Low temperature catalytic NO oxidation over microporous materials

It is shown that NO oxidation is catalyzed by chabazite zeolites in the proton (H+), sodium (Na+) and siliceous forms, by microporous carbons and by the metal-organic framework (MOF) material Basolite A100 (R) at temperatures between 298 K and 423 K. Reaction orders at low conversion for NO and O-2 are 2 and 1, as observed for the gas-phase reaction. At higher conversion and low temperatures, the rate decreases because of the presence of various NxOy species within the pores of the materials. Catalytic rates decrease with increasing temperature and yield negative apparent activation energies (-24.9 to -37.5 kJ mol(-1)). The catalytic properties of the samples are attributed to their ability to stabilize a [N2O4](double dagger) transition state within the micropores through van der Waals forces. Na-SSZ-13 samples exhibit faster catalytic rates than siliceous. chabazite due to the additional presence of electrostatic forces stabilizing the transition state. An enhancement of catalytic rates on H-SSZ-13 is also observed but is the result of more complex interactions due to the formation of NO+ and NO3- in the zeolite pores that can also stabilize the [N2O4](double dagger). (C) 2014 Elsevier Inc. All rights reserved.