Catalytic activity and selectivity of mechanically alloyed nickel-zirconium and nickel-platinum-zirconium powders.

摘要

Using a flow reactor, amorphous mechanically alloyed NiZr and NiPtZr powders milled in 1 × 10−6 Torr vacuum were studied as potential catalysts for the NO decomposition and Fischer-Tropsch reactions. A commercial Ni/SiO₂-Al₂O₃ catalyst was tested under the same conditions and used as a standard for comparison. Material characterization of the catalysts in the as-received and after reaction conditions was achieved using B.E.T., CO chemisorption, TGA, XRD, SEM, and TEM. The TOF's of the mechanically alloyed Ni₅₅Zr₄₅ and Ni₄₉PtZr ₅₀ catalysts for the NO decomposition reaction at a reaction temperature of 673 K were two orders of magnitude greater than the commercial Ni/SiO ₂-Al₂O₃ catalyst. The high activity of the mechanically alloyed catalysts for the NO decomposition reaction is believed to be due to an increase in the number of active sites, which occurred when the catalysts were exposed to reaction conditions. For the Fischer-Tropseh reaction, the most significant result was the selectivity of the mechanically alloyed NiZr and NiPtZr towards alkenes, compared to the commercial Ni/SiO₂-Al ₂O₃ catalyst, which did not produce any alkenes. Fischer-Tropsch activity results for both the mechanically alloyed NiZr and NiPtZr catalysts showed the TOF to be an order of magnitude greater than the commercial Ni/SiO ₂-Al₂O₃ catalyst. The high activity of the mechanically alloyed NiZr and NiPtZr catalysts was attributed to a strong metal support interaction between crystalline Ni-containing compounds and ZrO_x, which formed during exposure to isothermal reaction conditions. The transformation of the mechanically alloyed catalysts into crystalline Ni/NiZr and ZrO _x also affected the selectivity, resulting in a shift towards the production of primarily methane.