Inorganic membranes are well suited to gas separation applications due to their stability and functionality at elevated temperatures . Silica membranes show great promise in this field due to relatively low processing costs and the ability for material manipulation on the nanoscale. Sol-gel reactions can be finely tuned by controlling of reagent quantities, which has a marked impact on the porosity of silica . The controlled tailoring of the silica porosity is essential for gas separation based on the size exclusion.
Metals can be incorporated into the silica structure to enhance gas permeation characteristics. It has been found that the addition of nickel nanoparticles  or niobium  can selectively increase the permeation of H2 and CO2, respectively. Palladium has been found to enhance the permeation of hydrogen above levels predicted by molecular sieving theories.
In this work the ratio of water and acid to silica was varied, altering dissolution of the palladium chloride precursor. The impact this has on the porosity of silica is monitored through N2 adsorption measurements, while the distribution of silica bonds is monitored by solid state 29Si NMR before and after the calcination process. This analysis provides a basis for the optimisation of palladium doped silica materials for high temperature gas separations.
Solid-state NMR allows to distinguish between silicon atoms with different numbers of oxygen bonds and hence to characterise the porosity. Quantitative analysis included single-pulse 29Si experiments with high-power 1H decoupling. The recycle delay was chosen based on each sample’s spin-lattice relaxation rate.