The topics covered in this overview of zeolite catalysts in deN2O and deNOx processes are
direct decompositions, and selective (using NH3), or semi-selective (using paraffins and olefins),
reductions. To identify a process, notation including the reducing agent as well as the
nitrogen oxide processed is used in the text, e.g., NH3-SCR-N2O is used to identify a process
of reduction of nitrous oxide by ammonia. The material is organized according to the metal
present in the zeolite but, as will be shown, there is very broad literature on the use of materials
with two or more metallic components, and these will be summarized separately. We
attempt to stress the practical aspects of zeolite-based catalysts, and, accordingly, the systems
with basic restrictions for use under real conditions are presented to a limited extent, with the
aim only to show the history of the progress in the field.
Process expenses are naturally among the important aspects of the environmental catalysis.
This aspect is less important for laboratory research but could be decisive for the success of the
technology, as the price of the zeolite itself is well above the price of common oxide supports.
We could mention here a very cost-effective solution proposing the use of a waste zeolite-type
FCC catalyst as early as 1987 [1]. The proposed catalytic systems mostly rely on synthetic zeolites,
nevertheless, natural zeolites were also proposed, but without real success [2].