Direct Catalytic Decomposition Research Articles

Catalytic performances of CuGa and CuSn binary oxide catalysts towards N2O decomposition and reduction

Direct catalytic decomposition of N2O in inert and oxidative atmosphere was investigated over two series of binary oxide catalysts containing CuO coupled with Ga2O3 or SnO2 dispersed over a silica-alumina support (CuGa/SA and CuSn/SA series catalysts). The activity for N2O decomposition in the absence of oxygen was between 0.1 and 0.2 μmol gcat s−1 in the 500–600 °C interval over the CuSn/SA series catalysts with conversion between 80 and 90%. Lower activities with larger differences were observed within the CuGa/SA series catalysts. The presence of oxygen in the feed (O2/N2O ratio up to 20:1) did not affect the activity of the CuGa/SA series while a light decrease of activity could be noticed on the CuSn/SA series. The effect of methane reductant in the selective N2O reduction (N2O-SCR) was tested. On the CuGa/SA series samples, the best reaction selectivity was observed.

Direct catalytic decomposition of NO with Cu–ZSM-5: A DFT–ONIOM study

ONIOM calculations for the direct catalytic decomposition mechanism of NO 2 and NO by Cu–ZSM-5 were carried out. In two layer calculations, Density Functional Theory and Universal Force Field were employed for the high and low level models, respectively. Δ H° and Δ G° evaluations were performed in order to determine the thermodynamically more favored way for catalytic decomposition of NO 2 and NO. The results show that a novel copper κ 2 mononitrosyl species (Z– 2Cu–κ 2NO) is in equilibrium with the Z– 2CuNO and Z– 2CuON species. According to our results, the Z– 2Cu–κ 2NO species is the intermediary key of the direct catalytic decomposition mechanism of NO 2 and NO by Cu–ZSM-5.

Direct N 2O decomposition over ex-framework FeMFI catalysts. Role of extra-framework species

Extra-framework iron species in FeMFI prepared via an ex-framework route are essential for the formation of reactive oxygen species in direct catalytic decomposition of N 2O, while Lewis or Brønsted acid sites play a minor role in this reaction.

In situ infrared study of catalytic decomposition of NO on carbon-supported Rh and Pd catalysts

The direct catalytic decomposition of NO on Rh/Al 2O 3, Rh/C, Pd/Al 2O 3, and Pd/C catalysts was investigated at 673 K by in situ infrared (IR) coupled with mass spectroscopy (MS). NO decomposition on these catalysts initially produced N 2 and adsorbed oxygen. Different catalysts exhibit different capabilities for manipulating adsorbed oxygen. Rh/Al 2O 3 shows little activity for oxygen desorption, resulting in loss of catalyst activity; Rh/C shows the ability for promoting the adsorbed oxygen–carbon reaction, removing oxygen in the form of CO 2; Pd/Al 2O 3 shows some activity for O 2 desorption. Use of carbon as a support for Pd promotes O 2 desorption, resulting in improvement of NO decomposition activity. The in situ IR results provide evidence to support the behavior of adsorbed oxygen on carbon-supported Rh and Pd catalysts.

Reduction of nitrogen oxides in flue gases

In recent years there has been an unprecedented growth and development in flue gas control technologies capable of reducing NO x emissions to the low levels required by current legislation. Major post-combustion technologies include selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). The current status of these technologies is summarised, and the advantages and disadvantages of both methods are reviewed. SCR offers the advantage of greater NO x reduction and has therefore been widely adopted in industrialised countries with stringent emission limits, while SNCR requires lower capital costs and is increasingly being applied by industries in developing countries. Other techniques, such as hydrocarbon-selective catalytic reduction (HC-SCR) and direct catalytic decomposition of NO x, although showing some promise in laboratory experiments, are still not commercially viable.