Showing papers by "Changhai Liang published in 2004"

Ammonia synthesis on graphitic-nanofilament supported Ru catalysts

Abstract: Graphitic-nanofilaments (GNFs) supported ruthenium catalysts were prepared and characterized by NZ physisorption, X-ray diffraction (XRD), transmission electron microscope (TEM) and temperature programmed reduction-mass spectroscopy (TPR-MS) and used for ammonia synthesis in a fixed bed microreactor. The TEMs of the Ru/GNFs and Ru-Ba/GNFs catalysts indicate that the Ru particles are in the range of 2-4 nm, which is the optimum size of Ru particles for the maximum number of B5 type sites. The activity of Ru-Ba/GNFs catalysts is higher than that of Ru-Ba/AC by about 25%. The methanation reaction on the Ru/GNFs catalyst is remarkably inhibited compared with a Ru/AC catalyst. High graphitization of GNFs is likely to be the reason for the high resistance to the methanation reaction. The power rate law for ammonia synthesis on Ru-Ba/GNFs catalysts can be expressed by r = Kp(NH3)(-0.4) P-N2(0.8) P-H2(-0.7), indicating that H-2 is an inhibitor for N-2 activation on the catalyst. Catalysts with the promoters Ba, K and Cs show large differences in activity for ammonia synthesis. The catalyst promoted with Ba (Ba/Ru = 0.2 molar ratio) was found to be the most active, whereas that with a K promoter was the least active. (C) 2003 Elsevier B.V. All rights reserved.

An IR study on the surface passivation of Mo2C/Al2O3 catalyst with O2, H2O and CO2

Abstract: The surface active sites of a fresh Mo2C/Al2O3 catalyst and their evolution under passivation conditions were characterized by IR spectroscopy using CO as the probe molecule. It was found that adsorption properties of CO on the fresh sample were quite different from those of the reduced passivated one. Moδ+ (0 < δ < 2) sites are mainly present on fresh Mo2C/Al2O3 catalyst as probed by a characteristic IR band at 2054 cm−1 of adsorbed CO. When the fresh Mo2C/Al2O3 catalyst in the IR cell is exposed to trace amounts of O2 or H2O in situ at RT, the intensity of the 2075 cm−1 band declines. It shows that the fresh Mo2C/Al2O3 catalyst can be oxidized by trace amounts of O2 or H2O easily and the oxidation capacity of H2O is weaker than that of O2. IR spectra of adsorbed CO on a reduced Mo2C/Al2O3 catalyst passivated by a 1% O2/N2 mixture show that two weak bands at 2180 and 2095 cm−1 appear, which suggests that the passivation layer cannot be completely reduced, even by H2-reduction at high temperatures. For reduced Mo2C/Al2O3 passivated by H2O or CO2, IR spectra of adsorbed CO give characteristic IR bands at 2081 and 2030 cm−1, which indicates that the surface Mo atoms are in a state of Moϕ+ (0 < ϕ < 3). Thus, we found that the Mo2C/Al2O3 passivated by H2O or CO2 can be regenerated by H2 treatment at 673 K and most of the active sites can be recovered. It is too active to control the passivation extent using O2 as an oxidant, while Mo2C/Al2O3 passivated by H2O or CO2 can be regenerated by simple reduction with H2.

Synthesis of nanostructured ceria, zirconia and ceria–zirconia solid solutions using an ultrahigh surface area carbon material as a template

Abstract: Nanostructured ceria, zirconia and ceria-zirconia solid solutions have been synthesized via an easy route and characterized by XRD, nitrogen physorption, Raman spectroscopy and TEM. The route involves two steps: the impregnation of ultrahigh surface area carbon materials with nitrate solutions of ceria and/or zirconia and burn-off to remove the carbon materials in a controlled oxidation atmosphere. The results show that the particle sizes of ceria, zirconia and ceria-zirconia solid solutions are about 5-10 nm. The results also show that zirconia is in the monoclinic phase and tetragonal phase and ceria is in a cubic phase with a fluorite structure.

Multi-walled carbon nanotubes supported Pt-Fe cathodic catalyst for direct methanol fuel cell

Abstract: Multi-walled carbon nanotubes supported Pt-Fe cathodic catalyst shows higher specific activity towards oxygen reduction reaction as compared to Pt/MWNTs when employed as cathodic catalyst in direct methanol fuel cell.

Ammonia-treated activated carbon as support of a Ru-Ba catalyst for ammonia synthesis

Abstract: Ammonia-treated activated carbon has been studied as a support of Ru-Ba catalyst for ammonia synthesis. It is shown that the introduction of nitrogen leads to a decrease of ammonia synthesis activity for the catalysts with a low Ba/Ru molar ratio, while no significant changes are obtained for the catalysts with a high Ba/Ru molar ratio, confirming that electronegative impurities suppress the activity in ammonia synthesis and consume part of the promoters.

SbOx/SiO2 catalysts for the selective oxidation of methane to formaldehyde using molecular oxygen as oxidant

Abstract: SbOx and SbOx/SiO2 catalysts were prepared and investigated for methane selective oxidation to HCHO. HCHO selectivity up to 41% can be obtained on Sb2O5/SiO2 catalyst at 873 K and just drop gently to 18% with temperature up to 923 K. HCHO selectivity for SbOx/SiO2 catalysts decreases gently with reaction temperature, so considerable value of HCHO selectivity can still be obtained at high temperatures.