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Preferential Oxidation of H2 - CH4 Mixtures on Nickel-Silica Based Core-Shell Catalysts

Yahui, Yang (2015) Preferential Oxidation of H2 - CH4 Mixtures on Nickel-Silica Based Core-Shell Catalysts. Master's Thesis, University of Pittsburgh. (Unpublished)

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Abstract

Core-shell nanostructures have drawn a lot of attention thanks to their ability to isolate the nanoparticle cores inside the support and hence alleviate sintering problem. Metal-silica core-shell materials are among the most typical core-shell nanostructures. Considering the porosity of the silica shell, the silica layer in such metal-silica core-shell materials also could serve as a porous membrane for preferential diffusion of different molecules.
In the present work, we aim to apply this to H2 - CH4 mixtures, where we expect a preferential diffusion of H2 through the silica layer and hence a preferential conversion of H2 over the metal cores inside the silica shell.
Two core-shell materials with different configuration were synthesized to investigate the impact of nanostructure on the diffusion of H2 and CH4. These two materials are non-hollow Ni@SiO2 (denoted as nhNi@SiO2) where Ni nanoclusters are evenly dispersed in a porous silica nanoparticle, and hollow Ni@SiO2 (denoted as hNi@SiO2) where Ni nanoclusters decorate the inside wall of a pronounced cavity enclosed by a porous silica shell. A conventional Ni-SiO2 catalyst (where nickel nanoclusters are dispersed on external silica surface) was synthesized as a comparison.
In unmixed H2 and CH4 oxidation tests, we find the expected impact of diffusion through the porous silica shell on the conversion of H2 and CH4 with nickel oxide, suggesting that these materials might allow for selective conversion. Different diffusion pathway in these two materials results in different kinetics. In co-fed tests, H2 conversion curve precedes CH4 conversion on both materials, and this is more pronounced on hollow material, suggesting H2 diffuses more easily than CH4 and a shell with uniform diffusion distance can result in selectivity. It is hence expected to see the “selective” diffusion enhanced with an increased silica shell thickness.
Our future work will focus on hNi@SiO2 with thicker silica shell. Furthermore, we will investigate the preferential oxidation of hydrogen versus ethane, propane, or heavier hydrocarbon for which we expect the selective diffusion of hydrogen versus other hydrocarbons to be further enhanced as the difference in molecular weight between the hydrocarbon and hydrogen—and hence the difference in diffusion coefficient—become larger. Ultimately, we aim to apply these metal-silica core-shell materials to selective dehydrogenation reactions to remove the produced hydrogen from the product mixture.


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Details

Item Type: University of Pittsburgh ETD
Status: Unpublished
Creators/Authors:
CreatorsEmailPitt UsernameORCID
Yahui, Yangyay53@pitt.eduYAY53
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairVeser, Götz gveser@pitt.eduGVESER
Committee MemberEnick, Robert Mrme@pitt.eduRME
Committee MemberMpourmpakis, GiannisGMPOURMP@pitt.eduGMPOURMP
Thesis AdvisorVeser, Götz gveser@pitt.eduGVESER
Date: 4 June 2015
Date Type: Publication
Defense Date: 26 March 2015
Approval Date: 4 June 2015
Submission Date: 6 April 2015
Access Restriction: 5 year -- Restrict access to University of Pittsburgh for a period of 5 years.
Number of Pages: 73
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Chemical Engineering
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Core-shell catalysts, selective diffusion
Date Deposited: 04 Jun 2015 13:54
Last Modified: 15 Nov 2016 14:27
URI: http://d-scholarship.pitt.edu/id/eprint/24576

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