Synthesis and investigation of the physico-chemical properties of catalysts based on mixed oxides CexZr1−xO2 (original) (raw)
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PPC and PETROMAT Symposium 2020
This study investigates the characteristics of Ce0.75Zr0.25O2 (CZO) incorporated with Nickel as transition metal. The CZO was successfully synthesized by the sol-gel synthesis to form Ce-Zr mixed oxide solid solution as required. Ni was incorporated into the CZO by impregnation method. The impact of nickel loading (10, 15, and 20 wt%) on the morphology, textural and chemical properties was investigated by various techniques, i.e. X-ray fluorescence spectroscopy (XRF), Brunauer-Emmet-Teller surface analysis (N2-BET), X-ray diffraction (XRD), ammonia temperature programmed desorption (NH3-TPD), hydrogen temperature programmed reduction (H2-TPR), simultaneous thermal analysis (STA), and scanning electron microscopy (SEM). It was found that as an increase in nickel loading, BET surface areas of the Ni/CZO catalysts were decreased whereas their acidity was slightly augmented and alternated in acid strength. Moreover, the altered reducibility of Ni/CZO catalysts was observed as changes in Nickel loading.
Catalytic properties of Ce x Zr1–x O2 prepared using a template in the oxidation of CO
Russian Journal of Physical Chemistry A, 2016
The catalytic activity in CO oxidation of Ce x Zr 1-x O 2 double oxides prepared using pine sawdust and cetyltrimethylammonium bromide (CTAB) as templates is compared. It is found by means of SEM and the low-temperature adsorption of N 2 that biomorphic oxides reproduce the macropore structure of the template. It is shown via XRD and Raman spectroscopy that all samples contained mixed ceria-zirconia oxide. The double oxides form a cubic phase with a lattice of the fluorite type at a ratio of Ce : Zr = 4, regardless of the nature of the template; when Ce : Zr = 1, the biomorphic mixed oxide forms a tetragonal phase. According to Raman spectroscopy and XRD it was shown that the distortion of the oxygen sublattice is higher in biomorphic samples. Energy dispersive analysis shows that Ca impurities were present in the biomorphic samples, introducing additional distortions in the lattice of double oxide and leading to the formation of anionic vacancies. It is found that when Ce : Zr = 4, the conversion of CO on biomorphic oxide in the range of 100-350°C is higher than that observed for Ce x Zr 1-x O 2 (CTAB); reducing the Ce : Zr ratio in the biomorphic sample to 1 results in a marked decrease in CO conversion at 100-200°C. It is concluded that these differences are due to changes in the mobility of the lattice oxygen.
Applied Organometallic Chemistry, 2006
Ceria-zirconia mixed oxide was successfully synthesized via the sol-gel process at ambient temperature, followed by calcination at 500, 700 and 900 • C. The synthesis parameters, such as alkoxide concentration, aging time and heating temperature, were studied to obtain the most uniform and remarkably high-surface-area cubic-phase mixed oxides. The thermal stability of both oxides was enhanced by mutual substitution. Surface areas of the Ce x Zr 1−x O 2 powders were improved by increasing ceria content, and their thermal stability was increased by the incorporation of ZrO 2. The most stable cubic-phase solid solutions were obtained in the Ce range above 50 mol%. The highest surface area was obtained from the mixed catalyst containing a ceria content of 90 mol% (200 m 2 /g). Temperature programmed reduction results show that increasing the amount of Zr in the mixed oxides results in a decrease in the reduction temperature, and that the splitting of the support reduction process into two peaks depends on CeO 2 content. The CO oxidation activity of samples was found to be related to its composition. The activity of catalysts for this reaction decreased with a decrease in Zr amount in cubic phase catalysts. Ce 6 Zr 4 O 2 exhibited the highest activity for CO oxidation. Copyright
Catalysis Today, 2011
Nanosized ceria-zirconia, ceria-hafnia and ceria-terbia solid solutions were synthesized by a modified coprecipitation method and evaluated for oxygen storage/release capacity (OSC) and CO oxidation activity. The physicochemical characteristics were investigated by various techniques namely, XRD, Raman, XPS, ISS, UV-vis DRS, TEM and BET surface area. XRD and Raman results revealed formation of Ce 0.75 Zr 0.25 O 2 , Ce 0.8 Hf 0.2 O 2 and Ce 0.8 Tb 0.2 O 2−ı solid solutions typical of fluorite like cubic structure. Variation in the lattice parameter confirmed the successful incorporation of dopant cations into the ceria lattice. XPS measurements revealed that Ce is present in both 3+ and 4+ oxidation states in all samples. UV-vis DRS studies suggested the presence of Ce 3+ ← O 2− charge transfer transitions attributed to oxygen defects in all the samples. ISS measurements indicated surface enrichment of cerium in ceria-hafnia solid solutions. The ceria-hafnia solid solutions exhibited a high OSC and better CO oxidation activity among the investigated samples. Systematic investigation of these materials provided valid information about the key factors that control the catalytic efficiency of the solid solutions for OSC and CO oxidation.
Hydrothermal and Solvothermal Synthesis of Cerium-Zirconium Oxides for Catalyst Applications
Cerium oxide (CeO2) is a rare earth metal oxide that has high oxygen storage capacity at low temperature. In order to enhance this capacity, as well as its thermal stability, it is necessary to combine CeO2 with zirconium oxide (ZrO2). This work focuses on the synthesis of ceriumzirconium oxides by hydrothermal and solvothermal treatment at low temperature to obtain ones suitable for catalyst applications. The possibility of the application of ceria-zirconia oxide to the delignification reaction was investigated. The experiments were conducted at a constant pressure of 5 MPa, constant temperature of 150 o C, and constant synthesis time of 2 h, in an autoclave reactor made of SUS 316 with an internal volume of 100 mL. Precursor was prepared from Ce(NO3)3 and ZrO(NO3)2 at 0.06 M concentration, dissolved in various solvents. The solvents used were water, water/ethanol (70:30 vol/vol), and water/ethylene glycol (70:30 vol/vol). After hydrothermal and solvothermal synthesis, the colloid products were dried at 60 o C for 6 h and then calcined at 500 o C for 6 h. The characterizations of the particle products were analyzed using SEM and XRD. Furthermore, these products were used for the hydrothermal delignification process of wood biomass. The addition of ceria-zirconia particles dramatically increased the percentage of lignin removal from rapeseed wood up to 97.58%. Based on the results, ceria-zirconia oxide particles are effective for the pre-treatment of wood biomass in bio-refinery applications. Moreover, ceria-zirconia oxides may reduce the use of chemical compounds in the delignification process.
Catalytic activity of CeO2–ZrO2 mixed oxide catalysts prepared via sol–gel technique: CO oxidation
Catalysis Today, 2001
CeO 2 -ZrO 2 mixed oxide catalysts were prepared via a sol-gel technique and tested for carbon monoxide (CO) oxidation. Highly uniform nano-size solid solution particles of ceria-zirconia were attained under the conditions of this study (ca 100 • C). The stabilization of the surface areas of the catalysts can be achieved by the addition of zirconium. The CO oxidation activity of the mixed oxides was found to be dependent on Ce/Zr ratio, which relates to the degree of reducibility. The catalytic activity for CO oxidation decreases with a decrease in Ce/Zr ratio. This might be due to the difference in phase compositions of the mixed oxides. It can be postulated that the cubic phase, fluorite structure, which is mainly found in Ce 1−x Zr x O 2 (where x < 0.5) could be reduced easily than the tetragonal phase found in Ce 1−x Zr x O 2 (where x > 0.5). Among the mixed oxide catalysts, Ce 0.75 Zr 0.25 O 2 was reported to exhibit the highest activity for CO oxidation.
Synthesis of Ceria Zirconia Oxides using Solvothermal Treatment
MATEC Web of Conferences, 2018
Ceria oxide (CeO2) is widely used as catalyst with high oxygen storage capacity at low temperature. The addition of zirconia oxide (ZrO2) to CeO2 can enhance oxygen storage capacity as well as thermal stability. In this work, ceria zirconia oxides has been synthesized via a low temperature solvothermal treatment in order to produce ceria zirconia oxides composite with high oxygen storage capacity as electrolyte of solid oxide fuel cells (SOFC). Under solvothermal conditions, solvent may control the direction of crystal growth, morphology, particle size and size distribution, because of the controllability of thermodynamics and transport properties by pressure and temperature. Water, mixed of water and ethanol (70/30 vol/vol), and mixed of water and ethylene glycol (70/30 vol/vol) were used as solvent, while Ce(NO3)3 and ZrO(NO3)2 with 0.06 M concentration were used as precursor. The experiments were conducted at temperature of 150 °C and pressure for 2 h in a Teflon-lined autoclave ...
Synthesis, structure and catalytic properties of Zr–Ce–Pr–O mixed oxides
Journal of Materials Chemistry, 2001
Zr 0.10 (Ce 12x Pr x ) 0.90 O 2 mixed oxides (x between 0 and 0.75) were prepared by coprecipitation (nitrates) or by the sol-gel route. Zirconium n-propoxide and cerium and/or praseodymium nitrates were used as precursors. ''Sol-gel'' oxides calcined at 900 uC were shown to be cubic with a fluorite-type structure. Coprecipated oxides could not be obtained as solid solutions. The BET surface area of these samples rapidly decreases when xw0.50. A Raman study confirmed that all oxides were cubic and evidenced the presence of oxygen vacancies. The optimum oxygen storage capacity (OSC) was obtained for Zr 0.10 (Ce 0.50 Pr 0.50 ) 0.90 O 2 . It appears that the substitution of cerium by praseodymium in Zr 0.10 Ce 0.90 O 2 mixed oxides leads to a material with improved redox properties. The presence of vacancies, associated with Pr 3z /Pr 4z ions, is thought to be responsible for these enhanced OSCs.
Journal of Physical Chemistry C, 2008
In this study, Ce 0.65 Zr 0.25 RE 0.1 O 2−δ (RE = Tb, Gd, Eu, Sm, Nd, Pr, and La) solid solutions were successfully prepared by the glycine-nitrate process and tested for CO oxidation activity. The X-ray diffraction results confirmed the formation of complete Ce 0.65 Zr 0.25 RE 0.1 O 2−δ solid solutions. The Raman spectroscopy measurements suggested the presence of oxygen vacancies due to defective structure formation and further evidenced the formation of solid solution. The high-resolution transmission electron microscopy observations showed the nanocrystalline nature of the solid solutions. From X-ray photoelectron spectroscopy analysis it was revealed that the cerium, terbium, and praseodymium are present in +3 and +4 oxidation states. The UV−vis diffuse reflectance spectroscopy indicated that the Pr 3+ ions in the Ce 0.65 Zr 0.25 Pr 0.1 O 2−δ system provoked a significant increase in the Ce 3+ fraction on the surface. H 2 temperature-programmed reduction measurements showed an enhanced surface reduction at much lower temperatures for Ce 0.65 Zr 0.25 Pr 0.1 O 2−δ sample compared to others, indicating increased oxygen mobility in these samples, which enable the enhanced oxygen diffusion at lower temperatures. Significantly high CO oxidation activity is exhibited by Ce 0.65 Zr 0.25 Pr 0.1 O 2 solid solution.