The Adsorption of Nitric Oxide and Thiophene on Platinum Single Crystals
Lang, John Frederick
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https://hdl.handle.net/2142/69776
Description
Title
The Adsorption of Nitric Oxide and Thiophene on Platinum Single Crystals
Author(s)
Lang, John Frederick
Issue Date
1987
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Abstract
The adsorption of nitric oxide on Pt(210), Pt(100), and Pt(111) was studied using X-ray photoelectron (XPS) and Auger electron (AES) spectroscopies. Nitric oxide was found to molecularly adsorb on Pt(210) at room temperature but to dissociate upon heating to 450 K. The same behavior was noted on Pt(100). Pt(111) was considerably less active as nitric oxide adsorbed at room temperature desorbed when the crystal was heated to 380 K. These observations and those of other authors can be explained by an orbital symmetry model. The adsorption of carbon monoxide and oxygen on Pt(210) was also investigated.
The second half of this work utilized XPS, AES, TPD, and HREELS to study the adsorption of thiophene on Pt(210), Pt(100), and Pt(111). Thiophene adsorbs molecularly at 150 K to form a physisorbed layer. At 170 K a chemisorbed monolayer with the ring parallel to the surface is found. As the temperature of the crystal is increased, the ring is hypothesized to tilt as interaction between the sulfur atom and platinum substrate increases. At 350 K sulfur is extruded from the ring on all three surfaces; there are no apparent plane-to-plane variations. The two alpha carbon atoms on the C(,4)H(,4) remnant are believed to bond to either a single platinum atom (pseudometallocycle) or bridge across two platinum atoms. The structure is stable up to 400 K where dehydrogenation commences. Possible implications for the industrial HDS mechanism are discussed.
Tetrahydrothiophene adsorption was also investigated. Although the spectra are difficult to interpret, there is evidence to support ring opening upon adsorption of tetrahydrothiophene on Pt(100) at 170 K. At 350 K a structure similar to that described above for desulfurized thiophene appears to form.
Furan decomposes on platinum by a different pathway than thiophene because of the strong thermodynamic driving force to form carbon monoxide.
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