Mechanistic study in catalysis using dynamic and isotopic transient infrared spectroscopy: CO/H2C2H4 reaction on Mnsingle bondRh/SiO2 Original Research Article

In situ infrared (IR) spectroscopy coupled with dynamic and steady-state isotopic transient kinetic analysis permits observation of the transient response (i.e., dynamics) of IR-observable adsorbates as well as gaseous reactants and products. This technique was used to examine the reaction pathway, reactivity of adsorbates, and nature of sites for the CO/H2/C2H4 reaction on Mnsingle bondRh/SiO2. Dynamic infrared study reveals that Rh0 sites which chemisorb linear CO actively catalyze CO insertion, a key step for the formation of propionaldehyde from the CO/H2/C2H4 reaction. Tilted CO on Mnsingle bondRh/SiO2 is not active for the reaction, demonstrating a lack of connection in reactivity between the low wavenumber CO on metal surfaces and in metal complexes. Steady-state isotopic transient IR studies by pulse injection of D2 and13CO produce transient responses which carry mechanistic information for elucidation of catalysis of the CO/H2/C2H4 reaction. The broad response of D-containing propionaldehyde reveals that multiple pathways for hydrogenation take place simultaneously with a wide distribution of the reactivity of adsorbed deuterium or hydrogen; the sharp response of C2H513CHO unravels the narrow distribution of reactivity of adsorbed CO for CO insertion.