Adsorption and decomposition of H2S on Pd(111) surface: a first-principles study

Review of Theoretical and Computational Studies of Bulk and Single Atom Catalysts for H2 S Catalytic Conversion

Catalytic conversion of hydrogen sulfide (H2 S) plays a vital role in environmental protection and safety production. In this review, recent theoretical advances for catalytic conversion of H2 S are systemically summarized. Firstly, different mechanisms of catalytic conversion of H2 S are elucidated. Secondly, theoretical studies of catalytic conversion of H2 S on surfaces of metals, metal compounds, and single-atom catalysts (SACs) are systematically reviewed. In the meantime, various strategies which have been adopted to improve the catalytic performance of catalysts in the catalytic conversion of H2 S are also reviewed, mainly including facet morphology control, doped heteroatoms, metal deposition, and defective engineering. Finally, new directions of catalytic conversion of H2 S are proposed and potential strategies to further promote conversion of H2 S are also suggested: including SACs, double atom catalysts (DACs), single cluster catalysts (SCCs), frustrated Lewis pairs (FLPs), etc. The present comprehensive review can provide an insight for the future development of new catalysts for the catalytic conversion of H2 S.

Gas-Sensing Properties of B/N-Modified SnS2 Monolayer to Greenhouse Gases (NH3, Cl2, and C2H2)

The adsorption capacity of intrinsic SnS2 to NH3, Cl2 and C2H2 is very weak. However, non-metallic elements B and N have strong chemical activity, which can significantly improve the conductivity and gas sensitivity of SnS2. Based on density functional theory, SnS2 was modified with B and N atoms to analyze its adsorption mechanism and gas sensitivity for NH3, Cl2 and C2H2 gases. The optimal structure, adsorption energy, state density and frontier molecular orbital theory are analyzed, and the results are in good agreement with the experimental results. The results show that the adsorption of gas molecules is exothermic and spontaneous. Only the adsorption of NH3 and Cl2 on B-SnS2 belongs to chemical adsorption, whereas other gas adsorption systems belong to physical adsorption. Moderate adsorption distance, large adsorption energy, charge transfer and frontier molecular orbital analysis show that gas adsorption leads to the change of the conductivity of the modified SnS2 system. The adsorption capacity of B-SnS2 to these gases is Cl2 > NH3 > C2H2. The adsorption capacity of N-SnS2 is NH3 > C2H2 > Cl2. Therefore, according to different conductivity changes, B-SnS2 and N-SnS2 materials can be developed for greenhouse gas detection of gas sensors.

Breaking scaling relationships in alkynol semi-hydrogenation by manipulating interstitial atoms in Pd with d-electron gain

Pd catalysts are widely used in alkynol semi-hydrogenation. However, due to the existence of scaling relationships of adsorption energies between the key adsorbed species, the increase in conversion is frequently accompanied by side reactions, thereby reducing the selectivity to alkenols. We report that the simultaneous increase in alkenol selectivity and alkynol conversion is achieved by manipulating interstitial atoms including B, P, C, S and N in Pd catalysts. A negative linear relationship is observed between the activation entropies of 2-methyl-3-butyn-2-ol and 2-methyl-3-buten-2-ol which is highly related to the filling of d-orbital of Pd catalysts by the modification of p-block elements. A catalyst co-modified by B and C atoms has the maximum d charge of Pd that achieves a 17-fold increase in the turn-over frequency values compared to the Lindlar catalysts in the semi-hydrogenation of 2-methyl-3-butyn-2-ol. When the conversion is close to 100%, the selectivity can be as high as 95%.

Circumventing the linear scaling relationship in the semi-hydrogenation is challenging. Here the authors report a method for breaking the scaling relationships using ordered mesoporous carbon-supported Pd nanocatalysts with d-electron gain by p-block atoms occupying interstitial sites in the lattice as a greener alternative to Lindlar catalysts for the selective hydrogenation of alkynols.

Ab initio modeling of H2S dissociative chemisorption on Ag(100)

Natural sulfidation of silver nanomaterials can passivate the surface, while preserving desirable optical and electrical properties, which is beneficial for limiting Ag+ release and cytotoxicity. But little is known at...

Removal of H2S to produce hydrogen in the presence of CO on a transition metal-doped ZSM-12 catalyst: a DFT mechanistic study

Hydrogen sulfide (H₂S) leads to corrosion in transport lines and poisoning of many catalysts. Meanwhile, H₂S is an inexhaustible potential source of hydrogen, which is a very valuable chemical reagent and an environmentally friendly energy product. Therefore, removal of H₂S and producing hydrogen gas using potential catalysts has been intensively studied, according to the equation: H₂S(g) + CO(g) → COS(g) + H₂(g). In this study, hydrogen sulfide (H₂S) decomposition in the presence of CO over transition metal-doped ZSM-12 clusters (TM-ZSM-12) has been investigated based on DFT calculations at the B3LYP-D3/6-31G(d,p) level. The calculation results reveal that the proposed reaction mechanism is controlled by 4 key steps, (i) hydrogen dissociation (E_a1 = +0.04 eV for the 1st hydrogen and E_a2 = +0.22 eV for the 2nd hydrogen), (ii) COS desorption (the rate-determining step of this H₂S removal process, E_des = +1.18 eV), (iii) hydrogen diffusion to the transition metal with an energy barrier (E_a3) of +0.62 eV, and (iv) the H₂ formation step (E_a4 = +0.94 eV). Our results indicate that in the presence of CO, the Cu-ZSM-12 cluster has a potential application as a highly active catalyst for H₂S removal together with hydrogen production.

Development of Ni-based alloy catalysts to improve the sulfur poisoning resistance of Ni/YSZ anodes in SOFCs

Alloying Au into Ni surfaces provides a way to alleviate sulfur poisoning in the anode of solid oxide fuel cells.

Modeling Sulfur Poisoning of Palladium Membranes Used for Hydrogen Separation

Hydrocarbons are the most important source for hydrogen production. A combined reaction-separation process using inorganic membranes can significantly increase the reaction conversion by shifting the equilibrium toward product formation. Sulfur poisoning is a significant problem as it deactivates the most commonly used metallic membranes. The relationship of the membrane activity and surface coverage with the surface structure has been recognized in the literature. A theoretical model to simulate hydrogen transport in the presence of sulfur compounds is presented. This model accounts for active site deactivation and permanent structural damage to the membrane. Transport and reaction rate parameters used in the model have been estimated from experimental data. Qualitatively, the model represents well the behavior of inorganic membranes, including partial membrane activity regeneration after the sulfur source is removed.

Pd-loaded SnO2 hierarchical nanospheres for a high dynamic range H2S micro sensor

The sensitivity of Pd-loaded SnO₂ nanosphere sensor to H₂S gas: micro gas sensors based on Pd-loaded SnO₂ nanospheres have credible gas detection abilities down to 10 ppb and 4 orders of magnitude concentration detection ranges.

Density functional study on the resistance to sulfur poisoning of Ptx (x = 0, 1, 4 and 8) modified α-Mo2C(0001) surfaces

The tolerance of sulfur poisoning of α-Mo₂C(0001) surfaces with different Pt coverages is investigated combining the density functional theory (DFT) results with thermodynamics data using the ab initio atomistic thermodynamic method. It is found that on Mo₂C(0001), Pt clusters tend to form two dimensional planar structures instead of aggregating. The clean Mo₂C(0001) surface interacts with sulfides very strongly and is susceptible to sulfur poisoning. With increasing the coverage of Pt on the Mo₂C surface, the interaction between sulfur and substrate is weakened. The sulfur tolerance ability increases in the order of Mo₂C ≈ Pt₁/Mo₂C < Pt₄/Mo₂C < Pt₈/Mo₂C, where the coverage of Pt on the Mo₂C plays a very effective role. The results provide theoretical guidance for designing Mo₂C based catalysts with high activity and high sulfur resistance.

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.

DFT study on the adsorption and dissociation of H2S on CuO(111) surface

The pathways of the dissociation H₂S on the CuO(111) surface are presented in this work.

Density functional theory studies of methanol adsorption and decomposition mechanism on Al13 clusters

The adsorption and decomposition of the CH3OH molecule on Al13 clusters were investigated by generalized gradient approximation of the density functional theory. The strong attractive forces between the CH3OH molecule and aluminum atoms induce the breaking of the H–O and C–O bonds of CH3OH. Subsequently, the dissociated CH3O and OH radical fragments oxidize the aluminum clusters. The largest adsorption energy is –205.4 kJ/mol. We also investigated five reaction pathways of the CH3OH molecule on the Al13 clusters. The activation energies are in the range of 10.3−113.1 kJ/mol. Compared with the bond dissociation energies of the C–O and O–H bonds in the isolated methanol, Al13 performs very well in decreasing the bond break barrier of CH3OH. In addition, although the C–O bond is slightly weaker than the O−H bond, the O−H bond is even easier to decompose on the Al13 surface. The rate constants of five adsorption paths over the temperature range 300−700 K are presented.

Density functional theory studies on adsorption and decomposition mechanism of FOX-7 on Al13 clusters

The adsorption and decomposition of the FOX-7 molecule on Al13 clusters were investigated by generalized gradient approximation of the density functional theory. The strong attractive forces between the FOX-7 molecule and aluminum atoms induce the N−O bond breaking of FOX-7. Subsequently, the dissociated oxygen atoms and radical fragment of FOX-7 oxidize the aluminum clusters. The largest adsorption energy is −1020.4 kJ/mol. We also investigated three adsorption reaction paths of the FOX-7 molecule on the Al13 clusters in the A configuration. The activation energy for the adsorption steps are 0.2, 11.4, and 10.2 kJ/mol, respectively, and Al13 is more active than the Al(111) surface and the Al13 cluster performs better in decreasing the adsorption barrier of FOX-7 on the aluminum surface as well. The rate constants of three adsorption paths increase as temperature increases over the temperature range 275–500 K.

Characterization of hydrogen responsive nanoporous palladium films synthesized via a spontaneous galvanic displacement reaction

A model is presented regarding the mechanistic properties associated with the interaction of hydrogen with nanoporous palladium (np-Pd) films prepared using a spontaneous galvanic displacement reaction (SGDR), which involves PdCl(2) reduction by atomic Ag. Characterization of these films shows both chemical and morphological factors, which influence the performance characteristics of np-Pd microcantilever (MC) nanomechanical sensing devices. Raman spectroscopy, uniquely complemented with MC response profiles, is used to explore the chemical influence of palladium oxide (PdO). These combined techniques support a reaction mechanism that provides for rapid response to H(2) and recovery in the presence of O(2). Post-SGDR processing via reduction of PdCl(2)(s) in a H(2) environment results in a segregated nanoparticle three-dimensional matrix dispersed in a silver layer. The porous nature of the reduced material is shown by high resolution scanning electron microscopy. Extended grain boundaries, typical of these materials, result in a greater surface area conducive to fast sorption/desorption of hydrogen, encouraged by the presence of PdO. X-ray diffraction and inductively coupled plasma-optical emission spectroscopy are employed to study changes in morphology and chemistry occurring in these nanoporous films under different processing conditions. The unique nature of chemical/morphological effects, as demonstrated by the above characterization methods, provides evidence in support of observed nanomechanical response/recovery profiles offering insight for catalysis, H(2) storage and improved sensing applications.

Permanganate oxidation of sulfur compounds to prevent poisoning of Pd catalysts in water treatment processes

The practical application of Pd-catalyzed water treatment processes is impeded by catalyst poisoning by reduced sulfur compounds (RSCs). In this study, the potential of permanganate as a selective oxidant for the removal of microbially generated RSCs in water and as a regeneration agent for S-poisoned catalysts was evaluated. Hydrodechlorination using Pd/Al2O3 was carried out as a probe reaction in permanganate-pretreated water. The activity of the Pd catalysts in the successfully pretreated reaction medium was similar to that in deionized water. The catalyst showed no deactivation behavior in the presence of permanganate at a concentration level < or = 0.07 mM. With a residual oxidant concentration of > or = 0.08 mM, a significant but temporary inhibition of the catalytic dechlorination was observed. Unprotected Pd/Al2O3, which had been completely poisoned by sulfide, was reactivated by a combined treatment with permanganate and hydrazine. However, the anthropogenic water pollutants thiophene and carbon disulfide were resistant against permanganate. Together with the preoxidation of catalyst poisons, hydrophobic protection of the catalysts was studied. Pd/zeolite and various hydrophobically coated catalysts showed a higher stability against ionic poisons and permanganate than the uncoated catalyst. By means of a combination of oxidative water pretreatment and hydrophobic catalyst protection, we provide a new tool to harness the potential of Pd-catalyzed hydrodehalogenation for the treatment of real waters.

Tuning the surfaces of palladium nanoparticles for the catalytic conversion of Cr(vi) to Cr(iii)

This work reports the feasibility of using Pd nanoparticles as innovative catalysts in the conversion of reducible contaminants from toxic to benign forms. Cr(VI) is a known carcinogen while the trivalent chromium salts are believed to be non-toxic. The ability of Pd nanoparticles to catalyze the rapid reduction of Cr(VI) to Cr(III) using reactive sulfur intermediates produced in situ was therefore studied. Using a microchamber set at 130 degrees C, the reduction mixture consists of palladium nanoparticles and sulfur (PdNPs/S), which generated highly reducing sulfur intermediates that effected the reduction of Cr(VI) to Cr(III) by 1st order reaction kinetics. UV-visible spectroscopy and cyclic voltammetry were employed to monitor the reduction process. The results showed that 99.8% of 400 microM Cr(VI) was reduced to Cr(III) by PdNPs/S in one hour compared to 2.1% by a control experiment consisting of sulfur only. The rate of Cr(VI) reduction was found to be dependent on temperature and pH and was greatly enhanced by the addition of PdNPs. Subsequent application of this approach in the reduction of Cr(VI) in soil and aqueous media was conducted. In contrast to the control experiments with and without PdNPs or sulfur, greater than 92% conversion rate was obtained in the presence of PdNPs/S within 1 hour. This represents over a 500-fold improvement in conversion rate compared to current microbial approaches. XPS analysis provided the confirmation regarding the oxidation states of Cr(VI), Cr(III) and the nature of the reactive intermediates. This work offers PdNPs/S as a new interface for the reduction of high oxidation state heavy metal pollutants.