Nonlinear desorption activation energy from TPD curves: Analysis of the influence of initial values for the regression procedure

• Published in: Canadian journal of chemical engineering Vol. 98; no. 5; pp. 1115 - 1123
• Main Authors: Pirola, Carlo, Di Michele, Alessandro
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01-05-2020; Wiley Subscription Services, Inc
• Subjects: Activation energy; Catalysts; Desorption; desorption energy; initial values; Mathematical analysis; Parameters; Polanyi‐Wigner equation; Polynomials; regression; Regression analysis; TPD
• ISSN: 0008-4034; 1939-019X
• DOI: 10.1002/cjce.23700

Thermal programmed desorption (TPD) is a powerful technique for materials and catalysts characterization. By analyzing TPD curves, it is possible to calculate important parameters as the desorption activation energy,
E
d, that depends on the surface coverage (θ) by a nonlinear polynomial function, ie, Edθ=∑k=0Nαk1−θk. The Polanyi‐Wigner equation, −dθdT=Aθβθnexp−EdθRT, can be used as theoretical basis to calculate this parameter, by a fitting regression procedure starting from experimental TPD data. Different degrees (k) for this polynomial equation and different initial values of the frequency factor
A(θ) were considered and discussed to obtain the univocal value of desorption energy. Three different Pt and Co based catalysts, suitable for hydrogenation reactions, have been considered as case studies for the application and validation of the proposed calculation procedure.
By analysing TPD curves it is possible to calculate desorption activation energy (E).
In heterogeneous surfaces, E is non linearly dependent from the coverage surface.
The Polanyi‐Wigner equation can be used to calculate E.
To obtain meaningful E, it is suggested to explore large range of initial values.
Three different Pt and Co based catalysts have been considered as case studies.