Chemisorption and catalytic reactivity of cobalt and sulfur monolayers on ordered molybdenum surfaces

Thesis/Dissertation · Sun Mar 01 04:00:00 EST 1992

DOI:https://doi.org/10.2172/10179712· OSTI ID:10179712

Knight, Colette Clarissa ^[1]

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1. Univ. of California, Berkeley, CA (United States)

Complex Co/Mo sulfide catalysts are modelled by the chemisorption of layers on Mo single crystal surfaces. Growth and structure of overlayers on flat, stepped and kinked surfaces were investigated. Growth of Co overlayers on clean and S covered Mo surfaces was studied using AES and CO chemisorption; results reveal that Co grows as a flat monolayer on clean Mo surfaces. Co multilayers then form 3-D islands. When Co is deposited on S covered surfaces, the S overlayer migrates to the top; this topmost overlayer reduces CO adsorption capacity. While growth mode of Co overlayers are similar on flat and stepped surfaces, the number and type of ordered Co and S structures on flat and stepped surfaces are different. In the case of Co, an ordered (3 x 1) structure is formed on Mo(910) and (28,4,1) surfaces; this structure does not develop on clean (100) surface. Only one of two possible (3 x 1) Co domains are formed on Mo(910) and Mo(28,4,1) surfaces. These domains have one side of (3 x 1) unit cell parallel to the step edges, suggesting that Co adsorbs at the step edges. The (3 x 1) structure does not form on Mo(911) surface, indicating that step orientation can restrict formation of ordered overlayers. For chemisorbed S, only a subset of ordered overlayers on flat (100) surface nucleate on (910) and (911) and (28,4,1) surfaces. Ordered S overlayers also form domains that maximize the number of sulfur-step atom bonds. The adsorption and ordering of S overlayers on stepped and kinked Mo surfaces lead to doubling of step height and terrace width. Thiophene hydrodesulfurization (HDS) reactions were performed over Mo crystal surfaces modified by chemisorption of S, Co, C, and S + Co. The stepped and kinked Mo surfaces have reactivities greater than low Miller index (100) surface. Chemisorption of adsorbates decreased the thiophene HDS reactivity. Deposition of Co on Mo single crystal surfaces did not lead to increased HDS activity.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 10179712
• Report Number(s): LBL--32444; ON: DE92041175
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201
ADSORPTION
AUGER ELECTRON SPECTROSCOPY
CARBON MONOXIDE
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL AND PHYSICOCHEMICAL PROPERTIES
COBALT
DESORPTION
DESULFURIZATION
ELECTRON DIFFRACTION
HYDROGENATION
LAYERS
MOLYBDENUM
MOLYBDENUM SULFIDES
MONOCRYSTALS
PHYSICAL PROPERTIES
SORPTIVE PROPERTIES
SULFUR
SURFACES
THIOPHENE