The Study Of Preparation, Characterization And Catalytic Activity For PrO_y-ZrO₂ Solid Solutions

Zirconia appears to be attractive as a catalyst, a catalytic support and as a ceramic glasses. In dependence on the temperature, ZrO₂ appears in three different polymorphs: monoclinic, tetragonal and cubic. At room temperature, pure zirconia is monoclinic (m-ZrO₂). Between the temperature of 1170℃and 2370℃, zirconia is tetragonal (t-ZrO₂). Upon 2370℃, zirconia is cubic (c-ZrO₂). The phase of ZrO₂ takes an important role in the catalytical reaction, c-ZrO₂ asa material finds many applications as refractory because of their optimal thermomechanieal properties, t-ZrO₂ shows wonderful temper, intension and rigidity, so it turns out to be an very interesting phase, too. ZrO₂ is often combined with cationic dopants (Y₂O₃,CaO,MgO,Al₂O₃,MnO), which contribute to stabilization of the tetragonal or cubic phase at low temperature. So, with proper cationic dopants, the transformtion of c or t-ZrO₂ to m-ZrO₂ will be slowed down. In this article, PrO_y-ZrO₂ materials were obtained by coprecipitation process and by sol-gel method at different temperatures. The connection between the prepared method and the samples' performance will be reasearehed.Characterization for PrO_y-ZrO₂ solid solutions prepared by coprecipitation was performed by means of Raman, XRD, UV-Vis and so on. The effect of Pr content on the activity of solid solution for CO oxidation has been investigated, too. It is found that with increasing content of Pr, crystallization temperature of amorphous ZrO₂ increases and heating effect of crystallization decreases. At higher Pr content, phase transformation towords a higher-symmetrical phase (tetragonal or cubic) was observed. The phase composition obtained by Raman spectra is different from that by XRD, which implies a structure difference between the surface and the bulk of the samples. The results show that the oxidation activity highly depends on content of Pr. For CO oxidation, PZ-30 presents the best performance at high reaction temperature, while PZ-50 presents the best performance at low reaction temperathre.Mesoporous PrO_y-ZrO₂ materials were obtained by eopreeipitation process with proper Pr content. XRD patterns and TEM images reveal pore size growth with increase in the calcining temperature. N₂ adsorption-desorption isotherms of the PrO_y-ZrO₂ samples are indicative of typeâ…£behavior characteristic of mesoporous materials (as evidenced by low angle XRD patterns). PrO_y-ZrO₂ calcined at 500℃and 650℃show well-developed H2 type hysteresis loops, indicating the existence of ink-bottle-like pores with a narrow entrance and a large cavity. PrO_y-ZrO₂ calcined at 800℃and 950℃show H1 type hysteresis loops, whieh is often associated with porous materials known to consist of agglomerates of approximately uniform spheres, and hence to have narrow distributions of pore size. The phase analysis by Rieteld refinement method dearly shows the formation of cubic PrO_y-ZrO₂ solid solution from 500℃to 950℃.Characterization for PrO_y-ZrO₂ solid solutions prepared by improved Sol-Gel method was performed by means of Raman, XRD, TEM and so on. It is found that the grain size of prO_y-ZrO₂ solid solution calcined at 650℃is 5-10 nm, and that of PrO_y-ZrO₂ solid solution calcined at 950℃(Pr＞16ï¼…) is about 20 nm, At higher Pr content, phase transformation towords a higher-symmetrical phase (tetragonal or cubic) was observed. The results of phase analysis obtained by Raman spectroscopy were different from the corresponding results of XRD, which implie a structure difference between the surface and the bulk of the samples. With the increase of the Pr content, the m→t→c phase tramsformation occurred in the bulk area and the m→t→t" phase tramsformation occurred in the surface area. The surface region is more easily to form low symmetry and disorder structure. The phase and performance of the catalyst was subjected to theinfluence of prepared method and to the content of the cationic dopants.