H₂S splitting on Cu(110): Insight from combined periodic density functional theory calculations and microkinetic simulation

Abstract

Practical copper (Cu)‐based catalysts for the water–gas shift (WGS) reaction was long believed to expose a large proportion of Cu(110) planes. In this work, as an important first step toward addressing sulfur poisoning of these catalysts, the detailed mechanism for the splitting of hydrogen sulfide (H2S) on the open Cu(110) facet has been investigated in the framework of periodic, self‐consistent density functional theory (DFT‐GGA). The microkinetic model based on the first‐principles calculations has also been developed to quantitatively evaluate the two considered decomposition routes for yielding surface atomic sulfur (S*): (1) H2S → H2S* → SH* → S* and (2) 2H2S → 2H2S* → 2SH* → S* + H2S* → S* + H2S. The first pathway proceeding through unimolecular SH* dissociation was identified to be feasible, whereas the second pathway involving bimolecular SH* disproportionation made no contribution to S* formation. The molecular adsorption of H2S is the slowest elementary step of its full decomposition, being related with the large entropy term of the gas‐phase reactant under realistic reaction conditions. A comparison of thermodynamic and kinetic reactivity between the substrate and the close‐packed Cu(111) surface further shows that a loosely packed facet can promote the S* formation from H2S on Cu, thus revealing that the reaction process is structure sensitive. The present DFT and microkinetic modeling results provide a reasonably complete picture for the chemistry of H2S on the Cu(110) surface, which is a necessary basis for the design of new sulfur‐tolerant WGS catalysts. © 2013 Wiley Periodicals, Inc.

Adsorption and diffusion of sulfur on the (111), (100), (110), and (211) surfaces of FCC metals: Density functional theory calculations

“…Previous studies normally report the preferred sulfur adsorption binding site, the binding (adsorption) energy, the sulfur-surface interatomic distances, and the diffusion energy of sulfur. The preferred adsorption site and the binding energy have been reported for sulfur on Ni(111), 3,9,17,28,30,31 Cu(111), 9,[13][14][15]17,25,26,31,35 Rh(111), 17 Pd(111), 4,15,22,26,35 Ag(111), 2,15,17,25,35 Ir(111), 34 Pt(111), 4,17,37 Au(111), 15,16,22,26 Ni(110), 9 Cu(110), 5,9,13 Au(110), 21 Ni(100), 9,12,30 Cu(100), 9,12,14 Ir(100), 29 Au(100), 7,16 Pd(211), 36 and Au(211). 16 Th...…”

“…Density Functional Theory (DFT) calculations have been performed to study the adsorption of sulfur on the low-index surfaces of multiple Face Center Cubic (FCC) metals. [3][4][5]7,9,10,[12][13][14][15][16][17]21,22,25,26,[28][29][30][33][34][35][36][37] We surveyed the DFT calculations of sulfur on FCC metal surfaces reported since the year 2000; see Ref. 39 for an account of earlier calculations.…”

“…16 The surface diffusion energy of sulfur has been calculated for Ni(111), 3,33 Cu(111), 33,35 Pd(111), 35 Ag(111), 2,35 Ir(111), 34 Pt(111), 33 Au(111), 16 Au(100), 16 and Au(211). 16 The surfaces of Ni 3,9,12,17,28,30,31,33 and Cu 5,9,[12][13][14][15]17,25,26,31,33,35 have been studied more extensively than the other FCC metals. The reason is because Ni has a high melting temperature and it is extensively used as the anode in SOFC.…”

Comparative Theoretical Study of the Chemistry of Hydrogen Sulfide on Cu(100) and Au(100): Implications for Sulfur Tolerance of Water Gas Shift Nanocatalysts

“…Microkinetic Model. Previous theoretical studies of H 2 S splitting on the (111), ( 110), (211), and (311) Cu surfaces 29,30 have all reported that the disproportionation of two SH* molecules to H 2 S* and S* did not open up a pathway responsible for the H−S bond breakage in the SH* intermediate at all, which stems from the expectation of an extremely low surface coverage for SH*. In what follows, therefore, the present microkinetic modeling based on a meanfield treatment was developed only according to a total of four reaction steps implicated in the mechanism of sequential hydrogen removal from H 2 S on Cu(100) and Au(100), i.e., step i with i = 1−4, which are listed as eqs 10−13, respectively:…”

“…In reality, the rates of the constituent elementary events are remarkably influenced by the temperature factor. Within all the reported reaction networks, the H 2 recombinative desorption step, 2H* → H 2 + 2*, was also ignored, whose kinetics, however, affects the surface deposition of S* via H 2 S. More seriously, because of the impacts of surface overage upon the dissociation rate, just comparing alone the energy barriers to be overcome to carry out reaction pathways as in the prior theoretical modelings , might be misleading and can not ensure a reliable assessment of their relative ease or difficulty. , Hence, many fundamental puzzles, such as the actual reaction mechanism and equilibrium surface composition in the course of H 2 S decomposition, remain not understood well at the molecular level. To help improve this understanding, the present work showed a comprehensive comparative study of the chemical process leading to atomic sulfur under realistic conditions on the extended (100) facets of pure Cu and Au metals.…”