The abatement of nitric oxide emissions: new trends in the field

The Nitric oxides (NOx), a group that includes nitrogen oxide (NO), nitrogen dioxide (NO2) and nitrous oxide (N2O), are nowadays considered as one of the most dangerous air pollutants. They are known for their contribution to the greenhouse effect, and they take part in the photochemical reactions that cause acid rain and smog. These pollutants have also an important role in the eutrophication of lakes and rivers, and they are equally dangerous for human health as they can damage the respiratory system.
The  European Environmental Agency, had indicated in 2009 in  its status report  that the aggregate of the 27 European countries projections for nitric oxides emissions will be 6 % above the Directive ceilings. Looking at each country individually, we can see that France and Spain get the worst scores, releasing 300 and 400 Gg of nitric oxides above the ceilings established by the agency.
Some questions to Emilio Muñoz, PhD graduate on Chemical Engineering at the University of Oviedo (Spain), who has been working on the catalytic abatement of these pollutants:

Is the release of nitric oxides to the atmosphere finally becoming a major concern for the environmental agencies?
Yes, it is. Some new regulations are being introduced in order to diminish the NOx emissions. The nitrite oxides are highly toxic atmosphere pollutants. They are also responsible for the photochemical smog.

What are the main highlights of your research?
My research is nowadays focused on the optimization of one of the most spread techniques for the abatement of these pollutants.
The most common technique is the selective catalytic reduction (SCR), in which a reducing agent such as ammonia is added to the flue gas and a catalyst enhances the reduction of NOx to nitrogen and water.

Is there any other techniques?
SCR is one of the three major techniques used for NOx abatement, together with lean NOx traps and non-catalytic NOx removal.
Regarding the SCR, some guidelines are focused on the reducing agent, since ammonia is an atmospheric pollutant as well as the nitric oxides. Hydrocarbons and hydrogen are nowadays studied as a possible alternative to ammonia based compounds. Of course, using hydrogen is much more expensive that ammonia, but it could be more interesting, because ammonia can be an even more dangerous pollutant than nitrate oxides.

What kind of challenges do you face when experimenting with those reactions?
I guess that the issues that we confront in our field are similar to those faced in other chemical engineering fields. The choices in the reaction mechanisms, the reactor design, the operation costs… these are some of the key parameters that should be taken into account.
One of the actual trends is to try to obtain a great conversion at lower temperatures, so the research is focus on the development of new catalysts that could help us to achieve this goal.