Zirconium Modification Promotes Catalytic Activity of a Single-Site Cobalt Heterogeneous Catalyst for Propane Dehydrogenation.
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ABSTRACT: The effect of Zr modification on the catalytic activity of Co/SiO2 was investigated for nonoxidative propane dehydrogenation. Isolated Zr on SiO2 surface sites were prepared by organometallic synthesis using Zr(O t Bu)4 as a precursor. The resulting Zr/SiO2 support was functionalized with Co2+ ions via strong electrostatic adsorption. Spectroscopic (diffuse reflectance infrared Fourier transform spectroscopy, UV-vis, electron paramagnetic resonance) and microscopic characterization (transmission electron microscopy, scanning transition electron microscopy) results are consistent with single-site cobalt that preferentially associates with the mono-dispersed Zr at a variety of loadings and Co/Zr ratios. The oxidation state of Co in the as-prepared Co/SiO2 and Co-Zr/SiO2 was both +2 with tetrahedral and octahedral geometries, respectively. In situ X-ray absorption near edge structure and extended X-ray absorption fine structure results confirmed that the oxidation state of Co remained as +2 under reaction condition for both Co/SiO2 and Co-Zr/SiO2 samples and both catalysts have tetrahedral Co2+ as the active catalyst. Despite similar Co coordination environments, the catalytic activity and selectivity was significantly improved by the Zr modification of the silica support versus Co/SiO2. This was attributed to the change in oxygen donor ability and Co-O bond strength of the ?SiO-Zr-O sites of Co-Zr/SiO2 compared with the ?SiO- ligands in Co/SiO2. These results show that tuning of the support SiO2 oxygen donation ability by use of an anchoring site (e.g., ?SiO-Zr-O-) can be used to alter both rate and selectivity of propane dehydrogenation with single-site heterogeneous catalysts. These results also show some preference for Co2+ active sites to associate with ?SiO-Zr-O- sites over ?SiO-.
SUBMITTER: Zhao Y
PROVIDER: S-EPMC6645419 | biostudies-literature | 2018 Sep
REPOSITORIES: biostudies-literature
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