Different oxidation routes for lattice oxygen recovery of double-perovskite type oxides LaSrFeCoO6 as oxygen carriers for chemical looping steam methane reforming

Double-perovskite type oxide LaSrFeCoO（LSFCO） was used as oxygen carrier for chemical looping steam methane reforming（CL-SMR） due to its unique structure and reactivity. Two different oxidation routes,steam-oxidation and steam-air-stepwise-oxidation, were applied to investigate the recovery behaviors of the lattice oxygen in the oxygen carrier. The characterizations of the oxide were determined by X-ray diffraction（XRD）, X-ray photoelectron spectroscopy（XPS）, hydrogen temperature-programmed reduction（H-TPR） and scanning electron microscopy（SEM）. The fresh sample LSFCO exhibits a monocrystalline perovskite structure with cubic symmetry and high crystallinity, except for a little impurity phase due to the antisite defect of Fe/Co disorder. The deconvolution distribution of XPS patterns indicated that Co,and Fe are predominantly in an oxidized state(Feand Fe) and(Coand Co), while O 1s exists at three species of lattice oxygen, chemisorbed oxygen and physical adsorbed oxygen. The double perovskite structure and chemical composition recover to the original state after the steam and air oxidation, while the Co ion cannot incorporate into the double perovskite structure and thus form the CoO just via individual steam oxidation. In comparison to the two different oxidation routes, the sample obtained by steam-oxidation exhibits even higher CHconversion, CO and Hselectivity and stronger hydrogen generation capacity.

Evaluation of multi-cycle performance of chemical looping dry reforming using CO_2 as an oxidant with Fe–Ni bimetallic oxides

Chemical looping dry reforming（CLDR） is an innovative technology for CO2 utilization using the chemical looping principle.The CLDR process consists of three stages,i.e.CH4 reduction,CO2 reforming,and air oxidation.Spinel nickel ferrite（NiFe2O4） was prepared and its multi-cycle performance as an oxygen carrier for CLDR was experimentally investigated.X-ray diffraction（XRD） and Laser Raman spectroscopy showed that a pure spinel crystalline phase（NiFe2O4） was obtained by a parallel flow co-precipitating method.NiFe2O4was reduced into Fe-Ni alloy and wustite（FexO） during the CH4 reduction process.Subsequent oxidation of the reduced oxygen carrier was performed with CO2 as an oxidant to form an intermediate state：a mixture of spinel Ni（1-x）Fe（2＋x）O4,Fe（2＋y）O4 and metallic Ni.And CO was generated in parallel during this stage.Approximate 185 mL of CO was generated for 1 g spinel NiFe2O4 in a single cycle.The intermediate oxygen carrier was fully oxidized in the air oxidation stage to form a mixture of Ni（1＋x）Fe（2-x）O4 and Fe2O3.Although the original state of oxygen carrier（NiFe2O4） was not fully regenerated and agglomeration was observed,a good recyclability was shown in 10 successive redox cycles.

Waste pulp chemical-looping gasification using Ni-modified electroplating sludge as an oxygen carrier

Waste pulp(WP)is a typical byproduct of paper industry,and Chemical-looping gasification(CLG)as a recently developed technology is highly suited to dispose high-volatile wastes like WP.In order to make a high-efficiency oxygen carrier(OC)for CLG of WP,the Ni-containing electroplating sludge(NES)was used as the matrix and NiO modification was performed to enhance the hydrogen production in CLG.These resulted in a potentially high-efficiency OC denoted as NNES.Testing CLG of WP was in a fixed-bed reactor at 850℃by adopting NNES as the OC,injecting 2.4 mL/g(WP)water,and keeping a mass ratio of 1.0 between OC to WP.It produced 1.73 Nm^(3)/kg syngas that has an LHV of 11.9 MJ/Nm^(3)and a H_(2)/CO ratio of 3.63.In 10 redox cycles,the syngas yield did not have obvious decrease,but a certain reduction in the activity of NNES was observed.Characterization of the spent NNES revealed that it is the Ni agglomeration and inert silicate generation which reduced the activity of NNES.

Effect of attack angle on the electromagnetic wave transmission characteristics in the hypersonic plasma sheath of a re-entry vehicle

The attack angle may greatly affect the hypersonic plasma sheaths around the re-entry vehicle,thereby affecting the transmission characteristics of electromagnetic(EM)waves in the sheaths.In this paper,we propose an integrated three-dimensional(3D)model with various attack angles and realistic flying conditions of radio attenuation measurement C-II(RAM C-II)re-entry tasks for analyzing the effect of the attack angle on the transmission characteristics of EM waves in the sheaths.It is shown that the electron density and collision frequency of the sheath on the windward side can be increased by an order of magnitude with the increase of the attack angle.Meanwhile,the thickness of the sheath on the leeward side is increased where the electron density and collision frequency are reduced.The EM waves are mainly reflected on the windward plasma sheath due to the cutoff effect,and the radio-frequency(RF)blackout is mitigated if the antenna is positioned on the leeward side.Thus,by planning the trajectory properly and installing the antenna accordingly during the re-entry,it is possible to provide an approach for mitigation of the RF blackout problem to an extent.

Chemical-Looping Reforming of Methane Using Iron Based Oxygen Carrier Modified with Low Content Nickel

Fe_(2)O_(3)/Al_(2)O_(3) and Fe_(2)O_(3)/Al_(2)O_(3) modified by low content of Ni(below 2%in weight)oxygen carriers were prepared by mechanical mixing and impregnation method.The synthesized oxygen carriers were characterized by means of X-ray diffraction(XRD),X-ray fluorescence(XRF),scanning electron microscopy(SEM),BET-surface area and temperature programmed reduction(TPR).Besides,redox cyclic reactivity and the performance of chemical looping reforming of methane of the oxygen carriers were studied in a thermal gravimetrical analysis(TGA)and fixed bed at 850℃.It was observed that the redox reactivity of the oxygen carriers is improved by Ni addition because synergic effect may occur between NiO and Fe_(2)O_(3)/Al_(2)O_(3) to form NiFe_(2)O_(4) and NiAl_(2)O_(4) spinel phases.However,the improvement was not apparent as Ni addition reached 1 wt%or more because more nickel loaded resulted in methane decomposition into H2 and carbon leading to carbon deposition.The SEM and BET analysis showed that NiFe_(2)O_(4) and NiAl_(2)O_(4) particles dispersed into the pores of the Fe_(2)O_(3)/Al_(2)O_(3) particles in the course of preparation.In addition,the resistance to sintering of the modified samples increased with the Ni addition increasing.The results of successive redox cycles showed that the Ni modified Fe_(2)O_(3)/Al_(2)O_(3) oxygen carriers have good regenerability.With integration of reactivity and carbon deposition,the content 1.04 wt%of nickel doping was an optimal amount in the three modified samples.