M. Bandyopadhyay

Synthesis and characterization of silica MCM-48 as carrier of size-confined nanocrystalline metal oxides particles inside the pore system

Abstract The interpenetrating 3-dimensional channel system of silica MCM-48 has been selected for the deposition of Cu/Zn/O mixed metal oxide particles. With the wet impregnation technique aqueous solutions of metal acetates have been used to load the calcined form of the mesoporous silica. Successive impregnation yielded metal contents of ca. 9 wt.%. Calcination of the composite transformed the acetates to the metal oxides. X-ray powder diffraction and solid-state MAS NMR showed the uptake of the metal salt inside the pore system. N 2 -adsorption, X-ray diffraction and TEM confirmed the mesoporous structure. XPS measurements and EXAFS analysis (Cu K- and Zn K-edges) confirmed the metal uptake. Whereas nano-disperse CuO particles have been obtained ZnO shows no regular structure and seems to have reacted with the silicate channel surface by coating the channel wall.

The reduction of copper in porous matrices

Abstract The reduction of copper oxide species dispersed in microporous and mesoporous matrices has been studied by TPR, XPS/XAES, and XAFS. While the reduction of bulk CuO and of Cu(II) in mesoporous MCM-48 (5.6 wt-%) proceeded in one step without intermediate Cu(I) being detectable under the experimental conditions, Cu(II) in microporous matrices was reduced in two steps. The two-step scheme cannot be identified with the reduction steps Cu(II)→Cu(I) and Cu(I)→Cu(0). Instead, highly disperse Cu(0) may be present already after the first reduction step. In siliceous matrices, coexistence of Cu(0), and Cu ions was observed over a wide temperature range, obviously due to the absence of an autocatalytic reduction process. The latter occurred in Cu-ZSM-5, apparently involving simultaneous segregation of Cu metal from the matrix. This suggests that very small (oligomeric) Cu metal clusters are unable to activate hydrogen. The reduction behaviour of Cu in Y zeolite depends critically on the thermal history of the sample due to the population of hidden sites by copper upon calcination. Highly disperse Cu particles are stable in MCM-48 up to 500°C.

Mesoporous MCM-48 Immobilized with Aminopropyltriethoxysilane: A Potential Catalyst for Transesterification of Triacetin

The ordered mesoporous silicas MCM-48, MCM-41, and SBA-15 were synthesized and functionalized with 3-aminopropyltriethoxysilane (APTES). The X-ray diffraction patterns before and after functionalization revealed no structural degradation during the process. FT-IR spectra of the materials clearly indicated the anchoring of the aminopropyl moiety with silanol groups. The amine concentrations were calculated using TG-DTA and CHN analysis. The amine-loaded materials were assessed as catalysts for the transesterification of triacetin with methanol. MCM-48-NH2, in which the pores are interconnected in a three-dimensional manner, exhibited superior catalytic activity to one- dimensional MCM41-NH2 and SBA-15-NH2, even with lower concentrations of the amine group.Graphical Abstract

Comparison of sulfonic acid loaded mesoporous silica in transesterification of triacetin

Covalently linked sulfonic acid (–SO3H)-modified ordered mesoporous silicas MCM-48, MCM-41, and SBA-15 were synthesized, characterized and their catalytic activities were evaluated in the transesterification reaction of triacetin with methanol. Acid modified materials were prepared by oxidative transformation of immobilized functionalized unit, 3-mercaptopropyltriethoxysilane (MPTES) as a precursor. The mesophase and porosity of the catalysts were determined by means of X-ray diffraction and N2 adsorption techniques. No degradation of structure was observed in the preparation process. The acid concentrations were calculated using TG–DTA and NH3–TPD analysis. The acid modified materials were found to be active catalysts for the transesterification of triacetin with methanol. Especially, three-dimensional-MCM-48-SO3H showed better catalytic activity compared to its two-dimensional counterparts MCM-41 and SBA-15.