The control of nitrogen oxide (NOx) emissions remains one of the main problems surrounding diesel engines and poses a technological challenge that has yet to be resolved. In fact, this issue has been a huge point of contention over the last few years to the point where great limitations have been established not only on using but also on purchasing vehicles of this type.

Nitrogen oxides, generically (NOx), are produced by the high temperatures and pressures at which the engines function. Specifically, the fact that diesel engines work with high air/fuel ratios encourages a higher proportion of NOx in the vehicle’s exhaust gases. The nitrogen oxides emitted by exhaust systems are among the main causes of smog or polluting fog that forms over large cities or industrial hubs.

Efforts by automotive companies have focussed on developing efficient catalyst systems designed to control NOx emissions in diesel engines. So “this work has focussed on developing technologies that are capable of complying with the increasingly more stringent regulations being imposed, and at the same time, lowering the cost of the system and lengthening its service life”, said the UPV/EHU researcher Jon Ander Onrubia-Calvo.

 “The main function of catalytic converters in diesel vehicles is to convert the principal NOx pollutant into an inert compound that doesn’t have any consequences with respect to health or environmental pollution.  In this case, we try to turn the NOx into nitrogen, a major component of atmospheric air,” explained Onrubia.

As Jon Ander Onrubia went on to point out, “perovskites are a priori emerging as a good way of reducing the cost and prolonging the service life of catalytic converters based on noble metals, such as platinum, palladium or rhodium. The main drawback of these noble metals is that they are very expensive and also have low thermal stability. So if we can partly replace these metals by perovskites, we will be able to cut the cost of the system and extend its service life.”

The researcher stressed that “the results obtained in this work are opening up a new horizon in the development of new materials designed to remove NOx from the exhaust gases of diesel engines”. However, “the results reported are merely a starting point and broad scope for improvement still remains in the design of the materials as well as of the system. Enhanced knowledge of the reaction mechanisms of the chemical kinetics of the process will enable both the formulations and the catalytic converter to be redesigned more accurately. That way, it will be possible to develop improved alternatives that will enable diesel vehicles to adjust to the stringent emission standards governed by legislation,” said Jon Ander Onrubia.

Additional information

This research was conducted within the framework of the PhD thesis by Jon Ander Onrubia-Calvo (Bilbao, 1988), entitled Perovskite-based catalysts (Platinum free) as an economical alternative to Pt-based catalysts for NOx removal in diesel engines. His supervisors were Juan Ramón González-Velasco and Beñat Pereda-Ayo, Chemical Engineering lecturers at the Faculty of Science and Technology.