Genesis of micropores by thermal activation of Mg-Al layered double hydroxides possessing interlayer organic sulfonates under oxygen-free environments

Abstract

Microporosity and basic-site density of mixed oxides formed from Mg-Al layered double hydroxides possessing interlayer isethionate (MgAl-Ise) were investigated to seek for a potential application of them to basic catalyst supports for natural gas conversion. The oxide samples were prepared by thermal activation of MgAl-Ise at 500 °C in air, 5% O2 in N2, N2, vacuum, H2 in helium with various concentrations, H2, and NH3 to investigate effects of gas atmosphere. The N2 adsorption data show that Mg-Al mixed oxides obtained by thermal activation of MgAl-Ise in H2, NH3, and N2 possess substantially larger micropore volumes characterized by N2 uptake at the relative pressure <10–3 than those obtained in oxygen-containing atmospheres. The data indicate that these accessible micropores originate from interlayer spaces and form upon removal of a majority of sulfonates under H2, NH3, and N2 treatments. Thermal activation of MgAl-Ise in H2 and NH3 enhances the concentration of basic sites probed by CO2 relative to that conducted in N2 by facilitating removal of sulfonate-derived species. Upon conversion of MgAl-Ise to mixed oxides with removal of interlayer sulfonates, the material catalyzes H2-D2 exchange reaction.