Creation of VO_x Surface Species on Pure Silica MCM-48 Using Gas-Phase Modification with VO(acac)₂

Abstract

Pure silica MCM-48 is prepared by a novel synthesis method, using the [C18H37N+(CH3)2−(CH2)12−N+(CH3)2C18H37]·2Br- surfactant, abbreviated as GEMINI 18-12-18. The MCM-48, obtained after careful calcination, is a highly crystalline, mesoporous material with the characteristics of the Ia3d cubic phase, a surface area exceeding 1000 m2/g, and a narrow mesoporous pore size distribution (r = 1.4 nm; fwhh < 0.2 nm). This MCM support is grafted with VO x species using a designed dispersion of VO(acac)2 in a gas-deposition reactor. In the first step, the complex is anchored to the support. In a subsequent step the adsorbed complex is thermolyzed to yield chemically bonded VO x surface species. The final material contains 1.7 mmol V/g (8.7 wt % V) and still has a narrow pore-size distribution and a surface area of 800 m2/g. It is observed that all silanols are consumed during the adsorption of the VO(acac)2 complex to the MCM support. Therefore, the maximum achievable number of surface V species is limited by the silanol number and not by the geometrical surface, which has a higher capacity. After calcination of the adsorbed complex, the supported VO x species are present in a strictly tetrahedral configuration, mainly as chains of linked tetrahedra and not as isolated species.

Surface modification of a fuel cell material by ion implantation

“…P.van der Voort et al [15] reported about the deposition of vanadiumoxide on silica structures by means of Atomie Layer Epitaxy (ALE). This method is used to produce a monolayer of VOx on silica.…”

Gemini-Tenside

“…[71] Es zeigte sich, dass kationische Gemini-Tenside, insbesondere solche mit langen Spacern, wie 16-12-16 und 18-12-18, die Synthese von äuûerst hochwertigem MCM-48 mit groûer Oberfläche und geringer Bandbreite hinsichtlich der Porengröûe begünstigten. [72,73] Um die Dinge in den richtigen Zusammenhang zu bringen, ist es von Vorteil, zunächst eine Arbeitsvorschrift für die Herstellung von MCM-48 vorzustellen. [69] Das Gemini-Tensid wird in wässriger Base gelöst und dann mit Si(OEt) 4 [69] Beide Gemini-Tenside, 18-12-18 und 16-12-16, führen zu ausgezeichnetem MCM-48 mit einer Oberfläche von 1200 ± 1600 m 2 g À1 und Porenvolumina > 1.2 mL g À1 .…”

“…[69] Das Gemini-Tensid wird in wässriger Base gelöst und dann mit Si(OEt) 4 [69] Beide Gemini-Tenside, 18-12-18 und 16-12-16, führen zu ausgezeichnetem MCM-48 mit einer Oberfläche von 1200 ± 1600 m 2 g À1 und Porenvolumina > 1.2 mL g À1 . [ [73] Gemini-Tenside haben in den Materialwissenschaften eindeutig eine vielversprechende Zukunft.…”

Vanadium dispersion and catalytic activity of Pd/VOx/SBA-15 catalysts in the Wacker oxidation of ethylene

“…It was also shown that VO x /SBA-15 catalysts prepared by grafting/ion-exchange method were better oxidation catalysts than the conventional VO x /silica samples with the same vanadia loadings [21]. Van der Voort [22] grafted pure silica MCM-48 support with vanadyl acetylacetonate using gas-phase chemical vapor deposition. The final material contained 8.7wt% V, had narrow pore size distribution and a surface area of 800 m 2 /g.…”