Effects of Alloying on the Chemistry of CO and H₂S on Fe Surfaces

Abstract

Deleterious gases such as CO and H 2 S can cause degradation of steel by reacting with the metal surface. Here we consider whether alloying the steel surface might be able to inhibit these damaging surface reactions by raising the barriers to molecular dissociation. We employ first-principles density functional theory techniques to investigate the elementary reaction pathways and barriers for CO and H 2 S on FeAl and Fe 3 Si surfaces and compare them with pure Fe surfaces (as a model for steel). We find that H 2 S dissociates on iron surfaces much more easily than CO does. Although FeAl surfaces raise the barriers for H 2 S dissociation, they significantly lower the barriers for CO dissociation. On the other hand, Fe 3 Si surfaces raise the barriers for CO dissociation, but they are as vulnerable as Fe surfaces to H 2 S dissociation. Our findings suggest that alloying iron with Al or Si is unlikely to simultaneously increase its resistance to the initial stages of chemical degradation by CO and H 2 S.

Density functional theory for transition metals and transition metal chemistry

“…Carter and Yarovsky and their coworkers used the PBE and PW91 functionals, respectively, to study a variety of adsorption, dissociation, and diffusion processes on Fe, Al/Fe, Fe/Si and sulfur-covered-Fe surfaces [1082][1083][1084][1085][1086][1087][1088][1089][1090] and structure and magnetism at Cr/Fe interfaces. 1091 Yarovsky and coworkers 1092,1093 used the PW91 density functional to carry out spin-polarized direct dynamics simulations of H 2 S dissociation at the (110) and (100) surfaces of Fe at temperatures from 298 K to 1800 K. The dissociation mechanism was found to change as a function of temperature.…”

Adsorption and dissociation of H2S on Mo2C(001) surface-A first-principle study

“…Hydrotreating is one of the most important steps in both hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) processes [2]. Thus, the hydroprocessing of petroleum produces a great deal of toxic H 2 S. Because of the favorable thermodynamics and the relatively weak H-S bond, the molecule of H 2 S could dissociation on transition metal surface easily [3].…”

Nucleation and growth of H blisters in stacking fault on B2–FeAl {100} planes

“…Previous DFT-GGA calculations found a FM (ferromagnetic) state in FeAl nearly degenerate with an AFM (antiferromagnetic) state. 19 However, experiments found no magnetism in stoichiometric FeAl, 20 thus, we do not allow for magnetism to develop in B2-FeAl. Spin polarized calculations are performed by using GGA exchange correlation functional of Perdew and Wang (PW91) 21 and double numerical quality basis set with polarization functions (DNP) 22 and semi-core pseudopotential 23 with a convergence tolerance of energy of 2.7 Â 10 À4 eV, a maximum displacement of 0.05Å, a real-space cutoff of 5.3Å, and without any symmetry constraints.…”