Size and composition dependence in CO oxidation reaction on small free gold, silver, and binary silver-gold cluster anions

作者：Bernhardt TM^*; Socaciu Siebert LD; Hagen J; Woste L

来源：Applied Catalysis A: General , 2005, 291(1-2): 170-178.

DOI：10.1016/j.apcata.2005.02.041

• gold catalysts
• silver
• CO oxidation
• metal clusters
• gas phase kinetics
• mass spectrometry

Gas phase kinetics experiments with mass-selected gold, silver, and binary silver-gold cluster ions in a radio frequency (rf)-ion trap reactor are presented. For the catalytic CO combustion reaction, the adsorption of molecular oxygen onto the free clusters is identified as the first reaction step. A comparison of the measured O-2 adsorption reaction rate constants for the investigated AgnAum- (n + m = 1, 2, 3) clusters reveals, a pronounced size and composition dependence. Favorable activation of the oxygen molecular bond is only expected in the case of Au-2(-) . In the reaction of the gold diner with O-2 and CO, a coadsorption complex is identified at cryogenic temperatures as decisive reaction intermediate in the observed CO oxidation reaction. Through detailed reaction kinetics measurements in combination with first-principles calculations, a comprehensive understanding of the molecular details of the catalytic reaction cycle emerges. The obtained data also permit the determination of the CO2 formation rate and the catalytic turn-over-frequency in the rf-ion trap reactor. In contrast to gold, odd size silver cluster anions are found to adsorb two oxygen molecules. These AgnO4- complexes are proposed to be key intermediates oxidation reactions with silver clusters involved, and first experimental indications for catalytic activity of selected cluster sizes are presented.

• 出版日期2005-9-12