Preferential Oxidation Of CO Research Articles

Highly stable platinum catalyst encapsulated with mesoporous silica for preferential oxidation of CO in H2-rich stream

Preferential oxidation of CO in H₂-rich streams (PROX) is an effective method to reduce trace amounts of CO for proton exchange membrane fuel cells. However, developing highly stable catalysts for practical reaction conditions achieving the 50:50 goal—below 50 ppm CO concentration with 50% O₂ selectivity—remains challenging. Here, we report a highly stable Pt nanoparticle catalyst encapsulated in mesoporous silica (Pt@mSiO2) loaded on a monolith, which achieves the 50:50 goal. Over 1000 h of continuous PROX reactions in the presence of H2O and CO2, the catalyst maintained an average CO concentration of ca. 33 ppm and O2 selectivity of ca. 50%. The excellent activity, selectivity, and long-term stability of Pt@mSiO₂, which can be attributed to the small size (ca. 2.7 nm) of Pt nanoparticles stably encapsulated in interconnected micro- and meso-porous silica without agglomeration, offer great potential for practical PROX applications.

Construction of CuCoCe ternary catalyst via a porous organic polymer template approach for efficient CO-PROX with wide operating temperature window

Preferential CO oxidation (CO-PROX) is a promising approach for removing trace CO from hydrogen-rich streams, effectively preventing Pt anode poisoning in proton-exchange membrane fuel cells (PEMFCs). To effectively eliminate CO within the PEMFC operating temperature range, catalysts must exhibit high CO conversion and O2 selectivity. Expanding the operating temperature window of these catalysts is crucial. This study presents the synthesis of a CuCoCe ternary catalyst (CuCo/Ce-P) using an imidazole-functionalized porous organic polymer as a sacrificial template. Compared to the CuCoCe ternary catalyst prepared without a template (CuCo/Ce), CuCo/Ce-P exhibits significantly enhanced catalytic activity, with a T50 reduction from 85 °C to 55 °C and an expanded operating temperature window of approximately 40 ℃. Characterization results indicate that the imidazole-functionalized porous organic polymer facilitates improved dispersion of active species by anchoring metal ions through electron-rich groups, enhances intermetallic interactions, promotes electron transfer, and significantly improves the oxygen-deficient capacity of the CuCoCe ternary catalyst. Consequently, the catalyst exhibits a greater number of active interfaces, leading to enhanced catalytic activity and a wider operating temperature window.

Low pressure-drop CuO/CeO2/UiO-66 catalysts for H2 purification

Pressure drop is responsible of a great part of the energy cost in industry due the energy consumed by pumps driving a fluid through the installation, and heterogeneous catalysis industrial processes suffer from this pressure drop penalty. This study demonstrates that UiO-66 significantly improves the catalytic performance of the CuO/CeO2 active phase for preferential CO oxidation in H2 streams with regard to a conventional γ-Al2O3 carrier due to the particular porous and crystalline properties of MOF materials. A packed bed of UiO-66 produces very low-pressure drop in comparison to conventional catalytic carriers, such as γ-Al2O3 or beta zeolite, being 4 times lower for UiO-66 than for γ-Al2O3 under 2 L/min flow of N2, and this ratio increases and approaches ∞ for lower gas flow rates. This feature of UiO-66 not only decreases the energy required to pump gases through the catalytic bed, but also improves catalytic performance of UiO-66-supported catalysts due to the enhanced gas diffusion into the catalytic bed. The reaction gases flow through the interparticle space left by the catalyst in a packed bed of CuO/CeO2/γ-Al2O3, and this produces high pressure drop, preferential gas pathways and mass transport limitations, negatively affecting the reaction rate. On the contrary, the reaction gases are able to flow through the UiO-66 material without channel constrictions, and the CuO/CeO2/UiO-66 catalysts avoid the gas diffusion restrictions of conventional catalysts.

Highly Active Cerium Oxide Supported Solution Combustion Cu/Mn Catalysts for CO-PrOx in a Hydrogen-Rich Stream

Mono- and di-substituted cerium oxide catalysts, viz. Ce0.95Cu0.05O2-δ, Ce0.90Cu0.10O2-δ, Ce0.90 Cu0.05Mn0.05O2-δ, Ce0.85Cu0.10Mn0.05O2-δ, and Ce0.80Cu0.10Mn0.10O2-δ, were synthesized via a one-step urea-assisted solution combustion method. The elemental composition and textural and structural properties of the catalysts were determined by various physical, electronic, and chemical characterization techniques. Hydrogen temperature-programmed reduction showed that co-doping of copper and manganese ions into the CeO2-δ lattice improved the reducibility of copper. Powder XRD, XPS, HR-TEM, and Raman spectroscopy showed that the catalysts were a singled-phased, solid-solution metal oxide with a cerium oxide cubic fluorite (cerianite) structure, and evidence of oxygen vacancies was observed. Catalytic results in the preferential oxidation of CO in a hydrogen-rich stream showed that complete CO conversion occurred between 150 and 180 °C. Furthermore, at 150 °C, Ce0.90Cu0.05Mn0.05O2-δ, Ce0.90 Cu0.10O2-δ, and Ce0.85Cu0.10Mn0.05O2-δ catalysts were the most active, achieving complete CO conversion and CO2 selectivity of 81, 79, and 71%, respectively. The catalysts performed moderately in the presence of CO2 and water, with the Ce0.90Cu0.05Mn0.05O2-δ catalyst giving a CO conversion of 80% in CO2, which decreased to about 60% when water was added.

Performance of supported Co3O4 catalysts in the preferential oxidation of carbon monoxide: Effect of support type and synthesis method

This study investigated the performance of supported Co3O4 catalysts during the preferential oxidation of carbon monoxide (CO-PrOx) in a H2-rich environment, focusing on the effects of different catalyst synthesis methods, namely, wetness impregnation (WI) and solution combustion synthesis (SCS), and different support materials, namely, Al2O3 and SiC. During CO-PrOx, the SiC-supported Co3O4 catalysts attained higher CO2 yields when compared with the Al2O3-supported Co3O4 catalysts possibly because of the existence of weaker interactions between Co3O4 and SiC. Moreover, the catalysts prepared via SCS achieved higher CO2 yields than the catalysts prepared via WI likely due to the presence of smaller and well-dispersed Co3O4 particles in the SCS-prepared catalysts. Significantly high amounts of unwanted CH4 were produced over the SiC-supported catalysts between 225 and 250 °C. The high CO methanation activity was also attributed to the weaker Co3O4-SiC interactions, which enabled the easier reduction of Co3O4 to methanation active metallic Co.

Boosting the Performance of Pt-Based Honeycomb Monolithic Catalysts for CO Preferential Oxidation in Hydrogen-Rich Streams via the Channel Rotation

Boosting the Performance of Pt-Based Honeycomb Monolithic Catalysts for CO Preferential Oxidation in Hydrogen-Rich Streams via the Channel Rotation

Advanced PtCo Catalysts Based on Platinum Acetate Blue for the Preferential CO Oxidation in H2-Rich Mixture

Advanced PtCo Catalysts Based on Platinum Acetate Blue for the Preferential CO Oxidation in H2-Rich Mixture

Ultra-pure hydrogen from chemical looping preferential oxidation of CO over a Cu–O–Ce based dual function material

Hydrogen from hydrocarbon reforming contains small amounts of CO, necessitating further purification for its use in fuel cell applications. In this work, a novel chemical looping preferential oxidation (CL-PROX) process is proposed for efficient hydrogen purification. Enabled by a Cu–O–Ce based dual function material (DFM), the process uniquely combines both catalytic CO preferential oxidation and in-situ immobilization. This results in near-complete CO conversion and < 20 ppm COx concentration with hydrogen recovery of 97 % in the purification step. Experimental characterizations indicate that CO is converted into formate and carbonate on the DFM, which can easily decompose to CO2 during the regeneration step. The interaction between copper and ceria species increased the reducibility of the DFM, as well as the CO activation and immobilization. Facile and reversible transformations between Cu2+/Ce4+ and Cu+/Ce3+ were observed throughout the reduction and re-oxidation stages. This work suggests an intensification strategy for selective hydrogen purification, and provides insights into the redox chemistry of Cu–O–Ce DFMs.

In situ and Operando Characterisation in the Preferential Oxidation of Carbon Monoxide over Base Metal Oxide Catalysts: A Review

AbstractPolymer electrolyte membrane fuel cells (PEMFCs) are the core technology of the steadily growing hydrogen (H2) economy as they can convert chemical energy, in the form of H2, to electrical energy. If the H2 is derived from (green) hydrocarbons, via steam reforming and the water‐gas‐shift reaction, then it would contain small amounts of carbon monoxide (CO, 0.5–2 %), among other gases. CO poisons the platinum‐based anode catalyst in the PEMFC, and the current recommendation is to decrease its concentration to below 0.01 % (or 100 ppm) in the H2‐rich PEMFC feed. The preferential oxidation of CO (CO‐PrOx) is a promising strategy for decreasing the CO concentration, and base metal oxide catalysts have shown great potential in this regard. However, such catalysts tend to undergo physicochemical changes that cause undesirable catalytic activity and selectivity changes. This review discusses the different base metal oxide catalysts that have been evaluated in CO‐PrOx, while paying special attention to the various in situ and operando techniques that have been used to monitor the physicochemical changes of base metal oxides during operation. We conclude the review by highlighting the recent and possible future attempts of circumventing the undesired physicochemical changes of base metal oxides during CO‐PrOx.

MOF-derived high oxygen vacancies CuO/CeO2 catalysts for low-temperature CO preferential oxidation

The CO preferential oxidation reaction (CO-PROX) is an effective strategy to remove residual poisonous CO in proton exchange membrane fuel cells, in which oxygen vacancies play a critical role in CO adsorption and activation. Herein, a series of CuO/CeO2 catalysts derived from Ce-MOFs precursors were synthesized using different organic ligands via the hydrothermal method and the CO-PROX performance was investigated. The CuO/CeO2-135 catalyst derived from homophthalic tricarboxylic acid (1,3,5-H3BTC) exhibited superior catalytic performance with 100 % CO conversion at a relatively low temperature (T100% = 100 °C), with a wide reaction temperature range and excellent stability. The superior catalytic properties were attributed to the structural improvements provided by the 1,3,5-H3BTC precursors and the promotional effects of oxygen vacancies. Additionally, in-situ Raman spectroscopy was performed to verify the dynamic roles of oxygen vacancies for CO adsorption and activation, while in-situ DRIFTS analysis revealed key intermediates in the CO-PROX reaction, shedding light on the mechanistic aspects of the catalytic process. This work not only demonstrates insights into the effective CuO/CeO2 catalysts for CO preferential oxidation, but also provides a feasible way to synthesize MOF-derived catalysts.

In situ XRD and operando XRD-XANES study of the regeneration of LaCo0.8Cu0.2O3 perovskite for preferential oxidation of CO

Combinations of perovskite-type oxides with transition and precious metals exhibit remarkable regenerating properties that can be exploited for catalytic applications. The objective of the present work was to study the structural changes experienced by LaCo0.8Cu0.2O3 under reducing/oxidizing atmosphere (redox) and Preferential Oxidation of CO (PrOx, with high H2 concentration) conditions and their reversibility. LaCo0.8Cu0.2O3 was prepared by ultrasonic spray combustion and was characterized by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Structural changes were followed by operando XRD and XAS. Metallic Co and Cu were segregated under both sets of reducing conditions and re-dissolved into the perovskite upon oxidation at 500 °C. Simultaneously, the perovskite-type oxide disappeared under reducing conditions and formed again upon high-temperature oxidation. The effects of this reversible reduction/dissolution of B-site metals on catalyst structure and activity were studied concerning the catalytic process of PrOx. The active phases of cobalt and copper oxides suffer a reduction during the PrOx reaction due to the high H2 concentration; thus, the application of an intermediate oxidation treatment can regenerate the catalytic system and the perovskite can be used for several cycles of reaction and regeneration. In contrast, when this intermediate oxidation treatment is not applied, the catalytic performance decreases in successive activity cycles.

CO-PROX on MnO2 catalysts: DFT-based microkinetic and experimental macrokinetic approaches

A microkinetic analysis in terms of DFT-calculated temperature-dependent Gibbs free energies was performed for the oxidation reactions of CO and H2 on a model Mn4O8 cluster. Apparent activation energies data predict a peculiar CO preferential oxidation pattern of Mn(IV) sites in presence of hydrogen (PROX) substantiated by the unprecedented PROX behavior of a nanocomposite MnCeOx catalyst in the range of 353–423 K under both ideal and real process conditions. Micro- and macrokinetic data on the “model” cluster and “real” catalyst are discussed.

Effect of Copper Particle Size on the Surface Structure and Catalytic Activity of Cu–CeO2 Nanocomposites Prepared by Mechanochemical Synthesis in the Preferential CO Oxidation in a H2-Rich Stream (CO-PROX)

An effect of Cu powder dispersion and morphology on the surface structure and the physical–chemical and catalytic properties of Cu–CeO2 catalysts prepared by mechanochemical synthesis was studied in the preferential CO oxidation in a H2-rich stream (CO-PROX). Two catalysts, produced by 30 min ball-milling from CeO2 and 8 mass% of copper powders and with particle sizes of several tens (dendrite-like Cu) and 50–200 nm (spherical Cu obtained with levitation-jet method), respectively, were characterized by X-ray diffraction and electron microscopy methods, a temperature-programmed reduction with CO and H2, and with Fourier-transform infrared spectroscopy. The catalyst synthesized from the “large-scale” dendrite-like Cu powder, whose surface consisted of CuxO (Cu+) agglomerates located directly on the surface of facetted CeO2 crystals with a CeO2(111) and CeO2(100) crystal planes exposition, was approximately two times less active at 120–160 °C than the catalyst synthesized from the fine Cu powder, whose surface consisted of CuxO (Cu2+) clusters of 4–6 nm in size located on the steps of facetted CeO2 nanocrystals. Although a large part of CO2 reacted with a ceria surface to give carbonate-like species, no blockage of CO-activating centers was observed due to the surface architecture. The surface structure formed by the use of highly dispersed Cu powder is found to be a key factor responsible for the catalytic activity.

Initial Research on the 1%CuO – 6CeO2 – 4ZrO2 Catalysts by TPR-H2 for the Carbon Monoxide Preferential Oxidation (CO-PROX Reaction)

The 1wt%CuO – 6CeO2 – 4ZrO2 catalysts were synthesized by sol-gel method with two different procedures: (i) impregnating CuO on CeO2-ZrO2 support (CuO/CeO2-ZrO2), (ii) sol-gel of the Cu, Ce and Zr precursor together (CuO-CeO2-ZrO2). These catalysts were applied for the preferential oxidation of carbon monoxide (CO-PROX) to remove a small quantity of CO in an H2-rich stream (the new research direction in Viet Nam), fueling the proton exchange membrane fuel cell (PEMFC) energy system. The findings of the TPR-H2 experiment indicated that the catalyst produced through the first method exhibited an α reduction peak at 174 °C, which shows the effective dispersion of copper species. In combination with EPR results, the author anticipates a significant dispersion arising from isolated copper, which is recognized as a pivotal site in the CO-PROX reaction per numerous reputable studies. The catalyst synthesized by the second method did not provide a clear indication of the oxidation behavior of Cu-species. Therefore, it can be inferred that this catalyst is inappropriate for the low-temperature CO-PROX reaction.

New insights on the Cu–Ce interaction in Cu/Ce catalysts based on ZSM-5 and Beta for the preferential oxidation of carbon monoxide in excess hydrogen

Cu-Ce-modified zeolites are shown to be effective in preferential CO oxidation (CO-PROX) in H2-rich stream. Catalysts containing copper and cerium based on zeolites ZSM-5 (Si/Al = 15, 28 and 40) and Beta (Si/Al = 19) are synthesized by sequential incipient wetness impregnation and tested in total (CO-TOX) and preferential oxidation of CO. The influence of zeolite framework type, Si/Al ratio, metal loading and order of metal introduction on the formation of active sites and their activity and selectivity are studied. Based on XRD, TEM, XPS, adsorbed CO DRIFTS and H2-TPR studies it is shown that of the key importance is synergistic interaction of copper and cerium not only on the surface, but in the zeolite channels. Cu+ incorporated in CeO2 and mixed copper-cerium oxo/hydroxocations can both be active sites in CO oxidation. Wider channels of Beta framework favor the penetration of metal cations, but not formation of necessary active sites. The presence of CuO phase in the catalysts negatively affects the stability and selectivity in CO-PROX. ZSM-5-based catalyst containing largest amount of oxocations (2.6 wt% Cu, 10 wt% Ce, Si/Al = 15) makes it possible to completely remove CO from H2-rich mixture in CO-PROX at 150–190 °C.

Synergistic metal-support interaction promoting the formation of oxygen vacancies and their role in CO-PROX over CuO/NiO-CeO2 catalyst

A series of x/yCuO/NiO-CeO2 catalysts with a constant Cu+Ni molar content and low copper loading of 1 wt% had been prepared by the step-by-step impregnation method and characterized by various techniques (XRD, N2-adsorption/desorption, HR-TEM, H2-TPR, Raman and XPS). CO preferential oxidation (CO-PROX) under H2/CO2-rich conditions had been performed. Experimental results indicated that the catalytic activity of CuO/CeO2 could be enhanced by substituting partial Cu with Ni, and with a Cu/Ni molar ratio of 1/2, the highest catalytic performance was observed. Under the conditions of temperature 130 ℃, space velocity 20266 mL·gcat−1·h−1 and oxygen excess coefficient 1.2, the 1/2CuO/NiO-CeO2 catalyst gave rise to a maximum CO conversion of about 94.8%. The 1/2CuO/NiO-CeO2 catalyst also exhibited good catalytic stability up to 100 h, showing that this catalyst system could be further developed for potential commercial application. Combined with the detailed characterization data, it had been proposed that there was a synergistic interaction among Cu, Ni and CeO2 in the catalyst, generating more oxygen vacancies than the binary CuO/CeO2 and NiO/CeO2 catalysts. With a Cu/Ni molar ratio of 1/2, the formed ternary CuO/NiO-CeO2 catalyst had the highest content of oxygen vacancies, which was believed to play a crucial role in the CO-PROX reaction.

Ru/Ir nanojunctions supported on CNTs as active and ultrastable catalysts for CO preferential oxidation toward hydrogen purification

Hydrogen purification is animportanttechnological step for proton exchange membrane fuel cells (PEMFCs), which can promote the service life of batteries. The preferential oxidation of CO (PROX) in hydrogen is a promising solution for hydrogen purification to avoid poisoning of catalysts by the trace amount of CO present in thehydrogen-richfeedgas. Herein, we demonstrate an interface engineering strategy to prepare Ru/Ir-CNTs nanojunctionswith remarkablecatalyticactivity for CO oxidation. The as-prepared catalyst shows thetotal COconversionin awidetemperaturerange of 50-200℃ under a high feeding gas flow velocity of 72000 mL g-1h−1 and remains stable after 48 h of continuous working. The catalyst also exhibits 100 % CO conversion in temperature from 80 to 100℃ under a much higher feeding gas flow velocity of 108000 mL g-1h−1. Moreover, the CO conversion remains 100 % after intermittent performance testing over a one-week time period. Theoretical calculations reveal that the interface of Ru/Ir can weaken the adsorption of *CO2, thus greatly increasing the temperature range of the complete transformation of CO. Compared to oxide supports, CNTs are more difficult to combine with CO2, which makes the catalyst completely convert CO for a long time within the operating temperature range.

Effect of Realistic Operating Considerations on Preferential Oxidation of CO and Regulatory Strategies: A Review and Perspectives

Effect of Realistic Operating Considerations on Preferential Oxidation of CO and Regulatory Strategies: A Review and Perspectives

Different metal (Mn, Fe, Co, Ni, and Zr) decorated Cu/CeO2 catalysts for efficient CO oxidation in a rich CO2/H2 atmosphere.

In this work, CuM/CeO2 (M = Mn, Fe, Co, Ni, and Zr) catalysts with a low Cu content of 1 wt% were purposely designed and prepared using the co-impregnation method. The samples were characterized using various techniques (TG-DTA, XRD, N2-adsorption/desorption measurements, H2-TPR, XPS and Raman spectroscopy) and CO preferential oxidation (CO-Prox) under H2/CO2-rich conditions was performed. The results have shown that enhanced catalytic performance was achieved upon the introduction of Mn, Co and Ni, and little impact was observed with Zr doping, but Fe showed a negative effect, as compared with the Cu/CeO2 catalyst. Characterization data revealed that the M doping strongly changed the surface composition, revealing the decreased Cu/Ce ratios on the surface, which could be accounted for by the formation of more M/Cu-O-Ce solid solution, or strong Cu-M interactions. When Mn was used, the obtained CuMn/CeO2 catalyst revealed the highest concentration of the oxygen vacancies and Ce3+ ions, which could be correlated well with its superior catalytic performance. Compared with the Cu/CeO2 catalyst, the CO conversion rate increased by 24.7% at a low temperature of 90 °C over the CuMn/CeO2 catalyst. At 130 °C, the maximum CO conversion was 94.7% and the CO2 selectivity was 78.9%. Conversely, the Fe doped Cu/CeO2 catalyst demonstrated the poorest catalytic activity, which was due to the blockage effect of Fe species on Cu showing a high Fe/Cu ratio of 1.9 on the surface.

Mechanism and selectivity of MOF-supported Cu single-atom catalysts for preferential CO oxidation

MOFs can achieve atom-precision in the design of single-atom catalysts (SACs). We elucidated the PROX-reaction mechanism on a well-defined Cu-SAC supported by UiO-66 framework using a multitude of experimental methods and detailed DFT computations.