Effect Of Support Calcination Temperature On Structure And Performance Of Al₂o₃-supported Nickel Phosphide Catalysts

Al₂O₃-supported nickel phosphide catalysts were prepared by the temperature-programmed reduction (TPR) method. Effect of support calcination temperature on the structure and performance of the nickel phosphide catalysts was investigated by means of H₂-TPR, XRD, N₂ adsorption-desorption, CO chemisorption, H2-TPD, NH3-TPD, EDS, and the activity test.γ-Al₂O₃ kept its crystal structure even after calcination at 800℃, while it transfered toθ-Al₂O₃ andα-Al₂O₃ after calcination at 900℃and 1000℃, respectively. As the support calcination temperature increased, the interaction between Al₂O₃ and P species decreased, and the P species were more easily reduced. This leads to the formation of P-rich nickel phosphides. Moreover, the crystallinity of the nickel phosphides increased.With increasing support calcination temperature, the CO uptakes increased at first and then decreased. Ni3P-Ni₁₂P₅/Al₂O₃-700 and Ni₃P-Ni₁₂P₅/Al₂O₃-800 had larger CO uptakes. This is related to less amout of P on the catalyst surface as the support calcination temperature increased, leading to more amout of exposed Ni sites. However, higher calcination temperature than 900℃promoted the sintering of the catalysts, and so the dispersion of Ni phosphides decreased. When the support calcination temperature was below 1000℃, there was no remarkable difference in the amount of both hydrogen adsorbed on NixPy and spilt-over hydrogen. The amount of acid sites decreased with increasing support calcination temperature, while first increased and then dicreased for stronger acidic sites.As the support calcination temperature increased, the activities of the catalysts firstly increased and then decreased. Compared with Ni₃P-Ni₁₂P₅/Al₂O₃-550, Ni₃P-Ni₁₂P₅/Al₂O₃-800 had higher resistance to chlorine poison, larger amount of active sites and better crystallinity. These may account for better activity and stability of Ni₃P-Ni₁₂P₅/Al₂O₃-800.