Naijia Guan

Titania supported Pd-Cu bimetallic catalyst for the reduction of nitrate in drinking water

Abstract Titania supported palladium-copper bimetallic catalysts (Pd-Cu/TiO2) are prepared by the liquid phase chemical reduction method and then applied in the liquid phase catalytic reduction of nitrate ions (NO3−). Compared with the conventional impregnation method that needs the post-thermal reduction to prepare the supported metallic catalysts, the liquid phase chemical reduction at room temperature can inhibit the aggregation of metal active components and have been proved to exhibit high catalytic activity in this work. The conversions of NO3− are 29.18% and 54.12% over the catalysts treated at 873 and 298xa0K, respectively. The conversion of NO3− and selectivity to N2 influenced by the effect of the support, the loading of Pd+Cu, the molar ratio of Pd to Cu, the H2 flow rate, the addition of CO2 and the pH value of solution are also discussed in detail with the surface characterizations by X-ray photoelectron spectrum (XPS), X-ray diffraction (XRD), in situ FT-IR and transmission electron microscopy (TEM). A mechanism has been proposed that Cu2O component involved the reaction course and acted as the active center for nitrate-to-nitrite conversion. The spilt-over hydrogen on Pd is suggested to reduce the adjacent Cu2O into metal Cu, and on the latter the conversion of NO3− to NO2− occurs. However, in strongly acidic solution, copper is dissolved from the Pd-Cu/TiO2 catalyst and released into the solution in the form of copper(II) ions, so the reduction of Cu2O to Cu is inhibited and the nitrate reduction cannot be accomplished.

Photocatalytic reduction of nitrate ion in drinking water by using metal-loaded MgTiO3-TiO2 composite semiconductor catalyst

Abstract Photocatalytic reduction of nitrate ions was examined by using Cu/MgTiO 3 -TiO 2 catalyst in the presence of sodium oxalate as hole scavenger. Many factors such as catalyst calcination temperature, Cu:Mg atom molar ratio, different hole scavengers and different concentrations of sodium oxalate were tested to search for the optimal reaction conditions. X-ray diffraction (XRD) and Transmission Electron Micrograph (TEM) were performed to characterize the composite semiconductors catalyst. Our results indicated that Cu/MgTiO 3 -TiO 2 catalyst calcined at 873xa0K showed the highest photocatalytic activity and nitrate conversion reached 39.2% after 2xa0h irradiation. The enhanced effect for photocatalytic nitrate reduction activity was most likely to result from the formation of composite semiconductor MgTiO 3 -TiO 2 and the transformation of TiO 2 crystalline phase.

Development of catalysts for the production of aromatics from syngas

Abstract Different combinations of FT catalysts Fe/MnO and Cu-Fe/MnO with zeolites HZSM-5 and GaZSM-5 have been used for converting syngas directly to aromatics. The manganese rich Fe/MnO FT-catalyst was prepared from nitrates by continuous coprecipitation and the copper as modifier of Fe/MnO was introduced by impregnation. Commercially available HZSM-5 and its Ga substituted form were mechanically mixed with the FT-catalysts and was used in single-bed reaction at 543 and 573 K. Dual-bed reaction has also been tried with Cu-Fe/MnO in the first bed and GaZSM-5 in the second bed. It has been observed that mixing zeolite with FT-catalysts significantly changes the product distribution in alkene/alkane and aromatics. The selectivity to aromatic hydrocarbons over composite catalysts is higher than that in dual-bed. The highest selectivity to aromatics reached 50% over Fe/MnO-GaZSM-5 composite catalyst at 543 K after 5 h on stream, however, a serious deactivation was observed with this catalyst. The conversion of CO with this catalyst reduced from 80 to 9.37% during 22 h. Via XPS measurements, a strong enrichment of Ga was found on the surface, while Mn-content on the surface was reduced. The deactivation of this catalyst might be attributed to the migration of Ga-species.

Novel preparation of nanocrystalline magnesia-supported caesium-promoted ruthenium catalyst with high activity for ammonia synthesis

A caesium-promoted ruthenium catalyst supported on nanocrystalline magnesia with high activity for ammonia synthesis was conveniently prepared by using hydrated ruthenium trichloride and hexahydrate magnesium nitrate as precursors, whereas dechlorination post-treatment and ready-made magnesia were not necessary.

Synthesis and characterization of zeolite Nu-1

Abstract Disk-like zeolite Nu-1 with a diameter of about lμm has been synthesized in the system SiO2-Al2O3-Na2O-TEAOH-H2O at the temperature below 160°C. Longer crystallization time or higher temperature resulted in the formation of tsaregorodtsevite. By soaking aqueous H2O2 before calcination, complete removal of organic template can be achieved for the as-synthesized Nu-1 zeolite without damaging the framework. Zeolite Nu-1 was characterized by XRD, FTIR, TPDA, and SEM. The Catalytic activity of the zeolite Nu-1 was evaluated in the isomerization reaction of xylene and octane for the first time. Catalytic tests show that H form Nu-1 has no catalytic activity on m-xylene isomerization and has better catalytic selectivity for octane isomerization than HZSM-5 zeolite.

Transformation of 1D chain-like zincophosphite to 2D layered zincophosphate

Abstract Chain-like 1D and 2D layered structures, NH 3 (CH 2 ) 3 NH 3 ·Zn(HPO 3 ) 2 (Z1) and NH 3 (CH 2 ) 3 NH 3 ·Zn 4 (HPO 4 ) 2 (PO 4 ) 2 (Z2), respectively, were hydrothermally prepared at different temperatures from mixtures of zinc acetate, phosphorous acid, 1,3-propylenediamine, and water with a certain molar ratio. During the crystallization procedure of Z2, the valence of P transformed from P III to P V , from the initial phosphorous acid to the resultant phosphate. At the same time, Z2 can also be obtained with Z1 as precursor, which might be an indirect evidence of the proposed transformation mechanism of P III to P V .

Improving the Si/Al ratio of zeolite omega by boron adulteration

Abstract Boron substituted omega (MAZ) was directly synthesized and the synthesis conditions were systemically investigated, focusing on reducing the template usage by employing ageing and seeding processes. Boron substituted zeolite omega was characterized by 11 B, 27 Al, 29 Si and 2D 31 Al 3Q MAS NMR to study the structure and dealuminization process. The result suggested that boron adulteration is a good way to improve the Si/Al ratio of omega.