| 1. |
- Persson, K., et al.
(författare)
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Preparation of alumina-supported palladium catalysts for complete oxidation of methane
- 2003
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 249:1, s. 165-174
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Tidskriftsartikel (refereegranskat)abstract
- Alumina-supported palladium catalysts (Pd/Al2O3) have been prepared by incipient wetness (IW), grafting (G) and microemulsion techniques (ME). Two slightly different microemulsion methods have been used (ME1) and (ME2). The catalysts have been calcined at 1000 degreesC for 4 h. The catalysts have then been examined with respect to their activity for the combustion of methane, during heating and cooling ramps. Pd/Al2O3-IW and Pd/Al2O3-ME2 exhibit the highest activity whereas Pd/Al2O3-ME1 and Pd/Al2O3-G are the less active. There is not much of a difference in activity between Pd/Al2O3-IW and Pd/Al2O3-ME2, despite strong differences in palladium particle size observed by TEM analysis. TPO experiments show that Pd/Al2O3-IW and Pd/Al2O3-ME2 present a higher PdO/Pd ratio than the other samples exhibit. The preparation technique affects the reoxidation ability of palladium during cooling, hence the combustion activity of the fresh catalyst, as PdO is more active than Pd for the complete oxidation of methane under lean conditions.
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| 2. |
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| 3. |
- Thevenin, P. O., et al.
(författare)
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Catalytic combustion of methane over cerium-doped palladium catalysts
- 2003
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 215:1, s. 78-86
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Tidskriftsartikel (refereegranskat)abstract
- Various Pd-supported catalysts have been prepared using three different types of alumina as support material: (a) gamma-alumina, (b) Ba-stabilized alumina, and
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| 4. |
- Thevenin, P. O., et al.
(författare)
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Characterization and activity of supported palladium combustion catalysts
- 2002
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 207:1, s. 139-149
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic activity of Pd supported on gamma-Al2O3, Ba-Al2O3, and La-Al2O3 has been examined in complete oxidation of methane when operating in excess of oxygen. Two different sizes of I'd particles have been considered. Foreign ions have a strong influence with respect to the stabilization of alumina when submitted to a temperature as high as 1000 degrees C. In contrast, no specific effect can be detected when the samples are calcined at 500 degreesC. Interaction with the supported palladium particles, observed during the combustion reaction, has been investigated by X-ray photoelectron Spectroscopy and temperature-programmed oxidation. The difference in combustion activity is attributed to the difference in surface oxidation states of the Pd particles. The presence of foreign ions in the alumina structure results in surface PdO only. When supported on gamma-Al2O3, small amounts of metallic Pd can be detected, resulting in a lower ignition temperature.
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| 5. |
- Agrell, J., et al.
(författare)
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Production of hydrogen by partial oxidation of methanol over Cu/ZnO catalysts prepared by microemulsion technique
- 2001
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Ingår i: Applied Catalysis A. - 0926-860X .- 1873-3875. ; 211:2, s. 239-250
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Tidskriftsartikel (refereegranskat)abstract
- Production of hydrogen by partial oxidation of methanol, using air as oxidant. has been studied over a series of Cu/ZnO catalysts prepared by microemulsion technique. The catalytic activity was compared to that of a reference catalyst prepared by conventional co-precipitation. The BET surface areas of the microemulsion catalysts (30-70 wt.% Cu) ranged from 22 to 36 m(2)/g and were considerably lower than that of the reference (60 m(2)/g). Nevertheless, the microemulsion catalysts were more active in the partial oxidation reaction and exhibited high hydrogen and carbon dioxide selectivities. At a molar O-2/CH3OH ratio of 0.1, hydrogen production was initiated at about 185 degreesC over the microemulsion catalysts. Over the reference, hydrogen production began at 215 degreesC under the same conditions. The catalytic activity was Found to be strongly dependent on the partial pressure of oxygen, which also plays an important role in determining the product distribution. By increasing the O-2/CH3OH ratio, the methanol conversion and carbon dioxide selectivity increase. while production of water occurs at the expense of hydrogen. By TEM and TPR, it was observed that Cu is less well-dispersed in the microemulsion catalysts than in the reference. The higher catalytic activity is not expected considering the lower number of exposed Cu sites, i.e, the turnover frequencies are substantially higher over the microemulsion catalysts. It is possible that, a strong interaction between a small part of CuO and the ZnO lattice is responsible for the higher turnover frequencies of the microemulsion catalysts, or that particular crystallographic Cu planes or surface imperfections are the active sites of the reaction.
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| 6. |
- Agrell, J., et al.
(författare)
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Production of hydrogen by partial oxidation of methanol over ZnO-supported palladium catalysts prepared by microemulsion technique
- 2003
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Ingår i: Applied Catalysis A. - 0926-860X .- 1873-3875. ; 242:2, s. 233-245
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Tidskriftsartikel (refereegranskat)abstract
- Selective production of hydrogen by partial oxidation of methanol, using air as oxidant, was studied over a series of ZnO-supported Pd catalysts. Microemulsion-assisted synthesis and conventional impregnation techniques were used for preparation of catalysts containing Pd particles of different sizes. Catalyst characterisation included BET, XRD and TEM analyses. The influence of Pd particle size on catalytic activity and product distribution was studied by carrying out activity measurements at temperatures between 230 and 300 degreesC using a stoichiometric feed composition. All catalysts performed well with respect to methanol conversion and hydrogen yield. Both methanol conversion and hydrogen selectivity increased with increasing reaction temperature, the latter at the expense of water formation. Oxygen conversion was complete throughout the examined temperature range. These selectivity trends, with a strong dependence of hydrogen and carbon monoxide selectivities on methanol conversion and reaction temperature, support a reaction scheme consisting of consecutive methanol combustion, steam reforming and decomposition. More importantly, a correlation between Pd particle size and carbon monoxide selectivity was found. When the microemulsion catalysts are compared, carbon monoxide formation increases with increasing particle size. This was not observed over the impregnated reference catalysts, which exhibited high carbon monoxide-levels throughout the examined temperature range. Bimetallic PdZn particles were detected in spent catalysts by means of XRD and it is suggested that the catalytic activity is dependent on the formation of PdZn, the catalytic function being different from that of Pd-0.
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