Catalysis by platinum single crystal surfaces: low pressure hydrocarbon reactions and the effects of introducing strongly bound oxygen at the surface

Technical Report · Sat Jul 01 04:00:00 EDT 1978

DOI:https://doi.org/10.2172/6670796· OSTI ID:6670796

Smith, C E

The dehydrogenation of cyclohexene and cyclohexane, and the hydrogenation of cyclohexene were studied on the clean and preoxidized surfaces of three platinum single crystals: a Pt(111), a stepped Pt(S) - (6(111) x (100)) and a kinked Pt(S) - (7(111) x (310)). The choice of reaction conditions is discussed with respect to detection limits and the variation of the catalyst reactivity with reagent pressures and catalyst temperature; the reactions were carried out using flow conditions at low pressure (10/sup -6/ to 10/sup -5/ torr total pressure), at a platinum temperature of 150/sup 0/C. Oxygen coverages were monitored by Auger electron spectroscopy (AES), an Auger peak ratio of O/sub 510//Pt/sub 237/ = 0.5 having been determined to correspond to approximately 5 x 10/sup 14/ oxygen atoms/cm/sup 2/. The surface structures of the clean and oxidized platinum crystals were determined by low energy electron diffraction (LEED): after high temperature (800/sup 0/C) oxygen treatment, the predominant oxygen structure observed on the Pt(111) was a (2 x 2); the predominant oxygen structure observed on both the Pt(S) - (6(111) x (100)) and the Pt(S) - (7(111) x (310)) was a (radical 3 x radical 3) - R30/sup 0/. Low coverages of strongly bound oxygen enhanced the rates of the dehydrogenation and hydrogenation reactions, and changed the selectivity of cyclohexene dehydrogenation to benzene over hydrogenation to cyclohexane. These effects of preoxidation on catalytic rates and selectivity were found to be sensitive to the structure of the platinum surface, kink sites playing a particularly active role in the enhancement of dehydrogenation and hydrogenation activity by strongly bound oxygen. Three models are discussed which relate the oxidation of platinum surfaces to the observed effects on catalytic reactivity and the structure sensitivity. A change in the electronic structure of the platinum surface through oxidation provides the best general model for explaining the oxygen effects.

• Research Organization: California Univ., Berkeley (USA). Lawrence Berkeley Lab.
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 6670796
• Report Number(s): LBL-8044
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ALKANES
CATALYSIS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
CYCLOALKANES
CYCLOHEXANE
DEHYDROGENATION
ELEMENTS
HYDROCARBONS
HYDROGENATION
METALS
ORGANIC COMPOUNDS
OXIDATION
PLATINUM
PLATINUM METALS
SURFACE PROPERTIES
TRANSITION ELEMENTS