Guoxing Xiong

Ba effect in doped Sr(Co0.8Fe0.2)O3-δ on the phase structure and oxygen permeation properties of the dense ceramic membranes

BaxSr1-xCo0.8Fe0.2O3-δ (x=0∼1.0) composite oxides were prepared by a combined EDTA and citrate complexing method. The doping effect of Ba on the phase structure, phase stability and oxygen permeation properties of the mixed conductors was investigated with combined XRD, H2-TPR, O2-TPD techniques and oxygen permeation studies. It was found that the perovskite structure was sustained in the whole range of the oxygen activity investigated (0.21∼10−6 atm) when 0.3≤x≤0.5. But for the materials with a differed doping content of Ba (x=0∼0.1, 0.7∼1.0), a phase transition was accompanied which was deleterious to the integrality of the membrane during operation. The relationship of phase structure and stability with tolerance factor was proposed. The doping of Ba in Sr(Co0.8Fe0.2)O3−δ could not lead to the improvement of these materials in the resisting of reduction, but the synergetic effect between cobalt and iron in the material was improved. Considerable high oxygen permeation rates were found for the BSCFO membranes in the whole range of Ba doping content. The Ba0.3Sr0.7Co0.8Fe0.2O3−δ membrane had the highest oxygen permeation flux, (1.19 ml/cm2 min for 1.50 mm thickness membrane at 850°C), the lowest activation energy for oxygen transportation (37.8 KJ/mol at the temperature range of 731°C∼950°C), and the lowest critical temperature for the change in the activation energy (731°C).

Partial oxidation of methane to syngas over nickel-based catalysts modified by alkali metal oxide and rare earth metal oxide

Abstract The NiO/Al2O3 catalyst was modified by alkali metal oxide (Li, Na, K) and rare-earth metal oxide (La, Ce, Y, Sm) in order to improve the thermal stability and the carbon-deposition resistance during the partial oxidation of methane to syngas (POM) reaction at high temperature. The reaction performance, thermal stability, structure, dispersity of nickel and carbon-deposition of the modified NiO/Al2O3 catalyst and unmodified NiO/Al2O3 catalyst were investigated by a series of characterization techniques including flow-reaction, BET, XRD, CO chemisorption and TG analysis. The results indicated that the modification with alkali metal oxide and rare-earth metal oxide improves the dispersion of active component nickel and the activity for the POM reaction over the nickel-based catalysts, and enhances their thermal stability during high temperature reaction and the ability to suppress the carbon-deposition over the nickel-based catalysts during the POM reaction. The nickel-based catalysts modified by alkali metal oxide and rare-earth metal oxide have excellent POM reaction performance (CH4 conversion of 94.8%, CO selectivity of 98.1%, 2.7×104l/kg·h), excellent stability and carbon-deposition resistance.

Investigation on POM reaction in a new perovskite membrane reactor

A perovskite-type oxide of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCFO) shows mixed (electronic/oxygen ionic) conductivity at high temperatures. Membrane made of the oxide has high oxygen permeability under air/helium oxygen partial pressure gradient. At 850 ◦ C, oxygen permeation rate maintained about 1.15 ml/cm 2 min for more than 1000 h under ambient air/helium oxygen gradient. A membrane reactor constructed from the oxide membrane was applied for the partial oxidation of methane (POM) to syngas, LiLaNiOx/-Al2O3 with 10 wt.% Ni loading was used as the packed catalyst. At the initial stage, oxygen permeation rate, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation rate to reach its steady state. A membrane reactor made of BSCFO was successfully operated for POM reaction at 875 ◦ C for about 500 h without failure, with methane conversion of >97%, CO selectivity of >95% and oxygen permeation rate of about 11.5 ml/cm 2 min. Under membrane reaction condition, the POM reaction mechanism was suggested to obey the CRR (complete combustion of CH4 to CO2 and H2O and a subsequent reforming reaction of the residual CH4 and with CO2 and H2 Ot o CO and H 2) mechanism.

Preparation of palladium composite membranes by modified electroless plating procedure

A thin palladium composite membrane was produced by modified electroless plating procedure. Compared with the conventional electroless plating procedure, the modified electroless plating procedure consists of the activation of a ceramic substrate by the sol-gel process of a Pd(II)-modified boehmite sol. Additionally, the infiltration of an electroless plating solution to a porous substrate during the deposition of palladium was employed with the filter device to improve adherence of a palladium layer to a substrate. The resulting membrane with a thickness of about Ipm has a high compactness. The membrane shows a hydrogen selectivity of 20-130 for H-2/N-2, and a hydrogen flux of 1.8-87 m(3)/m(2).h, depending on operation conditions

Layer-by-layer assembly of TiO2 colloids onto diatomite to build hierarchical porous materials

TiO(2) colloids with the most probably particle size of 10 nm were deposited on the surface of macroporous diatomite by a layer-by-layer (LBL) assembly method with using phytic acid as molecular binder. For preparation of colloidal TiO(2), titanium(IV) isopropoxide (Ti(C(3)H(7)O)(4)) was used as titanium precursor, nitric acid (HNO(3)) as peptizing agent and deionized water and isopropanol (C(3)H(7)OH) as solvent. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N(2) adsorption-desorption, and UV-vis spectra are used to assess the morphology and physical chemistry properties of the resulting TiO(2) coated diatomite. It was shown that the mesoporosity has been introduced into macroporous diatomite by LBL deposition. The mesoporosity was originated from close-packing of the uniform TiO(2) nanoparticles. More TiO(2) could be coated on the surface of diatomite by increasing the deposition cycles. This hierarchical porous material has potential for applications in catalytic reactions involved diffusion limit, especially in photocatalytic reactions.

Preparation of novel uniform mesoporous alumina catalysts by the sol-gel method

A novel sol–gel process for preparing alumina sol is reported in this article. Ultrasound is used to prepare the alumina sol at room temperature. The study of the effect of ultrasound as a function of treatment time on the pH and the particle diameter distribution of the sol was also made. 27 Al NMR, TEM, XRD and DTA were used to detect the properties of the sol and the alumina materials. The result of 27 Al NMR shows that there existed Al13 7+ species in the sol. The acid used not only acted as catalyst for peptizing, but also as reactant to react with aluminum hydroxide to produce the Al13 7+ species. On the other hand, TEM results show that the morphology of the particles was spherical in the sol, but transformed to needle-like as well as spherical when calcined at 450 ◦ C. At the end, the morphology of the particles changed to spherical again at 550 ◦ C. By using this alumina sol as precursor, an alumina material with uniform mesoporous distribution was formed after calcination at 550 ◦ C without adding any templates or other organic additives. The results of this work also show that the formation of alumina with uniform mesoporous distribution is related to its crystalline phase, the morphology of the particles and the particle diameter distribution of the precursor sol.

Preparation and characterization of palladium-based composite membranes by electroless plating and magnetron sputtering

Pd and Pd-Ag (24 wt.%) alloy composite membrane were prepared by electroless plating and magnetron sputtering, respectively. The membranes were characterized by scanning electron microscopy (SEM) and H-2 permeation measurement. Commercial microfiltration ceramic membrane were coated with gamma-Al2O3-based layer by the sol-gel method and used as substrate of Pd and Pd-Ag alloy film. Both the as-prepared membranes were shown: to be He gas-tight at room temperature with a thickness of <1 mu m. Permeation results showed that H-2 permeation through these composite membranes is mainly dominated by the surface chemistry of H-2 on or/and in the membranes. The membranes exhibited a high permeation rate of H-2 and a H-2/N-2 permselectivity of higher than 60 in the optimized operation conditions

Investigation on the structure stability and oxygen permeability of titanium-doped perovskite-type oxides of BaTi0.2CoxFe0.8−xO3−δ (x=0.2–0.6)

Titanium-doped perovskite-type ceramic oxides of BaTi 0.2 Co x Fe 0.8-x O 3-δ (x=0.2-0.6) were synthesized by a combined citrate-EDTA complexing method. The results of XRD, TG-DTA, O 2 -TPD and H 2 -TPR indicated that the oxide of BaTi 0.2 Co 0.5 Fe 0.3 O 3-δ was more stable than other compositions and the famous membrane material of SrCo 0.8 Fe 0.2 O 3-δ . The oxygen permeation experiments showed that the contents of Co and Fe had a great effect on the oxygen permeability. The oxygen permeation flux of 0.90 ml/cm 2 .min at 950°C under air/He was obtained for the composition of BaTi 0.2 Co 0.5 Fe 0.3 O 3-δ .

Preparation of Pd/ceramic composite membrane. 1. Improvement of the conventional preparation technique

The Pd/ceramic composite membrane made is reported in this paper. The thin palladium film was deposited on the surface of a porous ceramic substrate by the conventional and improved electroless plating technique, respectively. The rate of palladium deposition increases and especially the sensitization and activation steps in the conventional electroless plating process has been omitted by an improved technique.

Diatomite as high performance and environmental friendly catalysts for phenol hydroxylation with H2O2

Abstract A series of diatomite catalysts were treated and characterized. For the first time, the resulting materials were used in catalysis for the hydroxylation of phenol with H2O2 and showed very high hydroxylation activity due to the Fe species in the diatomite. The effect of HCl treatment, contents of catalysts and H2O2 were investigated and the active components of diatomite were discussed. The results show that diatomite is the promising candidate for industrial output due to their high catalytic activity, easy physical separation and very low costs.