The mobility of H2 in microporous amorphous silica is studied using quasi-elastic neutron scattering. At T=90 K the self-diffusion coefficient is approximately Ds=1.2×10−8 m2 s−1 for low degrees of occupancy (<20%) and decreases slightly to Ds=0.95×10−8 m2 s−1 for an occupancy of 31%. A rough estimate for the energy of activation yields Em=1.4 kJ mol−1. Comparison of the results obtained for silica with those of zeolites indicates a pore size for silica in the range of 4–5 Å.
Benes, N. E., Jobic, H., Reat, V., Bouwmeester, H. J. M., & Verweij, H. (2003). Mobility of hydrogen in microporous silica studied with quasi-elastic neutron scattering. Separation and purification technology, 32(1-3), 9-15. https://doi.org/10.1016/S1383-5866(03)00026-1