LHHW and PSSA Kinetic Analysis of Rates and Adsorbate Coverages in CO/H2/C2H4Reactions on Mn–Rh/SiO2

Unveiling the Structure Sensitivity for Direct Conversion of Syngas to C2-Oxygenates with a Multicomponent-Promoted Rh Catalyst

“…The tail with a wavenumber ranging from 1750 cm −1 to 1650 cm −1 [CO(t)] is too low to be attributed to CO bridgebonded to several Rh atoms via carbon atom alone. Similar bands at 1725 cm −1 and 1696 cm −1 were also detected by Lisitsyn et al [21] These bridging sites have been considered as the metal/oxide interfacial sites, on which the C and O in CO molecule are bonded to metallic Rh and Mn δ+ cation, respectively, namely a tilted Rh-C-O-Mn species [21,38,47]. Such an adsorption state should weaken the C-O bond and enhance CO dissociation.…”

“…The introduction of Mn species can generate Rh-MnO interfacial sites on the surface of Rh nanoparticles. CO molecules adsorb on these sites in a tilted Rh-C-O-Mn mode, which shows a high CO dissociation activity [38,47]. Obviously, the larger Rh nanoparticle size and the higher fraction of tilted Rh-C-O-Mn species in CAT-I-773 than the '−673' samples lead to a higher hydrogenation activity.…”

“…However, the random deposition of Mn on the catalyst surface largely hinders the evaluation of distribution-promotion relations. In this sense, stepwise impregnation approach would be an alternative to accurately design multicomponent catalyst [32,38].…”

Mechanistic Investigation of Heterogeneous Catalysis by Transient Infrared Methods

“…SSITKA-IR was not able to discriminate the reactivity of linear, bridged, and gem-dicarbonyl due to the rapid exchange between adsorbed CO and gaseous 13 CO. One significant application of SSITKA-IR in mechanistic study of heterogeneous hydroformylation is the measurement of the coverage of h C 2 H 5 CHO , the intermediate leading to propionaldehyde formation, as a function of partial pressure of the reactants. h C 2 H 5 CHO versus reactant partial pressure data can be used to verify the isotherm equation derived from Langmuir Hinshelwood approach [40,41,59,[89][90][91][92]. The Langmuir Hinshelwood approach derives the rate law and the isotherm equations for the postulated intermediates with assumptions of uniform active sites and the absence of interactions among the adsorbed species.…”

“…Figure 6 shows the transient responses of C 2 H 5 13 CHO as a function of reactant partial pressures [89]. The pulse response is expressed in the form of E(t) which is calculated from EðtÞ ¼ CðtÞ The rate law, h CO and h C 2 H 5 CHO isotherm equations derived from the Langmuir Hinshelwood and pseudo-state state approximation approach were evaluated by comparing the model rate and coverage (value calculated rate equations and isotherm equations) with the measured rate and coverage of adsorbed CO and C 2 H 5 CHO [89,92]. The results of this evaluation show that data (i.e., rate, h C 2 H 5 CHO , and h CO ) obtained from hydroformylation on Rh/SiO 2 satisfactory fit with mode derived with postulating hydrogenation of acyl species to propionaldehyde as the ratedetermining step while the data from hydroformylation on Mn-Rh/SiO 2 fit well the model derived from pseudo-steady state approximation which do not have an assumption of the rate-determining step.…”