Catalysts based on tin and beta zeolite for the reduction of NOx under lean conditions in the presence of water

The catalytic performance of catalysts based on beta zeolite and tin for the NO reduction under lean burn conditions is discussed. The tin has been incorporated in the catalyst by different ways: in the zeolite framework, ion exchanged and in a physical mixture with the zeolite. The best results are obtained with a physical mixture of tin dioxide and the acid zeolite. The activity of this system has been improved by adding a second metal such as manganese or copper. At high oxygen concentration and using a catalyst formed by a physical mixture of Mn2O3, SnO2 and H-BEA, a 60% NO conversion, in presence of 14% of oxygen, has been obtained. These results suggest that the physical mixtures of metals with zeolites could be an interesting and inexpensive way to prepare active catalysts for this reaction. The role of the zeolite and the metal centers is discussed along the text.