Filip Acke

Comparison between ammonia and propene as the reducing agent in the selective catalytic reduction of NO under lean conditions over Pt black

The catalytic activity of Pt black towards the reduction of NO under lean conditions is examined. Ammonia and propene are tested as reducing agents. A scrambling between nitrogens is observed in the formation of N2 and N2O for NH3. For C3H6, a reduction of NO to mainly N2O is found. A minor formation of N2 is only observed for high C3H6 concentrations. The role of NO2 as an intermediate in the reduction of NO is examined by using a feed gas mixture containing NO2, as well as by studying the catalytic activity of Pt black towards the NO-O2 and NO2-O2 reactions. No effect is observed in the maximum NOx conversion for C3H6 whereas for NH3 a decreased activity is found. The presented results are put in perspective of the reaction mechanisms proposed in the literature.

Influence of the platinum-support interaction on the direct reduction of NOx under lean conditions

Catalysts containing Pt supported on SiC, Al2O3 and ZSM-5 were prepared and studied for NOx reduction by C3H6 in Oz excess under transient (temperature ramps) and steady-state conditions. The maximum NOx reduction activity in the heating ramp experiments was similar for Pt/SiC and Pt/ZSM-5, while Pt/Al2O3 showed higher maximum activity. Both N-2 and N2O formation was observed for all catalysts, although the respective amounts varied with the investigated system. Highest Nz selectivity was observed for Pt/Al2O3. When the NOx reduction activity was studied under steady-state conditions the activity of Pt/Al2O3 decreased substantially (mainly due to a loss in N-2 production). Pt/ZSM-5 became somewhat more selective towards Na production whereas the activity and selectivity of Pt/SiC remained at about the same values as far the heating ramp experiments. Adsorbed species on the surface of the different catalysts were investigated using in-situ FTIR in order to obtain information about the reaction mechanisms. The adsorption of species on Pt/SiC was negligible, while a number of absorption bands were observed for Pt/Al2O3 (N and C containing species, and -NCO) and Pt/ZSM-5 (HC).

Zeolite supported Pt catalysts for reduction of NO under oxygen excess: a comparison of C3H6, HNCO and NH3 as reducing agents

The effect of the zeolite SiO2/Al2O3 ratio of ZSM-5 supported Pt catalysts on the reduction of NO under oxygen excess has been investigated. The activity and selectivity of three reducing agents were compared, i.e. C3H6, HNCO and NH3. The maximum NO reduction with both C3H6 and HNCO as the reducing agent was affected by the SiO2/Al2O3 ratio of the support. Although no effect was observed on the maximum NO reduction for NH3, the yields of Nz and N2O were affected. The results are put in perspective of reaction mechanisms proposed in the literature.

Differences in reaction mechanisms for the selective reduction of NO under oxygen excess over Pt based catalysts using propane or propene as the reducing agent

The catalytic activity of Pt black towards the selective reduction of nitrogen oxides by propane under oxygen excess has been investigated and the results are put in perspective of reaction mechanisms as proposed in the literature. The absence of any NOx reduction provides further evidence for the active role of the Pt support in the selective reduction of nitrogen oxides by propane.

Transition metal complexes with (NO)(3)(-) anions

Density functional theory calculations are performed to determine structures, stabilities, and characteristic vibrational frequencies for metal complexes with nitric oxide trimer ligands. The study emphasizes the possible crucial importance of the 3.0 eV first ionization energy of the (NO)3− anion. Metal complexes with the composition M[(NO)3]2 are considered, where M is Mg, Ni, Cu, and Zn. Properties of the Cu(NO)3 complex are evaluated for reference. Possible technological importance to catalysis and drug delivery systems is implied.

Activation energy for calcination of lime stone by means of a temperature programmed reaction technique

Calcination of lime stone is considered in order to demonstrate the performance of a temperature programmed reaction technique to determine apparent activation energies for decomposition in the solid state. Influences of sample weight, particle size and sweep gas (He and Ar) are discussed, and comparisons made with thermogravimetric studies in the literature.

Activation energy of calcination by means of a temperature programmed reaction technique

Calcination of limestone is considered to demonstrate the performance of a temperature programmed reaction technique to determine apparent activation energies for decomposition in the solid state. Influences of sample weight, particle size and sweep gas (He and Ar) are discussed, and connections are made to thermogravimetry studies in the literature.