Weizhong Ding

Effect of CeO2 addition on Ni/Al2O3 catalysts for methanation of carbon dioxide with hydrogen

Abstract The Ni-CeO2/Al2O3 catalysts with a nickel content of 15 wt% prepared via impregnating boehmite were found to be highly active and stable for methanation of carbon dioxide with hydrogen at a H2/CO2 molar ratio of 4. The effects of CeO2 content and reaction temperature on the performance of the Ni-CeO2/Al2O3 catalysts were studied in detail. The results showed that the catalytic performance was strongly dependent on the CeO2 content in Ni-CeO2/Al2O3 catalysts and that the catalysts with 2 wt% CeO2 had the highest catalytic activity among the tested ones at 350 °C. The XRD and H2-TPR characterizations revealed that the addition of CeO2 decreased the reduction temperature by altering the interaction between Ni and Al2O3, and improved the reducibility of the catalyst. Preliminary stability test of 120 h on stream over the Ni-2CeO2/Al2O3 catalyst at 350 °C revealed that the catalyst was much better than the unpromoted one.

Hydrogen production from simulated hot coke oven gas by catalytic reforming over Ni/Mg(Al)O catalysts

Abstract Hydrogen production by catalytic reforming of simulated hot coke oven gas (HCOG) with toluene as a model tar compound was investigated in a fixed bed reactor over Ni/Mg(Al)O catalysts. The catalysts were prepared by a homogeneous precipitation method using urea hydrolysis and characterized by ICP, BET, XRD, TPR, TEM and TG. XRD showed that the hydrotalcite type precursor after calcination formed (Ni, Mg)Al 2 O 4 spinel and Ni-Mg-O solid solution structure. TPR results suggested that the increase in Ni/Mg molar ratio gave rise to the decrease in the reduction temperature of Ni 2+ to Ni 0 on Ni/Mg(Al)O catalysts. The reaction results indicated that toluene and CH 4 could completely be converted to H 2 and CO in the catalytic reforming of the simulated HCOG under atmospheric pressure and the amount of H 2 in the reaction effluent gas was about 4 times more than that in original HCOG. The catalysts with lower Ni/Mg molar ratio showed better catalytic activity and resistance to coking, which may become promising catalysts in the catalytic reforming of HCOG.

Facile strategy for synthesis of mesoporous crystalline γ-alumina by partially hydrolyzing aluminum nitrate solution

The facile synthesis of mesoporous γ-alumina is developed through the partial hydrolysis of Al(NO3)3 aqueous solution with (NH4)2CO3 without organic surfactants. In this synthesis, the stable NH4NO3/Al species (AN/Al) hybrid containing Keggin-Al13 polycations is first prepared, which is the key for the successful formation of mesoporous γ-alumina. XRD, 27Al MAS NMR, TEM, and N2 adsorption and desorption results demonstrate that the as-prepared AN/Al hybrid can be transformed to γ-alumina by treatment at 200 °C and exhibit a wormhole-like mesoporous structure with large surface area up to ∼450 m2 g−1, pore volume of ∼0.3 cm3 g−1 and narrow pore size distribution peaked at ∼3.9 nm after completely removing NH4NO3 at 300 °C. The obtained mesoporous γ-aluminas have high thermal stabilities up to 900 °C and excellent hydrothermal stability. The investigation shows that the synergetic effect of NH4NO3 and Al13 species promotes crystallization of Al species to γ-alumina, which may have a unique mechanism distinct from the mesoporous aluminas reported previously. CO2 adsorption measurements indicate that these mesoporous γ-aluminas have a much higher CO2 adsorption capacity than ordered mesoporous alumina synthesized by the surfactant-templating method and conventional γ-alumina derived from aluminum oxyhydroxides. We believe that this research should be useful for providing new insights into the transformation of transition alumina phases and for synthesizing mesoporous γ-alumina with promising properties for various chemical applications.

Electrochemical extraction of Ti5Si3 silicide from multicomponent Ti/Si-containing metal oxide compounds in molten salt

Ti5Si3 silicide has been extracted directly from complex multicomponent Ti/Si-containing metal oxide compounds by electro-deoxidation in molten calcium chloride using an inert solid oxide oxygen-ion-conducting membrane (SOM) based anode. Studies on the microstructure evolution and electrochemical extraction mechanism show that the formation of Ti5Si3 and the removal of impurity elements happened simultaneously during the electro-deoxidation process. It is found that the electro-deoxidation generated Ti5Si3 micro-particles typically possess a smooth surface, which could contribute to create a continuous anti-oxidation surface layer with excellent high-temperature oxidation resistance property. Consideration is also given to the parameters of electrolysis and the electrochemical characteristics including chemical and/or electrochemical reactions during the electro-deoxidation process, and then a relevant kinetic model is proposed.

Partial oxidation of simulated hot coke oven gas to syngas over Ru-Ni/Mg(Al)O catalyst in a ceramic membrane reactor

Abstract Hydrogen amplification from simulated hot coke oven gas (HCOG) was investigated in a BaCo0.7Fe0.2Nb0.1O3-δ (BCFNO) membrane reactor combined with a Ru-Ni/Mg(Al)O catalyst by the partial oxidation of hydrocarbon compounds under atmospheric pressure. Under optimized reaction conditions, the dense oxygen permeable membrane had an oxygen permeation flux around 13.3 ml/(cm2·min). By reforming of the toluene and methane, the amount of H2 in the reaction effluent gas was about 2 times more than that of original H2 in simulated HCOG. The Ru-Ni/Mg(Al)O catalyst used in the membrane reactor possessed good catalytic activity and resistance to coking. After the activity test, a small amount of whisker carbon was observed on the used catalyst, and most of them could be removed in the hydrogen-rich atmosphere, implying that the carbon deposition formed on the catalyst might be a reversible process.

Phase transitions, micro-morphology and its oxidation mechanism in oxidation of ilmenite (FeTiO3) powder

Abstract Phase transitions, morphology changes, and oxidation mechanism of the ilmenite oxidation process were investigated. FeTiO 3 transforms to hematite and rutile when oxidation at 700–800 °C, and pseudobrookite is formed when the oxidation temperature reaches 900 °C. The initial ilmenite powder exhibits paramagnetism; however, after being oxidized at the intermediate temperature (800–850 °C), the oxidation product exhibits weak ferromagnetism. The oxidation mechanism was discussed. The microstructure observations show that a lot of micro-pores emerge on the surfaces of ilmenite particles at the intermediate temperature, which is deemed to be capable of enhancing the mass transfer of oxygen during oxidation.

Phase transformation and reduction kinetics during the hydrogen reduction of ilmenite concentrate

The reduction of ilmenite concentrate by hydrogen gas was investigated in the temperature range of 500 to 1200°C. The microstructure and phase transition of the reduction products were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical microscopy (OM). It was found that the weight loss and iron metallization rate increased with the increase of reduction temperature and reaction time. The iron metallization rate could reach 87.5% when the sample was reduced at 1150°C for 80 min. The final phase constituents mainly consist of Fe, M3O5 solid solution phase (M=Mg, Ti, and Fe), and few titanium oxide. Microstructure analysis shows that the surfaces of the reduction products have many holes and cracks and the reactions take place from the exterior of the grain to its interior. The kinetics of reduction indicates that the rate-controlling step is diffusion process control with the activation energy of 89 kJ·mol−1.

Enhancing the Oxygen Permeability of BaCo0.7Fe0.2Nb0.1O3−δ Membranes by Coating GdBaCo2-xFexO5+δ for Partial Oxidation of Coke Oven Gas to Syngas

The dense ceramic membranes BaCo(0.7)Fe(0.2)Nb(0.1)O(3-δ) (BCFN) combined with GdBaCo(2-x)Fe(x)O(5+δ) (0 ≤ x ≤ 2.0) surface modification layers was investigated for hydrogen production by partial oxidation reforming of coke oven gas (COG). As oxygen permeation of BCFN membrane is controlled by the rate surface exchange kinetics, the GdBaCo(2-x)Fe(x)O(5+δ) materials improve the oxygen permeation flux of the BCFN membrane by 20-44% under helium atmosphere at 750 °C. The maximum oxygen permeation flux reached 14.4 mL min(-1) cm(-2) in the GdBaCoFeO(5+δ) coated BCFN membrane reactor at 850 °C, and a CH(4) conversion of 94.9%, a H(2) selectivity of 88.9%, and a CO selectivity of 99.6% have been achieved. The GdBaCo(2-x)Fe(x)O(5+δ) coating materials possess uniform porous structure, fast oxygen desorption rate and good compatibility with the membrane, which showed a potential application for the surface modification of the membrane reactor.

Hydrocracking of Tar Components from Hot Coke Oven Gas over a Ni/Ce-ZrO2/γ-Al2O3 Catalyst at Atmospheric Pressure

Abstract Ni/Ce-ZrO 2 /γ-Al 2 O 3 catalysts with different Ce-ZrO 2 contents and Ni loadings were prepared by a two step impregnation method and characterized by X-ray diffraction, transmission electron microscopy, N 2 adsorption, and temperature-programmed reduction. The catalysts were used for the hydrocracking of toluene and naphthalene, which were model tar compounds in hot coke oven gas, under atmospheric pressure at 800 °C. They showed excellent catalytic activity, stability, and some sulfur tolerance. Both toluene and naphthalene was converted into light fuel gases even at a low mole ratio of steam to carbon (S/C = 0.44). During the testing period of 7 h, no coke deposition was observed on the surface of the catalysts. The results indicated that the addition of Ce-ZrO 2 limited the sintering of Ni particles and enhanced the catalytic activity. The Ni/Ce-ZrO 2 /γ-Al 2 O 3 catalyst is promising for the direct removal of tar compounds in hot coke oven gas with low S/C ratios.

Hydrogen production from coke oven gas over LiNi/γ-Al2O3 catalyst modified by rare earth metal oxide in a membrane reactor

Abstract The performance of LiNi/-Al 2 O 3 catalysts modified by rare earth metal oxide (La 2 O 3 or CeO 2 ) packed on BCFNO membrane reactor was discussed for the partial oxidation of methane (POM) in coke oven gas (COG) at 875 °C. The NiO/γ-Al 2 O 3 catalysts with different amounts of La 2 O 3 and CeO 2 were prepared with the same preparation method and under the same condition in order to compare the reaction performance (oxygen permeation, CH 4 conversion, H 2 and CO selectivity) on the membrane reactor. The results show that the oxygen permeation flux increased significantly with LiNiREO x /γ-Al 2 O 3 (RE = La or Ce) catalysts by adding the element of rare earth especially the Ce during the POM in COG. Such as, the Li15wt%CeO 2 9wt%NiO/-Al 2 O 3 catalyst with an oxygen permeation flux of 24.71 ml·cm −2 ·min −1 and a high CH 4 conversion was obtained in 875 °C. The resulted high oxygen permeation flux may be due to the added Ce that inhibited the strong interaction between Ni and Al 2 O 3 to form the NiAl 2 O 4 phase. In addition, the introduction of Ce leads up to an important property of storing and releasing oxygen.