Search

In the synthesis of iron-chelating ordered mesoporous nitrogen-functionalized carbon (Fe–OMC) catalysts, the removal of the silica template is a crucial and critical step. The silica removal method used today for the Fe–OMCs is based on the very toxic hydrofluoric acid (HF), which usage should be limited where possible. Therefore, the aim of this study is to establish a mild (user-friendly), yet efficient, etch method based on dilute sodium hydroxide (NaOH), which does not impair the catalytic performance of the catalyst, to replace the currently used HF method. A comparison between catalysts etched with HF versus NaOH was performed in order to gain understanding how the two etch methods influence the final catalysts in terms of electrochemical, structural and catalytic properties. The NaOH etch was found to successfully remove the silica template, and interestingly, also improve the catalytic performance. The improved activity is explained by a carbon activation process occurring in the catalyst treated with the NaOH etch. With these findings, we show that it is possible to remove the silica in a more user-friendly way and simultaneously increase the catalysts’ performance by activation of the carbon.

The highly oxygenated hydrocarbon triethylene glycol dimethyl ether or triglyme (CH3O-(C2H4O-)(3)CH3) was found to efficiently reduce NOx under lean conditions over Ag/Al2O3, but gave a low NOx conversion over Cu-ZSM-5. Furthermore, triglyme showed an extraordinary promoting effect when added together with propene as reducing agent for NOx over Ag/Al2O3 at low temperature. This is most likely due to that triglyme promotes the activation of propene.

Above 300 °C, gas phase reactions occur between dimethyl ether (DME), NO and O2 generating NO2. The influence of these reactions on DME-SCR was studied in a setup that decoupled the occurrence of gas phase reactions from catalyst temperature. NOx conversion decreased at 350 °C and increased at 250 °C due to less DME available and higher NCO conversion with NO2, respectively.

The influence of syntheses parameters of zeolite ZSM-5 on the lean NOx reduction activity and hydrothermal stability of Cu-ZSM-5 has been investigated. The hydrothermal stability of Cu-ZSM-5 was found to depend on the aluminium source used and on the presence of Ca(OH)2 in the synthesis mixture for ZSM-5.

Dimethyl ether (DME) is an interesting alternative fuel to diesel, but is not an efficient reductant in lean NO x conversion over typical diesel HC-SCR catalysts. Comparatively high deNO x activity was found over H-ZSM-5 in the presence of water, giving reduction of 28% NO and 37% NO2 respectively with a DME/NO x -ratio of 4.

The formation of solid solutions of cerium oxide with the oxides of calcium, manganese, or neodymium enhances the catalytic activity of cerium oxide for the total oxidation of methane, whereas solid solutions with lead oxide showed an opposite effect. Reasons for this are discussed in terms of oxygen vacancy concentrations and mobilities, local structure configurations, number of oxidation states of dopant, and electron transfer properties. The effects of increased oxygen ion mobility and a more beneficial local structure support the increased catalytic activity for the calcium- and neodymium-doped cerium oxide samples. In addition, a reduced energy for charge transfer from oxygen to cerium supports a higher activity for the calcium-doped sample. The activity data were fitted to an Arrhenius equation, and the apparent activation energies were found to be between 110 and 130 kJ/mol. The particle sizes and the BET areas of the samples were only little affected by the reactor runs, and none of the samples were subjected to phase changes.