Catalytic Activity and Surface Characterization Study of Pd Supported on Nanocrystalline and Polycrystalline CeO2

1999 ◽  
Vol 581 ◽  
Author(s):  
Gar B. Hoflund ◽  
Zhenhua Li ◽  
Timothy J. Campbell ◽  
William S. Epling ◽  
Horst W. Hahn
Keyword(s):  
Catalytic Activity ◽  
Surface Area ◽  
Photoelectron Spectroscopy ◽  
Surface Characterization ◽  
Surface Concentration ◽  
Slow Step ◽  
Activity Increase ◽  
Area Basis ◽  
Surface Area Basis ◽  
Supported Pd

ABSTRACTThe catalytic activity of polycrystalline and nanocrystalline CeO2-supported Pd (Pd/pCeO2 and Pd/nCeO2) has been determined as a function of temperature and Pd loading. While the untreated nCeO2 support gives 50% methane conversion at 420°C, the untreated pCeO2 support exhibits little activity under the conditions examined due to its low surface area. A Pd loading of 5 wt% increases the activity of pCeO2 to 50% conversion at 260°C, while a 40 wt% Pd loading on nCeO2 exhibits a relatively smaller activity increase, yielding 50% conversion at 240°C. On a mass basis the 40 wt% Pd/nCeO2 catalyst is the most active tested in this study, but it is less active than the 5 wt% Pd/pCeO2 catalyst on a surface-area basis. Furthermore, the activity of the 40 wt% Pd/nCeO2 catalyst does not decrease during 100 hrs of exposure to CH4 and O2 at 250°C.X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) have been used to characterize the surfaces of both bare supports and Pd-containing catalysts before and after exposure to reactor conditions. The XPS results reveal that the Pd surface concentration is more than an order of magnitude higher for 5 wt% Pd/pCeO2 than for 5 wt% Pd/nCeO2 due to the larger surface area of nCeO2 and that the 40 wt% Pd/nCeO2 catalyst has a lower Pd loading on a surface-area basis than the 5 wt% Pd/pCeO2 catalyst. Most of the supported Pd is in the form of PdO, but higher PdO2/PdO ratios are observed for both CeO2 supports compared to Pd supported on ZrO2 or CO3O4. Furthermore, a significant amount of metallic Pd forms on Pd/nCeO2 but not on Pd/pCeO2 during reaction. The nanocrystalline and polycrystalline CeO2 behave differently chemically which is consistent with the fact that the nanocrystalline catalysts are less active on a surface-area basis. Accumulation of H20 on the Pd/pCeO2 surface during reaction is significant but not on the Pd/nCeO2 surface. This suggests that the rate limiting step may be H2O desorption on Pd/pCeO2 while for Pd on nCeO2 adsorption of methane appears to be the slow step. The ISS data indicate that the outermost atomic layer of Pd/nCeO2 consists mostly of O and C, which is not the case for Pd/pCeO2. Site blockage by these species may also contribute to the lower activity on a surface-area basis of Pd/nCeO2 compared to Pd/pCeO2.

scholarly journals Evolution of the pore and framework structure of NaY zeolite during alkali treatment and its effect on methanol oxidative carbonylation over a CuY catalyst

2020 ◽  
Vol 44 (11-12) ◽  
pp. 710-720
Author(s):  
Lifei Yan ◽  
Tingjun Fu ◽  
Jiajun Wang ◽  
Nilesh Narkhede ◽  
Zhong Li
Keyword(s):  
Catalytic Activity ◽  
Surface Area ◽  
Photoelectron Spectroscopy ◽  
Dimethyl Carbonate ◽  
Alkali Treatment ◽  
Oxidative Carbonylation ◽  
Framework Structure ◽  
Y Zeolite ◽  
Cage Structure ◽  
X Ray

Alkali treatment is widely used on aluminosilicate zeolites with high Si/Al ratios in order to fabricate mesopores in the framework. However, for zeolites with low Si/Al ratios, the effect of alkali treatment on the pore and framework structure needed further study. In this work, Y zeolite is treated with NaOH solutions of different concentrations and is used as the support for Cu-based catalysts for oxidative carbonylation of methanol to dimethyl carbonate. The physicochemical properties of the supports and corresponding catalysts are characterized by N2 adsorption–desorption, X-ray diffraction, X-ray fluorescence, transmission electron microscopy, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, and H2-temperature-programmed reduction analyses. The results show that no obvious mesopores are formed under alkali treatment, even at high NaOH concentration. However, amorphous species present in the micropores of Y zeolite are removed, which increases the micropore surface area as well as the crystallinity. Simultaneously, the cage structure is partially destroyed, which also leads to a slight increase of the pore volume and surface area. The altered micropore structure eventually increases the content and accessibility of the exchanged Cu species, which is beneficial to the catalytic activity. When the concentration of NaOH is 0.6 M, the space time yield of dimethyl carbonate for the corresponding catalyst was 151.4 mg g−1 h−1 which is 3.3-fold higher than that of the untreated-Y-zeolite-supported Cu catalyst. However, further increasing the alkali treatment strength can seriously destroy the basic aluminosilicate structure of the Y zeolite and decrease its intrinsic ion-exchange capacity. This results in the formation of agglomerated CuO on the catalyst surface, which was not conducive to catalytic activity.

scholarly journals Catalytic activity of nanostructured Au: Scale effects versus bimetallic/bifunctional effects in low-temperature CO oxidation on nanoporous Au

2013 ◽  
Vol 4 ◽  
pp. 111-128 ◽  
Author(s):  
Lu-Cun Wang ◽  
Yi Zhong ◽  
Haijun Jin ◽  
Daniel Widmann ◽  
Jörg Weissmüller ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Low Temperature ◽  
Co Oxidation ◽  
Surface Area ◽  
Photoelectron Spectroscopy ◽  
Scale Effects ◽  
Structural Parameters ◽  
Kinetic Measurements ◽  
X Ray ◽  
Low Temperature Co Oxidation

The catalytic properties of nanostructured Au and their physical origin were investigated by using the low-temperature CO oxidation as a test reaction. In order to distinguish between structural effects (structure–activity correlations) and bimetallic/bifunctional effects, unsupported nanoporous gold (NPG) samples prepared from different Au alloys (AuAg, AuCu) by selective leaching of a less noble metal (Ag, Cu) were employed, whose structure (surface area, ligament size) as well as their residual amount of the second metal were systematically varied by applying different potentials for dealloying. The structural and chemical properties before and after 1000 min reaction were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The catalytic behavior was evaluated by kinetic measurements in a conventional microreactor and by dynamic measurements in a temporal analysis of products (TAP) reactor. The data reveal a clear influence of the surface contents of residual Ag and Cu species on both O2 activation and catalytic activity, while correlations between activity and structural parameters such as surface area or ligament/crystallite size are less evident. Consequences for the mechanistic understanding and the role of the nanostructure in these NPG catalysts are discussed.

Reactions between boron and clays

Soil Research ◽  
1964 ◽  
Vol 2 (1) ◽  
pp. 83 ◽  
Author(s):  
FJ Hingston
Keyword(s):  
Boric Acid ◽  
Surface Area ◽  
Total Surface Area ◽  
Langmuir Equation ◽  
Adsorbed Species ◽  
Mannitol Solution ◽  
Clay Surface ◽  
Ph Values ◽  
Area Basis ◽  
Surface Area Basis

Sorption of boron by Kent sand kaolinite, WilIalooka illite, and Marchagee montmorillonite in 0.01M CaCl2 is consistent with a mechanism described by the Langmuir equation, except that deviations occur at solution concentrations greater than about 10 �g B/ml. The quantity of boron adsorbed increases markedly with pH, and is rapid, reversible, and unaffected by the concentration of calcium chloride present. Complete desorption of surface boron, without significant solution of lattice boron, is achieved with 0.01M mannitol solution. Comparing the three clays at pH 7.5 on a surface area basis, the illite is most reactive (1.18 �g B/m2), followed by the kaolinite (0.28 �g B/m2) and the montmorillonite (0.02 �g B/m2). For illite, which is the most reactive of the three minerals, the magnitude of the above values emphasizes the small proportion (less than 1.4%) of the total surface area occupied by boron. Consideration of the reaction between boron and clays suggests that either boric acid molecules or borate ions could be the adsorbed species. Increasing sorption with pH could be explained either by the increasing proportion of borate ions to boric acid with pH or by a greater number of sites on the clay surface at higher pH values.

scholarly journals Eco-Friendly Cavity-Containing Iron Oxides Prepared by Mild Routes as Very Efficient Catalysts for the Total Oxidation of VOCs

Materials ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 1387 ◽  
Author(s):  
Rut Sanchis ◽  
Daniel Alonso-Domínguez ◽  
Ana Dejoz ◽  
María Pico ◽  
Inmaculada Álvarez-Serrano ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Surface Area ◽  
Iron Oxides ◽  
Photoelectron Spectroscopy ◽  
Specific Activity ◽  
High Surface ◽  
Superior Performance ◽  
Porous Iron ◽  
Total Oxidation ◽  
X Ray

Iron oxides (FeOx) are non-toxic, non-expensive and environmentally friendly compounds, which makes them good candidates for many industrial applications, among them catalysis. In the present article five catalysts based on FeOx were synthesized by mild routes: hydrothermal in subcritical and supercritical conditions (Fe-HT, Few200, Few450) and solvothermal (Fe-ST1 and Fe-ST2). The catalytic activity of these catalysts was studied for the total oxidation of toluene using very demanding conditions with high space velocities and including water and CO2 in the feed. The samples were characterized by X-ray diffraction (XRD), scanning and high-resolution transmission electron microscopy (SEM and HRTEM), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption-desorption isotherms. It was observed that the most active catalyst was a cavity-containing porous sample prepared by a solvothermal method with a relatively high surface area (55 m2 g−1) and constituted by flower-like aggregates with open cavities at the catalyst surface. This catalyst displayed superior performance (100% of toluene conversion at 325 °C using highly demanding conditions) and this performance can be maintained for several catalytic cycles. Interestingly, the porous iron oxides present not only a higher catalytic activity than the non-porous but also a higher specific activity per surface area. The high activity of this catalyst has been related to the possible synergistic effect of compositional, structural and microstructural features emphasizing the role of the surface area, the crystalline phase present, and the properties of the surface.

Preparation and Applications of the Expandable Graphite Catalyst with Hierarchically Porous Structure in the Aldol Condensation

2014 ◽  
Vol 1053 ◽  
pp. 193-200 ◽  
Author(s):  
Xue Yan Wu ◽  
Kai Yao ◽  
Zhen Tao An ◽  
Ji Hui Li
Keyword(s):  
Catalytic Activity ◽  
Porous Structure ◽  
Photoelectron Spectroscopy ◽  
Aldol Condensation ◽  
Chemical Oxidation ◽  
Expandable Graphite ◽  
Activity Increase ◽  
Hierarchically Porous ◽  
X Ray ◽  
Hierarchically Porous Structure

The expandable graphite catalyst with hierarchically porous structure was prepared by chemical oxidation. The catalyst samples were characterized by X-ray diffraction, scanning electron microscope, N2 adsorption-desorption, X-ray photoelectron spectroscopy, UV spectroscopy. The results indicated that the expandable graphite is hierarchically porous structure catalyst. The concentrated sulphuric acid and the acetic acid had been inserted into the hierarchically pores. As the volume of the expandable graphite expanded, the amount of mixed acid in the hierarchically pores increased,as well as the acid catalytic centre increased. It can be concluded that the catalytic activity increase. The aldol condensation showed the expandable graphite with hierarchically porous structure has excellent catalytic activity and reusability. The reaction conditions were moderate and pollutions had not been found.

scholarly journals Removal of Phenolic Compounds from Water Using Copper Ferrite Nanosphere Composites as Fenton Catalysts

Nanomaterials ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 901 ◽  
Author(s):  
Carlos Moreno-Castilla ◽  
María Victoria López-Ramón ◽  
María Ángeles Fontecha-Cámara ◽  
Miguel A. Álvarez ◽  
Lucía Mateus
Keyword(s):  
Electron Microscopy ◽  
Catalytic Activity ◽  
Photoelectron Spectroscopy ◽  
Magnetic Measurements ◽  
Surface Concentration ◽  
Copper Ferrite ◽  
Electronic Effects ◽  
X Ray ◽  
Toc Removal ◽  
Cu Ions

Copper ferrites containing Cu+ ions can be highly active heterogeneous Fenton catalysts due to synergic effects between Fe and Cu ions. Therefore, a method of copper ferrite nanosphere (CFNS) synthesis was selected that also permits the formation of cuprite, obtaining a CFNS composite that was subsequently calcined up to 400 °C. Composites were tested as Fenton catalysts in the mineralization of phenol (PHE), p-nitrophenol (PNP) and p-aminophenol (PAP). Catalysts were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and magnetic measurements. Degradation of all phenols was practically complete at 95% total organic carbon (TOC) removal. Catalytic activity increased in the order PHE < PNP < PAP and decreased when the calcination temperature was raised; this order depended on the electronic effects of the substituents of phenols. The as-prepared CFNS showed the highest catalytic activity due to the presence of cubic copper ferrite and cuprite. The Cu+ surface concentration decreased after calcination at 200 °C, diminishing the catalytic activity. Cuprite alone showed a lower activity than the CFNS composite and the homogeneous Fenton reaction had almost no influence on its overall activity. CFNS activity decreased with its reutilization due to the disappearance of the cuprite phase. Degradation pathways are proposed for the phenols.

scholarly journals Zn/Cu SORBENT SYNTHESIS FOR SYN-GAS PURIFICATION FROM HYDROGEN SULFIDE

2017 ◽  
Vol 60 (3) ◽  
pp. 61
Author(s):  
Valentin Yu. Doluda ◽  
Mikhail G. Sulman ◽  
Valentina G. Matveeva ◽  
Natalia V. Lakina ◽  
Esfir M. Sulman
Keyword(s):  
Hydrogen Sulfide ◽  
Surface Area ◽  
Photoelectron Spectroscopy ◽  
Surface Concentration ◽  
Sample Surface ◽  
Precipitation Method ◽  
Hydrogen Chemisorption ◽  
Gas Purification ◽  
Mechanical Grinding ◽  
Microemulsion Method

The article is devoted to the synthesis of Zn/Cu sorbents and their study for the adsorption purification of synthesis gas from sulfur-containing compounds. The sorbents were synthesized using precipitation method, hydrothermal treatment, and mechanical grinding and microemulsion method. The article contains results of the physico-chemical studies of Zn/Cu sorbents with hydrogen chemisorption, nitrogen adsorption, X-ray photoelectron spectroscopy and electron microscopy. Studies showed that the most active sample, synthesized by microemulsion method, is characterized by highest surface area and highest concentration of surface active metal as compared with to other samples. The sample surface consists of 57-61 at. % Cu+2, Zn+2, Al+3 in form of oxides and 1.5-3.0 at. % Zn+2, Al+3 in form of aluminates. The sample synthesized by mechanical grinding of oxides showed the lowest activity in hydrogen sulfide sorption that explains by higher concentration of aluminates in the active face. The results of Zn/Cu sorption activity showed well correlation of hydrogen sulfide sorption capacity with sample surface area and surface concentration of active metal.Forcitation:Doluda V.Yu., Sulman M.G., Matveeva V.G., Lakina N.V., Sulman E.M. Zn/Cu sorbent synthesis for Syn-gas purification from hydrogen sulfide. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 3. P. 61-66.

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