Atomically Defined Iron Carbide Surface for Fischer-Tropsch Synthesis Catalysis

TY - JOUR

T1 - Atomically Defined Iron Carbide Surface for Fischer-Tropsch Synthesis Catalysis

AU - Li, Yijia

AU - Li, Zheshen

AU - Ahsen, Ali

AU - Lammich, Lutz

AU - Mannie, Gilbère J.A.

AU - Niemantsverdriet, J. W.Hans

AU - Lauritsen, Jeppe V.

PY - 2019/2

Y1 - 2019/2

N2 - With the purpose of investigating the reactivity of Fe carbide as an active phase in Fischer-Tropsch catalysis, we studied the formation of a well-defined Fe carbide surface structure resulting from carbon exposure of an Fe film on Au(111). Using two different sources of carbon (C), namely atomic carbon and ethylene gas, we used synchrotron X-ray photoelectron spectroscopy (XPS) to show that a 6 ML Fe film readily converts into a well-defined and thermodynamically stable carbide phase. Scanning tunneling microscopy (STM) showed that the surface of the Fe carbide film is crystalline and is dominated by Fe(110)-like facets perturbed into a (2 X 2) periodic structure due to insertion of C in the interstitial sites. The reactivity of the carbide film toward CO, H-2, and O-2 was furthermore probed by XPS under vacuum conditions. While the pristine Fe carbide surface was unreactive toward hydrogen gas at 500 K, we interestingly found that CO dissociation from a preadsorbed monolayer of CO takes place already at low temperature. This observation points to an intrinsic activity of the Fe carbide phase where additional carbon originating from CO can be placed in the Fe carbide surface. The catalytic significance of the model catalyst surface presented here is that it can be seen as a stable Fe carbide phase with intrinsically vacant sites for additional C insertion at elevated pressure, and we propose that such additional C may act as active species in C-C coupling reactions during FTS. The studies pave the way for a better understanding of FTS processes on Fe based catalysts on the basis of a well-defined model surface.

AB - With the purpose of investigating the reactivity of Fe carbide as an active phase in Fischer-Tropsch catalysis, we studied the formation of a well-defined Fe carbide surface structure resulting from carbon exposure of an Fe film on Au(111). Using two different sources of carbon (C), namely atomic carbon and ethylene gas, we used synchrotron X-ray photoelectron spectroscopy (XPS) to show that a 6 ML Fe film readily converts into a well-defined and thermodynamically stable carbide phase. Scanning tunneling microscopy (STM) showed that the surface of the Fe carbide film is crystalline and is dominated by Fe(110)-like facets perturbed into a (2 X 2) periodic structure due to insertion of C in the interstitial sites. The reactivity of the carbide film toward CO, H-2, and O-2 was furthermore probed by XPS under vacuum conditions. While the pristine Fe carbide surface was unreactive toward hydrogen gas at 500 K, we interestingly found that CO dissociation from a preadsorbed monolayer of CO takes place already at low temperature. This observation points to an intrinsic activity of the Fe carbide phase where additional carbon originating from CO can be placed in the Fe carbide surface. The catalytic significance of the model catalyst surface presented here is that it can be seen as a stable Fe carbide phase with intrinsically vacant sites for additional C insertion at elevated pressure, and we propose that such additional C may act as active species in C-C coupling reactions during FTS. The studies pave the way for a better understanding of FTS processes on Fe based catalysts on the basis of a well-defined model surface.

KW - carburization

KW - Fischer-Tropsch synthesis

KW - iron carbide

KW - model catalyst

KW - scanning tunneling microscopy

KW - X-ray photoelectron spectroscopy

KW - PHASES

KW - OXIDE

KW - ADSORPTION

KW - CO OXIDATION

KW - NANOPARTICLES

KW - MOSSBAUER-SPECTROSCOPY

KW - GROWTH

KW - RAY PHOTOELECTRON-SPECTROSCOPY

KW - CARBURIZATION

KW - FE

U2 - 10.1021/acscatal.8b03684

DO - 10.1021/acscatal.8b03684

M3 - Journal article

AN - SCOPUS:85060236001

SN - 2155-5435

VL - 9

SP - 1264

EP - 1273

JO - ACS Catalysis

JF - ACS Catalysis

IS - 2

ER -