DRIFTS/MS Studies during Chemical Transients and SSITKA of the CO/H2 Reaction over Co-MgO Catalysts

Diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) has been employed along with chemical and isotope transients to study the catalytic CO hydrogenation over Co/MgO catalysts in a single fixed-bed reactor at T = 523 K and ambient pressure conditions (H 2 /CO = 3). According to the operando DRIFTS measurements, the catalyst surface contains hydroxyl groups, adsorbed CO, formate, and methylene groups in the steady-state of the reaction. Transient experiments following fast changes in the feed (chemical transient kinetics, CTK) or isotope composition (steady-state isotopic transient kinetic analysis, SSITKA) have been carried out during DRIFTS and demonstrate that the formate/methylene “seen by DRIFTS” plays no role as imminent intermediates of the ambient pressure Fischer−Tropsch (FT) reaction. The SSITKA experiments (replacing 12 CO by 13 CO) show that the exchange rate of formate/methylene is significantly lower than that of ethane, which is one of the main reaction products of CO hydrogenation (followed by mass spectrometry). Formate is most probably bound as bidentate μ 2 -species to MgO or at the Co/MgO interface, while methylene stands for skeleton CH 2 in either hydrocarbon or carboxylate.