Dynamic Multiple Tracing with D2and C2D4in Ethylene Hydroformylation over Mn–Rh/SiO2

Combined FT-IR/mass spectrometry was used to study the dynamic behavior of hydrogen/deuterium adsorbates in response to D2and C2D4pulses during ethylene hydroformylation on Mn–Rh/SiO2at 513 K and 0.1 MPa. Variation of exposure time of the catalyst to the D2and C2D4pulses revealed that readsorption did not play a significant role in the product responses; long exposure time allows more deuterium to enter the slower pathway ofd1- andd2-propionaldehyde. The two-unequal-hump HD response from both the D2and C2D4pulses indicates the presence of an isotope effect on hydrogen/deuterium adsorption. The rapid responses of the deuterated ethylene and ethane can be described by the Horiuti-Polanyi mechanism and indicate that their intermediates have small θ (surface coverage) and τ (residence time) which cannot be resolved by the time resolution of their transient responses. Thed1- andd2-propionaldehyde products show a two-hump response, which can be explained by the different deuterium incorporation pathways into the propionaldehyde. The first hump is due to hydrogen/deuterium exchange on adsorbed acyl and acyl hydrogenation. The second hump is due to H/D exchange on the adsorbed alkyl species, which then undergoes CO insertion and acyl hydrogenation. The second hump decay is partly due to the reaction with Si–OD as indicated by the parallel decay ofd1- andd2-propionaldehyde and Si–OD.