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University of California, Berkeley

1. Ralston, Walter Thomas. Hydrogenation Reactions of CO and CO2| New Insights through In Situ X-ray Spectroscopy and Chemical Transient Kinetics Experiments on Cobalt Catalysts.

Degree: 2017, University of California, Berkeley

The catalytic hydrogenations of CO and CO2 to more useful chemicals is not only beneficial in producing more valuable products and reducing dependence on fossil fuels, but present a scientific challenge in how to control the selectivity of these reactions. Using colloidal chemistry techniques, a high level of control over the synthesis of nanomaterials can be achieved, and by exploiting this fact a simple model system can be realized to understand the reaction of CO and CO2 on a molecular level. Specifically, this dissertation focuses on understanding cobalt materials for the conversion of CO and CO2 into more useful, valuable chemicals. Colloidally prepared cobalt nanoparticles with a narrow size distribution were supported in mesoporous SiO2 and TiO2 to study the effect of the support on the Co catalyzed hydrogenation of CO and CO2. The 10nm Co/SiO2 and Co/TiO2 catalysts were tested for CO and CO2 hydrogenation at 5 bar with a ratio to hydrogen of 1:2 and 1:3, respectively. In addition, the effect of Co oxidation state was studied by using different reduction pretreatment temperatures (250°C and 450°C). The results showed that for both hydrogenation reactions, Co/TiO2 had a high activity at both reduction temperatures compared to Co/SiO2. However, unlike Co/SiO2 which showed higher activity after 450°C reduction, Co/TiO2 had a higher activity after reduction at 250°C. Through synchrotron x-ray spectroscopy, it was concluded that the TiO2 was wetting the Co particle at higher reduction temperatures and dewetting at lower reduction temperatures. In addition to the wetting, CoO was observed to be the surface species on Co/TiO2 catalyst after reduction at low temperatures, which catalyzed both CO and CO2 hydrogenation reactions with higher activity than the Co metal obtained after reduction at 450°C. Classical steady-state measurements are limited in so much as they are often unable to provide information on individual reaction steps in complex reaction pathways. To attempt to circumvent this, a chemical transient kinetics (CTK) reactor was designed and built. Verification of the reactor was performed by evaluating a catalyst from the literature and confirming the results. A CoMgO catalyst was used to accomplish this, and our original findings show that at short time scales steric hindrances at the surface may push the product distribution towards olefinic rather than branched compounds. Continuing work on the CTK, two distinct particle sizes of Co nanoparticles were synthesized and tested under atmospheric conditions (H2:CO = 2:1) on the transient reactor. 4.3 nm Co and 9.5 nm Co were supported on MCF-17 to study the previously observed size effect, where Co nanoparticles lose activity at smaller sizes. It was found that indeed, the 4.3 nm Co are less active because they contain less CO dissociation sites, which are necessary for populating the surface with carbon monomers and spurring subsequent chain growth. The specific CO dissociation site was identified as the…

Subjects/Keywords: Chemistry; Chemical engineering; Materials science

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APA (6th Edition):

Ralston, W. T. (2017). Hydrogenation Reactions of CO and CO2| New Insights through In Situ X-ray Spectroscopy and Chemical Transient Kinetics Experiments on Cobalt Catalysts. (Thesis). University of California, Berkeley. Retrieved from http://pqdtopen.proquest.com/#viewpdf?dispub=10282649

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Ralston, Walter Thomas. “Hydrogenation Reactions of CO and CO2| New Insights through In Situ X-ray Spectroscopy and Chemical Transient Kinetics Experiments on Cobalt Catalysts.” 2017. Thesis, University of California, Berkeley. Accessed August 23, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10282649.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Ralston, Walter Thomas. “Hydrogenation Reactions of CO and CO2| New Insights through In Situ X-ray Spectroscopy and Chemical Transient Kinetics Experiments on Cobalt Catalysts.” 2017. Web. 23 Aug 2017.

Vancouver:

Ralston WT. Hydrogenation Reactions of CO and CO2| New Insights through In Situ X-ray Spectroscopy and Chemical Transient Kinetics Experiments on Cobalt Catalysts. [Internet] [Thesis]. University of California, Berkeley; 2017. [cited 2017 Aug 23]. Available from: http://pqdtopen.proquest.com/#viewpdf?dispub=10282649.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Ralston WT. Hydrogenation Reactions of CO and CO2| New Insights through In Situ X-ray Spectroscopy and Chemical Transient Kinetics Experiments on Cobalt Catalysts. [Thesis]. University of California, Berkeley; 2017. Available from: http://pqdtopen.proquest.com/#viewpdf?dispub=10282649

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

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