| 1. |
- Persson, Katarina, et al.
(författare)
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Stability of palladium-based catalysts during catalytic combustion of methane: The influence of water
- 2007
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Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 74:3-4, s. 242-250
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Tidskriftsartikel (refereegranskat)abstract
- The stability of methane conversion was studied over a Pd/Al2O3 catalyst and bimetallic Pd-Pt/Al2O3 catalysts. The activity of methane combustion over Pd/Al2O3 gradually decreased with time, whereas the methane conversion over bimetallic Pd-Pt catalysts was significantly more stable. The differences in combustion behavior were further investigated by activity tests where additional water vapor was periodically added to the feed stream. From these tests it was concluded that water speeds up the degradation process of the Pd/Al2O3 catalyst, whereas the catalyst containing Pt was not affected to the same extent. DRIFTS studies in a mixture of oxygen and methane revealed that both catalysts produce surface hydroxyls during combustion, although the steady state concentration on the pure Pd catalyst is higher for a fixed temperature and water partial pressure. The structure of the bimetallic catalyst grains with a PdO domain and a Pd-Pt alloy domain may be the reason for the higher stability, as the PdO domain appears to be more affected by the water generated in the combustion reaction than the alloy. Not all fuels that produce water during combustion will have stability issues. It appears that less strong binding in the fuel molecule will compensate for the degradation.
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| 2. |
- Schwartz, W. R., et al.
(författare)
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Combustion of methane over palladium based catalysts - A study of catalytic deactivation & the use of electrochemical oxygen pumping
- 2007
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Ingår i: 5th US Combustion Meeting 2007. - : Combustion Institute. - 9781604238112 ; , s. 1787-1794
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Konferensbidrag (refereegranskat)abstract
- Methane oxidation over palladium is of interest due to its clean catalytic combustion properties, forming only carbon dioxide and water. A successful palladium based catalyst will virtually eliminate polluting by products including unburned hydrocarbons, carbon monoxide, soot, and NOx. These potential benefits have have not been realized, in part due to catalyst deactivation over time. In this study we identify a relationship between catalyst deactivation and hydroxyl formation on Pd/Al2O3 and Pd/TiO2 catalyst surfaces, using time series FTIR spectroscopy. FTIR analysis suggests that catalyst deactivation is caused by growth of surface hydroxyls at temperatures below 450°C, and that that oxygen mobility on the catalyst surface may correlate with the degree of catalytic deactivation. We also examine the use of electrochemical oxygen pumping through a yttrium stabilized zirconia (YSZ) membrane as a possible method of delivering oxygen to the methane catalytic combustion reaction and improving catalytic conversion. We observe that applying a potential across a YSZ membrane can result in moderate increases in methane conversion, and that oxygen concentration in reactant gas mixture has a dramatic effect on catalytic activity. Our study will also address electrochemical oxygen transport to determine its rate limiting impact on the methane catalytic combustion reaction.
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