H2 storage materials (22 KJ/mol) using organometallic Ti fragments as sigma-H2 binding sites

Low-coordinate Ti (III) fragments with controlled geometries designed specifically for sigma-H2 binding were grafted onto mesoporous silica using tri- and tetrabenzyl Ti precursors. The hydrogen storage capacity was tested as a function of precursor and precursor loading level. At an optimal loading level of 0.2 mol equiv tetrabenzyl Ti the total storage capacity at -196 degrees C was 21.45 wt % and 34.10 kg/m(3) at 100 atm, and 3.15 wt % and 54.49 kg/m(3) for a compressed pellet under the same conditions. The adsorption value of this material was 1.66 wt %, which equates to an average of 2.7 H2 per Ti center. The adsorption isotherms did not reach saturation at 60 atm, suggesting that the theoretical maximum of 5 H2 per Ti in this system may be reached at higher pressures. The binding enthalpies rose with surface coverage to a maximum of 22.15 kJ/mol, which is more than double that of the highest recorded previously and within the range predicted for room temperature performance. The adsorption values of 0.99 at -78 degrees C and 0.69 at 25 degrees C demonstrate retention of 2.4 H2 and 1.1 H2 per Ti at these temperatures, respectively. These findings suggest that Kubas binding of H2 may be exploited at ambient temperature to enhance the storage capacities of high-pressure cylinders currently used in hydrogen test vehicles.