An application of Nanoparticles. Application of ZrO 2 as a Catalyst and a Catalyst Support

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1 An application of Nanoparticles Application of ZrO 2 as a Catalyst and a Catalyst Support

2 Introduction Characteristics of ZrO 2 High T m (>3000K) Low K c High resistance for corrosion Refractories, pigments, piezoelectric devices, ceramic condensers, oxygen sensors Partially Stabilized Zirconia (PSZ) Application to fine ceramics due to high mechanical strength and high tenacity

3 Introduction (cont.) Ni/YSZ ll YSZ ll LaSrMnO 3 Steele, B.C.H and Heinzel A., Nature, 414, p (2001). YSZ: Oxygen ion conductivity

4 Introduction (cont.) To use as a catalyst/support - Single/combined oxides - High thermal stability rather than TiO 2, SiO 2, and Al 2 O 3 - Acid-base bifunctional catalysis Even if the surface area is actually not large compared with SiO 2, Al 2 O 3 which have frequently been used as catalytic supports

5 Preparation of zirconia Raw materials: Zircon, natural ores, or baddeleyite By alkali fusion, plasma fusion, or carbon reduction 1) Fusion of zircon and sodium hydroxide ZrSiO 4 +2NaOH Na 2 ZrSiO 5 +H 2 O 2) Washing and reduction Na 2 ZrSiO 5 +4HCl ZrOCl 2 +2NaCl+SiO 2 +2H 2 O 3) Neutralization of Zr salt with alkali ZrOCl 2 +2NH 4 OH ZrO(OH) 2 +2NH 4 Cl 4) Calcination ZrO(OH) 2 ZrO 2

6 Preparation of zirconia (cont.) Problem: Separation between Zr and Hf Due to the similarities of physical and chemical properties Impurities and contamination: Si, Na, Cl, Al, Fe, Ti, S may modify surface properties of ZrO 2 Using Zr(OH) 4 manufactured from zirconium alkoxide as a starting material can be avoided contamination

7 Preparation of zirconia (cont.)

8 Preparation of zirconia (cont.) Manufacturing of PSZ containing Ca or Y 1) Wet method Coprecipitation of solution of Zr +Y(Ca) salts 2) Thermal method Calcination of mixture of ZrO 2 and Y 2 O 3 (CaO) 3) Electric fusion Ores + Y 2 O 3 (CaO)

9 Change in the surface area and crystal form of ZrO 2 by calcination temperature (metastable)

10 Structure and Surface Properties Crystalline modifications Monoclinic (<1200 o C) Tetragonal(<1900 o C) Cubic Metastable tetragonal phase (<650 o C) exists Phase Transformation meta-zro 2 to m-zro 2 (about o C) m-zro 2 to t-zro 2 (>1000 o C): accompanied with volume change (3-5%) Addition of stabilizers to C and T (PSZ) Use meta-zro 2, m-zro 2, and t-zro 2 as a catalyst with active sites due to surface activity

11 Characterization nature ZrO 2 : Almost neutral metal oxide Acid site: Zr 4+ very weak strength Base site: O 2- cause high selectivity and long catalyst life since undesirable side reactions and catalyst deactivation due to coking often occur on strong acid/base sites. High activity due to acid-base bifunctional catalysis orientation of acid-base pair sites is important depends on preparation method, pretreatment condition, and addition amounts of other metal oxides

12 Characterization nature (cont.) For the activation of hydrogen

13 Effect of additives on the temperature of the exothermic peak in DTA (a) SO 4 2-, (b) Cr ion

14 Model structures of zirconium polycation proposed by Murase et al. in ZrO 2 obtained by calcination of zirconium hydroxide Without aging Vacuum treatment Precursor of t-zro 2 With aging Steam treatment Precursor of m-zro 2

15 TPD (Temperature Programmed Desorption) profiles of NH 3 (basic) and CO 2 (acid) on SiO 2 -Al 2 O 3, MgO and ZrO 2 SiO 2 -Al 2 O 3 (solid acid), MgO (solid base), ZrO 2 (acid-base bifunctional)

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17 Selectively dehydration of 1-amino-2-propanol to allylamine

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19 Promoted ZrO 2 Can be modified by the addition of cationic or anionic substances Acidic properties with alkali cation improve the selectivity in the dehydration of alcohols Acidic properties with anion addition of sulfate ions to produce the solid superacid (SO4/ZrO2) to catalyze the skeletal isomerization of alkanes, Fiedel- Crafts acylation and alkylation etc. SO 4 /ZrO 2 catalyst for n-butane isomerization

20 SO 4 /ZrO 2 catalyst Deactivation may originate from the removal or reduction of sulfur and the formation of carbonaceous polymers Solutions 1) Al 2 O 3, SiO 2 -promoted SO 4 /ZrO 2 2) Pt, Fe, Mn, W-promoted SO 4 /ZrO 2

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22 Catalytic activities of chromium oxide supported on SiO 2, ZrO 2, and Al 2 O 3 for CO oxidation

23 Surfaces of Sulfated Zirconia