Heats of Adsorption of Linear and Bridged CO Species Adsorbed on a 3% Ag/Al2O3 Catalyst Using in situ FTIR Spectroscopy under Adsorption Equilibrium
详细信息 查看全文
- 作者：Paul Gravejat ; Salim Derrouiche ; David Farrussengn ; Karine Lombaert ; Claude Mirodatos ; Daniel Bianchi
- 刊名：Journal of Physical Chemistry C
- 出版年：2007
- 出版时间：July 5, 2007
- 年：2007
- 卷：111
- 期：26
- 页码：9496 - 9503
- 全文大小：149K
- 年卷期：v.111,no.26(July 5, 2007)
- ISSN：1932-7455
文摘
The heats of adsorption of linear and bridged CO species adsorbed on Ag0 sites of a reduced 3% Ag/Al2O3catalyst and of the linear CO species on Ag+ sites of the oxidized catalyst are determined as the function oftheir respective coverages by using the adsorption equilibrium infrared spectroscopy method previouslydeveloped. The evolutions of the intensities of the IR bands of each adsorbed species: 2045 cm-1 and2000 cm-1 at 300 K, for the linear and bridged CO species, respectively, on Ag0 sites of the reduced solidand 2168 cm-1 for a linear CO species on Ag+ sites of the oxidized solid are determined as a function of theadsorption temperature Ta, at a constant CO adsorption pressure PCO. This provides the evolutions of thecoverages of each adsorbed CO species with Ta in isobar conditions that give the individual heats of adsorptionof the three adsorbed CO species at several coverages according to an adsorption model. The heats of adsorptionof the linear and bridged adsorbed CO species on Ag0 sites vary linearly with their coverages : from E0 =76 kJ/mol to E1 = 58 kJ/mol for the linear CO species and from E0 = 88 kJ/mol to E1 = 84 kJ/mol for thebridged CO species at coverages 0 and 1, respectively. Volumetric measurements indicate that the total amountof the adsorbed CO species represents a small fraction of the superficial sites of the reduced Ag particlessuggesting that they are adsorbed on defect sites. The heat of adsorption of the linear CO species on the Ag+sites linearly varies with its coverage from E0 = 66 kJ/mol to E1 = 41 kJ/mol at coverages 0 and 1, respectively.