Characterization and reaction mechanism for the selective catalytic reduction of nitrogen oxides using natural and copper modified clay catalysts with ammonia as a reducing agent

Natural and copper modified clays have shown potential for the selective catalytic reduction (SCR) of nitrogen oxide (NO· ) with ammonia (NH₃). SCR is a state-of-the-art technique used for the abatement of nitrogen oxides (NO_x) produced at elevated temperatures such as in the combustion chambers of power plants. One of the main elements that increase the cost for the implementation of SCR is the catalyst. Therefore, finding an inexpensive and yet efficient catalyst for the reduction of NO_x constitutes a challenge. The potential for clays and SCR was explored and NO_x abatement was achieved. Elucidation of the catalytic reaction mechanism becomes important to optimize the catalyst composition and reaction conditions.; The Langmuir-Hinshelwood mechanism has been proposed for the reduction of NO· by NH₃ using copper exchanged clay. For this mechanism, the copper Lewis acid sites on the catalyst adsorb NH ₃. NO· is sorbed on sites that are adjacent to NH₃. This arrangement on the clay surface provides the necessary orbital symmetry that allows the reaction between the two molecules to form N₂. Copper oxide is responsible for enhanced catalytic activity, however, there is an optimum amount of copper loading. This suggests that besides the copper oxide, the clay structure is also important in the reaction and the charge density becomes crucial in this respect. Copper modified Bentonite clay was an efficient catalyst when tested under real effluent conditions at the power plant. Natural regional clays without chemical modification have catalytic activity for NO· abatement.