Mass transfer of multi-pollutants over titania-based SCR catalyst: A molecular dynamics study

Mass transfer can significantly affect the SCR process which is designed for NOx removal. However, it is still challenging to characterize the transport of gaseous species involved in the process, especially at nano-scale. This work probes into the application of non-equilibrium molecular dynamics (NEMD) simulations to study the mass transfer of multi-pollutants over a titania-based catalyst. A dual control-volume (DCV) model was proposed to simulate transport of typical gaseous molecules (e.g. NO, NH3 and SO2). The impacts of temperature, pore width, hydroxyl sites and competitive diffusion on diffusivity of objective molecules were studied in details. The results showed that temperature and surface sites could affect NH3 more significantly than NO and SO2, yet the influence of surface sites was strongly size-dependent. The reduction in NH3 diffusivity caused by the presence of surface sites decreased from 32.37 % to 2.97 % when the pore width grows from 25 angstrom to 75 angstrom. The competitive transport between NH3 and SO2 has also mitigated the impacts of surface sites on both molecules.

Automated summary

Mass transfer has a significant impact on the NOx removal process in SCR, but characterizing the transport of gaseous species involved in the process at the nano-scale remains challenging. This study investigates the use of non-equilibrium molecular dynamics simulations to study the mass transfer of multi-pollutants over a titania-based catalyst. A dual control-volume model is proposed to simulate the transport of typical gaseous molecules, and the effects of temperature, pore width, hydroxyl sites, and competitive diffusion on diffusivity are studied. The results show that temperature and surface sites have a greater impact on NH3 than NO and SO2, with the influence of surface sites strongly dependent on size.