Girish Srinivas

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.

Au/metal oxides for low temperature CO oxidation

Room temperature CO oxidation has been investigated on a series of Au/metal oxide catalysts at conditions typical of spacecraft atmospheres; CO=50 ppm, CO2=7,000 ppm, H2O-40% (RH) at 25°C, balance=air, and gas hourly space velocities of 7,000–60,000 hr−1. The addition of Au increases the room temperature CO oxidation activity of the metal oxides dramatically. All the Au/metal oxides deactivate during the CO oxidation reaction, especially in the presence of CO2 in the feed. The stability of the Au/metal oxide catalysts decreases in the following order: TiO2>Fe2O3>NiO>Co3O4. The stability appears to decrease with an increase in the basicity of the metal oxides. In situ FTIR of CO adsorption on Au/TiO2 at 25°C indicates the formation of adsorbed CO, carboxylate, and carbonate species on the catalyst surface.

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.