Promoting the activity and selectivity of high surface area Ni–Ce–O mixed oxides by gold deposition for VOC catalytic combustion

2011 ◽  
Vol 175 ◽  
pp. 271-278 ◽  
Author(s):  
Benjamín Solsona ◽  
Tomás Garcia ◽  
Elvira Aylón ◽  
Ana M. Dejoz ◽  
Isabel Vázquez ◽  
...  
Keyword(s):  
Surface Area ◽  
Catalytic Combustion ◽  
Mixed Oxides ◽  
High Surface ◽  
High Surface Area ◽  
Gold Deposition

Σύνθεση, χαρακτηρισμός και καταλυτική δραστικότητα μικτών πορώδων οξειδίων με βάση το μαγγάνιο

2001 ◽  
Author(s):  
Βασίλειος Σταθόπουλος
Keyword(s):  
Surface Area ◽  
Mixed Oxides ◽  
High Surface ◽  
High Surface Area ◽  
Deionized Water ◽  
X Rays ◽  
Thermal Gravimetry ◽  
Reaction Proceeds ◽  
Heating Treatment ◽  
Hydrolysis Of

The subject of investigation of the present study has been the synthesis and characterization of porous manganese based mixed oxides as well as their catalytic properties in heterogeneous reactions of environmental interest. A group of mesoporous materials was prepared by hydrolysis of the trinuclear complex [Mn3 0 (CH3C0 0 )6(pyr>3]C1 0 4, by adding drop wise deionized water oraqueous solutions of nitrate salts of the elements: Mg, Al, Fe, La, La/Sr, La/Ce and La/Sr/Ce. The precursors of the materials were studied by thermal analysis (Thermal gravimetry TG, Differential thermal analysis DTA, Differential thermal gravimetry DTG). After calcination at 300 400 and 500 °C the materials were tested by N2 adsorption at 77K and powder X-rays diffraction. The same materials after heating at 500 °C were examined in catalytic tests and their surface composition was also investigated by X-rays photoelectron spectroscopy (XPS). The following three catalytic reactions were studied: I) CH4 combustion in a mixture of 4.84% CH4 , 9.68% O2 in He with a GHSV=74000h‘\ Π) interconversion of 2% NO and 2% CO in a mixture in He with a GHSV=54000h'' and finally III) a lean de-NOx reaction in the gas mixture CH4/NO/O2 = 0.67%/0.2%/5% in He with a GHSV=20000h'1. The latter reaction was studied for four materials. In this reaction the influence of 4% H2O in the gas mixture was also investigated. Experiments of NO and O2 temperature programmed desorption were carried out in order to illuminate the factors controllingthe activity of these catalysts. The main remarks of the whole study are summarized as following:□ A new method involving the hydrolysis of the [Mn3 0 (CH3C0 0 )6 (pyr)3 ]C1 0 4 complex for preparing mesoporous and/or microporous mangenese based mixed oxides was applied successfully. The composition and the heating treatment influence the specific surface area and the mean pore size of the materials. Correspondingly, as determined by the vplots, the percentage of microporosity varies. □ The XRD studies showed that after heating treatment at 300 °C - 500 °C, the majority of materials are amorphous with high surface area. In some cases Mn0 2 was apparent after heating at 300°C while Mn20 3 is found after heating at 500 °C. The presence of Mn(III) at 500°C was proved of the XPS studies. α The gradual dropwise hydrolysis of the complex [MnjO(CHjCOO)6 (pyr)3 ]C1 0 4 by deionized water results in mesoporous mangenese oxides with MnC>2 crystal structure and low thermal stability. The presence of nitrates salts of Al, La, La/Sr,L$/Ce and/or La/Sr/Ce increases the specific surface area and improves the thermal stability of the materials. The material prepared in the presence of AIJ+ (Al-ΜηΟχ) possessed a very high surface area 711 m2/g. a The hydrolysis temperature "did'not influence significantly the surface features ofthe materials but the best results obtained at SO °C. Changes in the pH also did not influence significantly the surface features of the materials. As soon as the hydrolysis takes place the solution is buffered by the stoichiometric presence of pyridine and acetic acid that coexist as ligands in the complex coordination sphere. These compounds are readily formed with the addition of H2O. a The surface compositions of the materials, as investigated by XPS, proved the presence of Mn3* but also the presence of the rest of the added elements in lower surface concentration. In all cases except those of the hydrolysis in the presence of iron and cerium nitrate salts where the surface was enriched. Also in all materials the surface was enriched in oxygen. □ All the materials proved very reactive for the catalytic combustion of CH 4 and best case was the La-MnO* catalyst. This fact was attributed to the increased surface area and the surface presence of Mn(III) compared to the rest of the materials. A correlation of the surface presence of Μη(ΠΙ) and catalytic activitywas observed. For this same reaction a comparison between the present materials and catalysts reported in the literature showed that the materials are very active with CH« combustion in very low temperature (e.g. Temperature for the 50% of conversion is 366 °C). 0 For the reaction NO+CO, the conversion of the reactants appears even from room temperature. At low temperatures (<280 °C) the reaction proceeds through the route 2NO + CO -> N2O + CO2 . In higher temperatures the reaction proceeds through the route 2NO + 2CO -» N2 + 2 CO2 . The shift of thereaction path occurs within the same temperature region for all the materials. □ For the NO reduction by CH« in the presence of excess O2. the materials proved active in the temperature region of the diesel engines exhaust gases. The mixed oxide La-Sr-Ce-MnOx in particular found very reactive and efficient to convert NO to N2 . This behaviour was even better when H2O was added to the reaction mixture with selectivity towards N2 up to 96%. This stability was proved even after 20h test on stream. This excellent catalytic behavior was attributed to the interaction of surface with NO and the possible synergistic effect among the crystal phases of Μη2θ 3 and Ce0 2 .□ The catalytic superiority o f the La-Sr-Ce-MnOx, especially in cohiparison with 1% ' wt. RI1-A I2O 3 for the same reaction mixture using data from literature, provides further proof for the excellent catalytic activity of these solids.

Structure and reactivity of high-surface-area Ni/Mg/Al mixed oxides

1995 ◽  
Vol 10 (1-2) ◽  
pp. 69-82 ◽  
Author(s):  
G Fornasari ◽  
M Gazzano ◽  
D Matteuzzi ◽  
F Trifirò ◽  
A Vaccari
Keyword(s):  
Surface Area ◽  
Mixed Oxides ◽  
High Surface ◽  
High Surface Area

High surface area Ti-based mixed oxides nanofibers prepared by electrospinning

2014 ◽  
Vol 134 ◽  
pp. 281-285 ◽  
Author(s):  
P. Frontera ◽  
L.A. Scarpino ◽  
C. Busacca ◽  
P.L. Antonucci ◽  
S. Siracusano ◽  
...  
Keyword(s):  
Surface Area ◽  
Mixed Oxides ◽  
High Surface ◽  
High Surface Area

scholarly journals Hydrothermal Synthesis of Lanthanide Stannates Pyrochlore Nanocrystals for Catalytic Combustion of Soot Particulates

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Xiaomin Zhang ◽  
Xuhui Liu ◽  
Peng Lu ◽  
Liguo Wang ◽  
Zhaoliang Zhang ◽  
...  
Keyword(s):  
Surface Area ◽  
Catalytic Combustion ◽  
High Surface ◽  
High Surface Area ◽  
Pyrochlore Structure ◽  
Soot Combustion ◽  
Hydrothermal Route ◽  
Spherical Structure ◽  
Surface Oxygen Vacancy ◽  
Gas Molecule

Nanocrystalline La2Sn2O7and La2Sn1.8Co0.2O7with a phase-pure pyrochlore structure were synthesized by a hydrothermal method, and their catalytic activity was investigated for soot combustion. The as-synthesized catalysts presented relatively larger surface area, and pore volume, which was benefit to the gas molecule diffusion in the reaction. A uniform spherical structure with particle size of 200–500 nm was found in SEM. The samples via hydrothermal route are more active for catalytic soot combustion, ascribing to the spherical morphology, high surface area and improved oxygen mobility. After Co, the reducibility was improved and surface oxygen vacancy was produced, resulting in the enhanced activity and selectivity to CO2formation.

Synthesis of high surface area boria–alumina mixed oxides characterization by 11B- and 27Al-NMR

1999 ◽  
Vol 158 (1-2) ◽  
pp. 75-81 ◽  
Author(s):  
F Dumeignil ◽  
M Guelton ◽  
M Rigole ◽  
J.-P Amoureux ◽  
C Fernandez ◽  
...  
Keyword(s):  
Surface Area ◽  
Mixed Oxides ◽  
High Surface ◽  
High Surface Area ◽  
27Al Nmr

scholarly journals Synthesis of thermally stable, high surface area anatase–alumina mixed oxides

2000 ◽  
Vol 43 (5-6) ◽  
pp. 286-290 ◽  
Author(s):  
S Rajesh Kumar ◽  
Suresh C Pillai ◽  
U.S Hareesh ◽  
P Mukundan ◽  
K.G.K Warrier
Keyword(s):  
Surface Area ◽  
Mixed Oxides ◽  
High Surface ◽  
High Surface Area ◽  
Thermally Stable
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