphere is shown to occur in two stages. At the first stage, the complexes decompose in the temperature range of 350–500 °C with the formation of platinum and silver chloride and the release of chlorine gas. At the second stage, silver chloride is sublimated in the temperature range of 700–900 °C, while metallic platinum remains in the solid phase. In contrast to the thermolysis of Ag2[PtCl6], the thermal decomposition of Ag2[PtCl4] at 350 °C is accompanied by significant heat release, which is associated with disproportionation of the initial salt to Ag2[PtCl6], silver chloride, and platinum metal. It is confirmed by DSC measurements, DFT calculations of a suggested reaction, and XRD. The thermolysis of Ag2[PtCl4] and Ag2[PtCl6] compounds is shown to occur in a hydrogen atmosphere in two poorly separable steps. The compounds are decomposed within 170–350 °C, and silver and platinum are reduced to a metallic state, while a metastable single-phase solid solution of Ag0.67Pt0.33 is formed. The catalytic activity of the resulting nanoalloy Ag0.67Pt0.33 is studied in the reaction of CO total (TOX) and preferential (PROX) oxidation. Ag0.67Pt0.33 enhanced Pt nano-powder activity in CO TOX, but was not selective in CO PROX.

Ceria-supported Pd catalysts with different size regimes ranging from single atoms to nanoparticles for the oxidation of CO

Supported metal catalysts are the most widely used in industrial processes and the metal particle size plays a crucial factor in determining the catalytic performance. Herein, CeO2-supported Pd catalysts with different Pd size regimes ranging from single atoms, to nanoclusters (1–2 nm), and to nanoparticles (>2 nm) were used for both CO oxidation and preferential oxidation of CO in H2 (CO-PROX). Compared to Pd nanoclusters and nanoparticles, CeO2-supported single Pd atoms (PdSA/CeO2) are the most intrinsically active in CO oxidation, with an apparent activation energy of ca. 40 kJ mol−1. Results of kinetic investigations and in situ diffuse reflectance infrared Fourier transformed spectroscopy demonstrate the CO oxidation proceeding through a Langmuir-Hinshelwood mechanism with the decomposition of formate species acting dominantly as the rate-determining step. The CO reaction rate is exclusively promoted on PdSA/CeO2 catalysts for the CO-PROX reaction, which could be ascribed to a stronger H-spillover effect on isolated Pd sites to produce bridged-OH on CeO2 surface, simultaneously facilitating the consumptions of bicarbonate and formate species. There results greatly deepen the fundamental understanding of the Pd size regimes over Pd/CeO2 catalysts for the oxidation of CO.

The effect of copper oxide on the CuO–NiO/CeO2 structure and its influence on the CO-PROX reaction

The effect of copper oxide species on the CuO–NiO/CeO 2 structure and the influence on the preferential CO oxidation in H 2 excess (CO-PROX) reaction at low and high temperatures were investigated. Temperature-programmed surface reaction (TPSR), In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS) results allowed determining the surface species. The maximum temperature of CO 2 formation or selectivity decreased about 40 °C for the CuO–NiO/CeO 2 catalyst compared to the NiO/CeO 2 , which suggests that the addition of Cu + species increases the active sites due to interaction with the Ni–Ce structure. Therefore, the activity of the catalyst was closely related to the oxygen in vacancies and the formation of Cu + -carbonyl species of the redox mechanism. Besides, the superior selectivity towards CO 2 below 150 °C depends on the carbonyl stabilization at the surface, inhibiting the adsorption and subsequent oxidation of H 2 . Using TPSR and spectroscopic analyzes by DRIFTS and XPS allowed us to propose the reaction mechanisms for low and high temperatures. • Synergistic interaction between dispersed CuO species and Ni–Ce–O solid solution. • The presence of Ce 3+ in CeO 2 indicate formation of oxygen vacancies on the surface. • The activity was closely related to oxygen vacancies and Cu + -carbonyl species. • The temperature of CuNiCeO catalyst decreased about 40 °C compared to the NiCeO. • The oxygen vacancies and Cu + -carbonyl species suggest a multiple-step process.

Co-promotion of two-type active sites: PtCux single-atom alloy and copper-ceria interface for preferential oxidation of CO

Isolated single atoms of a platinum-group dispersed in surface layer of a metal host to synthesize single-atom alloys (SAAs) has proven to be favorable for improving catalytic activity and while retaining high selectivity of host metal. Here we report a co-promotion strategy of PtCux single-atom alloy and copper-ceria interface for preferential oxidation of CO. The Pt0.1Cu0.19/CeO2 catalyst exhibits superior catalytic performance and excellent stability, attributable to the regulation of the electronic interaction between Pt and Cu as well as the high proportion of oxygen vacancies. Moreover, operando DRIFTS experiments prove that the partial of Cu0 on the surface of CeO2 is oxidized to Cu+ during catalysis. The adsorbed CO readily reacts with oxygen over the Pt0.1Cu0.19/CeO2 to produce CO2 due to the presence of two-type active sites. Density functional theory simulations in conjunction with isotopic experiments unequivocally reveal that the Mars-van Krevelen mechanism is prominent on the as-synthesized PtCu SAAs.

Magnesium as a Methanation Suppressor for Iron- and Cobalt-Based Oxide Catalysts during the Preferential Oxidation of Carbon Monoxide

The preferential oxidation of CO (CO-PrOx) to CO2 is an effective catalytic process for purifying the H2 utilized in proton-exchange membrane fuel cells for power generation. Our current work reports on the synthesis, characterization and CO-PrOx performance evaluation of unsubstituted and magnesium-substituted iron- and cobalt-based oxide catalysts (i.e., Fe3O4, Co3O4, MgFe2O4 and MgCo2O4). More specifically, the ability of Mg to stabilize the MgFe2O4 and MgCo2O4 structures, as well as suppress CH4 formation during CO-PrOx was of great importance in this study. The cobalt-based oxide catalysts achieved higher CO2 yields than the iron-based oxide catalysts below 225 °C. The highest CO2 yield (100%) was achieved over Co3O4 between 150 and 175 °C, however, undesired CH4 formation was only observed over this catalyst due to the formation of bulk fcc and hcp Co0 between 200 and 250 °C. The presence of Mg in MgCo2O4 suppressed CH4 formation, with the catalyst only reducing to a CoO-type phase (possibly containing Mg). The iron-based oxide catalysts did not undergo bulk reduction and did not produce CH4 under reaction conditions. In conclusion, our study has demonstrated the beneficial effect of Mg in stabilizing the active iron- and cobalt-based oxide structures, and in suppressing CH4 formation during CO-PrOx.

Computationally assisted, surface energy-driven synthesis of Mn-doped Co3O4 fibers with high percentage of reactive facets and enhanced activity for preferential oxidation of CO in H2

Surface engineering is central to heterogeneous catalysis. For Co3O4-based catalysts, the bulk extended Co3O4 {110} surface has been shown to be one of the most active surfaces. However, most available Co3O4 nanocrystals are terminated by the thermodynamically stable {111} and {010} facets, rather than the active {110} facets. The increasing portion of {110}-type facets in the Co3O4-based catalysts correlates with an enhancement of the catalytic activity, and synthesis strategies need to pursue them. Here, with the aid of theoretical calculation, we present doping-assisted growth strategy to modulate the facet termination of Co3O4-based nanocatalysts. Both theoretical and experimental studies demonstrate that Co3O4-based catalysts undergo profound surface termination changes in response to Mn bulk doping. Doping of Mn into Co3O4 lowers the surface energy of {110}-type facets, and reproduces hierarchy of surface energies as {111} > {010} ≈ {110}, providing thermodynamic driving force for morphology change and surface termination transformation. The resulting Mn-doped Co3O4 catalysts are mostly composed of fiber-like shapes, exposing a large fraction of {110} and {010} surfaces. In contrast, Mn-free Co3O4 consists of octahedron-shaped nanoparticles with planar geometries of {111} and {010} as their major and minor specific exposed facets. The Mn-doped Co3O4 catalysts reported herein also show high activity and excellent stability for preferential oxidation of CO in H2 during 40 h of reaction at 60 ℃. We anticipate that our theoretical and experimental findings provide a basis for the design and synthesis of new and high-performance catalysts though surface engineering strategies.

Improvement of PROX-CO catalytical performance by modulation of the pore structure of CeO2 nanorods decorated with Au nanoparticles

Au/CeO 2 -based materials are widely investigated catalytical systems used for the preferential oxidation of CO (PROX-CO). Recent research focused on their improvement via the development and optimization of nanostructures, where both metal and oxide may be individually tailored to provide the best combination of catalytic performance, stability, and cost. In this work, we synthesized CeO 2 porous nanorods using a facile hydrothermal synthesis and tailored their native porous structure using a simple acid lixiviation procedure to enlarge its pores and expose facets such as the {110} ones that are more susceptible to oxygen vacancy formation, one of the main requirements for PROX-CO. We decorated both lixiviated and as-synthesized CeO 2 nanorods with Au nanoparticles using deposition-precipitation, and evaluated the effect of lixiviation over the morphology, structure, oxygen storage capacity and catalytic activity for PROX-CO. Through HRSTEM we observed an increase in the pore size while maintaining the morphology and structure of the nanorods. This increase was accompanied by the facilitation of oxygen vacancy formation, resulting in almost tripling the oxygen storage capacity (OSC). This impacted the performance of the CeO 2 /Au nanorods for PROX-CO, allowing a maximum of 88% CO conversion rate at 181 °C, compared to 27% and 238 °C for the non-lixiviated nanorods, under the same catalytical conditions. • Low-cost, easy-to-purify acid lixiviation procedure to enlarge CeO 2 nanorod pores. • The enlargement exposes internal {110} facets, promoting oxygen vacancy formation. • The oxygen storage capacity (OSC) of the nanorods tripled after lixiviation. • Lixiviating CeO 2 /Au tripled CO conversion and lowered T max for PROX-CO to <200 °C. • AuNP hosted on CeO 2 nanorods did not undergo sintering after PROX-CO catalysis.

Understanding and application of metal-support interactions in catalysts for CO-PROX.

Preferential oxidation of carbon monoxide (CO-PROX) plays a vital role in H2 purification in the upstream systems of proton exchange membrane fuel cells (PEMFCs) for its high efficiency, low cost and practicability. The key to the application of CO-PROX is the design and preparation of catalysts, and the supported metal catalysts have been the mainstay after decades of development. The metal-support interaction (MSI), which acts as a bridge between the design of supported catalysts and atomic-level theoretical research, has triggered increasing attention. There is a growing body of literature that recognizes the importance of the MSI in heterogeneous catalysis. In this review, the impacts of the MSI including strong metal-support interactions and electronic metal-support interactions on the essential characteristics of supported single atom, nanocluster and nanoparticle catalysts, and therefore, on catalytic behaviors were discussed, respectively, primarily focusing on electron transfer, chemical bonding and the encapsulation of active sites induced by the MSI. We also presented an overview of how the MSI can be utilized to rationally design catalysts to meet target requirements such as high activity, selectivity or stability via appropriate selection and modification of support and active species. The perspectives of the future development for comprehensive understanding of the MSI were also proposed.

The Active Sites of Platinum-Ceria Catalysts in Propane Oxidation and Preferential Oxidation of Carbon Monoxide in Hydrogen

The Active Sites of Platinum-Ceria Catalysts in Propane Oxidation and Preferential Oxidation of Carbon Monoxide in Hydrogen

Insights into the Structure-Performance Relationship of Cuox-Ceo2 Catalysts for Preferential Oxidation of Co: Investigation on Thermally Induced Copper Migration Process

Insights into the Structure-Performance Relationship of Cuox-Ceo2 Catalysts for Preferential Oxidation of Co: Investigation on Thermally Induced Copper Migration Process