An Optimal Direct Synthesis of CrSBA-15 Mesoporous Materials with Enhanced Hydrothermal Stability

Mesoporous CrSBA-15 materials with different n Si / n Cr ratios have been synthesized, for the first time, using Pluronic P123 as a structure-directing agent by simply adjusting the molar ratio of water to hydrochloric acid ( n H 2 O / n HCl ). The effect of the nature of Cr-ion source on the synthesis of CrSBA-15 has been investigated using different chromium-ion sources: chromium(III) nitrate, chromium(III) chloride, and chromium(III) sulfate. To investigate the effect of structural and textural properties with a higher Cr incorporation, CrSBA-15 has also been synthesized with various n Si / n Cr ratios and synthesis temperatures. The synthesized CrSBA-15 materials have been characterized by ICP-AES, XRD, N 2 adsorption, ESR, TEM, and FE-SEM. ICP-AES results show that chromium(III) nitrate nonohydrate is found to be a good Cr-ion source for the synthesis of mesoporous CrSBA-15 material, with a n Si / n Cr ratio up to 9.1 successfully prepared by changing the n Si / n Cr ratio in the synthesis gel at a n H 2 O / n HCl of 295. For all calcined CrSBA-15 materials, XRD reflection peaks shift to lower angle with increasing Cr-content, resulting in the increase of the unit cell parameter. By increasing the crystallization temperature from 373 to 403 K, nitrogen adsorption measurement shows that the pore diameter of CrSBA-15 can be tuned from 89.4 to 94.7 Å, with an increase of pore volume from 1.10 to 1.20 cm 3 /g accompanied by the concomitant decrease of surface area from 987 to 797 m 2 /g and the decrease of pore wall thickness from 38 to 36.7 Å. ESR measurements show the amount of Cr-ions incorporated, as well as the location and coordination of Cr-ion on SBA-15 silica walls. TEM and FE-SEM images show the uniform pore diameter and ropelike hexagonal mesoporous structure of CrSBA-15. Furthermore, the hydrothermal stability of CrSBA-15 samples has also been investigated, with hexagonal CrSBA-15(8) having better hydrothermal stability than CrSBA-15(50).