Abstract
Airborne pollutants from the combustion of fossil fuels are a global problem. Emission of nitrogen oxides (NO{sub x}) is increasing with the worldwide increase in the use of energy. Atmospheric and photochemical reactions link nitrogen oxides to hydrocarbons and tropospheric ozone. The emission of NO{sub x} has to be tackled urgently in order to limit the harmful effects of anthropogenic activity on the environment. The subject of this thesis is catalytic nitrogen oxide abatement through direct decomposition and reduction by methane over ion-exchanged zeolite ZSM5. The work covers catalytic conversion and surface intermediates, including correlations with the level of exchanged Cu{sup 2+} cations and Ni{sup 2+} or Pd{sup 2+} co-cations. Special attention is given to the aluminium content of the support and changes in structural parameters. It was found that NO{sub x} conversion over cation-exchanged ZSM5 is strongly influenced by the ion-exchange procedure and by the above material parameters. Characterization of Cu-ZSM5 reveals that approximately two molecules of water per Cu{sup 2+} ion desorb at temperatures between 150 and 350 Deg C, in addition to the conventional dehydration at lower temperatures. The desorbed water comes from the decomposition of Cu(OH){sub 2}. Decomposition of hydroxylated copper ions results in the formation
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Citation Formats
Ganemi, Bager.
Zeolite ZSM5 catalysts for abatement of nitrogen oxide.
Sweden: N. p.,
1999.
Web.
Ganemi, Bager.
Zeolite ZSM5 catalysts for abatement of nitrogen oxide.
Sweden.
Ganemi, Bager.
1999.
"Zeolite ZSM5 catalysts for abatement of nitrogen oxide."
Sweden.
@misc{etde_20104236,
title = {Zeolite ZSM5 catalysts for abatement of nitrogen oxide}
author = {Ganemi, Bager}
abstractNote = {Airborne pollutants from the combustion of fossil fuels are a global problem. Emission of nitrogen oxides (NO{sub x}) is increasing with the worldwide increase in the use of energy. Atmospheric and photochemical reactions link nitrogen oxides to hydrocarbons and tropospheric ozone. The emission of NO{sub x} has to be tackled urgently in order to limit the harmful effects of anthropogenic activity on the environment. The subject of this thesis is catalytic nitrogen oxide abatement through direct decomposition and reduction by methane over ion-exchanged zeolite ZSM5. The work covers catalytic conversion and surface intermediates, including correlations with the level of exchanged Cu{sup 2+} cations and Ni{sup 2+} or Pd{sup 2+} co-cations. Special attention is given to the aluminium content of the support and changes in structural parameters. It was found that NO{sub x} conversion over cation-exchanged ZSM5 is strongly influenced by the ion-exchange procedure and by the above material parameters. Characterization of Cu-ZSM5 reveals that approximately two molecules of water per Cu{sup 2+} ion desorb at temperatures between 150 and 350 Deg C, in addition to the conventional dehydration at lower temperatures. The desorbed water comes from the decomposition of Cu(OH){sub 2}. Decomposition of hydroxylated copper ions results in the formation Of Cu{sup 2+}-O-Cu{sup 2+} dimers, which are suggested to be the active sites for catalytic decomposition of NO. Acid sites are important for the dispersion of copper ions on the catalyst surface. Acid sites are also important for the interaction between copper species and the zeolite. Increased acidity leads to a stronger interaction between the exchanged cation and the framework, i.e. the exchanged cations become more resistant to mobility. The stronger bond between the exchanged cations and lattice oxygen also prevents dealumination of the catalyst and decreases the thermal expansion at higher temperatures. The temperature of dehydroxylation of acid sites on H-ZSM5 overlaps with the light-off temperature for NO reduction over Cu-ZSM5. Bridged nitrato groups ligated to Cu{sup 2+}-O-Cu{sup 2+} dimers act as site blockers below the light-off temperature. At the light-off temperature zeolite lattice vibrations destabilize surface nitrates and open the sites for catalytic reactions via short-lived N{sub 2}O{sub 3} intermediates. The same lattice movements decompose OH-groups on the H-form of the zeolite and it was suggested that zeolite ZSM5 should be noted mainly for its flexibility rather than its narrow channels with strong electrostatic fields or metal exchange sites with open coordination.}
place = {Sweden}
year = {1999}
month = {Jul}
}
title = {Zeolite ZSM5 catalysts for abatement of nitrogen oxide}
author = {Ganemi, Bager}
abstractNote = {Airborne pollutants from the combustion of fossil fuels are a global problem. Emission of nitrogen oxides (NO{sub x}) is increasing with the worldwide increase in the use of energy. Atmospheric and photochemical reactions link nitrogen oxides to hydrocarbons and tropospheric ozone. The emission of NO{sub x} has to be tackled urgently in order to limit the harmful effects of anthropogenic activity on the environment. The subject of this thesis is catalytic nitrogen oxide abatement through direct decomposition and reduction by methane over ion-exchanged zeolite ZSM5. The work covers catalytic conversion and surface intermediates, including correlations with the level of exchanged Cu{sup 2+} cations and Ni{sup 2+} or Pd{sup 2+} co-cations. Special attention is given to the aluminium content of the support and changes in structural parameters. It was found that NO{sub x} conversion over cation-exchanged ZSM5 is strongly influenced by the ion-exchange procedure and by the above material parameters. Characterization of Cu-ZSM5 reveals that approximately two molecules of water per Cu{sup 2+} ion desorb at temperatures between 150 and 350 Deg C, in addition to the conventional dehydration at lower temperatures. The desorbed water comes from the decomposition of Cu(OH){sub 2}. Decomposition of hydroxylated copper ions results in the formation Of Cu{sup 2+}-O-Cu{sup 2+} dimers, which are suggested to be the active sites for catalytic decomposition of NO. Acid sites are important for the dispersion of copper ions on the catalyst surface. Acid sites are also important for the interaction between copper species and the zeolite. Increased acidity leads to a stronger interaction between the exchanged cation and the framework, i.e. the exchanged cations become more resistant to mobility. The stronger bond between the exchanged cations and lattice oxygen also prevents dealumination of the catalyst and decreases the thermal expansion at higher temperatures. The temperature of dehydroxylation of acid sites on H-ZSM5 overlaps with the light-off temperature for NO reduction over Cu-ZSM5. Bridged nitrato groups ligated to Cu{sup 2+}-O-Cu{sup 2+} dimers act as site blockers below the light-off temperature. At the light-off temperature zeolite lattice vibrations destabilize surface nitrates and open the sites for catalytic reactions via short-lived N{sub 2}O{sub 3} intermediates. The same lattice movements decompose OH-groups on the H-form of the zeolite and it was suggested that zeolite ZSM5 should be noted mainly for its flexibility rather than its narrow channels with strong electrostatic fields or metal exchange sites with open coordination.}
place = {Sweden}
year = {1999}
month = {Jul}
}