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Direct measurement of enthalpy and entropy changes in NH 3 promoted O 2 activation over Cu−CHA at low temperature
Author(s) -
Wang Xueting,
Chen Lin,
Vennestrøm Peter N. R.,
Janssens Ton V. W.,
Jansson Jonas,
Grönbeck Henrik,
Skoglundh Magnus
Publication year - 2021
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.202100253
Subject(s) - chabazite , isothermal microcalorimetry , chemistry , enthalpy , adsorption , inorganic chemistry , catalysis , oxygen , standard enthalpy of formation , zeolite , thermodynamics , organic chemistry , physics
Oxygen activation is a key step in the selective catalytic reduction of nitrogen oxides with ammonia (NH 3 ‐SCR) over Cu‐chabazite. We present direct measurements of oxygen adsorption at low temperatures over [NH 3 −Cu−NH 3 ] + complexes and framework‐bound Cu + species in Cu‐chabazite with Si/Al=14 using isothermal microcalorimetry combined with mass spectrometry. The enthalpy change for O 2 adsorption over [NH 3 −Cu−NH 3 ] + complexes at 200 °C is determined to be −79 kJ/mol. By fitting a Langmuir isotherm, the corresponding entropy change is determined to be −142 J/(mol*K) at 10 % O 2 . The results show that O 2 adsorption at low temperatures over [NH 3 −Cu−NH 3 ] + complexes is more facile than on framework‐bound Cu + species. The experimental results are in agreement with density functional theory calculations showing a lower barrier for O 2 activation over the [NH 3 −Cu−NH 3 ] + complexes as compared to the framework‐bound Cu + species.