Synthesis and Characterization of Silica-Supported Boron Oxide Catalysts for the Oxidative Dehydrogenation of Propane

Abstract

In this contribution we report on the oxidative dehydrogenation (ODH) activity of silica-supported boron oxide prepared via incipient wetness impregnation. Characterization of pristine and spent catalysts with infrared, Raman, and solid-state NMR spectroscopy reveals the presence of both isolated and aggregated oxidized boron sites. The results of these investigations, in combination with our earlier work on bulk boron-containing ODH catalysts (e.g., h-BN, metal borides, and elemental boron), bolster the hypothesis that oxidized boron species in situ formed on the surface of these materials are responsible for the exceptional catalytic behavior. We anticipate that investigation of supported boron materials can provide insight into the structural characteristics required for selective boron-containing ODH catalysts. Disciplines DisciplinesPhysical Chemistry Comments CommentsAbstract. In this contribution we report on the oxidative dehydrogenation (ODH) activity of silica-supported boron oxide prepared via incipient wetness impregnation. Characterization of pristine and spent catalysts with infrared, Raman, and solid-state NMR spectroscopy reveals the presence of both isolated and aggregated oxidized boron sites. The results of these investigations, in combination with our earlier work on bulk boron-containing ODH catalysts (e.g., h-BN, metal borides, and elemental boron), give direct evidence that oxidized boron species formed in situ on the surface of these materials are responsible for the exceptional catalytic behavior. We anticipate that investigation of supported boron materials can provide insight into the structural characteristics required for selective boron-containing ODH catalysts.

B‐MWW Zeolite: The Case Against Single‐Site Catalysis

“…This loading is within the 0.23–2.20 wt. % range for B/SiO 2 catalysts made by incipient wetness impregnation that all showed significant conversion under our ODH reaction conditions …”

“…Catalytic testing for the ODH of propane was performed at 500 °C under a flow of C 3 H 8 , O 2 , and N 2 with a pretreatment at 525 °C under the same gas composition . Surprisingly, the B‐MWW material showed no conversion above the background observed with a blank reactor (i.e.…”

“…This result was unexpected since a B/SiO 2 catalyst with 0.23 wt. % boron showed 92 % total olefin selectivity at 4 % propane conversion . The boron content did not change, within the error margin of the experiment, indicating that there was insignificant leaching during reaction.…”

“…As a further control, we performed ODH catalytic testing for a catalyst made by incipient wetness impregnation of boron onto the B‐MWW zeolite, denoted B/B‐MWW. B/B‐MWW was made by a similar procedure as B/SiO 2 (see Supporting Information) . The B/B‐MWW catalyst (1.3±0.1 wt.…”

“…This layer consists of three‐coordinate boron with varying numbers of hydroxyl and bridging oxide groups represented by the general formula B 2 (OH) x O (3− x /2) ( x= 0–6) . To understand the function of this oxidized boron phase, we recently investigated silica‐supported boron oxide (B/SiO 2 ) materials, which showed a similar conversion‐selectivity trend and product distribution to the bulk boron‐containing catalysts . While these results confirm that the active site is most likely contained in the oxidized boron phase, the precise reaction mechanism and active site structure have not been identified.…”