ZrO2 La2O3 Research Articles

Hydrogen production by methane reforming with H2S using Mo,Cr/ZrO2–SBA15 and Mo,Cr/ZrO2–La2O3 catalysts

A series of supported catalysts based on ceramic type supports (ZrO2–SBA15 and ZrO2–La2O3) and refractory metals (Mo,Cr) were prepared and tested in the methane reforming with hydrogen sulfide (H2S). The main products of the reaction were hydrogen (H2) and carbon disulfide (CS2). The physicochemical properties of these catalysts were characterized by XRD, STEM and N2-BET methods mainly. The evolution of crystalline phases along the reaction led to formation of sulfides and carbides, i.e., MoS2, ZrS2 and the carbides MoC, Mo3C2, which could be the active phases. At high temperatures (1073 K–1123 K) the SBA-15 structure collapses while formation of mixed phases occurs i.e., ZrSiO4; the CH4 and H2S conversion rates were dependent on temperature and catalysts composition, however, the evolution of crystalline phases at high temperatures seems essential for achieving high activity and selectivity.

Catalyst development for steam reforming of methane and model biogas at low temperature

Low temperature steam reforming (400–550°C) for the production of hydrogen offers significant advantages compared to the conventional process. The milder operating conditions lead to lower operation costs and cost of construction materials. Additionally, no CO shift reactor is required due to favorable temperature for the WGS reaction. In this work, we report the catalytic performance of Ni and Rh catalysts supported on La2O3–ZrO2 and La2O3–CeO2–ZrO2 for their application in a multifuel membrane reformer operating at low temperature. The performance of the catalysts is assessed in different operating conditions in methane steam reforming (GHSV, temperature, H2O/CH4 ratio) as well as in reforming of model biogas. Stability tests were conducted up to 90h on stream (1bar and 7bar) and the tendency toward carbon formation was investigated. All catalysts were active in the reforming reactions at 400–550°C and the catalysts supported on La2O3–CeO2–ZrO2 showed superiority in activity and stability probably due to the presence of ceria in the support which contributes to the reforming rate and the resistance to carbonaceous deposits. Ni(10)CeZrLa exhibited remarkably stable performance with minimum amount of carbon formed after 90h (ca. 0.05wt%). TPO and TPH analysis of the carbonaceous deposits showed that the dominating type of carbon is highly reactive and can be easily removed by oxidation or hydrogenation at 500°C. This fact makes the catalyst even more promising for the proposed low temperature process, since the catalyst can be hydrogenated by using part of the H2 production stream without further heating of the reactor.

Selective aerobic oxidation of 5-HMF into 2,5-furandicarboxylic acid with Pt catalysts supported on TiO2 - and ZrO2 -based supports.

Pt catalysts prepared over different metallic oxide supports were investigated in the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in alkaline aqueous solutions with air, to examine the combined effect of the support and base addition. The base (nature and amount) played a significant role in the degradation or oxidation of HMF. Increasing amounts of the weak NaHCO3 base improved significantly the overall catalytic activity of Pt/TiO2 and Pt/ZrO2 by accelerating the oxidation steps, especially for the aldehyde group. This was highlighted by a proposed kinetic model that gave very good concentration-time fittings. Moreover, the promotion of the catalyst with bismuth yielded a PtBi/TiO2 catalytic system with improved activity and stability. Y2 O3  and La2 O3 ZrO2 -supported catalysts exhibited lower activity than Pt/ZrO2 , which suggests no cooperative effect of the weakly basic properties introduced and the homogeneous base. Quantitative oxidation of HMF (0.1 M) and high yields of FDCA (>99 %) were obtained in less than 5 h by using an HMF/Pt molar ratio of 100 and Na2 CO3 as a weak base over PtBi/TiO2 (Bi/Pt=0.22).

Sulphated mesoporous La2O3–ZrO2 composite oxide as an efficient and reusable solid acid catalyst for alkenylation of aromatics with phenylacetylene

Sulphated mesoporous La2O3–ZrO2 composite oxides (SO42−/meso-La2O3–ZrO2) were firstly prepared by a surfactant-assisted co-precipitation/hydrothermal crystallization with subsequent impregnation method (SACPHC-IM). The prepared SO42−/meso-La2O3–ZrO2 catalyst was employed as solid acid to catalyze direct alkenylation of p-xylene with phenylacetylene for clean production of α-arylstyrene. Various characterization techniques such as N2 adsorption–desorption, X-ray diffraction (XRD), FT-IR, NH3 temperature-programmed desorption (NH3-TPD), and pyridine-IR were employed to reveal the relationship between catalyst nature and catalytic performance. The as-prepared SO42−/meso-La2O3–ZrO2 catalyst shows much superior catalytic activity and similar selectivity to SO42−/meso-ZrO2, ascribed to increasing acid properties, enlarging specific surface area and increasing pore volume, reducing average crystalline size resulting from the promoting effect of adding La into ZrO2 matrix. Furthermore, the SO42−/meso-La2O3–ZrO2 catalysts were optimized by varying the atomic ratio of La/(La+Zr) from 0.05 to 0.2. The SO42−/meso-La2O3–ZrO2 catalyst with the 0.1 of optimum La/(La+Zr) atomic ratio exhibited excellent catalytic performance, ascribed to the increase in amount acid sites and pore size. The results for stability test demonstrated that close to 100% of maximum conversion can be achieved, and more than 80% of conversion can be maintained with the time on stream up to 780min. Through simple calcination treatment, the spent catalyst can be almost complete recovered. The developed SO42−/meso-La2O3–ZrO2 catalyst could be a potential candidate for α-arylstyrene production via acid catalyzed direct alkenylation of aromatics with phenylacetylene.

Facile synthesis of luminescent and amorphous La₂O₃-ZrO₂:Eu³⁺ nanofibrous membranes with robust softness.

Novel luminescent and amorphous La2O3-ZrO2:Eu(3+) (LZE) nanofibrous membranes with robust softness are fabricated for the first time via a facile electrospinning technique. By incorporating zirconium oxide, the as-prepared lanthanum oxide nanofibrous membranes can be dramatically changed from extreme fragility to robust softness. Meanwhile, the softness and luminescent performance of LZE nanofibrous membranes can be finely controlled by regulating the doping concentration of zirconium oxide and europium in lanthanum oxide nanofibers. Additionally, the crystal structure analysis using X-ray diffractometer and high resolution transmission electron microscopy measurements have confirmed the correlation between the amorphous structure and softness. Furthermore, LZE membranes show the characteristic emission of Eu(3+) corresponding to (5)D(0, 1, 2)-(7)F(0, 1, 2, 3, 4) transitions due to an efficient energy transfer from O(2-) to Eu(3+). The LZE nanofibrous membranes with the optimum doping Eu(3+) concentration of 3 mol% exhibit excellent softness and luminescent properties, which make the materials to have potential applications in fluorescent lamps and field emission displays.

Studies of sulphated mixed oxides (ZrO2–SO4–La2O3) in the isomerization of n-hexane

A series of mixed oxides (ZrO2–La2O3) was investigated to establish the effect of the source of the sulphate ion and the modification of sol–gel zirconia with La2O3. Supports were synthesized varying the content of La2O3 (2, 3, 5 and 10wt.%). Sample sulphation took place in situ, maintaining the amount at 20wt.% using concentrated H2SO4 and a 1M (NH4)2SO4 solution as the sulphating agents. These catalytic materials were characterized by: X-ray diffraction, nitrogen adsorption (BET), FTIR pyridine, 2-propanol dehydration, Scanning Electron Microscopy (SEM) and isomerization of n-hexane. The modification of sol–gel zirconia with La2O3 originated an increase in the surface area. When increasing the content of La2O3 (3, 5 and 10wt.%) a diminution of the surface area for samples sulphated with H2SO4 (CASLn) occurred. On the contrary, for samples sulphated with (NH4)2SO4 (CSALn) a not defined behavior was presented. In mixed oxides, the tetragonal phase was present which is characteristic of sulphated zirconia. By SEM, the morphology of the support can be perfectly observed showing the presence of clusters in each of them. It was observed that the crystallite size did not change when increasing the lanthanum content for the CASLn supports. According with the FTIR pyridine technique all the samples exhibited the presence of Brönsted and Lewis sites, and the support that achieved the highest acidity was the one containing 2wt.% of La2O3 (CASL2). It was determined that the effect of the sulphate agent generated more active catalysts in terms of conversion of n-hexane and it was also observed that La2O3 provided a higher catalytic selectivity toward isomerization products.

The Al2O3–Zr(Hf)O2–La2O3 Phase Diagrams as a Scientific Basis for Developing New Thermal Barrier Coatings

Comparison of the isothermal sections in similar Al2O3–ZrO2–La2O3 and Al2O3–HfO2–La2O3 systems shows that equilibria between the α-Al2O3, Hf(Zr)O2, La2Zr2O7, La2Hf2O7, and LaAlO3 phases in these systems differ fundamentally. While the ZrO2−LaAlO3 equilibrium is observed in the system with ZrO2, the alternative La2Hf2O7–Al2O3 equilibrium takes place in the system with HfO2. The triangulation in the system with HfO2 changes. This phenomenon is probably due to higher thermodynamic stability of the La2Hf2O7 phase (melting point 2420°C) compared to the similar La2Zr2O7 phase (melting point 2280°C). Other equilibria in both systems are of the same type. Lanthanum hafnate can be directly deposited onto the binding coating without reacting with α-Al2O3 or destroying the thermal barrier coating. Stable performance of the lanthanum hafnate coating is expected.

Effects of noble metal-doping on Ni/La2O3–ZrO2 catalysts for dry reforming of coke oven gas

A series of noble metal (Ru, Pd, Ag) doped Ni catalysts supported on La2O3–ZrO2 mixed oxide were prepared using the sol–gel method and evaluated for use in dry reforming of coke oven gas (COG). The catalysts were investigated by means of N2 adsorption–desorption, XRD, H2-TPR, TPH, TEM and TG–DSC. TPH analysis revealed that two carbonaceous species formed on the used catalysts and that the low-temperature carbon species was sufficiently active for the reforming reaction. TEM observations indicated that highly dispersed and small metal particles were formed, suppressing coke deposition and improving catalytic performance. The test results indicated that the addition of trace amounts of noble metals effectively promotes catalytic activity. The 0.1Ru–10Ni/8LZ catalyst showed the highest performance among the bimetallic catalysts, because of the strong synergetic effect between Ru and Ni via the formation of a Ru–Ni alloy, which will be promising catalysts in the catalytic dry reforming of COG.

Hydrogen production from oxidative reforming of methane on Ni/γ-Al2O3 catalysts: Effect of support promotion with La, La–Ce and La–Zr

Ni/Al2O3 catalysts promoted by adding La2O3, La2O3–CeO2 and La2O3–ZrO2 were investigated on oxidative and steam reforming aiming the hydrogen production. The samples were characterized by surface area estimation (BET), XRD, TPR, TPD-H2 and XANES. Analysis of TEM and TPO was performed as complementary characterization for catalysts after reaction. The oxidative steam reforming of methane at temperatures above 500°C reveals that all the promoted catalysts presented better activities than the unpromoted. Below 500°C, the catalysts presented deactivation due to metallic nickel species oxidation and the TEM analysis of Ni/Al and Ni/La–Al catalysts revealed that the lanthanum addition led to a decrease in the Ni species particle size and also to a better active phase dispersion. The results suggest that below 500°C the activity may be related to differences in the metallic area values, although the Ni/La2O3–Al2O3 catalysts have shown a different behavior.

Effect of calcination conditions on time on-stream performance of Ni/La2O3–ZrO2 in low-temperature dry reforming of methane

A series of catalysts based on Ni supported on mesoporous La2O3–ZrO2 was prepared and tested in low-temperature (400 °C) dry reforming of methane for 100 h on stream. The catalysts were obtained from the same precursor by calcining in either flowing air or Ar at different temperatures. Both the temperature and the atmosphere had an effect on the catalytic activity and on-stream stability. With increasing calcination temperature, the dispersion of Ni decreased. Surprisingly, this resulted not in the lower, but in the higher intrinsic activity of Ni species. This increase can be rationalized by assuming that the rate-determining step is not CH4 decomposition, but the removal of carbon deposits from Ni particle by reaction with CO2. The catalysts calcined at 800 °C in Ar and air showed the strongest and the second strongest deactivation, respectively, caused by the formation of crystalline carbon coatings due to a lower number of CO2 adsorption sites. The size of Ni particles favoring the formation of layered carbon species was found to be the main origin of the catalysts deactivation in the low-temperature dry reforming of methane.

Phase relations in the ZrO2–La2O3–Y2O3–Al2O3 system: Experimental studies and phase modelling

Abstract Thermodynamic parameters of the La 2 O 3 –Y 2 O 3 and La 2 O 3 –Al 2 O 3 binary systems were re-assessed based on new experimental information. Phase relations in the La 2 O 3 –Y 2 O 3 –Al 2 O 3 system were investigated at temperatures 1523, 1673 and 1873 K by phase equilibration followed by phase identification by X-ray diffraction and microstructure investigation by scanning electron microscopy. Melting relations in the system were studied by differential thermal analysis. Temperature and liquid composition for two invariant reactions were determined. The obtained results were used to developed thermodynamic database for the La 2 O 3 –Y 2 O 3 –Al 2 O 3 system. Mutual solubility of La and Y in aluminates was taken into account. The obtained thermodynamic description was combined with already available databases of ternary systems and thermodynamic database of the ZrO 2 –La 2 O 3 –Y 2 O 3 –Al 2 O 3 was derived.

On processing and properties of liquid phase derived glass ceramics in Al2O3–La2O3–ZrO2 system

The role of Al2O3/La2O3 ratio in the processing and properties of sapphire-like glass ceramics in the Al2O3–La2O3–ZrO2 system is elucidated. We show that processing on an industrial scale (i.e. without a need for extremely rapid quenching and very high consolidation pressures) requires a certain degree of glass forming ability and glass stability. On the other hand, efficient crystallisation characterised by the ability to convert glass into a nanosized, fully devitrified product requires very unstable glasses. Development of glass converted nanoscale ceramics with properties similar to sapphire relies on compositions in which this interplay is conveniently balanced.

Controlled amorphous crystallization: An easy way to make transparent nanoceramics

Fabrication of transparent nanoceramics is attracting more and more interests recently. In this study a new method of amorphous sintering followed by controlled crystallization (ASCC) was developed, and transparent LaAlO3/t-ZrO2 nanoceramic was prepared as an example. Based on a eutectic composition of Al2O3–La2O3–ZrO2, glass powders were synthesized, sintered, and then converted to nanoceramics by post-heat-treatment. The heat-treatment performed at 1200°C for 2h produced a transparent LaAlO3/t-ZrO2 nanoceramic with an average grain size of 40nm. Due to the nanoscale microstructure, the ceramic showed a transparency up to 55% at 800nm (1mm thick), Vickers hardness of 19.05GPa, and fracture toughness of 2.64MPam1/2, respectively.

Study on Catalyst of Catalytic Wet Oxidation of High-concentration Industrial Organic Wastewater

A kind of compound catalyst containing the main activate component CuO, the second activate component ZrO2 and electronic promoter La2O3 was prepared. It was applicable to treat with high-concentration dimethyl acetylsuccinate (DMAS) production wastewater with catalytic wet air oxidation technology which was used in continuous bubble columns reactor. In this article the influences of concentration of soaked liquid of every component and the second activate component were studied, and the best preparation condition has been determined. The experimental results indicated that the catalyst of CuO-ZrO2-La2O3/ZSM-5 had a higher activity when handling high-concentration DMAS production wastewater. With this catalyst the CODcr removal rate could get 98.7% while non-catalyst only 35.8％ at the reaction conditions as follows: reaction temperature 240°C, reaction pressure 3.5MPa, liquor space velocity＝2.0 h-1, V (oxygen): V（wastewater）＝250:1 and influent wastewater pH=7.

Modified Lanthanum Zirconium Oxide buffer layers for low-cost, high performance YBCO coated conductors

Abstract The pyrochlore Lanthanum Zirconium Oxide, La2Zr2O7 (LZO), has been developed as a potential replacement barrier layer in the standard RABiTS three-layer architecture of physical vapor deposited CeO2 cap/YSZ barrier/Y2O3 seed on Ni–5%W metal tape. The main focus of this research is to ascertain whether: (i) we can further improve the barrier properties of LZO; (ii) we can modify the LZO cation ratio and still achieve a high level of performance; and (iii) it is possible to reduce the number of buffer layers. We report a systematic investigation of the LZO film growth with varying compositions of La:Zr ratio in the La2O3–ZrO2 system. Using a metal–organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of LaxZr1−xOy (x = 0.2–0.6) on standard Y2O3 buffered Ni–5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial LZO phase with only (0 0 1) texture can be achieved in a broad compositional range of x = 0.2–0.6 in LaxZr1−xOy. Both CeO2 cap layers and MOD–YBCO films were grown epitaxially on these modified LZO barriers. High critical currents per unit width, Ic of 274–292 A/cm at 77 K and self-field were achieved for MOD–YBCO films grown on LaxZr1−xOy (x = 0.4–0.6) films. These results indicate that LZO films can be grown with a broad compositional range and still support high performance YBCO coated conductors. In addition, epitaxial MOD LaxZr1−xOy (x = 0.25) films were grown directly on biaxially textured Ni–3W substrates. About 3 μm thick YBCO films grown on a single MOD–LZO buffered Ni–3W substrates using pulsed laser deposition show a critical current density, Jc, of 0.55 MA/cm2 (Ic of 169 A/cm) at 77 K and 0.01 T. This work holds promise for a route for producing simplified buffer architecture for RABiTS based YBCO coated conductors.

Experimental investigation and thermodynamic modelling in the ZrO2–La2O3–Y2O3 system

Abstract Phase equilibria in the La 2 Zr 2 O 7 –Y 2 O 3 join were studied in the temperature interval between 1250 and 1600 °C using the X-ray diffraction and thermal analysis. It was demonstrated that the maximal solubility of Y 2 O 3 in the La 2 Zr 2 O 7 (pyrochlore structure) was approximately 20 mol% of Y 2 O 3 . In mixtures containing more than 20 mol% Y 2 O 3 the La 2 Zr 2 O 7 reacted with Y 2 O 3 forming the fluorite structure at increasing temperature. The compound energy formalism was applied to describe solubility of Y 2 O 3 in pyrochlore structure assuming that Y 3+ can occupy both La 3+ and Zr 4+ enriched sites in the crystal structure. The Gibbs energies of compounds with pyrochlore structure were assessed. Ternary mixing parameters were included in thermodynamic description of the fluorite phase to reproduce in calculations its wide homogeneity range extending from ZrO 2 –Y 2 O 3 binary in the direction of LaYO 3 . Calculated phase diagrams reproduce general character of experimental data.

Experimental study of phase relations in the ZrO2–La2O3–Y2O3system

AbstractThermodynamic calculations in the ZrO2–La2O3–Y2O3system were used to select compositions for experimental investigations. The selected compositions were investigated using X-ray diffraction, scanning electron microscopy combined with energy dispersive X-ray spectroscopy and differential thermal analysis after prolonged heat treatment at 1250, 1400 and 1600 °C. The X-ray diffraction investigations indicated stability of the La2O2–A + (La,Y)2O3–B + La2Zr2O7and (La,Y)2O3–B + La2Zr2O7+ LaYO3-perovskite phase fields at 1250 °C, which is contrary to results found in the literature. The differential thermal analysis of the ZrO2-45.8La2O3-20.8Y2O3composition heat treated at 1250 °C showed no transformations up to 1500 °C. Two peaks were indicated at temperatures above 1450 °C: the first peak at 1530 °C could be attributed to the processes of Y2O3dissolution and disordering in the pyrochlore phase and the second peak at 1580 °C to transformation of perovskite to monoclinic B phase. The solubility of Y2O3in pyrochlore phase occurs by Y+3substitution of both Zr+4and La+3ions.

Thermally Stable CeO2–ZrO2–La2O3 Ternary Oxides Prepared by Deposition–Precipitation as Support of Rh Catalyst for Catalytic Reduction of NO by CO

The work mainly reported that CeO2–ZrO2–La2O3 mixed oxide was synthesized by deposition–precipitation method and used as support of Rh catalyst. The physicochemical properties of the resultant CeO2–ZrO2–La2O3 mixed oxides were characterized by X-ray powder diffraction (XRD), Vis-Raman, N2 adsorption, transmission electron microscopy, temperature-programmed reduction, and oxygen storage capacity and the catalytic activities of Rh-loaded CeO2–ZrO2–La2O3 catalysts were evaluated by the reduction reaction of NO by CO. The combination of XRD and Raman results demonstrates that the resultant CeO2–ZrO2–La2O3 mixed oxides have a mixed phase comprised mainly of m-phase, c-phase, and t-phase. Compared with the counterpart prepared by co-precipitation method, Rh-loaded CeO2–ZrO2–La2O3 catalysts prepared by the deposition–precipitation method exhibited higher heat tolerance and better catalytic activity for the reduction of NO by CO as well as more uniform and discrete nanoparticles. The structural and textural characteristics caused by synthesis technique and the high dispersity of Rh on the materials are dominant contributors to the improvement of catalytic performance.

Variation in the strength of base sites in the system La2O3–ZrO2 in the range 25-200°C

Based on electronic diffuse reflectance spectra of indicators adsorbed on La 2 O 3 -ZrO 2 , obtained at 25-200 °C, we have shown that the strength of its basic sites sharply increases from H -S ≤ +17.2 to H -S ≤ +33.0 in the range 25-140 °C.

Thermal ageing of Pt on low-surface-area CeO2–ZrO2–La2O3 mixed oxides: Effect on the OSC performance

This work aims at exploring the thermal ageing mechanism of Pt on ceria-based mixed oxides and the corresponding effect on the oxygen storage capacity (OSC) performance of the support material. Pt was supported on low-surface-area CeO2–ZrO2–La2O3 mixed oxides (CK) by impregnation method and subsequently calcined in static air at 500, 700 and 900°C, respectively. The evolutions of textural, microstructural and redox properties of catalysts after the thermal treatments were identified by means of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR) and high-resolution transmission electron microscope (HRTEM). The results reveal that, besides the sintering of Pt, encapsulation of metal by the mixed oxides occurs at the calcination temperature of 700°C and above. The burial of Pt crystallites by support particles is proposed as a potential mechanism for the encapsulation. Further, the HRTEM images show that the distortion of the mixed oxides lattice and other crystal defects are distributed at the metal/oxides interface, probably indicating the interdiffusion/interaction between the metal and mixed oxide. In this way, encapsulation of Pt is capable to promote the formation of Ce3+ or oxygen vacancy on the surface and in the bulk of support. The OSC results show that the reducibility and oxygen release behavior of catalysts are related to both the metal dispersion and metal/oxides interface, and the latter seems to be more crucial for those supported on low-surface-area mixed oxides. Judging by the dynamic oxygen storage capacity (DOSC), oxygen storage capacity complete (OSCC) and oxygen releasing rate, the catalyst calcined at 700°C shows the best OSC performance. This evident promotion of OSC performance is believed to benefit from the partial encapsulation of Pt species, which leads to the increment of Ce3+ or oxygen vacancies both on the surface and in the bulk of oxides despite a loss of chemisorption sites on the surface of metal particles.