Abstract
The water-gas shift (WGS) reaction has been studied by pulsing carbon monoxide (CO) into a steady-state water (H<sub>2</sub>O)-Ar flow over nickel(II) oxide-zinc oxide (NiO-ZnO) catalysts using in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) coupled with a mass spectrometer method using the pulse technique (in situ pulse DRIFTS-MS) for different flow rates (gas hourly space velocity [GHSV] of 24 000-72 000 h<sup>−1</sup>) and reaction temperatures (250-350 °C). The results obtained from the in situ pulse DRIFTS-MS revealed that there are two types of water adsorption bands on the surface of the catalyst: (i) molecular adsorption (infrared [IR] bands in the 2500-3600 cm<sup>−1</sup> range and at 1640 cm<sup>−1</sup>), and (ii) dissociative adsorption at 3700 cm<sup>−1</sup>, where carboxyl bands are formed at 1461 and 1368 cm<sup>−1</sup> and the gas-phase CO is adsorbed at 2187 and 2111 cm<sup>−1</sup> on the surface of the catalyst. After using a GHSV = 24 000 h<sup>−1</sup> H<sub>2</sub>O/Ar flow, we probed the existence of two active intermediates via the formation of two hydrogen production peaks. The products of hydrogen gas (H<sub>2</sub>) and carbon dioxide (CO<sub>2</sub>) had two pathways: the redox process and the associative process via the intermediate of the carboxyl group. In situ pulse DRIFTS-MS proves to be an effective approach for studying the nature of adsorbed species on the catalyst surface and the nature of the reaction product.
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