Catalytic activity of titania polymorphs towards desorption reaction of MgH2

Abstract

Hydrogen desorption properties of MgH2 ball milled with two different TiO2 polymorphs, rutile and anatase, were studied. Structural characterization has been done by X-ray diffraction (XRD) analysis, particle size analysis (PSD) and scanning electron microscopy (SEM). The mechanism of desorption and the apparent activation energy for desorption were investigated by applying isoconversional kinetic analysis of DTA spectra, while desorbed species were followed by TPD coupled with mass spectroscopy. It has been demonstrate that the addition of rutile TiO2 significantly decrease the apparent activation energy for desorption (E-des(a)), while addition of anatase titania has negligible influence on E-des(a). Such behaviour could be explained in terms of the same crystal structure of rutile TiO2 and MgH2. Further, the mechanism of desorption changes from Avrami-Erofeev n = 3 for pure MgH2 to Avrami Erofeev n = 4 for composite materials. Copyright (c) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.