Microwave-driven adsorption-desorption for NOx removal: A simplistic approach

Controlling transport-derived emissions of NOx is a huge challenge to meet stringent regulatory standards that force improvements in NOx abatement technologies. This study demonstrates an environmentally friendly process of NOx removal using microwave (MW) heating assisted adsorption-desorption method using Cu-ZSM-5 as well as Al 2 O 3 supported BaO and/or Pt. Outstanding benefits of MW irradiation, allows to overcome high activation energy for NO decomposition and tolerance against high temperatures by shortening the duration, resulted excellent NOx adsorption capacity (Cu-ZSM-5: 199 µmol g -1 ; Pt-BaO/Al 2 O 3 : 158 µmol g -1 ) in the presence of excess air at 200 ℃. Furthermore, temperature ramped NOx desorption was also explored. Contextually, an unprecedented adsorption and desorption behavior of NOx on Pt-BaO/Al 2 O 3 was highlighted and investigated thoroughly. For NOx adsorption, interpretation of experimental results confirmed the necessity of closeness between Pt and Ba to produce surface nitrate (NO 3 - ), which was ascertained by STEM and in-situ DRIFTS studies. Assessing the desorption (NOx-TPD) process, either under MW condition or conventional heating (CH), reflected same NOx release pattern but duration of the process was considerably shorter for MW. The faster desorption associated with beneficial effect of selective MW heating, reduces energy penalty of catalytic regeneration, and enhances adsorption capacity. Interestingly, excellent recyclability of Pt-BaO/Al 2 O 3 , despite the difference between adsorption and desorption amount was evident. All these results articulated the possibility of NOx decomposition under rapid MW heating. Finally, this study discloses an opportunity to develop an advanced NOx mitigating technology utilizing environmentally friendly MW technique. • Microwave-assisted NOx adsorption-desorption was tested on different catalysts. • Selective microwave heating offers high adsorption capacity in excess air at 200 ℃. • An unprecedented adsorption-desorption behavior of Pt-Ba/Al 2 O 3 was explained. • Significant impact of microwave on faster and efficient NOx desorption revealed.