Quantum chemistry of the Fischer–Tropsch reaction catalysed by a stepped ruthenium surface

Abstract

A comprehensive density functional theory study of the Fischer-Tropsch mechanism on the corrugated Ru(1121) surface has been carried out. Elementary reaction steps relevant to the carbide mechanism and the CO insertion mechanism are considered. Activation barriers and reaction energies were determined for CO dissociation, C hydrogenation, CH x + CH y and CH x + CO coupling, CH x CH y -O bond scission and hydrogenation reactions, which lead to formation of methane and higher hydrocarbons. Water formation that removes O from the surface was studied as well. The overall barrier for chain growth in the carbide mechanism (preferred path CH + CH coupling) is lower than that for chain growth in the CO insertion mechanism (preferred path C + CO coupling). Kinetic analysis predicts that the chain-growth probability for the carbide mechanism is close to unity, whereas within the CO insertion mechanism methane will be the main hydrocarbon product. The main chain propagating surface intermediate is CH via CH + CH and CH + CR coupling (R = alkyl). A more detailed electronic analysis shows that CH + CH coupling is more difficult than coupling reactions of the type CH + CR because of the σ-donating effect of the alkyl substituent. These chain growth reaction steps are more facile on step-edge sites than on terrace sites. The carbide mechanism explains the formation of long hydrocarbon chains for stepped Ru surfaces in the Fischer-Tropsch reaction. † Electronic supplementary information (ESI) available: Geometries and energies of the initial, transition and final states used in the electronic structure calculations. See

Kinetic aspects of chain growth in Fischer–Tropsch synthesis

“…The underlying microkinetic model contains kinetic parameters for elementary reaction steps determined by quantum-chemical DFT calculations for the stepped Ru(112 ത 1) surface. 5,17 The dataset is available in the Supporting…”

“…5,17 From these barriers and frequencies, the forward and backward rate constants for the elementary reaction steps were constructed using the Eyring equation:…”

“…: List of all elementary reaction steps surfaces and their corresponding forward and backward activation energies used to model FT synthesis over Ru (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21). The reported forward and reverse energies are in relation to the most stable states found for the reactants and products and include zeropoint-energy corrections.…”

First-Principles-Based Microkinetics Simulations of Synthesis Gas Conversion on a Stepped Rhodium Surface

“…[23][24][25] Due to the rapid advances in computing power, it has become feasible to carry out comprehensive studies of increasingly complex catalytic reactions such as the FischerTropsch reaction. [26][27] In our recent work, we resolved important issues relevant to the Fischerformation on Rh(211). 22 The ethanol decomposition reaction has also been studied in the past; 29,[35][36][37][38] for instance, Zhang et al reported that ethanol decomposition proceeds via CH 3 CO dissociation on Rh(111) and Rh(211) surfaces.…”

DFT study of the coverage-dependent chemisorption of molecular H 2 on neutral cobalt dimers

“…The interaction of hydrogen with cobalt surfaces is of particular industrial importance due to the use of cobalt as a Fisher-Tropsch (F-T) catalyst, in which the dissociation of hydrogen is one of the critical mechanistic steps towards the subsequent hydrogenation of carbon into hydrocarbons [7][8][9][10][11][12][13]. It is also an important process in the development of novel materials for H2-sensors, as small amounts of cobalt have been found to increase the sensitivity of potential materials for H2-sensors [14] and for trace-H2 detection [15][16][17][18].…”