Redox Behavior of Nanostructured Molybdenum Oxide−Mesoporous Silica Hybrid Materials

Abstract

Encapsulation of molybdenum oxide MoO 3 into ordered mesoporous silica materials is demonstrated using different synthetic routes. Either supramolecular polyoxometalates of the "Mü ller type" or Na 2 MoO 4 were used as precursors. Molybdenum oxide (MoO 3 )-silica hybrid materials were characterized using nitrogen-sorption experiments, transmission electron microscopy, small-angle X-ray scattering, and infrared spectroscopy. Under reducing conditions, the hybrid materials undergo an electrochromic transition from colorless or slightly yellow to blue without any leaching of Mo species from the materials. The electrochromic response, which is fully reversible, is caused by a transition from Mo VI to a mixed valence Mo VI /Mo V molybdenum oxide encapsulated in the pores. The reduction process was studied using in situ electron spin resonance (ESR) and UV/vis absorption measurements. Materials of different pore sizes were used, and it was found that pore size effects the kinetics of the reaction.

Selective Photocatalytic Oxidation of Alcohols to Aldehydes in Water by TiO2 Partially Coated with WO3

“…Reduced diffusion not only makes the reaction slower, it can also change the reaction order. To study the influence of CRFs on kinetics experimentally, we used mesoporous silica materials possessing different pore sizes and loaded them with molybdenum trioxide (MoO 3 ) 93. The reduction of the MoO 3 was achieved by the infiltration of an aqueous solution of hydrazinium sulfate.…”

“… Kinetic plots for the reduction of MoO 3 ‐confined mesoporous silica materials with different pore sizes ( D p ≈2 nm (triangles), D p ≈5 nm (squares)) 93…”

Cu/ZnO aggregates in siliceous mesoporous matrices: Development of a new model methanol synthesis catalyst

“…By embedding the catalytically active component into a well-defined superstructure (e.g., a hierarchically structured mesoporous matrix), it should be possible to simultaneously simplify and miniaturize the supported catalyst [14][15][16][17][18][19][20] and to utilize in the preparation the favorable effects of the spatially confined reaction conditions on the chemistry occurring in the porous solid [21]. However, this approach carries the risk of interference by the pore walls of the matrix.…”

Single-crystal micro/nanostructures and thin films of lamellar molybdenum oxide by solid-state pyrolysis of organometallic derivatives of a cyclotriphosphazene

“…A recent review [8] has poignantly highlighted the importance of micro-and nanostructured MoO 3 and related substoichiometric molybdenum oxides for charge storage/intercalation and particularly for electrochromics, which has been studied for a wide range of disordered partially crystalline or polycrystalline materials including amorphous MoO 3 films. Only brief studies of nanocrystalline MoO 3 materials for electrochromic applications have been reported to date [9] limited by the availability of single crystal MoO 3 synthesis with size and crystal structure control and suitable surface deposition methodologies.…”