Fluorinated Cu/Zn/Al/Zr hydrotalcites derived nanocatalysts for CO2 hydrogenation to methanol

• Fluorinated hydrotalcites are synthesized by incorporation of (AlF6)3− into layers.
• The incorporation of fluorine greatly improved the fraction of strongly basic site.
• CH3OH selectivity first increases obviously and then decreases with increased F/Al.
• The introduction of suitable amount of (AlF6)3− can enhance CH3OH yield markedly.

A series of fluorinated Cu/Zn/Al/Zr hydrotalcite-like compounds are synthesized by incorporation of different amount of (AlF6)3− into hydrotalcite-like sheets. The fluorine-modified Cu/ZnO/Al2O3/ZrO2 catalysts are then obtained by calcination and reduction of fluorinated precursors. With increasing of F/Al atomic ratios, the Cu particle size increases continuously and the Cu surface area and dispersion decrease gradually, as well as the amount of moderately and strongly basic sites first increases significantly and then decreases. The catalytic performance for the methanol synthesis from CO2 hydrogenation is examined. The change of CO2 conversion is small when F/Al ≤ 0.8, while the CO2 conversion decreases remarkably with further increase of fluorine content. It is also found that the CH3OH selectivity is closely related to the distribution of basic sites and the selectivity of CH3OH takes a volcanic trend with increased fluorine content. The introduction of suitable amount of (AlF6)3− into the hydrotalcite-like structure can enhance the methanol yield markedly and the fluorine-modified catalysts with F/Al = 0.83 affords the substantial stability and the best catalytic performance.

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