The optimally performing Fischer-Tropsch catalyst.
Ivo A W Filot1, Rutger A van Santen, Emiel J M Hensen
1Schuit Institute of Catalysis, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven (The Netherlands); Institute for Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven (The Netherlands).
Angewandte Chemie (International Ed. in English)
|August 30, 2014
Summary
Microkinetics simulations reveal that stepped ruthenium surfaces favor long-chain hydrocarbon formation in Fischer-Tropsch (FT) synthesis. Current catalysts are suboptimal due to limitations in CO activation and oxygen removal.
Area of Science:
- Catalysis
- Surface Science
- Chemical Kinetics
Background:
- The Fischer-Tropsch (FT) reaction is crucial for converting syngas into liquid fuels and chemicals.
- Understanding the reaction mechanism on ruthenium (Ru) surfaces is key to optimizing FT catalysts.
- Previous studies have highlighted the complexity of hydrocarbon formation pathways.
Purpose of the Study:
- To investigate the microkinetics of the Fischer-Tropsch reaction on ruthenium surfaces using DFT-determined elementary steps.
- To elucidate the role of surface structure (stepped vs. planar) and metal-support interactions in product selectivity.
- To identify the rate-limiting steps and surface coverages that dictate overall FT performance.
Main Methods:
- Density Functional Theory (DFT) calculations to determine elementary reaction steps and energetics.
- Microkinetics simulations to model the reaction network and predict product distributions.
- Systematic variation of metal-carbon and metal-oxygen interaction energies to explore different reactivity regimes.
Main Results:
- Stepped Ru surfaces promote long-chain hydrocarbon formation via CH insertion, while planar Ru surfaces predominantly produce methane due to slow CO activation.
- Three distinct reactivity regimes were identified, controlled by CO dissociation, chain-growth termination, or water removal.
- Predicted surface coverages are dominated by CO, C, or O depending on the operating regime.
Conclusions:
- Optimal Fischer-Tropsch performance is achieved at the interphase between limited CO dissociation and chain-growth termination regimes.
- Current FT catalysts are suboptimal, primarily limited by inefficient CO activation and/or challenging oxygen removal.
- Surface structure and electronic properties significantly influence the selectivity towards long-chain hydrocarbons.
Related Concept Videos
01:22Heterogeneous Catalysis
136
Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...
136
02:50Catalysis
22.8K
The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
22.8K
01:19Turnover Number and Catalytic Efficiency
16.0K
The turnover number of an enzyme is the maximum number of substrate molecules it can transform per unit time. Turnover numbers for most enzymes range from 1 to 1000 molecules per second. Catalase has the known highest turnover number, capable of converting up to 2.8×106 molecules of hydrogen peroxide into water and oxygen per second. Lysozyme has the lowest known turnover number of half a molecule per second.
Chymotrypsin is a pancreatic enzyme that breaks down proteins during digestion....
Chymotrypsin is a pancreatic enzyme that breaks down proteins during digestion....
16.0K
01:07Catalytically Perfect Enzymes
4.3K
The theory of catalytically perfect enzymes was first proposed by W.J. Albery and J. R. Knowles in 1976. These enzymes catalyze biochemical reactions at high-speed. Their catalytic efficiency values range from 108-109 M-1s-1. These enzymes are also called 'diffusion-controlled' as the only rate-limiting step in the catalysis is that of the substrate diffusion into the active site. Examples include triose phosphate isomerase, fumarase, and superoxide dismutase.
Most enzymes...
Most enzymes...
4.3K
02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
2.6K
Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
2.6K
02:13Reduction of Alkenes: Catalytic Hydrogenation
12.3K
Alkenes undergo reduction by the addition of molecular hydrogen to give alkanes. Because the process generally occurs in the presence of a transition-metal catalyst, the reaction is called catalytic hydrogenation.
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...
12.3K