| Sumario: | Low-coordinate Ti (III) fragments with controlled geometries designed specifically for σ-H 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 °C was 21.45 wt % and 34.10 kg/m³ at 100 atm, and 3.15 wt % and 54.49 kg/m³ 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 H per Ti center. The adsorption isotherms did not reach saturation at 60 atm, suggesting that the theoretical maximum of 5 H 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/rnol, 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 °C and 0.69 at 25 °C demonstrate retention of 2.4 H and 1.1 H per Ti at these temperatures, respectively. These findings suggest that Kubas binding of H may be exploited at ambient temperature to enhance the storage capacities of high-pressure cylinders currently used in hydrogen test vehicles.
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