Kinetic investigation of the effect of milling time on the hydrogen sorption reaction of magnesium catalyzed with different Nb2O5 contents

Abstract The effect of milling time and Nb 2 O 5 content on the magnesium hydrogen sorption reaction is investigated in this paper. The absorption and desorption kinetics of magnesium at 300 °C, with 0.05, 0.1, 0.2, 0.5, 1 mol% Nb 2 O 5 contents and after 2, 5, 10, 20, 50, 100 h milling were measured. Reaction kinetics can be enhanced up to a certain limit by increasing the milling time or increasing the Nb 2 O 5 content. The kinetic rate constants for different milling times and Nb 2 O 5 contents were calculated and compared. Furthermore the rate-limiting step of the absorption and the desorption reactions was determined by fitting the respective kinetic equations. While the absorption is diffusion controlled, the rate-limiting step for desorption changes, with increasing of milling time or Nb 2 O 5 content, from chemisorption to interface velocity of the transformed phase, demonstrating the effectiveness of the Nb 2 O 5 catalyst.