Porous silica materials derivatized with Cu and Ag cations for selective propene-propane adsorption from the gas phase:: Aluminosilicate ion-exchanged monoliths

Copper- and silver-derivatized aluminosilicate materials possessing uniformly sized mesopores have been synthesized and tested for selective separation of gaseous propene/ propane mixtures. Small monoliths of cylindrical shape were prepared via the direct liquid crystal templating (DLCT) pathway using commercially available nonionic surfactants as templates. Calcined samples prepared with Si:Al ratios of 20, 10, and 5 were characterized by powder X-ray diffraction and Al-27 magic-angle spinning NMR. The shaped aluminosilicates were subsequently functionalized with Cu(II) and Ag(I) by ion exchange from 0.5 mol L-1 Cu(NO3)(2) and 1 mol L-1 AgNO3 aqueous solutions. The overall Cu or Ag contents in the resulting samples were quantified by atomic absorption spectroscopy. Estimates of the BET specific surface area and porous structure parameters were based on nitrogen gas adsorption at 77 K. The ion-exchange procedure was found to lead to monolithic materials possessing larger pores and lower specific surface areas compared to the pristine samples. A Cu(I)derivatized sample was obtained by partial reduction of a Cu(II)-exchanged precursor. Individual adsorption of propene and propane onto derivatized shaped materials was studied under static conditions at room temperature, and the ideal propene/propane selectivity coefficient was calculated as a function of the molar fraction of propene in the binary gas mixture. The selectivity of all samples to propene exhibited a downward trend with increasing propene molar fraction. The nature and the number of surface metal sites were shown to be crucial for selective adsorption of propene against propane, monovalent cationic sites being the most appropriate for this purpose.