An Ab Initio Approach Towards Engineering Fischer-Tropsch Surface Chemistry

Neurock, Matthew

University of Virginia

关键词: Hydrocarbons;    Alloys;    Dissociation;    01 Coal, Lignite, And Peat;    Functionals;   

DOI  :  10.2172/909653
RP-ID  :  None
RP-ID  :  FG26-01NT41275
RP-ID  :  909653

美国|英语

来源: UNT Digital Library

【 摘 要 】

As the US seeks to develop an energy strategy that reduces the reliance on foreign oil, there is a renewed interest in research and development of the Fischer Tropsch synthesis of converting syngas into long chain hydrocarbon products. This report investigates some of the basic elementary steps for Fischer-Tropsch synthesis over ideal Co and Ru metal surfaces by using ab initio density functional theoretical calculations. This includes activation of CO of CO, the hydrogenation of CH{sub x} intermediates, and the adsorption and dissociation of water. The activation of CO is studied in detail showing a strong dependence on the surface coverage, defect sites and Co-Ru alloy formation. The barriers for CO activation over the ideal (0001) surfaces are quite high making CO activation at the terrace sites unlikely under operating conditions. The calculations for the overall reaction energies at the step edges indicate that these sites are much more reactive. The hydrogenation of the CHx intermediates occurs in a sequential fashion. CH1 was found to be the most stable intermediate over various surfaces. The barriers to form both CH* as well as CH{sub 4} are both found to be highly activated and potentially difficult steps. Water which is a reaction product was found to be weakly adsorbed on Co. Analysis of the microscopic reverse reaction of water activation indicates that this process has a very low activation barrier. Consequently, any water which forms desorbs or is activated to form surface hydroxyl intermediates.