Synthesis and characterization of Mn–MCM-41and Zr–Mn-MCM-41

Abstract

Mesoporous silica molecular sieves MCM-41 containing zirconium and manganese ions (Zr–Mn-MCM-41) with Si/(Zr+Mn) ratio equal to 49, 98, 147, 196, 262 and 327 and only manganese ions with Si/Mn ratio equal to 15, 31, 46, 61, 82 and 102 respectively, were synthesized under hydrothermal conditions using cetyltrimethylammonium (CTMA +) surfactants as template in the absence of auxiliary organics. The mesoporous materials, viz. Zr–Mn-MCM-41 and Mn-MCM-41 were characterized using several techniques, e.g. ICP-AES, XRD, FTIR, Nitrogen adsorption, TG/DTA, ESR, UV–Vis/DRS, SEM and TEM. ICP-AES studies indicated the content of zirconium and manganese in the mesoporous materials. XRD studies indicated that the materials had the standard MCM-41 structure. FTIR studies showed that zirconium and manganese ions were incorporated into the hexagonal mesoporous structure of Zr–Mn-MCM-41 and Mn-MCM-41. The thermal stability of the as-synthesized materials was studied using TG/DTA. Nitrogen adsorption was used to determine specific surface area, pore diameter, pore volume and wall thickness in the calcined Zr–Mn-MCM-41 and Mn-MCM-41 mesoporous molecular sieves. The incorporated of zirconium and manganese ions oxidation state was determined by ESR and UV–Vis/DRS. The morphology of Zr–Mn-MCM-41 and Mn-MCM-41 materials was determined by SEM. The inference that the Zr–Mn-MCM-41 and Mn-MCM-41 mesoporous materials had uniform pore size was obtained by TEM studies. The incorporated metal ions as Zr 4+, Mn 2+ and Mn 3+ in Zr–Mn-MCM-41 are coordinated to Si(IV) by tetrahedral, disordered octahedral and tetrahedral environments respectively. The zirconium and manganese ions are homogenously dispersed on the inside silica surface of the Zr–Mn-MCM-41, but only the manganese ion is not homogenously dispersed on the inside surface of the Mn-MCM-41 under hydrothermal conditions. Thus the Zr–Mn-MCM-41 mesoporous molecular sieves are more useful for oxidation of olefin reaction with TBHP, e.g., in the epoxidation of trans-stilbene, trans-stilbene-oxide (84.58%) was found to be the highest in the presence of Zr–Mn-MCM-41(49).