Raja Krishnamurthy

Carbon monoxide adsorption and hydrogenation on Cu-Rh/SiO2 catalysts

Abstract The effects of copper on carbon monoxide adsorption and carbon monoxide hydrogenation over Rh/SiO 2 have been studied. Copper decreases the activity for carbon monoxide hydrogenation and the rate of formation of methane, C 2 and C 3+ hydrocarbons. The selectivity for C 2 oxygenate formation shows a slight variation with addition of copper. Cu-Rh/SiO 2 catalyst with copper-to-rhodium ratio of 1.0 exhibits a high initial methanol selectivity which decreases with reaction time. The use of ethylene hydroformylation as a probe reaction shows that addition of copper causes little variation in carbon monoxide insertion activity; the propionaldehyde selectivity at copper-to-rhodium ratio of 0.05 is higher than that for the other catalysts studied. In situ infrared study reveals that copper blocks the formation of bridged CO. However, blockage of bridged CO site does not lead to enhancement in carbon monoxide insertion as observed with Ag-Rh/SiO 2 and sulfided Rh/SiO 2 catalysts. The lack of effect of copper promotion on carbon monoxide insertion can be attributed to a high hydrogenation activity of copper and a possible electronic interaction between copper and rhodium leading to a reduced rhodium surface that is less active for carbon monoxide insertion than the oxidized rhodium. The difference observed in the infrared spectra of adsorbed carbon monoxide at 303 K and 513 K in the presence and absence of reactants shows that carbon monoxide induces surface reconstruction at 513 K. Results of catalyst characterization at 303 K can not be extrapolated to elucidate the state of catalyst surface under reaction conditions.

Reactivity of adsorbed CO toward C2H4, H2, and NO on the surface of supported rhodium catalysts

Abstract The reactivity of adsorbed CO on supported rhodium catalysts for the insertion of CO during ethylene hydroformylation and for CO 2 formation during interactions of CO and NO has been studied by in situ infrared spectroscopy. Adsorption of CO on 0.5 wt.% Rh/SiO 2 produced Rh carbonyl species which are highly selective for CO insertion (i.e. ethylene hydroformylation) at 323 K. Adsorption of CO on highly dispersed Rh sites of 0.2 wt.% Rh/Al 2 O 3 produced linear CO and gem-dicarbonyl which are inactive for the CO insertion in contrast to linear CO on large Rh crystallites and gem-dicarbonyl on thermally decomposed Rh 6 (CO) 16 /SiO 2 catalysts. The reactivity and the mode of adsorbed CO on 4 wt.% Rh/SiO 2 strongly depends on the partial pressure of gaseous CO and NO. Linear and bridged CO on reduced Rh sites and gem-dicarbonyl on Rh + sites do not show any reactivity toward gaseous NO/CO for the formation of CO 2 at 373 K. Prolonged exposure of rhodium catalysts to NO/CO flow results in modification of catalyst surface, creating the active site for catalyzing CO 2 formation at 373 K. Strong dependence of the reactivity and mode of adsorbates on the partial pressure of reactants and temperature suggests that the nature of adsorbates should be studied under reaction conditions where both reactants and products are present.

X-ray diffraction characterization of Ag-Rh catalysts for oxygenate and hydrocarbon synthesis

ABSTRACT Ag-Rh/SiO2 catalysts which exhibit activity and selectivity for oxygenate and hydrocarbon synthesis have been characterized by X-ray diffraction (XRD). XRD patterns show that the catalysts prepared using Rh chloride precursor contain Rh, Ag, AgCl, and AgClO2 crystallites. The size of these crystallites varied with the amount of Ag in the catalyst. The variation in crystallite size of Rh, Ag, AgCl, and AgClO2 with Ag/Rh ratio has an impact on the activity and selectivity for synthesis of oxygenates and hydrocarbons during CO hydrogenation and ethylene hydroformylation reactions. The selectivity towards oxygenates is decreased on the Ag-Rh catalysts due to the presence of AgCl and AgClO2 crystallites on the catalyst surface. Ag-Rh catalyst with Ag/Rh ratio of 0.5 gives a higher activity and selectivity for ethanol and propanol during CO hydrogenation and ethylene hydroformylation than the other Ag-Rh catalysts. Ag-Rh catalysts prepared from Rh chloride and Ag nitrate precursors are less active and ...

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.