Fischer-Tropsch synthesis: Anchoring of cobalt particles in phosphorus modified cobalt/silica catalysts

• Addition of phosphorus to Co/SiO2 up to 1 wt% improved FT activity and stability.
• Higher P loadings on Co/SiO2 were found to hinder the reduction of Co3O4.
• P anchors Co particles to the support and thus hindering Co sintering rate.
• FT product selectivity did not change appreciably for 0.5 and 1.0 wt% P.

The effect of phosphorus addition on silica-supported cobalt catalyst was investigated for Fischer-Tropsch synthesis (FTS). As shown by STEM images and chemisorption, the addition of phosphorus to cobalt of up to 1 wt% increased the dispersion of cobalt. Further addition of phosphorus (e.g., 3 and 5 wt.%), as demonstrated by TPR, pulse reoxidation, and XANES, significantly hindered the reduction of cobalt oxides. The cobalt FTS catalysts containing 0.5 and 1.0 wt% P exhibited greater stability in comparison with undoped and 3.0 wt% P containing cobalt catalysts. Analysis of XANES spectra at the P and Co K-edges, along with DRIFTS results of H2-activated cobalt catalysts, suggest that cobalt particles interact with PO43− ions, indicating a role played by P in anchoring Co particles to the support, thus hindering the cobalt sintering rate. The initial selectivity to methane was slightly higher for 0.5%P-20%Co/SiO2 and 1.0%P-20%Co/SiO2 catalysts compared to the undoped catalyst, but at longer times differences were small. At higher loadings of P (3 wt.%), FT activity and selectivity were adversely and irreversibly affected.

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