High N2 Selectivity Research Articles

In situ FTIR Study of the Reduction of NO by H2 in the Presence of O2 over Carbon-Film-Supported Pt Catalyst

In situ FTIR measurements suggest that the high N2 selectivity on platinum-loaded oxidized carbon film catalysts depends on the presence of surface nitrite compounds, which were found to be reaction intermediates.

Selective wet air oxidation of diluted aqueous ammonia solutions over co-precipitated transition metal-aluminium catalysts

Catalytic wet air oxidation of ammonia over a co-precipitated transition metal-aluminium catalyst was investigated. Copper-aluminium (Cu-Al-O) catalyst exhibited the highest activity and N2 selectivity among those prepared from Co, Fe, Mn, and Ni. 50% of 1500 ppm of ammonia could be removed from wastewater of pH 12 at 503 K under 2.0 MPa of air by using 4.0 g of catalyst without formation of toxic nitrogen containing compounds. Cu and Al ions were not found in solution after the reaction. It has been found that the catalytic performance of Cu-Al-O catalyst was strongly dependent on the preparation methods. The co-precipitated Cu-Al-O catalysts showed high N2 selectivity. The presence of CuO is concluded to promote the reaction and CuAl2O4 in bulk phase is needed to stabilize the catalyst.

The Nature of the Active Metal Surface of Catalysts for the Clean Combustion of Biogas Containing Ammonia

The nature of the active surface of supported metal catalysts for the clean combustion of ammonia-containing simulated biogas has been investigated to understand the very high N2 selectivity of some catalysts. A comparison of the activities of Al2O3-supported precious group metals has shown that under conventional operating conditions the fuel is fully combusted but NH3 is converted predominantly into NOx. In contrast, it is shown that it is possible by operating under O2-deficient conditions to attain essentially zero emissions of NOx with Rh- or Ir-based catalysts, whereas Pt or Pd gave markedly lower selectivities to N2. These variations in selectivity are attributed to the differences in the state of the metal surface during reaction. For Rh- and Ir-based catalysts it has been shown that under fuel-rich conditions, surface carbon, derived from the dissociative adsorption of CO, results in self-poisoning toward CO and H2 oxidation at low temperatures. However, at higher temperatures a preference toward methanation of the Cads is observed. It is thought that this surface reaction between the Cads and Hads scavenges both reductants so that Oads can react with NH3 in a highly specific manner, to give NOx. The NOx thus formed is subsequently reduced by reaction with excess CO to give N2. A model is presented that shows the way in which the chemistry of the surface of the active metal changes as the reaction parameters are varied.

Stabilization of CuZSM-5 NOx reduction catalysts with lanthanum

The effects of high temperature steam treatment on the activity and selectiv ity of CuZSM-5 catalysts for the selective catalytic reduction of NO with propene have been examined. Loss of activity and selectivity on steam treatment is due to framework dealumination of the zeolite, which causes migration of Cu out of the zeolite pores to the external surface. Pre-exchange of the zeolite with La3+ cations inhibits the dealumination, preventing migration of Cu to the surface and allowing the catalyst to retain high activity and N2 selectivity after steam treatment. The deactivation of the catalysts was monitored using X-ray powder diffraction, magic angle spinning27Al and29Si nuclear magnetic resonance, X-ray photoelectron spectroscopy and ion scattering spectroscopy.