Transition of 2-D to 3-D SBA-15 by high temperature fluoride addition and its impact on the surface reactivity probed by isopropanol conversion.

: We report on a systematic variation of the SBA-15 synthesis conditions and its impact on the structural and chemical characteristics. An incremental alteration of the hydrothermal aging temperature and time was used to induce first changes of the highly ordered SBA-15 structure. Any effects on the total surface area, mesopores size, micropore contributions and pore connectivity are amplified by a combined incremental increase of the NH 4 F concentration. Based on changes of the unit cell parameter as a function of the mesopore size, and a feature in the low angle XRD, useful descriptors for the disorder of the corresponding SBA-15 are identified. An additional analysis of the BET surface area and pore size distributions enables investigations on the structural integrity of the material. Our systematic approach evidences  the identification of coherencies between the evolutions of physical SBA-15 properties. The obtained correlations of the surface and structural characteristics allow to discriminate between highly ordered 2-D SBA-15, disordered 3-D SBA-15 and highly nonuniform silica fractions with mainly amorphous character. The fluoride induced disintegration of the silica structure under hydrothermal conditions was also verified by TEM. A direct influence of the structural adaption on the chemical properties of the surface was demonstrated by isopropanol conversion and  H/D exchange monitored by FT-IR analysis  as sensitive probes for acid and redox active surface sites.