Low-Temperature NH ₃ Storage, Isothermal Desorption, Reactive Consumption, and Thermal Release from Cu-SSZ-13 and V ₂ O ₅ -WO ₃ /TiO ₂ Selective Catalytic Reduction Catalysts

Worldwide, regulations continue to drive reductions in brake-specific emissions of nitric oxide (NO) and nitrogen dioxide (NO₂) from on-highway and nonroad diesel engines. NO_x, formed as a byproduct of the combustion of fossil fuels (e.g., natural gas, gasoline, diesel, etc.), can be converted to dinitrogen (N₂) through ammonia (NH₃) selective catalytic reduction (SCR). In this study, we closely examine the low-temperature storage, isothermal desorption, reactive consumption, and thermal release of NH₃ on commercial Cu-SSZ-13 and V₂O₅-WO₃/TiO₂ SCR catalysts. Catalyst core-reactor, N₂ adsorption (BET) surface area, and in-situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) experiments are utilized to investigate the fundamental chemical processes relevant to low-temperature (T < 250°C) NH₃ SCR. Results show that NH₃ stored at low-temperature continuously, yet slowly releases from the SCR catalysts, and that nearly all of the weakly bound NH₃ stored on Cu²⁺ sites of the Cu-SSZ-13 catalyst will isothermally desorb from the catalyst in the absence of NO_x. However, in the presence of NO_x, a large fraction of this weakly bound NH₃ will react with NO_x, contributing to the total NO_x conversion of the catalyst. The authors anticipate that the results presented herein can benefit the research communities’ efforts to reduce NO_x emissions in comparison to today’s regulated limits by improving the understanding of critical low temperature chemical processes.