Prepatation Of Pr/Al₂O₃ And Its Activity In Catalytic Ozonation

In an attempt to utilize ozone effectively, a series of praseodymium-modifiedγ-Al₂O₃ (Pr/Al₂O₃) was prepared via incipient wetness impregnation using Pr(NO₃)₃·6H₂O as the precursor. The structure and properties of the catalysts were studied by X-ray diffraction (XRD), and the Brunauer–Emmett–Teller (BET) method. Catalytic activity was evaluated by monitoring the degradation of succinic acid (SA) in the presence of ozone. The praseodymium modification can effectively enhance the ozonation activity of ?-Al₂O₃ upon SA removal. Increasing the calcination temperature of Pr/Al₂O₃ is disadvantageous for the catalytic process, whereas increasing the load of praseodymium is helpful. After three successive recycles, the Pr/Al₂O₃ catalyst remained stable in the catalytic ozonation of SA. Overall, the initial degradation rate of SA, as well as the saturated adsorption capacity of SA was found to have a linear relation to changes of the surface hydroxyl groups of the catalyst. On this basis, we conclude that the significant enhancement of SA degradation using Pr/Al₂O₃ should be because the supported praseodymium, in the form of Pr6O11, promoted the formation of surface hydroxyl groups. Hence, the adsorption was ascended and the degradation rate of SA was then enhanced.The efficiency of catalytic ozonation on removing phenol was studied. The effects of ozone concentration, phenol concentration, pH, on the TOC removal rof phenol were evaluated. pH is the key factor to affect heterogeneous catalytic ozonation reactions. To study the effects of pH on catalytic ozonation, The Pr/Al₂O₃ powder was used as catalyst on catalyzed ozonation for degradation of phenol in different pH solutions. It was found that the TOC removal efficiency of phenol in Pr/Al₂O₃ catalytic ozonation showed the same trend as its adsorption process, the TOC removal efficiency of phenol was highest under neutral pH conditions. This result was different from the case of ozonation alone, in which higher pH had positive effect on the degradation of phenol due to the formation of hydroxyl radical. It was assumed that adsorption of organic pollutants on Pr/Al₂O₃ catalyst was an important step and would have direct influence on the effectiveness of catalytic ozonation. The catalytic ozonation efficiency may be affected by the ionization the dependency of phenol ionization on the pH value and point of zero charge (pHPZC) for Pr/Al₂O₃ catalyst. This means the phenol was beneficial to adsorb on the catalyst surface by electrostatic adsorption with opposite charge, and further decomposed on the surface of catalyst.