Michael W. Balakos

Transient in Situ Infrared Methods for Investigation of Adsorbates in Catalysis

This paper reports the details of a high-pressure and -temperature in situ transmission infrared reactor cell and experimental approaches for investigation of the nature of adsorbates in CO hydrogenation and NO-CO reaction on Rh/SiO2 catalyst. The infrared cell used in this study allows easy assembling and reliable operation up to 773 K and 6.0 MPa. The structure and coverage of adsorbates during reaction are determined by an infrared spectrometer, and the composition of gaseous effluent from the infrared cell is monitored by a mass spectrometer. The steady-state 13CO step transient shows that gaseous CO rapidly exchanges with adsorbed CO, which is slowly converted to CH4 during CO hydrogenation at 513 K and 0.1 MPa. The pulsing CO study reveals that linear CO is more reactive than bridged CO during methane and CO2 formation, and bridged CO sites are blocked from CO disproportionation. Steady-state 13CO pulse transients show that the CO2 response leads the CO response, and Rh-NCO and Si-NCO are not involved in the formation of CO2 from CO during NO-CO reaction. The advantages and limitations of the in situ infrared and transient approaches for catalysis research will be discussed.

Mechanistic study in catalysis using dynamic and isotopic transient infrared spectroscopy: CO/H2C2H4 reaction on MnRh/SiO2

Abstract 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 Mn Rh/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 Mn Rh/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.

CO disproportionation on Ni-based catalysts

Ni/SiO2 exhibits higher activity for CO dissociation than coprecipitated Na−Mn−Ni, which is a higher oxygenate synthesis catalyst at 303 K, while Na−Mn−Ni exhibited higher CO dissociation activities at 673 K.

The Effect of Adsorbed Sulfur on Heterogeneous Hydroformylation over Rh, Ni, and Ru Catalysts

Summary The effect of adsorbed sulfur on the ethylene hydroformylation reaction was studied on Rh/SiO2, Ni/SiO2, and Ru/SiO2 catalysts using in situ infrared spectroscopy under Fischer-Tropsch synthesis conditions of 240 °C and 10 atm. Adsorbed sulfur inhibits the Fischer-Tropsch synthesis, but slightly enhances the ethylene hydroformylation on Rh/SiO2 and Ni/SiO2. The adsorbed sulfur blocks the bridge-CO sites and enhances the formation of propionaldehyde. In the case of Ru/SiO2, the adsorbed sulfur inhibits the Fischer-Tropsch synthesis and permits hydroformylation to adsorbed propionaldehyde; however, the desorption of propionaldehyde is inhibited by sulfur.

Dynamics of C2+ Oxygenates Formation from the Fischer-Tropsch Synthesis over Rh-based Catalysts

A pulse 13 CO transient incorporated with in situ infrared technique has been used to study CO hydrogenation over Rh/Si0 2 catalysts. Increasing reaction temperature decreases TCH 4 (residence time of intermediates leading to methane); however, increasing reaction pressure increases TCH 4 High TCH 4 at high pressure allows the insertion of CO into CHX to occur leading to the formation of acetaldehyde.

The Selective Synthesis of C2+ Oxygenates from Syngas Related Reactions Over Ni- and Rh-Based Catalysts

Abstract The synthesis of C 2+ oxygenates from CO hydrogenation, ethylene addition to syngas, and methylene chloride addition to syngas has been studied over Rh/SiO 2 , Ni/SiO 2 , and coprecipitated Na-Mn-Ni catalysts. The formation of C 2+ oxygenates involves the insertion of CO into the adsorbed hydrocarbon species which can be produced from chlorinated hydrocarbons, olefins, and CO/H 2 . Rh/SiO 2 and Na-Mn-Ni are active for C 2 oxygenate synthesis in CO hydrogenation and exhibit a high CO insertion activity. Although Ni/SiO 2 is a methanation catalyst, the catalyst exhibited a good CO insertion activity for the conversion of CH 2 Cl 2 to acetaldehyde and for the conversion of C 2 H 4 to propionaldehyde.