Homogenous and Heterogeneous Catalytic Activity of Azo-Linked Schiff Base Complexes of Mn(II), Cu(II) and Co(II)

Abstract  

Azo linked Schiff-base[L] complexes of Mn(II)(1), Cu(II)(2) and Co(II)(3) obtained by template method, in the reaction of 4-(benzeneazo) salicylaldehyde with 1,2-propanediamine in the present of metal acetate, respectively. Complexes are used as catalyst for oxidation of cyclohexene with tert-butylhydroperoxide (TBHP); oxidation of cyclohexene catalyzed by these complexes gave 2-cyclohexene-1-one and 2-cyclohexene-1-ol as major products. Conversion of cyclohexene achieved was 95–100% with (1), (2) and (3), with selectivity of 57, 92 and 100% for 2-cyclohexene-1-one, respectively. The encapsulated Cu(II) complex (Cu–NaY) catalyzes the oxidation of cyclohexene using TBHP as oxidant in good yield. (Cu–NaY) under optimized reaction condition gave three reaction products. A maximum of 100% conversion of cyclohexene has been achieved where selectivity of 2-cyclohexene-1-one was 83%.     

Host (nanocavity of zeolite-Y)/guest (Mn(II), Co(II), Ni(II) and Cu(II) complexes of pentadendate Schiff-base ligand) nanocomposite materials (HGNM): application in the heterogeneous oxidation of cyclohexene

Transition metal (M = Mn(II), Co(II), Ni(II) and Cu(II)) complexes with pentadendate Schiff-base ligand; N,N′-bis(salicylidene)-2,6-pyridinediaminato, H₂ [sal-2,6-py]; was entrapped in the nanocavity of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of bis(salicylaldiminato)metal(II); [M(sal)₂]-NaY; in the supercages of the zeolite, and (ii) in situ Schiff condensation of the metal(II) precursor complex with the corresponding 2,6-pyridinediamine; [M(sal-2,6-py)]-NaY. The new materials were characterised by several techniques: chemical analysis, spectroscopic methods (DRS, BET, FTIR and UV/Vis), conductometric and magnetic measurements. Analysis of the data indicates that the M(II) complexes are encapsulated in the nanodimensional pores of zeolite-Y and exhibit different from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix. The Host–Guest Nanocomposite Materials (HGNM); [M(sal-2,6-py)]-NaY; catalyzes the oxidation of cyclohexene with tert-butylhydroperoxide (TBHP). Oxidation of cyclohexene with HGNM gave 2-cyclohexene-1-one, 2-cyclohexene-1-ol and 1-(tert-butylperoxy)-2-cyclohexene. [Mn(sal-2,6-py)]-NaY shows significantly higher catalytic activity than other catalysts.     

Synthesis and characterization of alumina-supported Mn(II), Co(II), Ni(II) and Cu(II) complexes of bis(salicylaldiminato)hydrazone as catalysts for oxidation of cyclohexene with tert-buthylhydroperoxide

Complexes of type [M(SAH)(OH₂)], where M is Mn(II),Co(II),Ni(II) and Cu(II), and SAH is the Schiff-base formed by condensation of salicylaldehyde (2 equiv.) and hydrazine (1 equiv.), bis(salicylaldiminato)hydrazone, or “2-({(z)-2-[(E)-1-(2-hydroxyphenyl)methylidene]hydrazono}methyl)phenol” have been prepared and characterized by elemental analysis, IR, UV–vis spectroscopy, conductometric, small area X-ray photoelectron spectroscopy and magnetic measurements. Elemental analysis suggests the stoichiometry to be 1:1 (metal:ligand). The results indicate that the Schiff-base ligand coordinates through one azomethine nitrogen and two phenolic oxygen to the metal ions. Conductance measurements suggest the non-electrolytic nature of the complexes. The atomic concentration of the complexes showed the ratio of M:N:O = 1:2:3, that indicates that a water molecule was in the complex. Alumina-supported complexes “[M(SAH)OH₂]-Al₂O₃” catalyze the oxidation of cyclohexene with tert-butylhydroperoxide (TBHP). The major products of the reaction were 2-cyclohexene-1-ol, 2-cyclohexene-1-one and 2-cyclohexene-1-(tert-butylperoxy). The influence of solvent on the oxidation reaction has been studied. [M(SAH)OH₂]-Al₂O₃ shows significantly higher catalytic activity than other alumina-supported complexes. These catalysts can also be reused in the oxidation of cyclohexene several times. The new materials “[M(SAH)OH₂]-Al₂O₃” were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV–vis, XRD, DRS).     

Nanodispersed Au/Al2O3 catalysts for low-temperature CO oxidation: Results of research activity at the Boreskov Institute of Catalysis

This paper presents some important results of the studies on preparation and catalytic properties of nanodispersed Au/Al₂O₃ catalysts for low-temperature CO oxidation, which are carried out at the Boreskov Institute of Catalysis (BIC) starting from 2001. The catalysts with a gold loading of 1–2 wt.% were prepared via deposition of Au complexes onto different aluminas by means of various techniques (“deposition-precipitation” (DP), incipient wetness, “chemical liquid-phase grafting” (CLPG), chemical vapor deposition (CVD)). These catalysts have been characterized comparatively by a number of physical methods (XRD, TEM, diffuse reflectance UV/vis and XPS) and catalytically tested for combustion of CO impurity (1%) in wet air stream at near-ambient temperature. Using the hydroxide or chloride gold complexes capable of chemical interaction with the surface groups of alumina as the catalyst precursors (DP and incipient wetness techniques, respectively) produces the catalysts that contain metallic Au particles mainly of 2–4 nm in diameter, uniformly distributed between the external and internal surfaces of the support granules together with the surface “ionic” Au oxide species. Application of organogold precursors gives the supported Au catalysts of egg shell type which are either close by mean Au particle size to what we obtain by DP and incipient wetness techniques (CVD of (CH₃)₂Au(acac) vapor on highly dehydrated Al₂O₃ in a rotating reactor under static conditions) or contain Au crystallites of no less than 7 nm in size (CLPG method). Regardless of deposition technique, only the Cl-free Au/Al₂O₃ catalysts containing the small Au particles (d_i ≤ 5 nm) reveal the high catalytic activity toward CO oxidation under near-ambient conditions, the catalyst stability being provided by adding the water vapor into the reaction feed. The results of testing of the nanodispersed Au/Al₂O₃ catalysts under conditions which simulate in part removal of CO from ambient air or diesel exhaust are discussed in comparison with the data obtained for the commercial Pd and Pt catalysts under the same conditions.     

Oxidation of alcohols with tert-butylhydroperoxide catalyzed by Mn (II) complexes immobilized in the pore channels of mesoporous hexagonal molecular sieves (HMS)

The oxidation of alcohols with tert-butylhydroperoxide (TBHP), in the presence of Mn²⁺ complexes immobilized in the pore channels of mesoporous hexagonal molecular sieves (HMS), were investigated. It was found that immobilized [Mn(bpy)₂]²⁺/HMS is an efficient catalyst for the oxidation of alcohols such as benzyl alcohol, n-hexanol and cyclohexanol. The effects of reaction time, amount of Mn²⁺ in the catalyst, type of substrates and oxidants in this catalysis system were investigated. At optimum conditions, TBHP is more efficient oxidant with respect to H₂O₂. Following order has been observed for the percentage of conversions of alcohols: benzylic >1° >2°.     

Cobalt(II), Zinc(II) and Cadmium(II)-Squarate Complexes with N-Methylimidazole

Three M(II)-squarate complexes, [Co(sq)(H₂O)(Nmim)₄] (1), [Zn(μ_1,3-sq)(H₂O)₂ (Nmim)₂] _n (2) and [Cd(μ_1,3-sq)(H₂O)₂(Nmim)₂] _n (3) (sq = squarate, Nmim = N-methylimidazole) have been synthesized and characterized by elemental, spectral (IR and UV–Vis.) and thermal analyses. The molecular structures of the complexes have been investigated by single crystal X-ray diffraction technique. The squarate ligand acts as two different coordination modes as a monodentate (in 1) and bis(monodentate) (O ^1– O ³ ) bridging ligand (in 2, 3). The Co(II) atom has a distorted octahedral geometry with the basal plane comprised of three nitrogen atoms of Nmim ligands and a oxygen atom of squarate ligand. The axial position is occupied by a nitrogen atom of Nmim and one aqua ligand. The crystallographic analysis reveals that the crystal structures of 2 and 3 are one-dimensional linear chain polymers along the c and b axis, respectively. The configuration around each metal(II) ions are distorted octahedral geometry with two nitrogen atoms of trans-Nmim, two aqua ligands and two oxygen atoms of squarate-O¹,O³ ligand. These chains are held together by the C–H···π, π···π and hydrogen-bonding interactions, forming three-dimensional network.     

Complexes of poly(2-<Emphasis Type="Italic">N,N</Emphasis>-dimethylaminoethyl) methacrylate with heavy metals II. Oxidation of cyclohexene with <Emphasis Type="Italic">tert</Emphasis>-butylhydroperoxide

Metal complexes of poly(2-N,N-dimethylaminoethyl) methacrylate were prepared by complex-forming with aqueous solutions of salts of FeSO₄.2H₂O; CoCl₂.6H₂O; CuCl₂.2H₂O; VOSO₄.5H₂O; Na₂MoO₄.2H₂O and Na₂WO₄.2H₂O. The catalytic activity of the complexes was studied in the oxidation of cyclohexene as a model reaction. The activities of the complexes synthesized towards the reaction of cyclohexene epoxidation can be arranged by the following order: PDMAEM-MoO₂ ²⁺> PDMAEM-VO²⁺ > PDMAEM-WO₂ ²⁺> PDMAEM-Co²⁺ > PDMAEM-Fe³⁺> PDMAEM-Cu²⁺. The complexes catalyzing the homolytic decomposition of tert-butylhydroperoxide increased the maximum yield of 2-cyclohexene-1-ol and 2-cyclohexene-1-on. The yield of cyclohexene oxide and 2-cyclohexene-1-ol were 58% and 13%, respectively.     

A novel 2D luminescent lead(II) framework with 3-carboxylic acid-4H-1,2,4-triazole based on binuclear Pb2Cl2(H2O)2 building blocks

Under hydrothermal conditions using a triazole derivative ligand 3-carboxylic acid-4H-1,2,4-triazole (HL) and corresponding lead(II) salts, a novel two-dimensional(2D) lead(II) complex {[Pb(L)(μ₂-Cl)(H₂O)}_n (1) has been isolated. In 1 Pb₂Cl₂(H₂O)₂ building blocks can be observed, which are extended by tetra-dentate coordinated L ligands to form a 2D corrugated layered structure. 1 also represents a novel example of luminescent lead(II) frameworks with triazole derivatives. Solid-state fluorescence spectrum of 1 exhibits the excited peak at 376 nm while the emission peak at 604 nm.     

Electron-rich salen-type Schiff base complexes of Cu(II) as catalysts for oxidation of cyclooctene and styrene with tert-butylhydroperoxide: A comparison with electron-deficient ones

Two square planar copper(II) complexes of tetradentate Schiff base ligands derived from aromatic aldehydes and 2,2′-dimethylpropandiamine (H₂{salnptn(3-OMe)₂}, H₂{hnaphnptn}) have been prepared and used as catalysts for oxidation of cyclooctene and styrene with tert-butylhydroperoxide (TBHP). Oxidation of cyclooctene with TBHP gave cyclooctene oxide as the sole product, but in the case of styrene a mixture of styrene oxide and benzaldehyde has been obtained in ca. 1:3 molar ratio. It has been shown that the rate and selectivity of reaction depend to the electron-donor ability of substituents at the phenyl groups of the ligand and can be improved by introduction of π-electron-donating groups at the aromatic rings of salen-type Schiff bases. The structure of Cu{salnptn(3-OMe)₂} has been determined by X-ray crystallography at 291 K with results generally in agreement with those previously reported. The results suggest that the symmetrical Schiff base ligands are bivalent anions with tetradentate N₂O₂ donors derived from the phenolic oxygen and azomethine nitrogen atoms.     

A crucial role of O2 and O2 on mayenite structure for biomass tar steam reforming over Ni/Ca12Al14O33

Newly synthesized nickel calcium aluminum catalysts (Ni/Ca₁₂Al₁₄O₃₃) were tested in a fixed bed reactor for biomass tar steam reforming, toluene as tar destruction model compound. Four catalysts (Ni/Ca₁₂Al₁₄O₃₃) were prepared with Ni loading amount from 1, 3, 5 to 7 wt%, even 1% loading catalyst also showed excellent performance. Catalysts aged experiments in the absence (60 h on stream) and presence of H₂S were characterized by BET, X-ray diffraction (XRD), and Raman spectra. It was observed that Ni/Ca₁₂Al₁₄O₃₃ showed excellent sustainability against coke formation due to the “free oxygen” in the catalysts. It also exhibited higher H₂S-poisoning resistance property compared to the commercial catalysts Ni/Al₂O₃ (5%) and Ni/CaO_0.5/MgO_0.5. Raman spectra revealed that “free oxygen O₂⁻ and O₂²⁻” in the structure of the catalysts could be substituted by sulfur then protected Ni poisoning on some degree, but reactivation experiments by O₂ flowing showed that the sulfide Ni/Ca₁₂Al₁₄O₃₃ was difficult to completely restore, incorporation of sulfur in the structure only partly regain by O₂. The kinetic model proposes, as generally accepted, a first-order reaction for toluene with activation energy of 82.06 kJ mol⁻¹ was coincident with the literature data. The Ni/Ca₁₂Al₁₄O₃₃ catalyst was effective and relative cheap, which may be lead to reduction in the cost of hot gas cleaning process.     

Formation, Characterization and Electrical Conductivity of Polycarbosilazane-Cu(II), -Ni(II) and -Cr(III) Chloride Metallopolymers

A series of transition metal-polycarbosilazane complexes have been prepared by the reaction of poly(N,N-bis(dimethylsilyl)ethylenediamine), [–Si(CH₃)₂NHCH₂CH₂NH–] _n , with Cu(II), Ni(II), and Cr(III) chloride. The resulting complexes were characterized by infrared (FT-IR) and UV-visible spectroscopy, magnetic susceptibility measurements, thermogravimetric analysis (TGA), and powder X-ray diffraction (XRD). The average chain-chain spacing in these materials were estimated from XRD data and found to be 6.88, 7.91, 7.09, and 6.33 Å in metal-free, Cu(II)-, Ni(II)-, and Cr(III)-containing polycarbosilazanes, respectively. DC electrical conductivity measurements showed that all these metal-polycarbosilazane complexes exhibit semiconductor behavior while the metal-free matrix is an insulator.     

Non-thermal plasma-assisted catalytic NOx storage over Pt/Ba/Al2O3 at low temperatures

NO_x storage performances have been investigated on a Pt/Ba/Al₂O₃ catalyst by comparison using two types of non-thermal plasma (NTP) reactor: the “PDC system” reactor and the “PFC system” reactor. In the PDC system, the catalyst was placed in the discharge space and was activated by the plasma directly, whereas in the PFC system, the plasma reactor was followed by the catalyst. The results showed that the NO_x storage capacity (NSC) of the Pt/Ba/Al₂O₃ catalyst was significantly enhanced by the non-thermal plasma in the PDC and PFC system, and the PDC system exhibited better promotional effect than the PFC system in the temperature range of 100–300 °C. The NSC of the catalyst was increased with the increase of the input energy density both in the PDC and PFC system due to the higher NO oxidation at higher input energy density. It was also found that the ionic wind induced by plasma in the PDC system enhanced the quantity of the NO adsorbed onto the catalyst surface and therefore could react with the O-radical to form more NO₂, and thus promote the formation of nitrate on the catalyst.     

Effect of large cations (La and Ba) on the catalytic performance of Mn-substituted hexaaluminates for N2O decomposition

Mn-substituted La-hexaaluminate (LaMn_xAl_(12−x)O₁₉) and Ba-hexaaluminate (BaMn_xAl_(12−x)O₁₉) catalysts were prepared using the carbonates route and investigated for high-concentration of N₂O decomposition. It was for the first time found that the Ba-hexaaluminate exhibited higher activity than the La-hexaaluminate at a given Mn content, both of which were much more active than Mn/Al₂O₃ after being subjected to high-temperature (1400 °C) treatment. The catalytic activity varied with the Mn content and attained the best one at x = 1. X-ray diffraction (XRD) characterizations showed that a small amount of Mn (up to x = 1) promoted greatly the formation of phase-pure hexaaluminate, while excess Mn caused formation of catalytically inactive impurity phases, such as LaAlO₃, BaAl₂O₄, Mn₃O₄, and LaMnO₃, which covered partially the active sites and then led to a loss of the activity. UV–visible spectra showed that Mn²⁺ preferentially enter tetrahedral Al sites at a low Mn content (x = 0.5) for the La-hexaaluminate, which is quite different from the case of Ba-hexaaluminate where Mn³⁺ can substitute octahedral Al sites even at x = 0.5. Such a difference in the number of catalytically active Mn³⁺ sites in the octahedral position should be responsible for the higher activity of the Mn-substituted Ba-hexaaluminate.     

Support modification to improve the sulphur tolerance of Ag/Al2O3 for SCR of NOx with propene under lean-burn conditions

Ag/Al₂O₃ catalysts with 1 wt% SiO₂ or TiO₂ doping in alumina support have been prepared by wet impregnation method and tested for sulphur tolerance during the selective catalytic reduction (SCR) of NO_x using propene under lean conditions. Ag/Al₂O₃ showed 44% NO_x conversion at 623 K, which was drastically reduced to 21% when exposed to 20 ppm SO₂. When Al₂O₃ support in Ag/Al₂O₃ was doped with 1 wt% SiO₂ or TiO₂ the NO_x conversion remained constant in presence of SO₂ showing the improved sulphur tolerance of these catalysts. Subsequent water addition does not induce significant deactivation. On the contrary, a slight promotional effect on the activity of NO conversion to nitrogen is observed after Si and Ti incorporation. FTIR study showed the sulphation of silver and aluminum sites of Ag/Al₂O₃ catalysts resulting in the decrease in the formation of reactive intermediate species such as –NCO, which in turn decreases NO_x conversion to N₂. In the case of Ag/Al₂O₃ doped with SiO₂ or TiO₂, formation of silver sulphate and aluminum sulphate was drastically reduced, which was evident in FTIR resulting in remarkable improvement in the sulphur tolerance of Ag/Al₂O₃ catalyst. These catalysts before and after the reaction have been characterized with various techniques (XRD, BET surface area, transmittance FTIR and pyridine adsorption) for physico-chemical properties.     

Solvothermal synthesis of 1D and 2D cobalt(II) and nickel(II) coordination polymers with 2,5-dihydroxy-p-benzenediacetic acid

1D cobalt(II) and nickel(II) coordination polymers {[Co(dba)(H₂O)₄] · H₂O}_n (1) and {[Ni(dba)(H₂O)₄] · H₂O}_n (2) (H₂dba = 2,5-dihydroxy-p-benzenediacetic acid) were synthesized under low temperature solvothermal condition. When 4,4′-bipyridine (bpy) was introduced to the synthetic systems of 1 and 2, respectively, two novel 2D coordination polymers {[Co(dba)(bpy)] · 0.5H₂O}_n (3) and [Ni(dba)(bpy)(H₂O)₂]_n (4) with different structures were obtained. All of the compounds were characterized by elemental analysis, FT-IR, UV–Vis spectra and single crystal X-ray diffraction.     

Photoassisted hetero-Fenton mineralisation of azo dyes by Fe(II)-Al2O3 catalyst

Photoassisted Fenton mineralisation of two azo dyes Direct Red 23 (DR 23) and Reactive Orange 4 (RO 4) was studied in detail using a Fe(II) loaded Al₂O₃ as a heterogeneous catalyst in presence of H₂O₂ and UV-A light. 25 and 15% FeSO₄ loaded Al₂O₃ show the maximum efficiency in the degradation of DR 23 and RO 4 respectively. The effects of catalyst loading, H₂O₂ concentration, initial solution pH and initial dye concentration on photodegradation were investigated and the optimum conditions are reported. DR 23 undergoes easy degradation when compared to RO 4. The difference is due to the presence of stable triazine ring system in RO 4. The catalyst is reusable and the leaching of Fe(II) from the catalyst in each run is less than 10% in the pH range 2–7.     

Chemical zoning of calcium aluminoferrite formed during melt crystallization in CaO-SiO2-Al2O3-Fe2O3 pseudoquaternary system

In the CaO-SiO₂-Al₂O₃-Fe₂O₃ pseudoquaternary system, the solid solutions of Ca₂(Al_xFe_1−x)₂O₅, with x<0.7 (ferrite), Ca₂SiO₄ (belite), Ca₃Al₂O₆ (C₃A) and Ca₁₂Al₁₄O₃₃ (C₁₂A₇), were crystallized out of a complete melt during cooling at 8.3 °C/min. Upon cooling to 1370 °C, both the crystals of ferrite with x=0.41 and belite would start to nucleate from the melt. During further cooling, the x value of the precipitating ferrite would progressively increase and eventually approach 0.7. At ambient temperature, the ferrite crystals had a zonal structure, the x value of which successively increased from the cores toward the rims. The value of 0.45 was confirmed for the cores by EPMA. The chemical formula of the rims was determined to be Ca_2.03[Al_1.27Fe_0.68Si_0.02]_Σ1.97O₅ (x=0.65). As the crystallization of ferrite and belite proceeded, the coexisting melt would become progressively enriched in the aluminate components. After the termination of the ferrite crystallization, the C₃A and belite would immediately crystallize out of the melt, followed by the nucleation of C₁₂A₇. The C₁₂A₇ accommodated about 2.1 mass% Fe₂O₃ in the chemical formula Ca_12.03[Al_13.61Fe_0.37]_Σ13.98O₃₃, being free from the other foreign oxides (SiO₂ and P₂O₅).     

A novel disubstituted Lindqvist-type polyoxomolybdate [Te2Mo4O19] supporting two organic vanadyl moieties: Synthesis, characterization, and crystal structure of {[V(2,2-bipy)2]2(4,4-bipy)[Te2Mo4O19]}

The first example of disubstituted Lindqvist-type polyoxomolybdate {[V(2,2-bipy)₂]₂(4,4-bipy)[Te₂Mo₄O₁₉]} has been synthesized hydrothermally and characterized by elemental analyses, XPS, IR, TG-DTA and X-ray single crystal diffraction. The structural analysis shows that the neutral molecular unit [V(2,2-bipy)₂]₂[Te₂Mo₄O₁₉] consists of a novel Lindqvist-type polyanion [Te₂Mo₄O₁₉]⁶⁻ supporting two vanadyl moieties [V(2,2-bipy)₂]³⁺, and such neutral molecules are joined together by π − π stacking interactions between the pyridine groups to form a two-dimensional grid-like network with non-coordinating “guest” 4,4-bipys encapsulated.     

Effect of SO2 on the catalytic activity of Ga2O3–Al2O3 for the selective reduction of NO with propene in the presence of oxygen

The effect of coexisting SO₂ on the catalytic activity of Ga₂O₃–Al₂O₃ prepared by impregnation, coprecipitation and sol–gel method for NO reduction by propene in the presence of oxygen was studied. Although the activity of Al₂O₃ and Ga₂O₃–Al₂O₃ prepared by impregnation (Ga₂O₃/Al₂O₃(I)) and coprecipitation (Ga₂O₃–Al₂O₃(CP)) was depressed considerably by the presence of SO₂, NO conversion on Ga₂O₃–Al₂O₃ prepared by sol–gel method (Ga₂O₃–Al₂O₃(S)) was not decreased but increased slightly by SO₂ at temperatures below 723 K. From catalyst characterization, SO₂ treatment was found to cause two important effects on the surface properties: one is the creation of Brønsted acid sites on which propene activation is promoted (positive effect), and the other is the poisoning of NO_x adsorption sites on which NO reduction proceeds (negative effect). It was presumed that the influence of SO₂ treatment on the catalytic activity is strongly related to the balance between the negative and positive. The activity enhancement of Ga₂O₃–Al₂O₃(S) by SO₂ was accounted for by the following consideration: (1) increase of the propene activation ability by SO₂, (2) incomplete inhibition of NO_x adsorption sites by SO₂.     

Thermal shock resistance of in situ formed Si2N2O–Si3N4 composites by gelcasting

Thermal shock resistance of Si₂N₂O–Si₃N₄ composites was evaluated by water quenching and subsequent three-point bending tests of strength diminution. Si₂N₂O–Si₃N₄ composites which was prepared with in situ liquid pressureless sintering process using Yb₂O₃ and Al₂O₃ powders as sintering additives by gelcasting showed no macroscopic cracks and the critical temperature difference (ΔT_c) could be up to 1400 °C. A mass of pores existed in the sintered body and the irregular shaped fibers extended from the pores increased the thermal shock property.