科研之友
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摘要
Bimetallic Au-Pt nanoparticles on cerium oxide supports were prepared using pulsed laser deposition (PLD) at room temperature and investigated using X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) of isotopically labelled carbon monoxide (CO)-C-13-O-18. The metal deposition caused a partial reduction of Ce4+ to Ce3+. Two components in the spectra of Au (41) and Pt (41) photoelectrons were observed and assigned to the charged and metallic state of metals in the nanodeposits. The abundance of the charged species decreased with an increasing amount of the deposited metals and with thermal treatment of the samples. The adsorption properties of the prepared nanodeposits were examined using repeated adsorption-desorption runs of the labelled (CO)-C-13-O-18 molecules. Carbon monoxide desorbed as (CO)-C-13-O-18 with a maximum at temperatures ranging from 420 K to 500 K and as (CO)-C-13-O-16 containing O-16 oxygen exchanged from the supporting oxide at temperatures from 480 to 580 K. The TPD curves from bimetallic Au-Pt nanoparticles differed from those obtained from Pt monometallic deposits by (1) a lower temperature of maximum (T-max) of the (CO)-C-13-O-16 desorption peak in the first desorption run and a higher T-max of (CO)-C-13-O-18 for the second desorption, (2) a substantial decrease in the adsorption capacity after repeated adsorption-desorption cycles and (3) stable (CO)-C-13-O-16/(CO)-C-13-O-18 desorption peak area ratios during repeated adsorption-desorption cycles. Oxidation of CO to CO2 was observed on all metal deposits on CeO2-x and also to a lower extent on bare CeO2-x surfaces. In contrast to the CO desorption, the desorption curves of CO2 from Pt/CeO2-x were similar to those from bimetallic Au-Pt nanodeposits.
- 出版日期2013-3
