Biofuel Impacts on Cu-Zeolite Emissions Control Catalysis

Todd J. Toops

Oak Ridge National Laboratory

One way to decarbonize the transportation industry is to adopt renewable low-lifecycle carbon fuels (LLCF), especially relevant for hard to electrify sectors—heavy duty (HD) trucks, marine, rail, and off-road. The most promising LLCF candidates are typically derived from plant-based sources which all contain phosphorous (P) and is known to impact emissions control devices from earlier P-containing lubricant studies [1]. Biodiesel is one such fuel that has a specified P limitation of 10 ppm [2] and it also has a newly defined combined limit of 4 ppm for total metals on Ca, Mg, Na, and K metals. Although some studies have been performed on these metals [3], an improved understanding of their interactions with zeolites is needed. Additionally, understanding how biofuel-based P differs from lubricant sources is important. The emissions control systems and regulations can vary significantly for these lean combustion engines, especially as emissions regulations get more stringent [4], but generally diesel oxidation catalysts (DOCs), Cu-zeolite based selective NOx reduction catalysts (SCR), and diesel particulate filters (DPFs) will be required either in current or future systems. With these considerations in mind two systematic studies were initiated to expose emissions control systems to either fuel-borne P or Na/Ca/K metals using a diesel genset followed by flow reactor evaluations to investigate the impact.

A range of emissions control configurations were deployed in these studies. The first is relevant to the light duty (LD) with the DOC first, followed by two SCR monoliths, and finally the DPF: DOC->SCR->DPF. The second is relevant to current HD configurations with the SCR last: DOC->DPF->SCR. A third configuration was introduced for future HD configurations considerations where an upstream light-off SCR (LO-SCR) catalyst is expected to be needed to aid in low temperature NOx conversion: LO-SCR->DOC->DPF->SCR. Accelerated aging was performed with 7-28x acceleration factors.

A range of behaviors were observed in the results with some very unexpected behavior and some critical material transformations. For the metal-exposed SCR in the LD-configuration, DOC->SCR->DPF, the Na and K showed deactivation in the front portion of the SCR and resulted in substitution for the Cu in the zeolite framework.