Abstract
The turn-over-rate (TOR) for the water gas shift (WGS) reaction at 200 degrees C, 7% CO, 9% CO(2), 22% H(2)O, 37% H(2) and balance Ar, of 1.4 nm Au/Al(2)O(3) is approximately 20 times higher than that of 1.6 nm Pt/Al(2)O(3). Operando EXAFS experiments at both the Au and Pt L(3) edges reveal that under reaction conditions, the catalysts are fully metallic. In the absence of adsorbates, the metal-metal bond distances of Pt and Au catalysts are 0.07 A and 0.13 A smaller than those of bulk Pt and Au foils, respectively. Adsorption of H(2) or CO on the Pt catalysts leads to significantly longer Pt-Pt bond distances; while there is little change in Au-Au bond distance with adsorbates. Adsorption of CO, H(2) and H(2)O leads to changes in the XANES spectra that can be used to determine the surface coverage of each adsorbate under reaction conditions. During WGS, the coverage of CO, H(2)O, and H(2) are obtained by the linear combination fitting of the difference XANES, or DeltaXANES, spectra. Pt catalysts adsorb CO, H(2), and H(2)O more strongly than the Au, in agreement with the lower CO reaction order and higher reaction temperatures.
Highlights
The water gas shift (WGS) reaction (eqn (1)), is an industrially important reaction for H2 production and CO removal.[1,2] It is mildly exothermic (DH = À40.6 kJ molÀ1), it is thermodynamically favored at lower temperatures
It was predicted that until 2030, approximately 10% of the world annual energy consumption will originate from the WGS reaction.[1]
Assuming a H-to-surface Pt atomic ratio of 1, the dispersions estimated from hydrogen chemisorption experiments of both catalysts are near 1.0, i.e., every atom is at the surface of the particles
Summary
The water gas shift (WGS) reaction (eqn (1)), is an industrially important reaction for H2 production and CO removal.[1,2] It is mildly exothermic (DH = À40.6 kJ molÀ1), it is thermodynamically favored at lower temperatures. Due to kinetic limitations, the reaction is typically conducted at temperatures between 200 and 450 1C. WGS is, typically, a two-stage process with a high-temperature stage (320–450 1C) employing iron oxide-based catalysts and a low-temperature stage (180–250 1C) employing copper-based catalysts. It was predicted that until 2030, approximately 10% of the world annual energy consumption will originate from the WGS reaction.[1] the development of new, higher activity low-temperature WGS catalysts is of scientific and practical interest
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