Structural properties and catalytic performance of the LaCuZn mixed oxides for CO2 hydrogenation to methanol

A series of La-Cu-Zn-O mixed oxide catalysts were synthesized by a co-precipitation method and calcined under different temperatures. The XRD, BET, TPR, N_2 O-adsorption, XPS, SEM and TPD techniques were carried out to measure the aimed catalysts. The results indicated that the chemical environment of lanthanum element changes with the increase of calcination temperature. The La_2 CuO_4 perovskite structure is obtained at the temperature higher than 823 K and the special copper species appear in the perovskites due to the special structure property. The catalysts with La_2 CuO_4 perovskite structure show higher methanol selectivity compared with the mixed copper catalyst. For the perovskite catalysts, the conversion of CO_2 changes with the same tendency of the copper species ratio((Cu~(α+)+Cu~0)/(Cu_(Total))%), which implied both Cu~(α+) and Cu~0 are important active sites in the perovskite catalyst for the reaction.     

Promoting effect of tantalum and antimony additives on deNOx performance of Ce3Ta3SbOx for NH3-SCR reaction and DRIFT studies

A superior Ce-Ta-Sb composite oxide catalyst prepared using homogeneous precipitation method exhibited excellent deNOx efficiency and nearly 100% N_2 selectivity with broad operation temperature window and better resistance to higher space velocity, meanwhile strong resistance to H_2 O and SO_2. This catalyst was systematically characterized using XRD, N_2 adsorption, SEM, TEM, XPS, ESR, Raman, H_2-TPR,NH3-TPD and in situ DRIFTS. There exists a synergistic effect between Ce, Ta and Sb species. It is further indicated that the prominent deNOx performance of the Ce3 Ta3 SbOx catalyst is attributed to the elevated Ce3+ concentrations, abundant active surface oxygen species, as well as surface acidity and reducibility,which is closely linked with the synergistic effect between Ce, Sb and Ta species. Results from DRIFTS reveal that the reaction mechanism of surface-adsorbed NH3 and NO_x species is linked to temperature,the L-H mechanism mainly occurs at low temperature(300 ℃),while the E-R mechanism occurs at high temperature(300 ℃). Overall,these findings indicate that Ce3 Ta3 SbOx is promising for NO_x practical abatement.     

Synergistic effects of PtFe/CeO2 catalysts afford high catalytic performance in selective hydrogenation of cinnamaldehyde

Selective hydrogenation of unsaturated aldehydes remains a grand challenge in controlling chemoselectivity up to now.We synthesized a series of PtFe_x/CeO₂ catalysts,which were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS) as well as temperature-programmed-reduction by hydrogen(H₂-TPR).The catalytic performance of PtFe_x/CeO₂,including cinnamaldehyde(CAL) conversion and sele...     

CeO2-supported Fe,Co and Ni toward CO2 hydrogenation: Tuning catalytic performance via metal-support interaction

The chemical transformation of CO₂ produces carbon compounds that can be used as precursors for the production of chemicals and fuels.Here,we investigated the activity and selectivity of the transition metals(Fe,Co,and Ni) supported on CeO₂ catalyst for CO₂ hydrogenation at atmospheric pressure.We found that Ni/CeO₂ shows the highest CO₂ conversion compared with Fe/CeO₂ and Co/CeO₂.Besides,Co/CeO₂ and Ni/CeO<...     

Effect of impregnation strategy on catalytic hydrogenation behavior of PtCo catalysts supported on La2O2CO3 nanorods

Small Pt and Pt-Co nanoparticles (NPs) stabilized on La₂O₂CO₃ nanorods (LOC) were prepared by wet impregnation method, and probed in liquid-phase chemoselective hydrogenation of crotonaldehyde (CRAL) to crotyl alcohol (CROL). It is found that incorporation of Co atoms into Pt catalyst significantly improves the hydrogenation activity and desired selectivity to CROL as it destroys the Pt-lanthanum interfaces and results into the formation of Pt-Co particles. In addition, a close examination of catalyst surface and reactive performance suggests that the impregnation sequence of Pt and Co exerts great influence on the physicochemical property and the catalytic hydrogenation behavior of PtCo/LOC catalysts. As a result of the interaction between Pt and Co species, high alloying degree of Pt-Co NPs is obtained in the co-impregnated catalyst (Pt-Co/LOC), thus achieving the highest hydrogenation activity. The selective deposit of Co atoms onto the low-coordinated Pt sites leads to the smallest metal particle size and high dispersion of Pt-Co NPs over the Pt/Co/LOC, giving rise to the highest selectivity and yield to CROL.     

Influence of ammonium sulfate on YAG nanopowders and Yb:YAG ceramics synthesized by a novel homogeneous co-precipitation method

Homogeneous and dispersed Y_3 Al_5 O_(12)(yttrium aluminum garnet,YAG) nanopowders were synthesized via a homogeneous co-precipitation method from the mixed solutions of yttrium nitrate,aluminum nitrate and a small amount of ammonium sulfate using hot urea as the precipitant.The method has the superiorities that co-precipitation of cations is ensured and continuous decomposition of the hot urea is achieved to obtain the narrow size distribution particles.The addition of small amount of ammonium sulfate surfactant,although has no influence on YAG garnet phase formation,has significant effect on dispersion,particles distribution and sinterability of the resultant YAG and Yb:YAG powders.Compared with the undoped sample,the green body of Yb:YAG doped with ammonium sulfate has higher total shrinkage,linear shrinkage rate and relative density through sintering at 1600 ℃.The resultant Yb:YAG powders can be sintered into transparent ceramics at 1700 ℃ through vacuum sintering.The influence of the sulfate ions on characteristics of the resultant powders was thoroughly studied.     

Study on alkali mechanical activation for recovering rare earth from waste fluorescent lamps

Recycling of rare earth from waste fluorescent lamps is becoming increasingly important in future sustainable development. However, cerium and terbium are usually difficult to recover due to the stable spinel structure. In the research, alkali mechanical activation was innovatively used to pretreat the waste phosphors for recovering rare earths. The effect of alkali mechanical activation on the structural changes of waste phosphors was explored using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Meanwhile, the effects of different parameters including milling speed, activation time, and amount of alkali on the leaching rates of rare earth were investigated. The rare earth elements recovery rates are observed to increase rapidly, particularly with increases in rotational speed and activation time. Under optimal conditions, the maximum leaching rates of Ce and Tb reach 85.0% and 89.8%, respectively. And the total recovery rates of rare earth reach 95.2%. All the results indicate that alkali mechanical activation can effectively destroy the spinel structure and produce substantial physicochemical changes. These changes lead to the easy dissolution of rare earths in acid solution, and greatly improve the leaching of cerium and terbium.     

Rare earth elements: Properties and applications to methanol synthesis catalysis via hydrogenation of carbon oxides

Methanol (CH₃OH) is an important industrial chemical with a wide variety of uses. Industrial methanol synthesis catalysts are typically composed of Cu, Zn, and Al, but the use of catalysts incorporating rare earth elements has been shown to improve the catalytic performance. Due to their unique chemical and physical properties, the use of rare earth elements (scandium, yttrium, and the lanthanides) in catalysis in general has continued to increase over the past few decades, while the use of rare earth in methanol synthesis catalysts has not, despite often improving performance. The ability of several of the rare earth elements (Pr, Ce, Eu, Tb, Yb) to easily switch between oxidation states makes them beneficial for many different types of catalysts. However, for methanol synthesis the surface basicity is an important property, and the basic nature of the rare earth elements can be used to tune the basicity of catalysts. A small number of correlations between rare earth properties and catalytic performance have been observed, but often do not apply to other catalysts. Properties such as strength of basic sites, ionic radius, and electronegativity have been found to correlate with performance results such as activity or selectivity.     

Synergistic effects of CeO2/Cu2O on CO catalytic oxidation: Electronic interaction and oxygen defect

For CO catalytic oxidation, Cu and Ce species are of great importance, between which the synergistic effect is worth investigating. In this work, CeO₂/Cu₂O with Cu₂O {111} and {100} planes were comparatively explored on CO catalytic oxidation to reveal the effects of interfacial electronic interactions and oxygen defects. The activity result demonstrates that CeO₂/o-Cu₂O {111} has superior performance compared with CeO₂/c-Cu₂O {100}. Credit to the coordination unsaturated copper atoms (Cu_CUS) on o-Cu₂O {111} surface, the interfacial electronic interactions on CeO₂/o-Cu₂O {111} are more obvious than those on CeO₂/c-Cu₂O {100}, leading to richer oxygen defect generation, better redox and activation abilities of CO and O₂ reactants. Furthermore, the reaction mechanism of CeO₂/o-Cu₂O {111} on CO oxidation is revealed, i.e., CO and O₂ are adsorbed on the Cu_CUS on Cu₂O {111} and oxygen defect of CeO₂, respectively, and then synergistically promote the CO oxidation to CO₂. The work sheds light on the designing optimized ceria and copper-based catalysts and the mechanism of CO oxidation.     

Chemical Bond and Spectral Effect of Rare Earth Compound Crystals

The chemical bond parameters and ionic polarizabilities in complex crystals are calculated.Themechanism of host influence on the nephelauxetic effect and hypersensitive transition is discussed.     

Magnetic and magnetocaloric properties in GdZn2 synthesized by ball milling

In this study, we prepared GdZn₂ by mechanical alloying method and measured its magnetization to reveal the magnetic and magnetocaloric properties. For a milling time (MT) ≥ 10 and 20 h, the GdZn₂ phase was confirmed by X-ray diffraction measurements. For MT = 40 and 60 h, amorphous like patterns are observed. For MT = 10 and 20 h, magnetization (M) as a function of temperature below 80 K shows ferromagnetic-like increase. The observed values of M are 4.5 μ_B at 5 K for MT = 10 and 20 h, which is smaller than that of the theoretical expected value of 7 μ_B. For MT = 40 and 60 h, the long-range ferromagnetic order collapses because there is no spontaneous magnetization. The value of ΔT, where ΔT is the full width at half maximum of the magnetic entropy change (ΔS_m (T)), increases significantly for MT ≤ 20 h because of the gradual release of magnetic entropy by the milling effect. Since M decreases with increasing MT, the maximum values of |ΔS_m|, the relative cooling power, and the refrigerant capacity also decreases.     

Synthesis and catalytic performance of macroporous La_(1-x)Ce_xCoO_3 perovskite oxide catalysts with high oxygen mobility for catalytic combustion of soot

The disordered macroporous-mesoporous La_(1-x)Ce_xCoO_3 catalysts were prepared by complexcombustion method with ethylene glycol as complexing agent at relatively low calcination temperature.The samples were characterized by means of X-ray diffraction,N2 adsorption-ndash;desorption,Xray photoelectron spectroscopy,transmission electron microscopy,hydrogen temperature-programmed reduction and soot temperature-programmed reduction,and so on.The results show that the use of complexing agent and relatively low calcination temperature increase the specific surface area of the catalyst and have abundant pore structure.The Ce ions introduced into lattice of LaCoO_3 mainly exist in the form of tetravalent.At the same time,Ce ions enhance the redox performance of the catalyst and the mobility of active oxygen species,which enhances the catalytic activity of the catalyst for soot combustion.The results of activity test show that La_(0.9)Ce_(0.1)CoO_3 catalyst exhibits the highest activity in the absence of NO and NO_2,and its T_(10),T_(50) and T_(90) are 371,444,and 497℃,respectively.At the same time,a possible reaction mechanism is proposed in this study based on the turnover frequency(TOF) calculated by isothermal anaerobic titrations,XPS and XRD results.     

Effect of interaction between different CeO2 plane and platinum nanoparticles on catalytic activity of Pt/CeO2 in toluene oxidation

The plane exposure of support vitally affects the catalytic performance of the catalyst. In this work, CeO₂ nanorods ((110) plane exposure), nano-octahedrons ((111) plane exposure) and nano-cubes ((100) plane exposure) were prepared as the supports of Pt/CeO₂ samples to investigate the effect of CeO₂ plane exposure on total toluene oxidation. Characterizations reveal that the (110) plane of CeO₂ is more helpful to the dispersion of Pt species, followed by (111) face. The improved dispersion of Pt species can enhance the metal-supports interaction, which promotes the electron transfer of CeO₂ carrier to Pt nanoparticles and the adsorption-activation of O₂, thereby facilitating the total oxidation of toluene via the Langmuir–Hinshelwood (L-H) mechanism. Therefore, Pt/CeO₂-r (nanorods) sample expresses excellent catalytic performance of toluene oxidation. Finally, the procedure of toluene total oxidation was studied by in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. We expect that this work can contribute to the development of an effective sample for the decomposition of volatile organic compounds (VOCs).     

Promotion effect of niobium on ceria catalyst for selective catalytic reduction of NO with NH3

The CeO₂, Ce–Nb–O_x and Nb₂O₅ catalysts were synthesized by citric acid method and the promotion effect of Nb on ceria for selective catalytic reduction (SCR) of NO with NH₃ was investigated. The catalytic activity measurements indicate that the mixed oxide Ce–Nb–O_x presents a higher SCR activity than the single oxide CeO₂ or Nb₂O₅ catalyst. In addition, the Ce–Nb–O_x catalyst shows high resistance towards H₂O and SO₂ at 280 °C. The Raman, X-ray photoelectron spectra and temperature programmed reduction with H₂ results indicate that the incorporation of Nb provides abundant oxygen vacancies for capturing more surface adsorbed oxygen, which provides a superior redox capability and accelerates the renewal of active sites. Furthermore, the Fourier transform infrared spectra and temperature programmed desorption of NH₃ results suggest that niobium pentoxide shows high surface acidity, which is partly retained in the Ce–Nb–O_x catalyst possessing a high content of Lewis and Brønsted acid sites. Therefore, the incorporation of Nb improves both the redox and acidic capacities of Ce–Nb–O_x catalyst for the SCR reaction. Here, the redox behavior is primarily taken on Ce and the acidity is well improved by Nb, so the synergistic effect should exist between Ce and Nb. In terms of the reaction mechanism, in situ DRIFT experiments suggest that both NH₃ on Lewis acid sites and NH₄⁺ on Brønsted acid sites can react with NO species, and adsorbed NO and NO₂ species can both be reduced by NH₃. In the SCR process, O₂ primarily acts as the accelerant to improve the redox and acid cycles and plays an important role. This work proves that the combination of redox and acidic properties of different constituents can be feasible for catalyst design to obtain a superior SCR performance.     

Hydrogen Fixation Effect of Rare Earths in Pure Aluminium and Aluminium Alloys

The areal distribution of some elements in the rare earth bearing spheroidal phases in pure aluminium andAl-Mn alloys was studied by SIMS(secondary ion mass spectrometry).The results show that cerium,iron.silicon and hydrogen are significantly segregated in the phases.Thus the existence of hydrogen-rich rare earthbearing eompounds is confirmed.It indicates that the rare earths have a hydrogen fixation effect in aluminiumand aluminium alloys.     

Effects of cerium doping position on physicochemical properties and catalytic performance in methanol total oxidation

The physicochemical properties of Pd and PdPt catalysts which possess different Ce doping position were investigated by techniques of TEM, XRD, N₂ adsorption-desorption, XPS and FT-IR. The catalytic performance for methanol total oxidation was examined to study the effects of Ce adding position. CeO₂Al₂O₃TiO₂ (CAT) catalysts that Ce is directly introduced into support show higher reactivity and CO₂ selectivity than CeO₂/Al₂O₃TiO₂ (Ce/AT) samples in which Ce is loaded by impregnation method. The characterization results reveal that the Ce doping position does not cause obvious otherness of basic crystalline phase and mesoporous structure of support. However, the Ce doping position affects the pore shapes of support and then influences the pore diameter. CAT catalysts possess more abundant adsorbed oxygen and more Ti³⁺ can transform the more gaseous oxygen into the active oxygen species on the catalyst surface, which is beneficial to the reaction. The AlOTi bridges in CAT facilitate the cooperation of Al and Ti species, which further speeds up the reaction rate.     

RE-NiOx (RE=Ce,Y, La) composite oxides coupled plasma catalysis for benzene oxidation and by-product ozone removal

Plasma-coupled catalysis is a promising volatile organic co mpounds(VOCs) removal technology because of its interactional principles of plasma decomposition and catalytic oxidation.However,the problem of harmful by-products is still in trouble.A series of rare earth doped RE-NiO_x(RE=Ce,Y,La) composite oxides were synthesized by metal organic frameworks(MOFs)-derived method for coupled plasma oxidation of benzene and by-product ozone removal.Compared with plasma alone,the 1%La-NiO_...     

Green mediated synthesis of lanthanum doped zinc oxide: Study of its structural,optical and latent fingerprint application

The present paper summarises the synthesis of La³⁺ doped zinc oxide nanoparticles using Aloe vera gel by solution combustion method and the characterization using a powder X-ray diffractometer (PXRD), a transmission electron microscope (TEM), an X-ray photometric spectrometer (XPS), a Raman spectrometer and their applications in optical devices and latent fingerprinting. PXRD pattern confirms the crystallite size of La³⁺ doped ZnO varies from 13 to 20 nm. Crystallite size varies inversely with doping concentration. Photoluminescence properties are found to be the maximum for 2 mol% doping concentration. PL spectra extends the use of ZnO:La³⁺ nanoparticles in blue green LED. These nanoparticles also have superior property as a fluorescent labels in fingerprints.     

Modifying Effect of Rare Earths and Titanium on Austenitic Manganese Steel

ＭｏｄｉｆｙｉｎｇＥｆｅｃｔｏｆＲａｒｅＥａｒｔｈｓａｎｄＴｉｔａｎｉｕｍｏｎＡｕｓｔｅｎｉｔｉｃＭａｎｇａｎｅｓｅＳｔｅｌＺｈｕＲｕｉｆｕ（朱瑞富），ＬüＹｕｐｅｎｇ（吕宇鹏），ＬｉＳｈｉｔｏｎｇ（李士同）ＣｈａｏＺｈｉｑｉａｎｇ（朝志强），Ｗａ...     

Advances and prospects of rare earth metal-organic frameworks in catalytic applications

In recent years,rare earth metal-organic frameworks(RE-MOFs) have attracted increasing attention because of abundant coordination behaviors,adjustable channels and stable networks.The various electron structures of rare earth ions contribute to the catalytic applications of RE-MOFs and their derivates.In this review,we systematically summarize the research progress that using RE-MOFs and their derivates as catalysts for organic reaction,photocatalytic reaction,and CO oxidation reaction.The major parts include synthetic strategies and catalytic applications of the RE-MOFs.Finally,impressive achievements of RE-MOF catalysts are emerging and a prospect is provided for the development of RE-MOF catalysts at the end of the review.