Studies on the mechanism of ethylene hydrogenation over iridium (111) single crystals

Technical Report · Sat Aug 01 04:00:00 EDT 1987

OSTI ID:6086325

Lloyd, J T

The kinetics of ethylene hydrogenation on iridium (111) single crystals were measured in the temperature range of 312K to 625K. The pressure of hydrogen was varied from 0.4 to 626 torr and the pressure of ethylene was varied from 0.08 to 588 torr to determine the kinetic order of each reactant at 473K. The hydrogen kinetic order was determined to be 1. The ethylene kinetic order varied from 1 at low pressures to 0 at higher pressures. The data were fit to a Langmuir Hinshelwood mechanism. The temperature dependence of ethylene hydrogenation yielded an activation energy of 12.5 kcal/mole between 312K and 400K. A maximum in the temperature versus rate plot is attributed to a change in the form of the adsorbed ethylene which is hydrogenated on the surface. Thermal desorption and Auger electron spectroscopies supported this argument by providing additional information on the nature of partially hydrogenated carbonaceous surface species on the surface after ethylene hydrogenation. The yield of side product, methane, was determined under the same conditions as the hydrogenation reaction. Methane was observed to originate from ethylene and not hydrogenolysis of the hydrogenation product, ethane. The quality of the data did not allow accurate determination of the orders for methane formation. The activation energy is 4.88 kcal/mole. 62 refs., 27 figs.

• Research Organization: Ames Lab., IA (USA)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 6086325
• Report Number(s): IS-T-1248; ON: DE87013611
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ACTIVATION ENERGY
ALKANES
ALKENES
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
CRYSTALS
ELEMENTS
ENERGY
ETHANE
ETHYLENE
HYDROCARBONS
HYDROGENATION
IRIDIUM
KINETICS
METALS
METHANE
MONOCRYSTALS
ORGANIC COMPOUNDS
PLATINUM METALS
REACTION KINETICS
TRANSITION ELEMENTS
YIELDS