The twin bogies of reducing vehicle mass and reducing tailpipe emissions are driving OEMs and their suppliers to develop solutions that achieve both goals. BASF recently unveiled a new catalyst technology aimed at light-duty diesel engines that the company claims is a significant step toward cleaner exhaust with lower mass, less complexity, and potentially lower cost.
BASF’s innovation consolidates the four major components of a typical diesel aftertreatment system—the De-NOx catalyst, diesel oxidation catalyst (DOC), soot filter, and the selective catalytic reduction (SCR) system—into two major elements: a DOC/lean-NOx trap (LNT) and an SCR catalyst integrated with the soot filter substrate.
The arrangement requires just two catalyst “bricks,” the substrates coated with precious-metal catalytic material that dramatically lower HC, CO, NOx, and particulate levels in the exhaust stream, prior to exiting the tailpipe. The design greatly simplifies the aftertreatment suite underneath the vehicle and reduces weight, according to Dr. Marius Vaarkamp, BASF’s Global Product Manager, Mobile Emissions Catalysts.
The DOC/LNT is a ceramic monolith with a catalyst coating. The SCR-on-filter is a “wall flow” ceramic monolith with a SCR catalyst coating. The DOC/LNT catalyst traps NOx under “lean” operating conditions. The trapped NOx is released from the catalyst when the engine operation is switched to “rich” conditions.
During “rich” regeneration, the NOx is converted to N2 (nitrogen), and NH3 (ammonia) is generated over the DOC/LNT and used by the SCR catalyst to remove excess NOx, while the filter removes particulate matter.
“The real innovation here, we believe, is we’ve found a way to generate the ammonia (urea) in situ—we do this with an LNT upstream of the SCR,” he explained in an AEI interview with the BASF team in mid-April.
Vehicles with smaller-displacement engines that do not require high levels of NOx conversion “may not require the SCR/filter brick, needing only the combined DOC/LNT,” noted Dr. Thomas Droege, Global Marketing Director in the Mobile Emissions Catalysts group.
Providing the capability to meet NOx emission standards without requiring the heavy, bulky urea tank, injector, control unit, wiring, and related mounting fitments offers OEMs a significant mass benefit, which will vary per vehicle application depending on engine displacement, Dr. Vaarkamp said. Reduced system mass helps improve vehicle fuel efficiency.
The first vehicle to feature BASF’s two-brick aftertreatment system is Hyundai’s i-Flow concept car, which debuted last month at the Geneva Auto Salon. The i-Flow showcases BASF and Hyundai’s collaboration on advanced material applications across the vehicle. The two companies focused on key areas that impact overall operating efficiency, packaging, and emissions reduction.
“This project was a great way to look at the emission-reduction challenges comprehensively with one of our OEM partners, and to optimize the actual system at all levels, from the engine intake through the tailpipe,” Dr. Vaarkamp noted. “We saw the lightweighting and downsizing trend coming, and we prepared ourselves well for these market challenges—to combine the functionality and take it to a market situation. Hyundai was very receptive.”
BASF’s engineering interface with Hyundai is via the company’s South Korea joint venture, Heesung Catalyst Co. BASF began its first experiments aimed at consolidating subsystem functionality around 2000-2001.
“A number of things enabled our R&D group and materials engineers to accomplish this,” Dr. Vaarkamp explained. “The first was our analytical capability, to really understand the individual components, and the catalysis piece, on a fundamental level. In the SCR-on-filter piece, we made really great steps forward in the stability of the SCR catalyst.”
Among the material innovations that enabled BASF’s two-brick architecture was development of what Dr. Mikhail Rodkin, Vice President of Catalyst R&D, described as “an absolutely new SCR catalyst,” the manufacturing of which is very complicated, he said.
On the LNT side, Dr. Rodkin’s team also devised an all-new catalyst composition. “There are new materials to ensure the LNT doesn’t only reduce NOx in certain parts of the drive cycle but also generates ammonia in the appropriate amount to actually help the SCR work correctly. There are material innovations in both areas,” he noted.
The BASF team is satisfied with the two-brick system’s durability and effectiveness as far as it can be tested in the laboratory environment, said Dr. Vaarkamp. He noted that BASF is not unique in developing on-board ammonia generation in an LNT-based system, citing efforts by Honda and Ford in this area.
“As our collaboration with Hyundai indicates, we’re engaging our customers at this point,” he explained. “Getting this program to a point of sufficient engineering and customer confidence—that’s the next step.”