Reaction-Relevant Gold Structures in the Low Temperature Water-Gas Shift Reaction on Au-CeO2

Journal Article · Tue Jan 01 04:00:00 EST 2008 · Journal of Physical Chemistry C

DOI:https://doi.org/10.1021/jp800075y· OSTI ID:960125

Deng, W; Frenkel, A; Si, R; Flytzani-Stephanopoulos, M

Combined in situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies have been conducted to follow gold structural changes of low-content (<1%Au) gold-ceria catalysts in water-gas shift (WGS) reaction tests at 100 and 200 C; and after heating the used catalysts in oxygen gas at 150 C. Gold in the fresh (400 C-calcined) material was atomically dispersed in cerium oxide. Under WGS reaction conditions, reduction of the oxidized gold species was observed, accompanied by gradual gold aggregation. The Au-Au coordination number is zero for the fresh material, but increases with the reaction temperature, to 6.5 {+-} 2.4 (after use at 100 C) and to 8.7 {+-} 1.5 (after 200 C) in a gas mixture containing 5% CO- 3% H2O in helium. The second important parameter is the reaction gas composition which determines the extent of Au-O reduction. The lower the reduction potential of the reaction gas mixture, the more oxidized the gold is in the used catalyst, and the higher its activity. The maximum activity of Au-CeO2 was that of the fully dispersed Au-O-Ce fresh material. Loss of surface oxygen took place during reaction, as measured by H2-TPR of the used samples, and it was commensurate with the activity loss. Attempts to reoxidize and redisperse the gold by heating in oxygen gas at 150 C were not effective. However, we report here that complete recovery of the surface oxygen amount and redispersion of gold in ceria was possible after a 400 C- oxygen treatment of both the 100 C- and 200 C- used catalyst samples, with concomitant recovery of the initial catalyst activity. These tests were conducted by consecutive H2-TPR/steady-state catalyst activity measurements in the same microreactor.

• Research Organization: Brookhaven National Laboratory (BNL) National Synchrotron Light Source
• Sponsoring Organization: Doe - Office Of Science
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 960125
• Report Number(s): BNL--83111-2009-JA
• Journal Information: Journal of Physical Chemistry C, Journal Name: Journal of Physical Chemistry C Journal Issue: 33 Vol. 112; ISSN 1932-7447
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABSORPTION
CATALYSTS
CERIUM OXIDES
COORDINATION NUMBER
FINE STRUCTURE
GOLD
HEATING
HELIUM
MIXTURES
OXYGEN
WATER GAS
national synchrotron light source