28 research outputs found
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Probe molecule studies: Active species in alcohol synthesis
The goal of this research is to develop a better understanding of the mechanisms of formation of alcohols and other oxygenates from syngas over supported catalysts. Probe molecules are added in situ during the reaction to help delineate reaction pathways and identify reaction intermediate species. The key of our study is to investigate how the species generated by these probe molecules interact with surface species present during oxygenate formation. The catalysts chosen for tills investigation is Co/Cu/ZnO/Al[sub 2]O[sub 3]. Detailed motivations for studying this system as well as using CH[sub 3]NO[sub 2] as the probe molecule were given in a previous report. (A) Pretreatment of a Co(O%)/Cu/ZnO/Al[sub 2]O[sub 3] to be used as a base catalyst was carried out. (B) XRD experiments were carried out with the calcined and reduced samples of the O%-Co, 5%-Co and 10%-Co catalysts. (C) Temperature programmed reduction was performed with the O%-Co, 5%-Co and 10%-Co catalysts. (D) CO hydrogenation under the same conditions used for the 5%-Co and 10%-Co catalysts was conducted over the Co(O%)/Cu/ZnO/Al[sub 2]O[sub 3] catalyst. (E) CH[sub 3]NO[sub 2] addition to the steady state reaction of CO hydrogenation was conducted over both the O%-Co and the 10%-Co catalysts
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Probe molecule studies: Active species in alcohol synthesis. Eighth quarterly report, July 1992--September 1992
Goal is to understand the mechanisms of formation of alcohols and other oxygenates from syngas over supported catalysts. Work during this period: BET surface areas and XRD patterns of Cu/ZnO/Al{sub 2}O{sub 3} and Co(5%)/Cu/ZnO/Al{sub 2}O{sub 3} suggest that Co did not change the structure. CO was hydrogenated over 10% Co catalyst. C{sub 2}H{sub 4} additions increased the isopropanol and decreased the methanol production. Blank runs with H{sub 2}/He/CH{sub 3}OH/C{sub 2}H{sub 4} showed that C{sub 2}H{sub 4} does not react with CH{sub 3}OH
Revealing Correlation of Valence State with Nanoporous Structure in Cobalt Catalyst Nanoparticles by in Situ Environmental TEM
Simultaneously probing the electronic structure and morphology of materials
at the nanometer or atomic scale while a chemical reaction proceeds is
significant for understanding the underlying reaction mechanisms and optimizing
a materials design. This is especially important in the study of nanoparticle
catalysts, yet such experiments have rarely been achieved. Utilizing an
environmental transmission electron microscope (ETEM) equipped with a
differentially pumped gas cell, we are able to conduct nanoscopic imaging and
electron energy loss spectroscopy (EELS) in situ for cobalt catalysts under
reaction conditions. Analysis revealed quantitative correlation of the cobalt
valence states to the particles' nanoporous structures. The in situ experiments
were performed on nanoporous cobalt particles coated with silica while a 15
mTorr hydrogen environment was maintained at various temperatures
(300-600\degreeC). When the nanoporous particles were reduced, the valence
state changed from cobalt oxide to metallic cobalt and concurrent structural
coarsening was observed. In situ mapping of the valence state and the
corresponding nanoporous structures allows quantitatively analysis necessary
for understanding and improving the mass activity and lifetime of cobalt-based
catalysts, i.e., for Fischer-Tropsch synthesis that converts carbon monoxide
and hydrogen into fuels, and uncovering the catalyst optimization mechanisms.Comment: ACS Nano, accepte
Adsorption and reaction of CO and H2 on K-promoted Rh/SiO2 catalysts
The adsorption of CO and H2 on a series of alkali-promoted Rh/SiO2 catalysts was investigated by IR spectroscopy and volumetric chemisorption. The characteristics of the support as well as the method of addition of the alkali species were found to influence the adsorptive properties of the catalysts. Alkali species on wide-pore Rh/SiO2 tended to partition to the support and did not interact strongly with the Rh crystallites. When alkali and metal salts were coimpregnated onto a nonporous SiO2 support, intimate alkali-metal contact resulted in significant electronic interactions between the alkali species and the metal. When alkali species were added to a prereduced Rh/SiO2 (nonporous) catalyst, a chemical interaction between a tilted adsorbed CO and the alkali species was suggested. The nature and location of the alkali species were suggested to be important parameters in determining the effect of alkali promoters on Rh/SiO2 catalysts. The rate of CO conversion decreased substantially with promotion for all of the promoted catalysts. An unusually low apparent activation energy was found for the sequentially impregnated (nonporous SiO2) promoted catalyst, and it was suggested that this might be related to the unusually low frequency peak seen in the IR spectrum of adsorbed CO on this catalyst
Adsorption and reaction of CO and H2 on K-promoted Rh/SiO2 catalysts
The adsorption of CO and H2 on a series of alkali-promoted Rh/SiO2 catalysts was investigated by IR spectroscopy and volumetric chemisorption. The characteristics of the support as well as the method of addition of the alkali species were found to influence the adsorptive properties of the catalysts. Alkali species on wide-pore Rh/SiO2 tended to partition to the support and did not interact strongly with the Rh crystallites. When alkali and metal salts were coimpregnated onto a nonporous SiO2 support, intimate alkali-metal contact resulted in significant electronic interactions between the alkali species and the metal. When alkali species were added to a prereduced Rh/SiO2 (nonporous) catalyst, a chemical interaction between a tilted adsorbed CO and the alkali species was suggested. The nature and location of the alkali species were suggested to be important parameters in determining the effect of alkali promoters on Rh/SiO2 catalysts. The rate of CO conversion decreased substantially with promotion for all of the promoted catalysts. An unusually low apparent activation energy was found for the sequentially impregnated (nonporous SiO2) promoted catalyst, and it was suggested that this might be related to the unusually low frequency peak seen in the IR spectrum of adsorbed CO on this catalyst