Acceleration of Fast-SCR Reaction by Eliminating "the Ammonia Blocking Effect"

Electricity, e-fuel and H2 are considered important recent and future sources of energy for heavy-duty vehicles. Heavy-duty battery electric vehicles (BEV) have many technical challenges. Therefore, internal combustion engines (ICE) powered by e-fuel and hydrogen can be used as an alternative to batteries in heavy-duty trucks. Selective catalytic reduction (SCR) systems are necessary for achieving the goals of zero-emission internal combustion engines that use e-fuel or H2 as a fuel. The Japanese automotive industry mainly utilizes Cu-Zeolite-based SCR catalysts since vanadium-based catalysts have been difficult to be used to prevent the release of vanadium into the atmosphere due to the relatively low evaporation temperature. This study investigated whether improving the conversion rate by pulsing the NH3 supply was possible. Experiments were conducted in a mini-reactor with an inflow of simulated exhaust gas to examine the effect of the pulse amplitude, frequency, and duty ratio on the conversion rate when an NH3 pulse supply was applied to a test piece Cu-chabazite catalyst. The results of the reactor experiment were compared with numerical simulations that considered the detailed surface reaction processes on the catalyst. The experimental results showed that purification of NOx at low temperatures (200°C) improved from 45% to 62% by providing a pulsed supply of reducing agent (NH3) rather than a continuous supply. During the time when the pulse supply was off, the decomposition of ammonium nitrate (NH4NO3) was promoted, enhancing the conversion rate of NOx. The results of the simulations demonstrated that the gas concentrations and conversion rate in the catalyst and unique phenomena at low temperatures, such as the formation and decomposition of NH4NO3 and the ammonia-blocking effect, could be accurately reproduced and simulated.