“Hard” vs. “Soft” Templating Synthesis of Mesoporous Nb2O5 Catalysts for Oxidation Reactions

Abstract

Nanoporous niobia with crystalline walls has been formed within the mesopores and on the outer surface of SBA-15 and FDU-1 by impregnation with niobium salts followed by calcination and silica template removal. The influence of niobium source and silica templates on the physicochemical properties of niobia particles was evaluated by powder X-ray diffraction, nitrogen adsorption, scanning electron microscopy, temperature-programmed reduction and thermogravimetry. The resulting nanoniobia was tested in the liquid phase oxidation of cyclohexene with hydrogen peroxide and appeared to be catalytically active contrary to amorphous niobia.

Changes in Surface Property and Catalysis of Mesoporous Nb2O5 from Amorphous to Crystalline Pore Walls

“…As pure Nb 2 O 5 catalysts for the same reaction, mesoporous silica-templated crystalline Nb 2 O 5 catalysts were found to be active and efficiency of H 2 O 2 at more than 98% was reported [26], which is different from the present study. While crystallization occurs in pores of mesoporous silica to expose stable surfaces with less numbers of defect sites in the reported study [26], the surfaces of the presently prepared crystalline mesoporous Nb 2 O 5 appearing after silica removal would probably rich in defect. Such defect-rich surfaces are considered, at present, to work as decomposition sites for H 2 O 2 .…”

“…On the other hand, Nb 2 O 5 -coated mesoporous silica resulted in forming 1, 2-cyclohexanediol as a major product [26] because of the exposure of amorphous Nb 2 O 5 as in the case of present study. As pure Nb 2 O 5 catalysts for the same reaction, mesoporous silica-templated crystalline Nb 2 O 5 catalysts were found to be active and efficiency of H 2 O 2 at more than 98% was reported [26], which is different from the present study.…”

“…Briefly, 7 mmol NbCl 5 was added to 10 wt% P-85 (a block copolymer; HO(CH 2 CH 2 O) 26 (CH 2 CH(CH 3 )) 39 (CH 2 CH 2 O) 26 H) propanol solution and stirred for 1 h. After the addition of 70 mmol of water with stirring, the solution was kept at 40 8C in air for 10 days to obtain template-containing niobium oxide or hydroxide gel. The surfactant was removed by calcination at 400 8C for 10 h.…”

Polystyrene-block-poly(ethylene oxide) copolymers as templates for stacked, spherical large-mesopore silica coatings: dependence of silica pore size on the PS/PEO ratio

“…A sol–gel process, carried out in combination with a templating method and spin-coating deposition, is the easiest and the most versatile way for preparing well-organized, mesoporous, thin films. Among all the different templating approaches, the most widely used for the synthesis of nanostructured porous and high surface area oxides are soft templating (endotemplating) and hard templating (exotemplating) [6–7]. …”

Synthesis of mesoporous Nb2O5 with crystalline walls and investigation of their photocatalytic activity

“…29), 30) For the preparation of mesoporous Nb 2 O 5 , we utilized a solvent evaporation method, which is very useful for controlling the morphology, using PC or PAA membranes, 25)27) although a hard templating method using mesoporous silica has been reported. 31) We prepared various types of mesoporous Nb 2 O 5 by using two types of surfactants while changing the amount of surfactants by applying various calcination temperatures. The effect of these parameters in the framework on the mesostructural ordering and crystallinity was carefully examined.…”