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Where and when?
Catalysts usually have two basic components: the base and the
active phase. The base usually involves a porous solid (in order to
achieve the maximum surface for reaction). As regards the active phase,
this is the compound that initiates the reaction, normally a metal
such as platinum or palladium or, as in the case of the Leioa research,
a zeolite.
In the process of catalysis, the contaminant gas enters the pores
of the catalyst and it is there that it reacts with the active phase.
Water, carbon dioxide and a halogenated compound are produced as a
result of this reaction. This last product is subsequently neutralised
in a shower of caustic soda. Thus, only H20 and CO2 are liberated into
the atmosphere.
In this case the researchers worked with zeolite catalysts and the
results obtained showed that the canals present within the structure
of the zeolites are of great importance in the reaction.
Zeolites may have parallel or intercrossing; and it would seem that
the zeolites with the second structure are better for this type of
reaction. This is because an obstacle in a zeolite structure of
parallel canals will prevent the gas passing through while this does
not happen in the case of zeolites with a structure of intercrossing
canals.
The kinetics of the reaction
But apart from the type of canal there are other characteristics
that influence the reaction. Very important, for example, is the
amount of contaminant gas, the quantity of catalyst used and the
temperature of combustion. Two more factors are the kinetics of the
reaction and its evolution.
Temperature, in fact, is one of the most important parameters. The
lower the temperature of combustion, the less will be the energy spent.
The researchers are currently trying to establish the durability of
the catalysts, i.e. to ascertain when active phase compound has to be
replaced or renewed so that the "cleaning" of the volatile organic
compounds continues to operate. |
