Ordered epitaxial ZrO2 films were grown on Pt(111) and characterized by low energy electron diffraction (LEED), synchrotron radiation photoemission spectroscopy (SRPES) and X-ray photoelectron spectroscopy (XPS). The films were prepared by vapor deposition of zirconium in an O2 atmosphere followed by annealing under ultra high vacuum. At low coverages, the films grew as discontinuous two-dimentional islands with ordered structures. The size and structure of these islands were dependent on the coverage of ZrO2 films. At coverage <0.5 monolayer (ML), ( 19^(1/2) × 19^(1/2)) R23.4° and (5×5) structures coexisted on the surface. As the coverage increased, the (19^(1/2) × 19^(1/2) ) R23.4° structure developed with increasing degree of long-range order, while the (5×5) structure gradually faded. When the coverage reached >6 ML, a continuous ZrO2(111) film was formed with a (1×1) surface LEED pattern coexisting with a (2×2) pattern. These ordered thin ZrO2 films provide good model surfaces of bulk ZrO2 and can be used for further fundamental studies of the surface chemistry of ZrO2 using modern surface science techniques.
GAO Yan ZHANG Liang PAN YongHe WANG GuoDong XU Yang ZHANG WenHua ZHU JunFa
We report our investigation of the interaction of NO2 with the Au(997)vicinal surface by high-resolution photoelectron spectroscopy using synchrotron radiation as the excitation source.At 170 K,both core-level and valence-band photoemission results illustrate the decomposition of NO2 on the Au(997)surface at low NO2 exposures,forming coadsorbed NO(a)and O(a)species.After annealing at 300 K,NO(a)desorbs from Au(997)whereas O(a)remains on the surface.Upon annealing at 750 K,we observe no signal for adsorbed oxygen on Au(997).These results clearly demonstrate that thermal decomposition of NO2 is an effective method to generate oxygen adatoms on Au(997)under ultrahigh-vacuum conditions.
A combined cavity ringdown （CRD） and laser induced fluorescence （LIF） spectroscopic study on the A1∑＋-X1∑＋ transition of Cull has been presented. The Cull molecule, as well as its deuterated isotopologue CuD, are produced in a supersonic jet expansion by discharging H2 （or D2） and Ar gas mixtures using two copper needles. Different profiles of relative line intensities are observed between the measured LIF and CRD spectra, providing an experimental evidence for the predissociation behavior in the A1∑＋ state of Cull. The lifetimes of individual upper rotational levels are measured by LIF, in which the J＇-dependent predisso- ciation rates are obtained. Based on the previous theoretical calculations, a predissociation mechanism is concluded due to the strong spin-orbit coupling between the A1∑＋ state and the lowest-lying triplet 3∑＋ state, and a tunneling effect may also be involved in the predis- sociation. Similar experiments are also performed for CuD, showing that the A1∑＋ state of CuD does not undergo a predissociation process.
Conversion of biomass to chemicals or fuels under mild condition is still a challenge. As a platform molecule for chemicals and fuels, levulinic acid （LA） has been prepared by lique-faction of biomass at high pressure. In order to carry out the conversion from wheat straw to LA at atmosphere pressure, continuous extraction of the reactive system by an organic solvent with a higher density than that of water was utilized for degradation of pretreated biomass. Yields of LA were measured by means of gas chromatography-mass spectrometry and nuclear magnetic resonance. The results revealed that a maximum yield of 30.66% of LA can be obtained from wheat straw. In addition, the effects of biomass pretreated conditions on the LA conversion have been studied. The study provides a new route to convert biomass to valuable chemicals at atmosphere pressure.
