Ce ZrO2 Research Articles

Comparative Study on Nano-Sized 1 wt% Pt/Ce0.8Zr0.2O2 and 1 wt% Pt/Ce0.2Zr0.8O2 Catalysts for a Single Stage Water Gas Shift Reaction

A comparative study on nano-sized Pt/Ce0.8Zr0.2O2 and Pt/Ce0.2Zr0.8O2 catalysts in a single stage water gas shift (WGS) reaction was carried out. These catalysts were prepared by impregnating 1 wt% Pt on nano-sized cubic (Ce0.8Zr0.2O2) and tetragonal (Ce0.2Zr0.8O2) supports. Both catalysts have been applied to WGS under identical conditions to understand beneficial effect of cubic/tetragonal phases of Ce(1 − x)Zr(x)O2. 1 wt% Pt/Ce0.8Zr0.2O2 exhibited higher CO conversion than 1 wt% Pt/Ce0.2Zr0.8O2. In addition, 1 wt% Pt/Ce0.8Zr0.2O2 catalyst showed relatively stable activity with time on stream. The high activity/stability of 1 wt% Pt/Ce0.8Zr0.2O2 catalyst was correlated to its higher Pt dispersion and easier reducibility.

Reaction characteristics of chemical-looping steam methane reforming over a Ce–ZrO 2 solid solution oxygen carrier

The Ce–ZrO2 solid solution oxygen carrier is active and stable in chemical-looping steam methane reforming for the co-production of syngas (synthesis gas) and hydrogen.

Combined H2O and CO2 Reforming of Methane Over Ni–Ce–ZrO2 Catalysts for Gas to Liquids (GTL)

Ni–Ce–ZrO2 catalysts with various CeO2/ZrO2 ratios have been prepared by co-precipitation method and applied for combined steam and carbon dioxide reforming of methane (CSCRM) to produce synthesis gas (H2/CO = 2) for gas to liquid (GTL) process. 15% Ni–Ce0.8Zr0.2O2 exhibits the highest activity as well as stability in CSCRM due to finely dispersed NiO with intimate contact with support and high oxygen storage capacity.

Thermodynamic Investigation of the Redox Properties for Ceria−Hafnia, Ceria−Terbia, and Ceria−Praseodymia Solid Solutions

Ceria-hafnia, ceria-terbia, and ceria-praseodymia solid solutions were prepared by the citric-acid (Pechini) method and characterized using X-ray diffraction (XRD) for structure and coulometric titration for redox thermodynamics. Following calcination at 973 K, XRD showed that both Ce(0.5)Hf(0.5)O2 and Ce(0.8)Hf(0.2)O2 exist as single-phase solid solutions and that the lattice parameters of the cubic fluorite structures shifted linearly with Hf content. Following calcination at 1323 K, Ce(0.8)Hf(0.2)O2 remained single phase but Ce(0.5)Hf(0.5)O2 separated into two phases with compositions of Ce(0.81)Hf(0.19)O2 and Ce(0.15)Hf(0.85)O2. At 973 K, oxidation isotherms for Ce(0.8)Hf(0.2)O2 and Ce(0.5)Hf(0.5)O2 were almost identical to oxidation isotherms for Ce(0.8)Zr(0.2)O2 and Ce(0.5)Zr(0.5)O2. Mixed oxides of ceria with terbia and praseodymia also formed single-phase fluorite structures, but each of the solid solutions was phase stable to calcination at 1323 K. The oxidation isotherms for the solid ceria-terbia and ceria-praseodymia solutions were similar to what would be expected for physical mixtures of these oxides.

Preparation of Pd‐Based Metal Monolithic Catalysts and a Study of Their Performance in the Catalytic Combustion of Methane

A series of Pd/SBA-15/Al2O3/FeCrAl and Pd/5 wt% Ce(1-x)Zr(x)O2/SBA-15/Al2O3/FeCrAl (x = 0-1) metal monolithic catalysts were prepared and characterized by various techniques. The catalytic activity and the stability of the catalysts for methane combustion were evaluated. All the catalysts retain the SBA-15 mesoporous structure, with PdO being confined in its channels. The results show that the addition of Ce(1-x)Zr(x)O2 as promoters can improve the activity and stability of the catalysts. The stabilities of the metal monolithic catalysts are much better than those of Pd/ SBA-15 particle catalysts. The catalyst with ZrO2 as promoter exhibits the best activity and stability (T90= 395 degrees C), and the conversion of methane remains constant during the 700 h test.

Structure and Catalytic Properties of Ceria-based Nickel Catalysts for CO2 Reforming of Methane

Carbon dioxide reforming (CDR) of methane to synthesis gas over supported nickel catalysts has been reviewed. The present review mainly focuses on the advantage of ceria based nickel catalysts for the CDR of methane. Nickel catalysts supported on ceria–zirconia showed the highest activity for CDR than nickel supported on other oxides such as zirconia, ceria and alumina. The addition of zirconia to ceria enhances the catalytic activity as well as the catalyst stability. The catalytic performance also depends on the crystal structure of Ni–Ce–ZrO2. For example, nickel catalysts co-precipitated with Ce0.8Zr0.2O2 having cubic phase gave synthesis gas with CH4 conversion more than 97% at 800 °C and the activity was maintained for 100 h during the reaction. On the contrary, Ni–Ce–ZrO2 having tetragonal phase (Ce0.8Zr0.2O2) or mixed oxide phase (Ce0.5Zr0.5O2) deactivated during the reaction due to carbon formation. The enhanced catalytic performance of co-precipitated catalyst is attributed to a combination effect of nano-crystalline nature of cubic Ce0.8Zr0.2O2 support and the finely dispersed nano size NiO x crystallites, resulting in the intimate contact between Ni and Ce0.8Zr0.2O2 particles. The Ni/Ce–ZrO2/θ–Al2O3 also exhibited high catalytic activity during CDR with a synthesis gas conversion more than 97% at 800 °C without significant deactivation for more than 40 h. The high stability of the catalyst is mainly ascribed to the beneficial pre-coating of Ce–ZrO2 resulting in the existence of stable NiO x species, a strong interaction between Ni and the support, and an abundance of mobile oxygen species in itself. TPR results further confirmed that NiO x formation was more favorable than NiO or NiAl2O4 formation and further results suggested the existence of strong metal-support interaction (SMSI) between Ni and the support. Some of the important factors to optimize the CDR of methane such as reaction temperature, space velocity, feed CO2/CH4 ratio and H2O and/or O2 addition were also examined.

Catalytic steam reforming of dimethyl ether (DME) over high surface area Ce–ZrO2 at SOFC temperature: The possible use of DME in indirect internal reforming operation (IIR-SOFC)

This study was aimed at developing a suitable reforming catalyst for later application in an indirect internal reforming solid oxide fuel cell (IIR-SOFC) fuelled by dimethyl ether (DME). It was found that, at temperature higher than 800 °C, DME decomposed homogeneously, producing CH4 and CH3OH with small amount of CO, CO2, and H2. High surface area Ce–ZrO2 can reform DME with steam efficiently at 900 °C, producing high contents of H2, CO, and CH4 without the presence of CH3OH in the product gas. The combination use of Ce–ZrO2 (as a pre-reforming catalyst) and Ni/Al2O3 in the single unit was proven to significantly improve the reforming performance. According to this combination, the role of Ce–ZrO2 is to first decompose CH3OH and some CH4 generated from the homogeneous decomposition of DME, while the role of Ni/Al2O3 is to reform CH4 left from the pre-reforming section and to maximize the yield of H2 production. As another approach, IIR-SOFC model was studied using an annular ceramic reactor, in which DME initially reacted with steam on Ce–ZrO2 + Ni/Al2O3 at the inner side of the reactor and then Ni/YSZ at the outer side. The stability and the yield of hydrogen production over this configuration were considerably higher than those of systems packed with single Ce–ZrO2, single Ni/Al2O3, and without the filling of catalyst. In addition, the degree of carbon formation on the surface of Ni/YSZ was significantly low. The successful development of this reforming pattern improves the efficiency of IIR-SOFC fueled by DME by eliminating the requirement of an external reforming unit installation.

Structural Characterization and Oxidative Dehydrogenation Activity of V2O5/CexZr1-xO2/SiO2 Catalysts

The thermal stability of a nanosized Ce(x)Zr(1-x)O2 solid solution on a silica surface and the dispersion behavior of V2O5 over Ce(x)Zr(1-x)O2/SiO2 have been investigated using XRD, Raman spectroscopy, XPS, HREM, and BET surface area techniques. Oxidative dehydrogenation of ethylbenzene to styrene was performed as a test reaction to assess the usefulness of the VOx/Ce(x)Zr(1-x)O2/SiO2 catalyst. Ce(x)Zr(1-x)O2/SiO2 (1:1:2 mol ratio based on oxides) was synthesized through a soft-chemical route from ultrahigh dilute solutions by adopting a deposition coprecipitation technique. A theoretical monolayer equivalent to 10 wt % V2O5 was impregnated over the calcined Ce(x)Zr(1-x)O2/SiO2 sample (773 K) by an aqueous wet impregnation technique. The prepared V2O5/Ce(x)Zr(1-x)O2/SiO2 sample was subjected to thermal treatments from 773 to 1073 K. The XRD measurements indicate the presence of cubic Ce0.75Zr0.25O2 in the case of Ce(x)Zr(1-x)O2/SiO2, while cubic Ce0.5Zr0.5O2 and tetragonal Ce0.16Zr0.84O2 in the case of V2O5/Ce(x)Zr(1-x)O2/SiO2 when calcined at various temperatures. Dispersed vanadium oxide induces more incorporation of zirconium into the ceria lattice, thereby decreasing its lattice size and also accelerating the crystallization of Ce-Zr-O solid solutions at higher calcination temperatures. Further, it interacts selectively with the ceria portion of the composite oxide to form CeVO4. The RS measurements provide good evidence about the dispersed form of vanadium oxide and the CeVO4 compound. The HREM studies show the presence of small Ce-Zr-oxide particles of approximately 5 nm size over the surface of amorphous silica and corroborate with the results obtained from other techniques. The catalytic activity studies reveal the ability of vanadium oxide supported on Ce(x)Zr(1-x)O2/SiO2 to efficiently catalyze the ODH of ethylbenzene at normal atmospheric pressure. The remarkable ability of Ce(x)Zr(1-x)O2 to prevent the deactivation of supported vanadium oxide leading to stable activity in the time-on-stream experiments and high selectivity to styrene are other important observations.

Low Temperature Selective CO Oxidation in Excess of H2over Pt/Ce—ZrO2Catalysts

Pt/Ce—ZrO2 catalysts have been designed and applied to selective CO oxidation at low temperature. Both tetragonal and cubic phase Ce—ZrO2 supports were prepared by co-precipitation method to get high surface area materials after calcination at 500 °C for 6 h in air. Selective CO oxidation was conducted using stoichiometric amounts of O2. Cubic Ce—ZrO2 supported Pt catalyst exhibited 78% CO conversion and 96% CO2 selectivity even at 60 °C, while Pt/Al2O3 catalyst showed less than l% CO conversion at the same condition. The higher CO conversion and CO2 selectivity (to CO2 as opposed to H2O) of Pt/Ce—ZrO2 catalyst is mainly due to the high oxygen storage capacity of Ce—ZrO2 and nano-crystalline nature of cubic Ce0.8Zr0.2O2.

Redox Properties and Catalytic Behavior of Praseodymium-Modified (Ce-Zr)O2 Solid Solutions in Three-Way Catalysts

The three-way catalyst promoters (Ce-Zr)O2, (Pr-Ce-Zr)O2 and (Pr-Zr)O2 were prepared by the sol-gel method. The reduction/oxidation behavior of these mixed oxides was compared. It is shown that the formation of (Pr-Zr)O2 cubic solid solution at high temperature up to 800 °C makes it more reducible, and that the ternary solid solution that formed in (Pr-Ce-Zr)O2 mixed oxides plays an important role in the reduction process. The catalytic performance tests reveal that the introduction of a small amount of praseodymium into (Ce-Zr)O2 favors the light-off temperature of C3H6 and NO and the effectiveness for NO conversion at the lean region.

Manufacture of synthesis gas

In general, there are three processes for production of synthesis gas; steam reforming, CO2 reforming and partial oxidation of methane or natural gas. In the present work, we refer to tri-reforming of methane to synthesize syngas with desirable H2/CO ratios by simultaneous oxy-CO2-steam reforming of methane. In this study, we report the results obtained on tri-reforming of methane over the Ni/ZrO2 based catalyst in order to restrain the carbon deposition and to evaluate the catalytic performance. Results of tri-reforming of CH4 by three catalysts (Ni/Ce–ZrO2, Ni/ZrO2 and Haldor Topsoe R67-7H) are showed that the coke on the reactor wall and the surface of catalyst were reduced dramatically. It was found that the weak acidic site, basic site and redox ability of Ce–ZrO2 play an important role in tri-reforming of methane conversion. Carbon deposition depends not only on the nature of support, but also on the oxidant as like steam or oxygen. Therefore, the process optimization by reactant ratios is important to manufacture the synthesis gas from natural gas and carbon dioxide.

Highly stable Ni catalyst supported on Ce–ZrO2 for oxy-steam reforming of methane

A novel catalyst, Ni/Ce–ZrO2, exhibits very high catalytic activity and stability even in the stoichiometric steam reforming of methane (H2O/CH4 = 1). Furthermore, when it was employed in oxy-steam reforming, it gave enhanced CH4 conversion (99.1%) at 750 °C and the activity was maintained for 100 h. The high catalyst stability is mainly ascribed to the synergistic effect of the Ce modifier resulting from high capacity to store oxygen and high ability to produce mobile oxygen.

Cylindrical Al2O3/TZP functionally graded materials by EPD

AbstractCylindrical Al2O3/Ce–TZP functionally graded com posites were fabricated by electrophoretic deposition and pressureless sintering in air. Negatively charged Ce–TZP and Al2O3 powders were deposited on a cylindrical electrode from an acetone based suspension. A continuous composition change is realised by chang ing the composition of the suspension. Sintering of the FGM at different temperatures, showed that a temper ature higher than 1550°C was necessary for densification. The resultant FGM cylinder with 5·6 mm dia. had an ideal mechanical structure: a central open channel, a tough Ce–ZrO2 core (KIc > 10 MPa m1/2), a continuous gradient interlayer, and a hard surface layer with HV higher than 15 GPa.