Stabilized tetragonal zirconium oxide as a support for catalysts Evolution of the texture and structure on calcination in static air

Abstract

Single-phase tetragonal zirconium oxides have been made by the incorporation of 5.4 mol-% of Y3+ or La3+ in ZIG, to form solid solutions Tbe samples were prepared by controlled coprecipitation from aqueous solutions of the respective metal chlorides at room temperature and at a constant pH of 10, followed by calcination at 500°C (in the case of the Y3+-doped sample) or 600" C (in the case of the La3+ -doped sample) to effectuate the crystallization into the tetragonal phase. The process of crystallization of the hydrous zirconia precurso r was found to be retarded by the incorporation of Y3+ or La3+, the latter giving the greater effect. Upon crystallization, stabilized tetragonal samples were obtained * with high specific surface areas (Sn, ca. 88 m g -' for both the samples) and well-developed mesoporous textures but without any microporosity. Both the Y3+-and the La3'-alloyed ZrG2 samples were found to fully retain the tetragonal phase upon calcination over the entire range of temperatures studied (up to 9OO'C). The thermal stability of the texture of zirconia was found to bs considerably improved, in comparison with the undoped monoclinic material, by the stabilization of the crystal structure in the defect tetragonal form. In particular, incorporation of 5.4 mol-% of La'+ resulted in a support material which bad a remarkable thermal stability. It is shown that the improvements in the thermal stability are derived from a strong inhibition of the processe s of crystallite growth and the accompanying intercrystallite sinking and thus of the process of mass transport; the mass transport probably occurs by a mechanism of surface diffusion.

Physico-Chemical and Catalytic Properties of Mesoporous CuO-ZrO2 Catalysts

“…Yamamoto et al [24] reported that the tetragonal ZrO 2 phase shows a strong Raman band at 263 cm´1 and several other bands at 148, 325, 472, 608 and 640 cm´1. On other hand, the monoclinic ZrO 2 phase shows strong bands at 173, 185 and 472 cm´1 and some other bands at 140, 216, 260, 301, 328, 342, 500, 553 and 632 cm´1 [25]. The Raman spectra for all the samples are shown in Figure S1 (supporting information).…”

“…553 and 632 cm −1 [25]. The Raman spectra for all the samples are shown in Figure S1 (supporting information).…”

Visbreaking of heavy petroleum oil catalyzed by SO 4 2− /ZrO2 solid super-acid doped with Ni2+ or Sn2+

“…1. The peaks that appeared at the angle 2h 5 30.2u, 50.3u, 59.8u are assigned to the tetragonal phase [11]. The figure reveals a well-crystallized tetragonal phase.…”

Inhibition of Rh sintering and improved reducibility of Rh on ZrO2 nanocomposite with an Al2O3 diffusion barrier

“…These results indicate that the Al 2 O 3 diffusion barrier suppresses the sintering of ZrO 2 particles after not only the final calcination at 900 • C but also higher temperature durability test (1000 • C) and the barrier in A80ZL most effectively inhibit the crystallite growth of ZrO 2 . Since pure ZrO 2 prepared by the conventional precipitation method generally forms a monoclinic crystal phase after thermal aging [6], rare earth elements have been added to improve the thermal stability of the crystallite itself [26]. In the case of a solid solution formed with these additives, the ZrO 2 crystal phase changes from monoclinic to cubic or tetragonal, hence improving its thermal stability.…”