Synthesis and Spectroscopic Characterization of Vanadosilicate Mesoporous MCM-41 Molecular Sieves

Citations Over TimeTop 10% of 1996 papers

Abstract

A series of mesoporous vanadosilicate VMCM-41 molecular sieves with variable Si/V ratios have been hydrothermally synthesized at pH 11 using 2-propanol as a phase stabilizer. The chemical environment of the vanadium centers in VMCM-41 is investigated by powder X-ray diffraction (XRD), electron probe microanalysis (EPMA), framework FTIR, diffuse reflectance UV-visible spectroscopy (UV−vis), electron spin resonance (ESR), and 29Si and 51V NMR. XRD, EPMA, and ESR show that the solid products have the MCM-41 structure and contain only atomically dispersed vanadium consistent with framework vanadium in VMCM-41. UV-vis, ESR, and 51V NMR reveal that most of the vanadium exists as tetrahedral V5+ ions in as-synthesized samples, but some square pyramidal VO2+ ions simultaneously occur. Both tetrahedral V5+ and square pyramidal VO2+ centers occur at two different sites inside and on the surface of the hexagonal tubular walls of MCM-41. Upon calcination and hydration, only vanadium species on the wall surfaces can be completely oxidized to tetrahedral V5+ and transformed to square pyramidal and then distorted octahedral V5+ species by additional coordination to water molecules. Vanadium species located inside the walls remain stable upon calcination and hydration. Upon thermal or CO reduction, also only the V5+ species on the wall surfaces of VMCM-41 are reversibly reduced to VO2+ species or lower valences.

Related Papers

• → Reduction of vanadium(V) to vanadium(IV) by NADPH, and vanadium(IV) to vanadium(III) by cysteine methyl ester in the presence of biologically relevant ligands(2007)23 cited
• → Octahedral SeO66− and Square-Pyramidal SeO54−, Two New Oxoselenate Anions(2000)22 cited
• → Effect of Ligands on the Iron(III)/Iron(II) System and Its Novel Application to the Simultaneous Flow Injection Determination of Vanadium(IV) and Vanadium(V)(1994)14 cited
• → Hydrothermal Synthesis and Structural Characterization of a Manganese(II) Wire Made Up of Octahedral and Square Pyramidal Mn(II) Ions(2005)2 cited
• Vanadium Recovery from Vanadium-containing Leaching Solution with High Iron Concentration by Reducing Precipitating-Redissolving(2012)