kitNano-SCR – Development of nanoscale SCR catalysts for combined NOx and soot reduction in diesel engines
The Nano-SCR project was dedicated to developing diesel engine particulate filters provided with nanoscale catalysts for NOx reduction. In addition to stressing the requirement of manufacturing smallest possible catalysts, emphasis was placed on the systems’ aging resistance, the space- and weight-saving properties of the new generation of filter/catalyst systems, and an easier installation in diesel vehicles or systems for the after-treatment of exhausts.
Within the joint project Nano-SCR, NanoScape has developed and implemented novel nanoscale zeolite catalysts for reduction of nitrogen oxides (NOx, NO, NO2) from diesel exhausts. A novel catalyst which can be applied directly from aqueous suspensions in very thin layers to surfaces was manufactured upon development and charging of nanoscale zeolites with metal ions. The catalyst suspensions are scalable and can be produced without agglomeration. The SCR properties of these suspensions can be compared to those of standard catalysts. Besides, diverse metal ions can be integrated as early as in the liquid phase.
In the course of the project, NANO-X proved that aqueous coating systems with mixed oxides functioning as SRC catalysts on sinter metals provide good NOx conversion rates starting from 350°C and, in particular, from 450°C. Materials most active under Fast-SCR-conditions convert 50 percent of the nitrogen oxides at 350°C and 70 to 80 percent at 450°C. Doping with cerium oxide of <1mol percent cerium or mixed oxide causes significant improvement of the activity. The geometry of the sintered-metal substrate clearly affects the catalytic activity of mixed-oxide coatings that can be considerably influenced by the application and drying parameters of the coating solutions.
HJS had defined the performance specifications for coating suspensions, had coated porous sintered metal with the newly developed nano-suspensions and characterised the respective result, and had produced test filters to be tested on the engine test stand. Since the new nano-suspensions showed good adhesion with the metallic substrate, no catalyst particles are expected to be released during operation. Most engine test stand experiments were found to yield results comparable to the NOx reduction results of the synthesis gas test stand.
At TU Bergakademie Freiberg, a large number of SCR materials were screened within Nano-SCR. Besides, promising materials were comprehensively characterised and tested for their aging stability. Methods to enable a knowledge-based design of cerium oxide-containing catalysts were developed based on UV/VIS spectroscopy. Moreover, the mechanism of SCR reactions on nanoscale BEA zeolites was determined successfully by means of spectroscopic methods.
