Cu-ZSM-5 samples with various Cu(+)/Cu(2+) ratios have been successfully prepared in three different methods and studied by XPS and FTIR. Cu(+) ions are found, by XPS, to mainly exist in the samples prepared by solution ion exchange and microwave solid-state reaction exchange. On the basis of the chemical shift of the Al 2p core level to a higher binding energy [Al(species II)], with the atomic ratio of Cu(+)/Al(species II) being approximately one, and the vanishing of the IR band at 3640 cm(-)(1) due to copper exchange, it is suggested that Cu(+) ions locate in the open channels of the ZSM-5 framework and bind to mixed (Si- and Al-) bridged oxide ion. From the ZSM-5 pore structure consideration, as well as from the observed decrease in the IR intensity ratio of bands 550/450 cm(-)(1) with enhanced Cu(2+) loading, it is also suggested that Cu(2+) ions are a predominant Cu species in solid-state reaction exchanged Cu-ZSM-5 samples and exist as a CuO cluster in small cages as well as in open channels. The IR bands at 907 and 964 cm(-)(1) are identified as zeolite asymmetric internal vibration perturbed by exchanged Cu(2+) and Cu(+) ions, respectively. Cu ions in Cu-ZSM-5 samples can be reduced to Cu(0) by CO adsorption at room temperature. The IR bands at 2128, 2158, and 2176 cm(-)(1) are observable and ascribed to the CO adsorbed on Cu(0), Cu(+), and Cu(2+) sites, respectively. Methanol formation from syngas over Cu-ZSM-5 is observed at 250 degrees C and 2 MPa.

Decomposition of N2O on Cu‐ZSM‐5 was studied by temperature‐programmed reaction (TPR), in situ Fourier transform infrared spectroscopy (FTIR) and XPS. It is found that the decomposed intermediates of N2O— dinitrogen and oxygen ion— show adsorption bands at 2161 cm−1 and 910 cm−1 in the IR spectrum, which can be assigned respectively to as N–N stretching vibration and a T–O stretching vibration perturbed by Cu2+. Both bands increase in intensity with temperature in the range 25–250 °C. Unlike the band at 2161 cm−1, whose intensity decreases sharply above 250 °C, the band at 910 cm−1 still persists at higher temperatures. The IR results agree with the TPR profiles of N2 and O2: N2 starts to desorb at 250 °C whereas O2 remains until 310 °C, where N2O decomposes. An oscillation in the O2 signal is observed between 400 and 550 °C, along with a more evident but opposite oscillation in the N2O signal. The oscillation of N2O decomposition and the release rates of O2 are found to correlate with the oxidation–reduction of copper sites by XPS. Based on this evidence, Cu+ is proposed to be the active centre for dissociative adsorption of N2O. The removal of adsorbed oxygen ions through recombination as O2 or through interaction with protons trapped in the zeolite cavities may preserve Cu in the +1 oxidation state, which enables continuous decomposition of N2O. Copyright © 1999 John Wiley & Sons, Ltd.

The influence of antiferromagnetic (AF) thickness on static and dynamic magnetic properties and their thermal stability in NiFe/FeMn multilayered thin films was investigated systematically. It was found that dynamic magnetic anisotropy rises at the AF thickness lower than that of static magnetic anisotropy and exchange bias. This behavior is suggested to be due to the contribution of rotatable anisotropy arising from time-dependent rotatable part of the AF spins. It is also due to the contribution of rotatable anisotropy and exchange bias that makes the thermal stability of static and dynamic anisotropies varied with AF thickness. The temperature dependences of ferromagnetic resonance frequency, Gilbert damping factor and frequency linewidth dependent on AF thickness are also discussed in conjunction with the variations of the dynamic anisotropy and exchange bias field to provide a comprehensive picture of the physical origin of their thermal stability.

By altering component formulation and modifying a conventional coprecipitation procedure, we have synthesized a high-Zn-, low-Cu-level Cu/ZnO/Al2O3 catalyst which showed a 54.4 mmol/(mL catalyst h) of methanol yield and 66% CO conversion measured at 230 °C, 8 MPa, and 10000 h-1. Comparative surface studies of this catalyst and the catalyst prepared according to the commercial standard (low-Zn-, high-Cu-level) were performed using microreactor study, gas (N2 and N2O) adsorption and X-ray photoelectron and Fourier transfer infrared spectroscopies and temperature-programmed desorption. It was found that the high-Zn-level catalyst had better performance, including a substantial (15−25%) increase in methanol yield and some other advantages under identical conditions imitating industrial process. The high catalytic activity is ascribed to the high concentrations of Cu, Zn, and oxygen vacancies detected on the surface of the high-Zn catalyst. It is proposed that the active center is Cu□ZnO and that the catalytic process may follow a carbonate−formate−methoxy−methanol mechanism. The high Zn level of the catalyst facilitates the hydrogen heterolysis with the presence of Cu, resulting in the high concentration of oxygen vacancies, as well as the existence of more Cu1+ ions on the surface, and thus leading to the increased CO/CO2 adsorption, activation, and conversion.

Diffuse reflectance infrared spectroscopy and static secondary ion mass spectrometry (SIMS) were employed to study the surface species formed during the adsorption and reaction of propylene on a copper-exchanged ZSM-5 catalyst. Propylene showed characteristics of chemisorption on Cu-ZSM-5 at room temperature and total decomposition to CO, CO2 and CH 4 at 350°C. The ir bands of =C–H stretching at 3101 cm -1, =C–C stretching at 916 cm -1 and C=CH 2 twisting at 575 cm -1 for propylene disappeared upon adsorption, indicating the breaking of the C=C double bond, while the decrease in the signal intensity of zeolite isolated and vicinal SiOH groups at 3700 and 3592 cm -1 implied that the adsorbed di-σ species was bound to zeolite SiO–. Static SIMS showed two distinguished peaks at 73 and 147 amu, which were assigned to the adsorbed species H2OSi2(C3H5O2) due to the interaction of propylene with ZSM-5 and Cu-ZSM-5. The adsorption and reaction of propylene were enhanced by the presence of Cu+ in ZSM-5. The mechanism for these processes was discussed.