Activation energy in the thermal decomposition of MgH2 powders by coupled TG–MS measurements Part II. Catalytic effects of tin oxide doping

The catalytic effect of SnO2 doping on the hydrogen thermal desorption of MgH2 was investigated by coupled thermogravimetric–mass spectrometric (TG–MS) analyses, among a set of samples prepared with different SnO2/MgH2 molar ratios. A small release of water and carbon dioxide was detected at temperatures preceding to the reductive thermal decomposition of MgH2 yielding molecular hydrogen. While TG and DTA data collected at different heating rate provided an apparent activation energy for the entire thermal process, appropriate ion-current signals from the MS-data were used to obtain the activation energies of the single chemical reactions yielding the formation of H2O, CO2, and H2. The most common equations derived from model-free isoconversion methods (Kissinger–Akahira–Sunose; Flynn–Wall–Ozawa; Starink) were used by processing temperatures referred to the different kinds of signals (TG-, DTG-, DTA-, TIC-, molecular-ion IC-curves) for isoconversion points corresponding to the maximum rate of transformation. Temperature and activation energy values were used to compare the kinetic behavior of MgH2 powder with the best performance of a doped sample, prepared by high energy grinding of SnO2/MgH2 mixture. Doped-MgH2 samples prepared with SnO2 mass ratio of 0.2 showed the best kinetic thermal decomposition behavior, with respect to the pristine MgH2 powder: a decreasing of the main thermal decomposition event of ca. 51–57 °C associated to a coherent decreasing of ca. 20 % (ca. 30 kJ mol−1) of its activation energy value.