In Situ Pulse Diffuse Reflection Infrared Fourier Transform Spectroscopy (DRIFTS) Mass Spectrometry Study of the Water-Gas Shift Reaction on Nickel(II) Oxide–Zinc(II) Oxide Catalysts

The water-gas shift (WGS) reaction has been studied by pulsing carbon monoxide (CO) into a steady-state water (H₂O)-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⁻¹) 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⁻¹ range and at 1640 cm⁻¹), and (ii) dissociative adsorption at 3700 cm⁻¹, where carboxyl bands are formed at 1461 and 1368 cm⁻¹ and the gas-phase CO is adsorbed at 2187 and 2111 cm⁻¹ on the surface of the catalyst. After using a GHSV = 24 000 h⁻¹ H₂O/Ar flow, we probed the existence of two active intermediates via the formation of two hydrogen production peaks. The products of hydrogen gas (H₂) and carbon dioxide (CO₂) 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.