Activation of Surface ReO<sub><i>x</i></sub> Sites on Al<sub>2</sub>O<sub>3</sub> Catalysts for Olefin Metathesis


The nature of activated surface ReO<sub><i>x</i></sub> sites and surface reaction intermediates for supported ReO<sub><i>x</i></sub>/Al<sub>2</sub>O<sub>3</sub> catalysts during propylene self-metathesis were systematically investigated for the first time using in situ spectroscopy (Raman, UV–vis, XAS (XANES/EXAFS) and IR). In situ Raman spectroscopy reveals that olefins selectively interact with the surface dioxo ReO<sub>4</sub> sites anchored at acidic alumina hydroxyls. In situ UV–vis indicates that surface Re<sup>5+</sup> and some Re<sup>6+</sup> sites form, and in situ XAS indicates a reduction in the number of ReO bond character in the propylene self-metathesis reaction environment, especially as the temperature is increased. The appearance of oxygenated products during propylene activation supports the conclusion that catalyst activation involves removal of oxygen from the surface rhenia sites (pseudo-Wittig mechanism). Isotopic CD<sub>3</sub>CDCD<sub>2</sub> → CH<sub>3</sub>CHCH<sub>2</sub> switch experiments demonstrate the presence of surface ReCD<sub>2</sub> and ReCDCD<sub>3</sub> reaction intermediates, with the surface ReCD<sub>2</sub> species being the most abundant reaction intermediate. In situ IR spectroscopy indicates the presence of significant surface propylene π complexes on alumina and rhenia sites of the catalyst, which complicates analysis of surface reaction intermediates during propylene self-metathesis

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oai:figshare.com:article/2111608Last time updated on 2/12/2018

This paper was published in FigShare.

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