Construction of mesoporous ceria-supported gold catalysts with rich oxygen vacancies for efficient CO oxidation

Bearing unique redox nature and high oxygen storage capacity, ceria (CeO₂) has always been a promising CO oxidation catalyst support for gold (Au) catalysts and the like. Herein, a series of Au–CeO₂–P (P stands for pH value) samples was prepared by a co-precipitation method with the assistance of an alkaline environment and amino groups functionalized ordered mesoporous polymer (OMP-NH₂). Afterward, all samples described above were characterized that the Au–CeO₂–P catalysts are made of Au–Ce–O solid solution and Au nanoparticles (NPs) supported on CeO₂. It turns out that OMP-NH₂ is not just a simple sacrificial template for mesoporous structure, but also plays an important role as an amino source, explaining the presence of rich oxygen vacancies. Due to the concentration of oxygen vacancies in Au–Ce–O solid solution is the key factor for the oxygen mobility of CO oxidation, the catalytic results also demonstrate that the catalytic activity of Au–CeO₂–P catalysts is related to the concentration of their oxygen vacancies. Moreover, Au–CeO₂-9.6 with a highest concentration of oxygen vacancies (as high as 13.98%) in Au–CeO₂–P catalysts exhibits the best catalytic activity (complete conversion at 10 °C).     

Fabricating PdCe/OMS-2 catalysts with boosted low-temperature activity for toluene deep degradation

Porous cryptomelane-type octahedral molecular sieve(OMS-2) with mixed Mn valence and abundant lattice oxygen species has attracted much attention in volatile organic compounds(VOC) catalytic elimination.However,complete conversion of arene over OMS-2 catalysts at relatively low temperature is still a challenge due to its limited crystal structure and inferior stability.Here,a series of PdCe/OMS-2 catalysts with different Pd/Ce molar ratios was fabricated by a facile impregnation method and the p...     

Support interaction of Pt/CeO_2 and Pt/SiC catalysts prepared by nano platinum colloid deposition for CO oxidation

The interaction between Pt and its various supports can regulate the intrinsic electronic structure of Pt particles and their catalytic performance.Herein,Pt/CeO_2 and Pt/SiC catalysts were successfully prepared via a facile Pt colloidal particle deposition method,and their catalytic performance in CO oxidation was investigated.XRD,TEM,XPS and H_2-TPR were used to identify the states of Pt particles on the support surface,as well as their effect on the performance of the catalysts.Formation of the Pt-O-Ce interaction is one of the factors controlling catalyst activity.Under the oxidative treatment at low temperature,the Pt-O-Ce interaction plays an important role in improving the catalytic activity.After calcining at high temperature,enhanced Pt-O-Ce interaction results in the absence of metallic Pt~0 on the support surface,as evidenced by the appearance of Pt~(2+) species.It is consistent with the XPS data of Pt/CeO_2,and is the main reason behind the deactivation of the catalyst.By contrast,either no interaction is formed between Pt and SiC or Pt nanoparticles remain in the metallic Pt~0 state on the SiC surface even after aging at 800℃in an oxidizing atmosphere.Thus,the Pt/SiC shows better thermal stability than Pt/CeO_2.The interaction between Pt and the active support may be concluded to be essential for CO oxidation at low temperature,but strong interactions may induce serious deactivation of catalytic activity.     

Fluorescent lamp promoted formaldehyde removal over CeO2 catalysts at ambient temperature

Exploring an alternative strategy with high efficiency and low cost to abate formaldehyde (HCHO) in indoor environment, is of increasing significance for people's health. CeO₂ catalysts prepared by hydrothermal, precipitation and calcination methods were investigated for HCHO removal at ambient temperature. It is found that indoor fluorescent light visibly boosts the catalytic performance of CeO₂ catalysts for HCHO decomposition at ambient temperature. Among the CeO₂ catalysts, CeO₂ prepared from hydrothermal method (CeO₂–H) exhibits a superior catalytic performance and an excellent durability by eight recycle times. Based on the characterization and analysis, the excellent catalytic performance of CeO₂–H is mainly contributed by its abundance of surface oxygen vacancies, and photogenerated electrons and hole activated by fluorescent light. This work shows a potential practicability in HCHO pollution elimination by taking full advantage of the existing lighting in indoor environments.     

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 Al_91.3Ce₈Rh_0.7 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.     

Acid modified carrier on catalytic oxidation of dichloromethane over CeO2/HZSM-5 catalysts

In this study, a series of Hydrogen-Zeolite Socony Mobil-5-X (HZSM-5-X) catalysts were prepared by acid modification, then Ce/HZSM-5-X (X = 0, 0.2, 0.4, 1.0, 2.0) catalysts were prepared by impregnation method. The catalytic performance of the catalysts on dichloromethane (DCM) oxidation was investigated. Through different characterizations, HZSM-5-X exhibit high specific surface area, good redox ability, rich acidity and much suitable acidic site distribution after acid treatment. Among them, Ce/HZSM-5-0.4 shows better catalytic activity with the lowest by-product and the best CO₂ yield. Its T₉₀ is 302 °C and the CO₂ yield of T₉₀ is more than 80 wt%, which demonstrates that the acid modification of carrier plays the positive effect on the catalytic capacity for DCM oxidation.     

Synergistic effects of CeO2/Cu2O on CO catalytic oxidation: Electronic interaction and oxygen defect

For CO catalytic oxidation, Cu and Ce species are of great importance, between which the synergistic effect is worth investigating. In this work, CeO₂/Cu₂O with Cu₂O {111} and {100} planes were comparatively explored on CO catalytic oxidation to reveal the effects of interfacial electronic interactions and oxygen defects. The activity result demonstrates that CeO₂/o-Cu₂O {111} has superior performance compared with CeO₂/c-Cu₂O {100}. Credit to the coordination unsaturated copper atoms (Cu_CUS) on o-Cu₂O {111} surface, the interfacial electronic interactions on CeO₂/o-Cu₂O {111} are more obvious than those on CeO₂/c-Cu₂O {100}, leading to richer oxygen defect generation, better redox and activation abilities of CO and O₂ reactants. Furthermore, the reaction mechanism of CeO₂/o-Cu₂O {111} on CO oxidation is revealed, i.e., CO and O₂ are adsorbed on the Cu_CUS on Cu₂O {111} and oxygen defect of CeO₂, respectively, and then synergistically promote the CO oxidation to CO₂. The work sheds light on the designing optimized ceria and copper-based catalysts and the mechanism of CO oxidation.     

Regulating local coordination environment of rhodium single atoms in Rh/CeO2 catalysts for N2O decomposition

Rh single atom catalysts(SACs) have been insensitively investigated recently due to the maximum utilization efficiency of Rh,one of the most expensive precious metals.Although great efforts have been made in the development and application of Rh SACs,there are few reports on the precise control of the local coordination environment of Rh single sites on CeO₂ and their catalytic performance for N₂O decomposition.Herein,Rh/CeO₂ catalysts with different Rh-O coordin...     

New insights into the role of vanadia species as active sites for selective catalytic reduction of NO with ammonia over VO_x/CeO_2 catalysts

A series of VO_x/CeO_2 catalysts we re synthesized via vanadia supported on ceria with different BET surface areas.The catalysts were employed to investigate the active sites for the selective catalytic reduction of NO with NH_3(NH3-SCR).The kinetic results show that VO_x/CeO_2 catalysts exhibit nearly constant apparent activation energies(E_a),indicating the same SCR reaction mechanism.The V-O-Ce bridging modes and oligomeric VO_x were identified and quantified by Raman,FT-IR and H_2-TPR.The amounts of the V-O-Ce bridging modes calculated by H_2-TPR are correlated to the NH_3-SCR intrinsic reaction rates.The turnover frequencies(TOFs) show a constant value at the same temperature,which were calculated based on the number of V-O-Ce bridging modes of VO_x/CeO_2 catalysts.Therefore,it can be concluded that the V-O-Ce bridging modes are the active sites of VO_x/CeO_2 catalysts for the NH3-SCR reaction.     

Effect of interaction between different CeO2 plane and platinum nanoparticles on catalytic activity of Pt/CeO2 in toluene oxidation

The plane exposure of support vitally affects the catalytic performance of the catalyst. In this work, CeO₂ nanorods ((110) plane exposure), nano-octahedrons ((111) plane exposure) and nano-cubes ((100) plane exposure) were prepared as the supports of Pt/CeO₂ samples to investigate the effect of CeO₂ plane exposure on total toluene oxidation. Characterizations reveal that the (110) plane of CeO₂ is more helpful to the dispersion of Pt species, followed by (111) face. The improved dispersion of Pt species can enhance the metal-supports interaction, which promotes the electron transfer of CeO₂ carrier to Pt nanoparticles and the adsorption-activation of O₂, thereby facilitating the total oxidation of toluene via the Langmuir–Hinshelwood (L-H) mechanism. Therefore, Pt/CeO₂-r (nanorods) sample expresses excellent catalytic performance of toluene oxidation. Finally, the procedure of toluene total oxidation was studied by in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. We expect that this work can contribute to the development of an effective sample for the decomposition of volatile organic compounds (VOCs).     

Low temperature catalytic oxidation of NO over different-shaped CeO2

To investigate the effect of CeO₂ nanomaterial morphology on its performance for NO catalytic oxidation. Three kinds of CeO₂ nanomaterials including CeO₂ nanorods, nanospheres and nanoparticles were prepared by hydrothermal method and used for catalytic oxidation of NO at low temperature. The experimental results show that CeO₂ nanorods are of the best catalytic performance. Characterization techniques including TEM, XRD, H₂-TPR, NO-TPD and XPS were used to determine the relationship between the morphology of CeO₂ nanomaterial and its catalytic performance. TEM images show that CeO₂ nanorods predominantly exposed (110) and (1 0 0) planes, while CeO₂ nanospheres and CeO₂ nanoparticles predominantly exposed (1 1 1) plane. The excellent catalytic performance of CeO₂ nanorods could be ascribed to the low crystallinity, high reducibility, strong NO adsorption ability and the presence of more surface chemisorbed oxygen.     

Ce-Fe-Mn ternary mixed-oxide catalysts for catalytic decomposition of ozone at ambient temperatures

Ce-modified Mn-Fe mixed-oxide catalysts were prepared by a citric acid sol-gel method and characterized by X-ray diffraction,Raman,N_2 adsorption-desorption,infrared spectra H_2 temperature-programmed reduction and thermogravimetric analyses.Their catalytic properties were investigated in ozone(O_3)decomposition reaction.Results show that the small amount of rare earth metal Ce added during Mn-Fe(FM) mixed-oxide synthesis greatly improves the catalytic performance in O_3 decomposition.Among the prepared catalysts.the C_(0.04)(FM)_(0.96) mixed-oxide catalyst exhibits the highest catalytic activity and stability.The O_3 conversion over C_(0.04)(FM)_(0.96) is 98% after 24 h reaction at 25℃ under dry condition,and that over FM decreases to 90% after 16 h reaction.At 0℃,the O_3 conversion over C_(0.04)(FM)_(0.96) is 95% after 7 h reaction under dry condition.and that over FM slows down to 70%.Under humid condition(RH 65%),the O_3 conversion over C_(0.04)(FM)_(0.96) is 63% after 6.5 h reaction at 25℃.while that over FM decreases to 55%.When Ce is doped into Mn-Fe mixed oxides,the small amount of Ce enters the crystal lattice of MnO_2.and partial Fe is separated to form Fe_2O_3.This changes cause lattice distortion and increase defects and enable the as-synthesized Ce-Fe-Mn ternary mixed-oxide catalysts to acquire additional oxygen vacancies and increase their specific surface area,thereby increasing the number of reaction sites and enhancing the catalytic performance of the catalysts forO_3 decomposition.     

Effect of yttrium addition on water-gas shift reaction over CuO/CeO2 catalysts

This paper presented a study on the role of yttrium addition to CuO/CeO2 catalyst for water-gas shift reaction. A single-step co-precipitation method was used for preparation of a series of yttrium doped CuO/CeO2 catalysts with yttrium content in the range of 0-5wt.%. Properties of the obtained samples were characterized and analyzed by X-ray diffraction (XRD), Raman spectroscopy, H2-TPR, cyclic voltammetry (CV) and the BET method. The results revealed that catalytic activity was increased with the yttrium content at first, but then decreased with the further increase of yttrium content. Herein, CuO/CeO2 catalyst doped with 2wt.% of yttrium showed the highest catalytic activity (CO conversion reaches 93.4% at 250℃) and thermal stability for WGS reaction. The catalytic activity was correlated with the surface area, the area of peak y of H2-TPR profile (I.e., the reduction of surface copper oxide (crystalline forms) interacted with surface oxygen vacancies on ceria), and the area of peak C2 and A1 (Cu0→Cu2+ in cyclic voltammetry process), respectively. Besides, Raman spectra provided evidences for a synergistic Cu-Ovacancy interaction, and it was indicated that doping yttrium may facilitate the formation of oxygen vacancies on ceria.     

Ce(Ⅲ)-modulation over non-enzymatic Pt/CeO2/GO biosensor with outstanding sensitivity and stability for lactic acid detection

A series of non-enzymatic graphene functionalized biosensors was developed via deposition precipitation method for lactic acid(LA) detection,which we re characterized by transmission electron micro scopy(TEM),Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),gas chromatography-mass spectrometry,liquid chromatography-mass spectro metry,and proton nuclear magnetic re sonance(¹H NMR).The electrochemical performances of the non-enzymatic biosensors were measured by means of the ele...     

Improved sulfur-resistant ability on CO oxidation of Pd/Ce0.75Zr0.25O2 over Pd/CeO2-TiO2 and Pd/CeO2

The influence of sulfation on Pd/Ce0.75Zr0.25O2, Pd/Ce O2-Ti O2 and Pd/Ce O2 was investigated. Physical structure and chemical properties of different catalysts were characterized by N2 adsorption, X-ray diffraction(XRD), CO chemisorption, X-ray photoelectron spectroscopy(XPS), Fourier transform infrared spectroscopy(FT-IR) and X-ray fluorescence(XRF). After 10 h SO2 sulfation, it was found that the decrement on CO oxidation catalytic activity was limited on Pd/Ce0.75Zr0.25O2 compared to Pd/Ce O2-Ti O2 and Pd/Ce O2. It demonstrated that Pd/Ce0.75Zr0.25O2 was more sulfur resistant compared to the other two catalysts. After sulfur exposure, catalyst texture was not much influenced as shown by N2 adsorption and XRD, and surface Pd atoms were poisoned indicated by CO chemisorption results. Pd/Ce0.75Zr0.25O2 and Pd/Ce O2-Ti O2 exhibited less sulfur accumulation compared to Pd/Ce O2 in the sulfation process. Furthermore, XPS results clarified that surface sulfur amount, especially surface sulfates amount on the sulfated catalysts was more crucial for the deactivation in sulfur containing environment.     

Active oxygen species and oxidation mechanism over Ce-doped LaMn_(0.8)Ni_(0.2)O_3/hierarchical ZSM-5 in pentanal oxidation

Hierarchical ZSM-5(HZ) molecular sieves based on fly ash were synthesized using a method combining water heat treatment with step-by-step calcination.The coupling catalysts between La_(1-x)Ce_xMn_(0.8)-Ni_(0.2)O_3(x ≤ 0.5) perovskites and HZ were prepared through the impregnation method,which were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(HRTEM),N_2 adsorption,X-ray photoelectron spectroscopy(XPS),NH_3-temperature programmed desoprtion(NH_3-TPD),H_2-temperature programmed reduction(H_2-TPR) and O_2-TPD techniques and investigated regarding pentanal oxidation at 120-390℃ to explore the effects of Ce doping on the catalytic activity and the active oxygen species of the coupling catalysts,meanwhile,the reaction mechanism and pathway of pentanal oxidation were also studied.The results reveal that Ce substitution at La sites can change the electronic interactions between all the elements and promote the electronic transfer among La,Ce,Ni,Mn and HZ,influencing directly the physicochemical characteristics of the catalysts.Moreover,the amount and transfer ability of surface adsorbed oxygen(O_2~-and O~-)regarded as the reactive oxygen species and the low temperature reducibility are the main influence factors in pentanal oxidation.Additionally,La_(0.8)Ce_(0.2)Mn_(0.8)Ni_(0.2)O_3/HZ exhibits the best catalytic activity and deep oxidation capacity as well as a better water resistance due to its larger amount of surface adsorbed oxygen species and higher low temperature reducibility.What's more,appropriate Ce substitution can significantly enhance the amount of O_2~-ions,which can distinctly enhance the catalytic activity of the catalyst,and moderate acid strength and appropriate acid amount can also facilitate the improvement of the pentanal oxidation activity.It is found that there is a synergic catalytic effect between surface acidity and redox ability of the catalyst.According to the in situ DRIFTS and GC/MS analyses,pentanal can be oxidized gradually to CO_2 and H_2 O by the surface oxygen species with the form of adsorption in air following the Langmuir-Hinshelwood(L-H) reaction mechanism.Two reaction pathways for the pentanal oxidation process are proposed,and the conversion of the formates to carbonates may be one of the main rate-determining steps.     

Catalytic wet oxidation of N,N-dimethyl formamide over ruthenium supported on CeO2 and Ce0.7Zr0.3O2 catalysts

A series of Ru supported on CeO₂ and Ce_0.7Zr_0.3O₂(CeZrO) was prepared by incipient-wet impregnation method and investigated in the catalytic wet oxidation of N,N-dimethyl formamide (DMF) in batch reactor. The physicochemical property of the catalysts was characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and thermogravimetry (TG). Compared with 3%Ru/CeO₂, 3%Ru/Ce_0.7Zr_0.3O₂ catalyst exhibits much higher performance for DMF degradation due to the promotion of Ru dispersion and the transfer of active oxygen, and 99% DMF conversion and 97% COD elimination are obtained at 453 K, 2.5 MPa oxygen pressure after 5 h. The reaction mechanism of DMF degradation was suggested. The carbonaceous species deposition and oxidation of Ru can be responsible for catalyst deactivation. And the catalyst activity can be recovered by air calcination and H₂ reduction.     

Preferential Oxidation of CO in H2 over CuO／CeO2 Catalysts

Over the past few years, the design and researchon fuel cells have been made a great development. Avariety of fuel cells for different applications has beenunder development[1,2]: solid polymer fuel cells(SPFC), also know as proton exchange …     

Hydrogen production from ammonia decomposition over Ni/CeO2 catalyst: Effect of CeO2 morphology

Ammonia(NH₃) decomposition to release CO_x-free hydrogen(H₂) over non-noble catalysts has gained increasing attention.In this study,three nanostructured CeO₂ with different morphologies,viz.rod(R).sphere(Sph),and spindle(Spi),were fabricated and served as supports for Ni/CeO₂ catalyst.The CeO₂supports are different in particle sizes,specific surface area and porosity,resulting in the formation of Ni nanoparticles with distinguished...     

Constructing a high concentration CuO/CeO2 interface for complete oxidation of toluene: The fantastic application of spatial confinement strategy

In this paper,CeO₂ substrate was prepared by the sol-gel method,further CuO was introduced by adding the copper complexes with chelating agents into the sol-gel precursors of CeO₂,in which different chelating agents(β-cyclodextrin,glucose and trimesic acid) were tried.This synthesis method helps the CuO species to disperse very uniformly in the CeO₂ substrates.When the amount of copper oxide is up to33 mol%,the CuO/CeO₂ samples can still maintain a hig...