Appraisal of a De-NOx System Based on H2 for Light-Duty Diesel Engine Vehicles

The present paper describes a novel, fully integrated after-treatment system based on the use of hydrogen for de-NOx purposes, designed for light-duty diesel engine applications. Hydrogen is generated by an autothermal reformer, placed as a bypass unit of the close-coupled DOC and DPF, and it promotes an NOx reduction in a specific catalytic converter in the under-floor position. The results of the tests on commercial reforming catalysts and on H-2-selected catalytic reductions (SCR) perovskite catalysts that were synthesized by our group are presented. The best catalyst, on the basis of TPRe activity tests, was La0.8Sr0.2Fe0.9Pd0.1O3. At a lab-scale, the fuel penalty of the system is around 4% for an NOx to N-2 conversion of 60%, under the best operating conditions. T-50 is very low (150 degrees C) compared to other de-NOx strategies. The system was then integrated on board a vehicle, and several testing protocols were performed (NEDC2000 cycle, stationary driving conditions on the roller test bench, and real driving conditions on the road). It has been demonstrated that the system is able to work independently in many driving conditions and that the reforming reaction can be effectively controlled and maintained. The NOx emissions were kept below Euro 6 levels, even though undesired CO and HC secondary emissions were produced. This performance was reached with a fuel penalty of 10%. Although this value is presently too high to envisage direct application on the market, it has been demonstrated that this technology is already fully functional on board a real vehicle, which encourages further refining research activity.