Direct measurement of enthalpy and entropy changes in NH ₃ promoted O ₂ activation over Cu?CHA at low temperature

Oxygen activation is a key step in the selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR) over Cu-chabazite. We present direct measurements oxygen adsorption at low temperatures [NH3?Cu?NH3]+ complexes and framework-bound Cu+ species Cu-chabazite Si/Al=14 using isothermal microcalorimetry combined mass spectrometry. The enthalpy change for O2 200 °C determined to be ?79 kJ/mol. By fitting Langmuir isotherm, corresponding entropy ?142 J/(mol*K) 10 % O2. results show that more facile than on species. experimental are agreement density functional theory calculations showing lower barrier as compared