Pt-supported catalysts are widely used industrially for hydrogenation reactions. However, the kinetics of hydrogen activation, a critical step for any hydrogenation reaction, is still not well understood on supported Pt surfaces. Recent studies had shown that activity and selectivity vary with Pt nuclearity for the acetylene semihydrogenation reaction, increasing in activity and decreasing in selectivity while increasing the particle size from single atoms (SA) to sub-nanoclusters to nanoparticles (NP), attributing the cause of these differences on activities to the activity of H2 activation in the H/D isotopic exchange reaction. In this work, the kinetics of H2 is studied by performing the H2-D2 isotopic exchange reaction on Pt-supported catalysts with different nuclearity to extract the activation barriers and pre-exponential factors for dissociating adsorption and associative desorption (Eads, Edes, and vads, vdes respectively) from the microkinetic model derived from the Bonhoeffer Farkas mechanism, this to perform a more in-depth analysis regarding the differences in activity when comparing the H2 adsorption energy (Eads+ = Eads-Edes) and frequency factors as a function of nuclearity. Experiments were carried out in a quartz tubular fixed bed reactor coupled with a Mass Spectrometer to analyze the product gas by carrying out both, an integral analysis (from 0 to equilibrium conversion) by performing light-off experiments and differential analysis (low conversions) by performing Arrhenius experiments in the low and high coverage regions. / Master of Science / Hydrogenation is a chemical reaction widely used in the petrochemical industry for the refining process where a substance reacts with molecular hydrogen H2 adding pairs of H atoms to compounds. However, hydrogen is unreactive towards other substances in the absence of metal catalysts such as platinum (Pt), which dramatically accelerates the reaction rates making hydrogenation reaction possible. In industry, metallic catalysts are found as supported catalysts where the precious metal is supported on materials with higher thermal and mechanical stability to endure the operation conditions. Depending on the pretreatment conditions the size of metallic particles on the support can be manipulated, giving place to samples made of the same materials but different particle sizes with different properties. There are two critical steps during hydrogenation reactions the first one is the hydrogen activation which consists of the dissociation and adhesion of the two hydrogen atoms from the molecular hydrogen on the metallic surface and the second one is the reverse process where two hydrogen atoms recombine and are released from the metallic surface. Both steps involve a minimum amount of energy to dissociate and recombine hydrogen atoms which are strongly dependent on the metallic particle sizes. The goal of this thesis is to extract these dissociation and recombination energies of hydrogen on platinum particles of different sizes supported on alumina.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/111848 |
| Date | 16 September 2022 |
| Creators | Pool Mazun, Ricardo |
| Contributors | Chemical Engineering, Karim, Ayman M., Xin, Hongliang, Morris, John R. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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