Hydrogenation of S to H2S on Pt(111): A first-principles study

A systematic mid-infrared spectroscopic study of thermally processed H2S ices

The positive identification of the molecular components of interstellar icy grain mantles is critically reliant upon the availability of laboratory-generated mid-infrared absorption spectra which can be compared against data acquired by ground- and space-borne telescopes. However, one molecule which remains thus far undetected in interstellar ices is H2S, despite its important roles in astrochemical and geophysical processes. Such a lack of a detection is surprising, particularly in light of its relative abundance in cometary ices which are believed to be the most pristine remnants of pre-solar interstellar ices available for study. In this paper, we present the results of an extensive and quantitative mid-infrared spectroscopic characterisation of H2S ices deposited at 20, 40, and 70 K and thermally processed to sublimation in an ultrahigh-vacuum system. We anticipate our results to be useful in confirming the detection of interstellar H2S ice using high-resolution and high-sensitivity instruments such as the James Webb Space Telescope, as well as in the identification of solid H2S in icy environments in the outer Solar System, such as comets and moons.

Three-dimensional platinum nanoparticle-based bridges for ammonia gas sensing

This study demonstrates the fabrication of self-aligning three-dimensional (3D) platinum bridges for ammonia gas sensing using gas-phase electrodeposition. This deposition scheme can guide charged nanoparticles to predetermined locations on a surface with sub-micrometer resolution. A shutter-free deposition is possible, preventing the use of additional steps for lift-off and improving material yield. This method uses a spark discharge-based platinum nanoparticle source in combination with sequentially biased surface electrodes and charged photoresist patterns on a glass substrate. In this way, the parallel growth of multiple sensing nodes, in this case 3D self-aligning nanoparticle-based bridges, is accomplished. An array containing 360 locally grown bridges made out of 5 nm platinum nanoparticles is fabricated. The high surface-to-volume ratio of the 3D bridge morphology enables fast response and room temperature operated sensing capabilities. The bridges are preconditioned for ~ 24 h in nitrogen gas before being used for performance testing, ensuring drift-free sensor performance. In this study, platinum bridges are demonstrated to detect ammonia (NH₃) with concentrations between 1400 and 100 ppm. The sensing mechanism, response times, cross-sensitivity, selectivity, and sensor stability are discussed. The device showed a sensor response of ~ 4% at 100 ppm NH₃ with a 70% response time of 8 min at room temperature.

Gas Phase Electrodeposition Enabling the Programmable Three-Dimensional Growth of a Multimodal Room Temperature Nanobridge Gas Sensor Array

Parallel three-dimensional (3D) growth of different nanomaterials with submicrometer resolution is a promising approach to overcome some technological and economic limits encountered in planar integrated homogeneous films. The programmable multimaterial gas phase nanoparticle electrodeposition concept enables the fabrication of a 3D multimodal conductometric gas sensor array. The approach requires the deposition of more than one nanomaterial to achieve orthogonal sensing capabilities and multigas sensitivity and selectivity. The demonstrated "electronic nose"-like array contains 1080 self-aligning 3D nanobridge-based electrical connections of platinum, nickel oxide, and gold on a single chip. The nanobridges form through a nearest neighbor Coulombic interaction. Each gas sensitive bridge is a 3D structure composed of a porous but electrically conducting nanoparticle network. It was found that this architecture is unique, because it does not require external heating to operate. A trimodal sensor array will be demonstrated to detect various levels of ammonia (NH₃), carbon monoxide (CO), and hydrogen sulfide (H₂S). A 3 × 3 transfer matrix will be discussed to correlate the recorded signals with the gas composition.

The role of H2S addition on Pt/Al2O3 catalyzed propane dehydrogenation: a mechanistic study

Effects of H₂S addition on the Pt/Al₂O₃ catalyzed propane dehydrogenation.

Strategies for Carbon and Sulfur Tolerant Solid Oxide Fuel Cell Materials, Incorporating Lessons from Heterogeneous Catalysis

Solid oxide fuel cells (SOFCs) are a rapidly emerging energy technology for a low carbon world, providing high efficiency, potential to use carbonaceous fuels, and compatibility with carbon capture and storage. However, current state-of-the-art materials have low tolerance to sulfur, a common contaminant of many fuels, and are vulnerable to deactivation due to carbon deposition when using carbon-containing compounds. In this review, we first study the theoretical basis behind carbon and sulfur poisoning, before examining the strategies toward carbon and sulfur tolerance used so far in the SOFC literature. We then study the more extensive relevant heterogeneous catalysis literature for strategies and materials which could be incorporated into carbon and sulfur tolerant fuel cells.

Density functional theory study of hydrogenation of S to H2S on Pt–Pd alloy surfaces

In this work, the adsorption of S-containing species (S, HS, and H₂S) and the hydrogenation of S on the Pt–Pd alloy were investigated by using the periodic density functional theory (DFT).

First principle calculations of hydrogen sulfide adsorption and dissociation on pure Pd (111) and Au (111), and alloy Pd/Au (111) and Au/Pd (111) surfaces

The hydrogen sulfide adsorption and dissociation on pure Pd (111) and Au (111), alloy Pd / Au (111) and Au / Pd (111) surfaces have been investigated using the pseudo-potential plane wave method within the generalized-gradient approximation density functional theory (GGA+DFT). The results show that H 2 S tends to be adsorbed on top site, HS prefers to locate on bridge site, and the S and H locate on fcc site on various surfaces. Compared the adsorption of sulfur-containing species and hydrogen on pure and alloy metal surfaces, a similar trend of adsorption energies on the metal surfaces ( Pd / Au (111) > Pd (111) > Au (111) > Au / Pd (111)) is found. In addition, the dissociation process on the Pd (111) and Pd / Au (111) surfaces is predicted to be exothermic. However, on Au (111) and Au / Pd (111), the dissociation process is endothermic. The work reveals that H 2 S dissociation is more likely to happen on Pd / Au (111) surface. Finally, the adsorption energies of adsorbate on metal surfaces have strong correlation with the d-band center. The d-band center moves away from the Fermi level, and the adsorption energy decreases. According to the LDOS analysis, the inner Au atoms of Pd / Au (111) can enhance the top-layer d-band intensity, whereas the inner Pd atoms of Au / Pd (111) cause the opposite effect. The further electronic state analysis reveals the interaction between H 2 S and metal surfaces.

A DFT INVESTIGATION OF SULFUR ADSORPTION ON Ir(100)

The adsorptions of sulfur atom on the Ir (100) surface at p (2 × 2) and c (2 × 2) phases were investigated by the density functional calculations within the generalized gradient approximation. The adsorption energy, adsorption geometry, work function change, and charge density distribution were analyzed. The hollow site was found to be the most stable, followed by the bridge and the top sites. The calculated adsorption geometries were in good agreement with the observed results. Particularly, it was found that the adsorption of S on Ir (100) caused a work function decrease. A charge accumulation at the interface between the S layer and the Ir substrate, which centered closer to the S atom, suggests a polar covalent bonding. Density of states (DOS) analysis showed that the adsorption of S induces a reduction of the surface Ir d-orbital DOS around the Fermi level.

Decomposition of methanthiol on Pt(111): a density functional investigation

Decomposition of methanthiol on Pt(111) is systematically investigated using self-consistent periodic density functional theory (DFT), and the decomposition network has been mapped out. The most stable adsorption of the involved species tends to form the sp(3) hybridized configuration of both C and S atoms, in which C is almost tetrahedral and S has the tendency to bond to three atoms. Spontaneous dissociation rather than desorption is preferred for adsorbed methanthiol. Based on the harmonic transition state theory calculations, the decomposition rate constants of the thiolmethoxy and thioformaldehyde intermediates are found to be much lower than those for their formation, leading to long lifetimes of the intermediates for observation. Under the ultrahigh vacuum (UHV) condition, the most possible decomposition pathway for methanthiol on Pt(111) is found as CH(3)SH --> CH(3)S --> CH(2)S --> CHS --> CH + S --> C + S, in which the C-S bond cleavage mainly occurs at the CHS species. However, the decomposition pathway is CH(3)SH --> CH(3)S --> CH(3) + S under the hydrogenation condition; the C-S bond scission mainly occurs at CH(3)S. The Brønsted-Evans-Polanyi relation holds for each of the S-H, C-H, and C-S bond scission reactions.

A critical assessment of theoretical methods for finding reaction pathways and transition states of surface processes

The performance of a variety of techniques for locating transition states on potential energy surfaces is evaluated within the density functional theory framework. Diffusion of a water molecule across NaCl(001) and HCl bond breaking on the same surface are treated as general test cases; the former is an example of a low barrier diffusion process and the latter an example of a relatively high barrier covalent bond rupture event. The methods considered include the nudged elastic band (NEB), Dewar, Healy and Stewart (DHS), dimer, constrained optimization (CO), activation-relaxation technique (ART) and one-side growing string (OGS) as well as novel combinations of the DHS with growing string (DHS + GS) and DHS plus climbing image (CI-DHS). A key conclusion to come from this study is that the NEB method is relatively fast, especially when just a single (climbing) image is used. Indeed, using more images represents an unnecessary computational burden for our set of processes. The dimer method exhibits variable performance; being poor for the water diffusion processes, which have small activation energies, but much more efficient for the HCl bond breaking process which has a higher barrier. When only a poor initial guess of the transition state geometry is available, the CI-DHS scheme is one of the most efficient techniques considered. And as a means to quickly establish an approximate minimum energy pathway the DHS + GS scheme offers some potential.