Nanocasting of Perovskites

The first synthesis of mesoporous mbced oxides was reported by Schwickardi et al. [64]. These authors reported the synthesis of a series of phase-pure spinels (ZnCr204, CoCr204, and NLA.I2O4) and LaFeOs perovskites with disordered pore structure using activated carbon as the hard templates and metal nitrates as 

---

Table 3.2 Structural parameters of the nanocast mesoporous perovskites obtained by performing N2 physisorption analysis at -196°C...

Figure 3.3 TEM images of nanocast mesoporous perovskites synthesized using ordered mesoporous KIT-6 siiica as hard tempiate.

The use of oxide-type perovskites as dry reforming catalysts will be dealt with extensively in Volume II of this book. In this chapter, we report one example of such catalyst in order to highlight the potentiahty of the nanocasting preparation method as a way to control bulk and smface properties of perovskite-derived catalysts. 

F. (2014) Nanocast LaNiOs perovskites as precursors for the preparation of coke-resistant dry reforming catalysts. 

Two topics of perovskite-type oxides were browed and discussed in this chapter one is the synthesis method and the other is its application in catalysis. Because of the diverse applications of perovskite-type oxides, special properties are usually required depending on the ultimate use, while the desired properties could be achieved by choosing a proper synthesis method. For example, using coprecipitation method could lead to a well crystallized stmcture, while by a nanocasting method perovskite with high surface area could be achieved. Thus, an overview of synthesis method for perovskite-type oxides reported in the publications was made for better understanding the advantage of each method. 

Synthesis and Catalytic Applications of Nanocast Oxide-Type Perovskites... 

Initial monitoring of the catalytic activity was performed using as-synthesized perovskites without any reduction step. In the case of conventional LaNiOs, very low values of conversions were observed for both CH4 and CO2 until 800 °C. For nanocast LaNiOs, comparatively higher conversions (approximately 40%) were... 

For many oxides, including mixed metal oxides, of catalytic interest, preparing a high-surface-area solid with thermally stable porous structure was extremely difficult until recentiy. The hard templating procedure provides a systematic solution to this problem. Nanocasting that makes use of a mesostructured solid template is a special case. Both mesostructured silica and mesostructured carbon have been demonstrated so fer as hard templates. Rather precise replicas of these nanomolds have been obtained for a variety of oxide-type perovskites. Unprecedented specific surface areas in the 150-200 m /g were reached. 

Wang, Y., Ren, J., Wang, Y., Zhang, F., Liu, X., Guo, Y., and Lu, G. (2008) Nanocasted synthesis of mesoporous LaCo03 perovskite with extremely high surfece area and excellent activity in methane combustion. /, Phys. Chem. C, 112 (39), 15293-15298. 

Wang, Y, Wang, Y, Liu, X.,etal. (2009). Nanocasted Synthesis of the Mesostructured LaCo03 Perovskite and Its Catalytic Activity in Methane Combustion, J. Nanosci. Nanotechno., 9, pp. 933-936. 

LaFei.xCOxOs (x = 0 or 0.4) perovskites were obtained by nanocasting using Fluka 05120 and Black Pearls 2000 conunercial carbons, which act as hard template during the gel formation and subsequently limiting the particle growing during the perovskite formation. Perovskites with the same nominal composition were also conventionally prepared. The results clearly showed that both commercial carbons was efficient to prepare perovskites with nanosized nature and specific surface area substantially improved. In addition, catalytic tests in the reduction of NO with CO evidenced the better activity of the nanocast perovskites. 

---