Kinetic study and modelling of ammonia desorption from HZSM-5 zeolite
A. I. LYSIKOV1,2, A. B. AYUPOV1,2, S. WANG2,3, A. V. SHNAYDER1,2, R. A. MASLENKIN1,2, E. V. PARKHOMCHUK1,2, Zh. ZHOU4, Zh. ZHENG4
1Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
3Heilongjiang University, Harbin, China
4Sun Yat-sen University, Guangzhou, China
Keywords: temperature-programmed desorption, kinetics, ammonia, Polanyi-Wigner model, Schroeder-Eyring model, heterogeneous catalysts, HZSM-5
Abstract
In this work, an approach to kinetic modelling of temperature-programmed desorption of ammonia (TPD-NH3) on zeolites is proposed, based on the Schroeder-Eyring equation and taking into account the temperature dependence of the pre-exponential factor. It is demonstrated that the use of thermodynamic activation parameters (ΔH0≠ and ΔS0≠) allows the desorption curves obtained at different heating rates to be described with a single set of converging parameters, thus providing a pathway for TPD method standardisation for comparative analysis of the acidic properties of zeolites. The modelling results suggest that the low-temperature peaks are most likely associated with desorption from the outer solvation (fluid) shell around the acid sites of the zeolite, whereas the high-temperature peaks (with activation enthalpies of 136.6 and 214.7 kJ/mol) correspond to ammonia desorption from strong Brønsted acid sites.
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