ABSTRACT
The structural evolutions and electronic properties of AulPtm (l + m ≤ 10) clusters are investigated by using the first-principles methods. We use the inverse design of materials using the multi-objective differential evolution (IM2ODE) package to globally search the equilibrium structures and investigate the evolving trend from a two-dimensional structure to a three-dimensional structure on horizontal extension and vertical extension for AulPtm (l + m ≤ 10) clusters. The three-dimensional stable geometry of Au8Pt and Au8Pt2 is discovered for the first time in our work. We also notice that the equilibrium structures of AulPtm (l + m = 10 and l ≤ 8) tend to form a tetrahedral geometry and can be obtained by replacing the Au atom in the most stable structure of Aul+1Ptm-1 with the Pt atom, where Pt atoms assemble together and occupy the center of clusters and Au atoms prefer to lie on the vertex or edge position. The average binding energy (Eb) is mostly decided by Pt-Pt bond numbers, namely the numbers of Pt atoms, followed by Au-Pt bond numbers. The second-order energy difference (Δ2Ev and Δ2Eh) and the nearest-neighbor energy difference (Δ4Enn) show that Au6Pt, Au4Pt2, Au3Pt3, Au2Pt4 and AuPt7 clusters exhibit high relative physical stability, so we suggest that these clusters could be defined as the magic number clusters for AulPtm (l + m ≤ 10) clusters. The HOMO-LUMO energy gap (Eg), adiabatic ionization potential (AIP) and the adiabatic electron affinity (AEA) are also investigated to elaborate the relative electronic stability of all the clusters.
ABSTRACT
The catalytic properties of the magic gold-platinum bimetallic clusters (Au4Pt2 and Au6Pt) for the reduction of SO2 by CO, without or with preadsorbing CO molecules, are firstly investigated using density functional theory calculations. We find that the catalytic activities improve effectively with the preadsorption of CO onto the catalysts and that the catalytic activities of Au6Pt(CO)n are better than those of Au4Pt2(CO)n as more CO molecules are adsorbed onto the catalysts. During the reaction process, the Au4Pt2(CO)n clusters always keep two-dimensional morphologies except for when n = 5 and the Au6Pt(CO)n clusters have three-dimensional geometries except for when n = 0. The most stable adsorption site for SO2 molecules on the catalysts is the site of preadsorbing the next CO molecule on the corresponding catalysts. The largest activation energy (E) is related to the metal 5d (M-5d) band center and the charge transfer (Ct) as well as the bond length (Rb) between COS and the catalyst contribute to the desorption energy (Ed) of COS corporately. We propose that Au6Pt(CO)6 is a cost-effective gold-platinum bimetallic catalyst for the reduction of SO2 by CO.
ABSTRACT
OBJECTIVES: Live demonstrations of endoscopic retrograde cholangiopancreatography (ERCP) have a high educational value and contribute significantly to endoscopy development and training. However, the success and safety of live demonstration have been questioned. The aim of this study was to evaluate the success rate and complications of therapeutic ERCP among patients who participated in live demonstrations. METHODS: Patients who underwent therapeutic ERCP during live demonstrations at gastrointestinal endoscopy conferences in China between January 2002 and December 2007 were included. The matched control for each patient was a patient admitted to the same ERCP unit with similar indication, who received ERCP by an endoscopist with similar experience as those who performed the live demonstration. Patient's age, gender, indication, success rate, and complications of ERCP were collected and compared. ERCP outcomes between local and visiting faculty were also compared. RESULTS: In total, 36 conferences with live ERCP demonstrations involving 406 patients were held in 14 endoscopy centers. There were no significant differences in patients' gender, age, and indications between live demonstrations and controls. The overall complication rate of ERCP in live demonstrations was not significantly different compared with controls (10.3% vs. 8.6%, P=0.473). However, the success rate was significantly lower in live demonstrations than in controls (94.1% vs. 97.5%, P=0.021). The success and complication rates of ERCP performed by local faculty, domestic visiting, and foreign visiting faculties were similar. CONCLUSIONS: Although the success rate of therapeutic ERCP performed during live demonstrations was lower than that of routine procedures, the overall complication rate did not significantly increase. ERCP performed by visiting endoscopists was as safe as that done by local faculty in live demonstrations.
