Hydrogen production from coke oven gas over LiNi/γ-Al_2O_3 catalyst modified by rare earth metal oxide in a membrane reactor

The performance of LiNi/γ-Al2O3 catalysts modified by rare earth metal oxide （La2O3 or CeO2） packed on BCFNO membrane reactor was discussed for the partial oxidation of methane （POM） in coke oven gas （COG） at 875 ℃. The NiO/γ-Al2O3 catalysts with different amounts of La2O3 and CeO2 were prepared with the same preparation method and under the same condition in order to compare the reaction performance （oxygen permeation, CH4 conversion, H2 and CO selectivity） on the membrane reactor. The results show that the oxygen permeation flux increased significantly with LiNiREOx/γ-Al2O3 （RE = La or Ce） catalysts by adding the element of rare earth especially the Ce during the POM in COG. Such as, the Li15wt%CeO29wt%NiO/γ-Al2O3 catalyst with an oxygen permeation flux of 24.71 ml·cm^-2·min^-1 and a high CH4 conversion was obtained in 875 ℃. The resulted high oxygen permeation flux may be due to the added Ce that inhibited the strong interaction between Ni and Al2O3 to form the NiAl2O4 phase. In addition, the introduction of Ce leads up to an important property of storing and releasing oxygen.

Probing crystalline phase effect of rare earth metal oxides(REO)on Cu/REO(RE=Gd,Eu,Sm)catalysts for methanol steam reforming(MSR)to produce H_(2)

In this work,to study the phase structure effect,three groups of Cu/REO catalysts were prepared with cubic and monoclinic Gd_(2)O_(3),Eu_(2)O_(3)and Sm_(2)O_(3) supports for MSR reaction to produce H_(2).Based on CH3OH conversion and H_(2)yield,the reaction perfo rmance of the catalysts ranks as Cu/Sm_(2)O_(3)-M>Cu/Sm_(2)O_(3)-C>Cu/Gd_(2)O_(3)-M>Cu/Gd_(2)O_(3)-C>Cu/Eu_(2)O_(3)-M>Cu/Eu_(2)O_(3)-C.For the same kind of REO,Cu supported on the monoclinic support shows better performance than on the cubic one.Despite the phase structure difference,Sm_(2)O_(3) is the best support among all the three kinds of REOs.Compared with Cu/REO catalysts prepared with cubic supports,the corresponding catalysts prepared with monoclinic supports generally possess mo re surface oxygen vacancies,which can generate mo re surface active oxygen(O_(2)^(-)) and moderate basic sites.Moreover,the contents of Cu^(+) on the catalysts follow the same sequence.The reaction performance is positively related to the amount of these three types of surface sites.But metallic Cuo species is necessary to maintain the Cu^(+)■Cu^(0) redox cycle.Furthe rmore,on a catalyst with good perfo rmance,those vital surface reaction intermediates can be stabilized during the reaction.Cu/Sm_(2)O_(3)-M possesses the largest quantities of these surface sites,and has the appropriate amount of Cu^(+) and Cu^(0) after reduction,thereby displaying the optimal performance in all the catalysts.In conclusion,evident support crystal structure effect is observed for Cu/REO catalysts,and a monoclinic phase REO is a better support than the respective cubic phase one.

Comparative studies on promotional effect of Pr_(6)O_(11),Nd_(2)O_(3)and Sm_(2)O_(3)on Ni-SiO_(2) for pressurized carbon dioxide reforming of methane

The 7 wt%rare earth metal oxide promoted Ni-SiO_(2) catalysts of Ni-7Pr_(6)O_(11)-SiO_(2),Ni-7Nd_(2)O_(3)-SiO_(2),and Ni-7Sm_(2)O_(3)-SiO_(2) were prepared by the complex-decomposition method,and were comparatively evaluated for pressurized carbon dioxide reforming of methane(CRM)under severe conditions of 750℃,1.0 MPa,CH_(4)/CO_(2)=1,and gas hourly space velocity of 53200 mL/(g·h).The addition of rare earth metal oxide does not affect the Ni dispersion,and all of the catalysts show similarly high Ni dispersion of16.0%±0.2%.As a result,all of the catalysts are highly active for pressurized CRM,the initial CH_(4) conversions of which approach the thermodynamic equilibrium(47.0%±0.2%).In contrast,a clearly favorable effect of the added rare earth metal oxide on the stability of Ni-SiO_(2)was revealed from the CRM results for a time-on-stream of 50 h,and the highest stability without an observable decrease in the conversions of CH_(4)and CO_(2)was obtained over Ni-7Sm_(2)O_(3)-SiO_(2).Based on the characterization results of thermogravimetric differential scanning calorimetry(TG-DSC)and transmission electron microscopy(TEM),the improved stability of Ni-7Pr_(6)O_(11)-SiO_(2),Ni-7Nd_(2)O_(3)-SiO_(2),and Ni-7Sm_(2)O_(3)-SiO_(2)for pressurized CRM was manifested mainly as the suppressed formation of carbon nanotubes over the catalyst surface,the extent of which is dependent on the specific rare earth metal oxide.Moreover,the consecutive temperature programmed surface reaction of CH_(4),CO_(2),and O_(2)over Ni-7Sm_(2)O_(3)-SiO_(2)vigorously reveals that the addition of Sm_(2)O_(3)into Ni-SiO_(2)inhibits the CH_(4)decomposition but enhances the oxidization of the carbon species by CO_(2),leading to the well-balanced rates for forming and removing the coke over Ni-7Sm_(2)O_(3)-SiO_(2).These findings are not only beneficial to deeply understanding the promotional effect of rare earth metal oxides on Ni-based catalysts for CRM,but also important for extending the application of the less studied rare earth metal oxides as promoters for the metalsupported catalysts.

Review on Enhancement of Nitridation of Si Powder

This paper reviewed the effect of powder characteristics and additives including metals,rare earth oxides,and ZrO2 on nitridation of Si powder.The decrease of particle size of Si powder increased nitridation.Most of metal additives inhibited nitridation,while some metal additives such as Fe,Cu,Cr,and Ca increased nitrida—tion.Otherwise,the addition of metals might lead to the degradation of physical and mechanical properties of Si3N4.All the rare earth oxides,especially CeO2 and Eu2O3,showed nitridation enhancing effect.In addition,ZrO2 with small particle size showed a stronger enhancing effect.

Investigation of N-（Hydroxylethyl）pyrrolidone Dehydration over REOx-doped Nano-ZrO2 Catalyst

Catalyst plays an important role in the dehydration of N-（hydroxylethyl）pyrrolidone （NHP） to prepare N-vinyl-pyrrolidone （NVP）. At present, NVP yield is only about 30% on commercial ZrO2 catalyst. A coupled precipitation and solid dispersion technique was designed to prepare the nano-ZrO2 catalyst, in which rare earth metal oxides （REOx） was used as electronic promoter. The results indicated that the catalyst doped REOx （S-1.0） exhibits the optimum performance of NHP dehydration at moderate conditions. NHP conversion and NVP selectivity are respectively 97.0%, 82.3%. Of special interest is that the indexes of the catalyst （S-1.0-1.0） are up to 98.4% and 89.2% respectively. Furthermore, this catalyst bears the good stability. It means that nano-ZrO2 doped REOx catalyst might be a potential commercial catalyst for the NHP dehydration.

Evolution hydrothermal aging resistance mechanism study of zirconium and manganese doped CeO_(2)catalysts in soot catalytic combustion based on low Miller indices crystal surface effect

The thermogravimetric analysis(TGA)experiments were carried out to reveal the mechanism of Zr and Mn doping on catalytic activity of CeO_(2)catalyst both fresh and after hydrothermal aging,and the lattice morphology and valence changes were characterized by means of Brunauer-Emmett-Teller(BET)method,X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),and H_(2)-temperature programmed reduction(H_(2)-TPR).Density functional theory(DFT)and molecular thermodynamics calculations were applied to investigate the change in catalytic activity,crystal surface energy and crystal morphology caused by hydrothermal aging.The maximum reaction rate temperature of fresh Mn/CeO_(2)(389℃)is similar to that of CeO_(2)(371℃)and lower than that of Zr/CeO_(2)(447℃),but the catalytic performance of CeO_(2)decreases more severely after hydrothermal aging.The catalyst crystals show different degrees of crystal surface migration after hydrothermal aging,which leads to the reduction of Ce^(3+)/Ce^(4+) ratio and the active sites shift.DFT calculations indicate that the doping of Zr and Mn reduces the surface energy of the low Miller indices surface and increases the oxygen vacancy formation energy,leading to better thermal stability and lower catalytic activity.The Zr and Mn doping also changes the adsorption energy and Gibbs free energy of H_(2)O,which dominates the migration of(111)to(110)and(100)in the vapor environment.The crystal surface migration mechanism of CeO_(2)catalysts doped with Zr and Mn induced by H_(2)O molecules at high temperature obtained in this study can provide a valuable addition to the regeneration of CeO_(2)catalysts in the after-treatment systems of diesel engines.

Low temperature synthesis of high-entropy(Y_(0.2)Yb_(0.2)Sm_(0.2)Eu_(0.2)Er_(0.2))_(2)O_(3)nanofibers by a novel electrospinning method

High-entropy ceramics(HECs)show outstanding properties such as amorphous-like thermal conductivities,colossal dielectric constant,superionic conductivity,enhanced electromagnetic wave absorption ability,super hardness and strength,which are promising for structural and functional applications.However,the high synthesis temperature has become the bottleneck that hinders the scale-up production and practical applications of HECs.It is thus appealing to develop a novel low-temperature process for the synthesis of HECs.To demonstrate the feasibility of low-temperature synthesis,herein,an electrospinning method has been utilized,for the first time,for the synthesis of high-entropy(Y_(0.2)Yb_(0.2)Sm_(0.2)Eu_(0.2)Er_(0.2))_(2)O_(3)nanofibers.It has been found that after electrospinning from liquid precursors single phase(Y_(0.2)Yb_(0.2)Sm_(0.2)Eu_(0.2)Er_(0.2))_(2)O_(3) solid solution with bixbyite structure can be formed by calcining at a temperature as low as 500℃,which is at least about 1000℃ lower than that used in the solid-state synthesis method.The as-prepared(Y_(0.2)Yb_(0.2)Sm_(0.2)Eu_(0.2)Er_(0.2))_(2)O_(3) nanofibers are continuous and uniform with a smooth surface and a small diameter of 150 nm.It is also intriguing that the average grain size of(Y_(0.2)Yb_(0.2)Sm_(0.2)Eu_(0.2)Er_(0.2))_(2)O_(3) is only about 10 nm,which is much smaller than that in the solid-state synthesized powders.In addition,all the elements are homogeneously distributed along the nanofibers.This work demonstrates that high-entropy ceramic nanofibers can be synthesized from liquid precursors at low temperatures through a simple,efficient,and low-cost electrospinning method,which opens up a new avenue for the low-temperature synthesis of HECs.