Dissociation Of HCl Research Articles

Probing the Role of Solvent Configurations and Local Electric Fields on HX (X = F, Cl, Br and I) Dissociation in Water Clusters.

The acidity of hydrohalic acids increases down the group, with HF and HI being the weakest and strongest acids. Electronic structure calculations suggest that the critical electric fields required for the dissociation of HF, HCl, HBr, and HI are 347, 193, 163, and 153 MV cm-1, respectively, which are proportional to their corresponding pKa values and emphasize that in these systems the bond dissociation energy determines the pKa. The solvent configuration plays a significant role in the acid dissociation process, which is illustrated by a particular configuration of three water molecules around HX and favors dissociation of only HBr, even though the critical electric field required for the dissociation of HI is lower than that of HBr, as depicted in the graphical abstract. Further, the Born-Oppenheimer molecular dynamics (BOMD) simulations suggest that the spontaneity of HX dissociation depends on both the solvent configuration and thermal fluctuations, which hold higher significance in the case of weaker acids. In general, it was observed that the solvent electric field required for the acid dissociation process is marginally lower at higher temperatures.

Development of a ReaxFF Reactive Force Field for Pt/Cl Systems with Application to Platinum Metal Etching with Chlorine and Hydrogen Chloride Gases.

In this study, we present the development of a ReaxFF Pt/Cl/H reactive force field designed to elucidate the etching process by Cl for Pt surfaces. The ReaxFF force field parameters were optimized based on a quantum mechanical training set, which included adsorption energies of Cl and dissociation of HCl on Pt(100) and Pt(111) surfaces, energy/volume relations of PtCl2 crystals, and Cl diffusion on Pt(100) and Pt(111) surfaces. The predictive capability of the force field was further established through molecular dynamics simulations, which investigated the interactions of Cl2 and HCl molecules with the (100) and (111) surfaces of c-Pt crystalline solid slabs. A comparative analysis revealed that the Pt (100) surface exhibited higher susceptibility to chlorination and etching, leading to a more dominant removal of surface Pt atoms, whereas the Pt (111) surface showed greater resistance to these processes. This resistance impeded the access of Cl atoms to the Pt surface, resulting in a slower formation of PtxCly molecules. The etching ratios between HCl and Cl2 were compared with experimental results, yielding satisfactory agreement. This indicates that the developed ReaxFF protocol serves as a valuable tool for studying atomistic-scale details of the etching process in platinum metal systems.

Electric nuclear quadrupole coupling reveals dissociation of HCl with a few water molecules

Investigating the dissociation of acids in the presence of a limited number of water molecules is crucial for understanding various elementary chemical processes. In our study, focusing on HCl(H 2 O) n clusters (where HCl is hydrogen chloride and H 2 O is water) formed in a cold and isolated jet expansion, we used the nuclear quadrupole coupling tensor obtained through rotational spectroscopy to decipher the nature of the hydrogen-chlorine (H-Cl) chemical bond in a microaqueous environment. For n = 1 to 4, the H-Cl bond is covalent. At n = 5 and 7, the contact ion pair of H 3 O + Cl − is spontaneously formed within the hydrogen bond networks of book and cube acid-water clusters, respectively.

Revelation of HCl poisoning and enhancement mechanism on N-modified Al2O3 catalysts for COS and CS2 hydrolysis

The presence of HCl in blast furnace gas significantly inhibits hydrolytic activity and catalyst stability. The anti-chlorine capacity and poisoning mechanism of Al2O3 catalysts before and after nitrogen modification was investigated by activity evaluation, characterization analysis and theoretical calculations. In the presence of 0.01 vol% HCl, the COS and CS2 conversions of K0.1Al2O3 catalysts decreased rapidly after 4 h of reaction, which was amended by N doping. The N0.1K0.1Al2O3 catalyst maintained 48.23 % COS conversion and 45.41 % CS2 conversion, respectively, after 16 h reaction. The deteriorated reactivity was mainly associated with the decreased specific surface area, reduced chemisorbed oxygen, disrupted basicity and COS and CS2 adsorption ability. Sulfate and HCl on the surface of the unmodified catalyst mainly destroyed the Al sites and led to catalyst deactivation. N doping reinforced the tendency of toxic molecules to adsorb at the K site (K2SO4 and KCl) and thus protected the Al active site. DFT calculation results demonstrated the inhibition of HCl adsorption at the Al site by N modification, while the trapping of HCl by both K and N sites efficiently protected the Al site from acidification. The reaction pathway calculations certified that N doping increased the energy barrier of the HCl dissociation reaction, which inhibited the acidification and deactivation of Al2O3 to some extent.

Mechanism of ionic dissociation of HCl in the smallest water clusters.

The dissociation of strong acids into water is a fundamental process in chemistry and biology. Determining the minimum number of water molecules that can result in an ionic dissociation of hydrochloric acid (HCl → H+ + Cl-) remains a challenging subject. In this study, the reactions of H2O with HCl(H2O)n-1 (HCl-H2O cluster), i.e., HCl(H2O)n-1 + H2O (n = 3-7), were investigated by using the direct ab initio molecular dynamics (AIMD) method. Direct AIMD calculations were performed to set the collision energy of H2O to zero for all trajectories. For n = 3, no reaction occurred. In contrast, HCl dissociated to H+ + Cl- at n = 4, forming a contact ion pair (cIP) and solvent-separated ion pair (ssIP) as products. The reactions were expressed as HCl(H2O)3 + H2O → H3O+(H2O)2Cl- (ssIP), and HCl(H2O)3 + H2O → H3O+(Cl-)(H2O)2 (cIP). The ion pair (IP) products were dependent on the collision site of H2O relative to HCl(H2O)3. For n = 5-7, both IPs were formed through the reaction between H2O and HCl(H2O)n-1 (n = 5-7). The reaction between HCl and (H2O)4 (HCl + (H2O)4 → HCl(H2O)4) was non-reactive in IP formation. The reaction mechanism was discussed based on the theoretical results.

Charge-Transfer-Controlled Quantum Dynamics of HCl Dissociation on the Ag/Au(111) Bimetallic Alloy Surface.

Understanding polar molecule dynamics on bimetallic surfaces, especially electropositivity and electronegativity, remains a challenge. Here, we report the reactivity of HCl on a strained Ag monolayer on Au(111) using six-dimensional quantum dynamics with a new machine-learning-based potential energy surface. Surprisingly, HCl reactivity is significantly suppressed by the Ag-Au interaction despite a lower HCl+Ag/Au(111) barrier than pure Ag(111). This arises from charge transfer between Ag and Au, where electronegative Au makes the top Ag layer on Ag/Au(111) electropositive, unlike that on pure Ag(111). Electropositive Ag in HCl+Ag/Au(111) attracts Cl, yielding an unfavorable H-Cl configuration and reduced reactivity. These findings deepen our understanding of polar molecule interactions on bimetallic surfaces, highlighting the role of charge transfer in dissociative chemisorption and the implications for catalyst design in heterogeneous catalysis.

High-Index Faceted Cu2 O@CuO Mesocrystals Act as Efficient Catalyst for Si Hydrochlorination to Trichlorosilane.

Mesocrystals (MCs) with high-index facets may have superior catalytic properties to those with low-index facets and their nanocrystal counterparts. However, synthesizing such mesocrystal materials is still very challenging because of the metastability of MCs and energetic high-index crystal facets. This work reports a successful solvothermal method followed by calcination for synthesizing copper oxide-based MCs possessing a core-shell structure (denoted as Cu2 O@CuO HIMCs). Furthermore, these MCs are predominantly bounded by the high-index facets such as {311} or {312} with a high-density of stepped atoms. When used as catalysts in Si hydrochlorination to produce trichlorosilane (TCS, the primary feedstock of high-purity crystalline Si), Cu2 O@CuO HIMCs exhibit significantly enhanced Si conversion and TCS selectivity compared to those with flat surfaces and their nanostructured counterparts. Theoretical calculations reveal that both the core-shell structure and the high-index surface contribute to the increased electron density of Cu sites in Cu2 O@CuO HIMCs, promoting the adsorption and dissociation of HCl and stabilizing the dissociated Cl* intermediate. This work provides a simple method for synthesizing high-index faceted MCs and offers a feasible strategy to enhance the catalytic performance of MCs.

Chemo-hydro-mechanical effects of CO2 injection into a permeable limestone

CO2 storage in carbonate aquifers is a way to mitigate atmospheric CO2 emissions, but it leads to acid-producing reactions that may induce alterations in the rock pore structure and hydromechanical properties. To gain a better understanding of these changes in rock properties, percolation experiments under constant flow-rate conditions with (i) CO2-saturated water (PCO2 = 100 bar and T = 60 °C) and (ii) HCl solutions (P = 1 bar and T = 60 °C) were performed on centimetric cores of the grain-supported Pont du Gard Limestone (permeability about 10−14–10−13 m2). Effluent chemistry analyses, X-ray imaging, and measurements of the hydromechanical properties of intact and altered specimens were used to quantify acid-induced changes in the two acid-rock systems. Experimental results show that the rock dissolution patterns highly depend on the acid type and pore space heterogeneity. Under the flow conditions of these experiments, complete HCl dissociation (strong acid) and rapid HCl-rock reaction result in a compact dissolution pattern that only affects the hydromechanical properties of the core inlet. Conversely, partial dissociation of H2CO3 (weak acid) produces chemical reactions all along the core. Initial structural heterogeneities localize chemical reactions along preferential flow pathways, causing instabilities in the reaction front and wormhole formation, which markedly enhances permeability. A powerlaw relationship with a very large exponent (as high as 24) accounts for the variation in permeability as a function of porosity. Altered cores render both a significant attenuation in mechanical rock properties and ultrasonic velocities, which is reproduced using a Differential Effective Medium (DEM) homogenization approach. The high-pressure percolation experiments of this study using CO2-saturated water represent an extreme scenario of CO2-brine-rock interactions in carbonate reservoirs, which needs to be considered to improve the prediction and monitoring of the storage performance.

Improvement mechanism of Ru species on Hg0 oxidation reactivity over V2O5/TiO2 Catalyst: A density functional theory study

With the increasing demand for Hg0 removal, the heterogeneous catalytic oxidation using modified V/Ti catalysts has attracted more attention, among which the VRu/Ti doped with RuO2 has higher activity and Cl2 yield than V/Ti. In this work, the surface performance, adsorption properties and Hg0 oxidation pathways of V/Ti and VRu/Ti catalysts were studied in DFT method and explain in mechanism level. The doping of Ru species in low oxidized state causes the oxygen vacancies and the further electronic structure change, which strengthens the nucleophilicity while weakening the electrophilicity. Therefore, the dissociation of HCl on VRu/Ti changed more active. In addition, the mixed reaction pathway on VRu/Ti shows a lower energy barrier than that on V/Ti catalyst, indicating that Ru species improves the oxidation activity through the special Semi-Deacon reaction, which is rarely reported in other research. The conclusions of this paper provide important support for the future modification research.

First-Principles Study of Hg0 Immobilization on a Defective Pyrite Surface

The formation of defects over a crystal surface could significantly improve the elemental mercury (Hg0) removal performance of pyrite (FeS2). Herein, the role of surface defects in Hg0 immobilization over FeS2(100) was investigated by adopting quantum chemistry. The contribution of surface defects to mercury immobilization over pyrite was mainly manifested in facilitating Hg0 adsorption. Compared with a perfect pyrite surface, a defective pyrite surface exhibited a higher affinity to Hg0, whose adsorption energy was up to −53.03 kJ/mol. In addition, surface defects could induce the dissociation of HCl, a common component in coal combustion flue gas, which provided active chlorine (Cl*) for subsequent Hg0 oxidation. The Langmuir–Hinshelwood mechanism is responsible for Hg0 oxidation over the defective FeS2(100) surface. First, Hg0 and HCl were simultaneously adsorbed over the defective surface, and the presence of defects could promote Hg0 adsorption and HCl dissociation. Subsequently, adsorbed Hg0 would combine with the adjacent active Cl* site, whose energy barrier was 92.60 kJ/mol. Eventually, HgCl could spontaneously react with another Cl* site to form a HgCl2 molecule. Thus, the formation of a HgCl intermediate was the rate-determining step for Hg0 oxidation over a defective pyrite surface. This work reveals the role of defects in Hg0 immobilization over a pyrite surface, which provides a scientific basis for the design and modification of natural mineral sulfide sorbents.

Engineering the catalytic properties of CeO2 catalyst in HCl-assisted propane dehydrogenation by effective doping: A first-principles-based microkinetic simulation.

HCl-assisted propane dehydrogenation (PDH) is an attractive route for propene production with good selectivity. In this study, the doping of CeO2 with different transition metals, including V, Mn, Fe, Co, Ni, Pd, Pt, and Cu, in the presence of HCl was investigated for PDH. The dopants have a pronounced effect on the electronic structure of pristine ceria that significantly alters the catalytic capabilities. The calculations indicate the spontaneous dissociation of HCl on all surfaces with a facile abstraction of the first hydrogen atom except on V- and Mn-doped surfaces. The lowest energy barrier of 0.50 and 0.51eV was found for Pd- and Ni-doped CeO2 surfaces. The surface oxygen is responsible for hydrogen abstraction, and its activity is described by the p-band center. Microkinetics simulation is performed on all doped surfaces. The increase in the turnover frequency (TOF) is directly linked with the partial pressure of propane. The adsorption energy of reactants aligned with the observed performance. The reaction follows first-order kinetics to C3H8. Furthermore, on all surfaces, the formation of C3H7 is found as the rate-determining step confirmed by the degree of rate control (DRC) analysis. This study provides a decisive description of catalyst modification for HCl-assisted PDH.

Change in the Electronic Environment of the VOx Active Center via Support Modification to Enhance Hg Oxidation Activity

Oxidation of elemental Hg (Hg0) is catalytically and economically an efficient way to remove the harmful Hg contained in the flue gas from coal combustion facilities. Thus, the development of a highly active V2O5/TiO2 catalyst, which is active to the Hg oxidation, is very essential. Support modification can change the reactivity of V2O5/TiO2 by affecting the V2O5 active center which is critical to the surface–reactant interaction, so understanding the effects of support tuning methods, e.g., crystallographic phase control and reduction treatment, on the Hg oxidation activity is valuable. Herein, density functional theory calculations were performed to mechanistically investigate the change of Hg oxidation reactivity by the support tuning methods and to elucidate the change of the electronic environment at the active site. The phase control to the TiO2 support was found to improve the Hg oxidation activity, but the reduction treatment decreased the activity, which is attributed to the change of the charge density at V2O5. Furthermore, the origin of the reactivity change was elucidated within a Sabatier-like principle that the interaction between the V site and the surface Cl critically contributes to the change of the Hg oxidation reactivity by balancing the competition between two key reaction steps of HCl dissociation and HgCl2 desorption. Our results provide guidance to improve the activity of the VOx/TiO2 catalyst for various reactions such as Hg oxidation and selective catalytic reduction of NOx and so on.

Acid Enriched with Methanol: Formation of a Prebiotic Cluster in the Interstellar Medium.

Organic molecules are a potential source of prebiotic chemistry in the interstellar medium (ISM). Methanol (MetOH) is a very important source of more complex molecules. H3 O+ (aq) and Cl- (aq) are fundamental to living organisms and can be generated in the ISM from the dissociation of HCl with just four water molecules, yielding the (H3 O)+ (H2 O)3 Cl- ion-pair. Here, a detailed mechanism, based on density functional theory (DFT) and ab-initio (2nd order Mϕller-Plesset perturbation theory, MP2) calculations, is suggested for the substitution reactions of these water molecules by MetOH. The time required for formation of an appreciable amount of the product ((H3 O)+ (MetOH)3 Cl- ) can be only few years. Such reaction can take place in Sagittarius B2, where HCl, H2 O and MetOH have already been identified and it can be an important source for the formation of more complex prebiotic structures.

Role of acidic fluids in Earth’s deep lithosphere: Insights from the Neoarchean magmatic roots of the Nilgiri Block, southern India

Fluids play a major role in facilitating igneous/metamorphic processes in the Earth’s crust and mantle. In this study, we investigate the nature and composition of fluids in Earth’s interior by studying the lower crustal rocks. We compare accessory minerals (e.g., apatite, monazite, allanite, and titanite), their texture, mineral reactions and composition among regionally distributed metamorphosed mafic and felsic rocks representing the roots of Neoarchean arc magmatism from the Nilgiri Block of the Southern Granulite Terrane in India. Regional trends in accessory minerals show the formation of monazite, allanite, and titanite in the felsic rocks. Apatite is depleted in REEs in all the rock types, irrespective of the difference in their whole-rock chemistry. Textural features and mineral reactions show that these accessory minerals were affected by fluids present in the lower crustal conditions. By comparing our results with those from previous experimental results, we further show that acidic CO2-H2O-HCl-HF fluids stable in lower crustal conditions could have resulted in these chemical and textural features. Dielectric constant of water is high (10–35 compared to lower crustal conditions) in high-pressure and low-temperature conditions of subduction zones and the upper mantle. Such conditions would enhance dissociation of HCl (compared to lower crust) and result in acidic fluids during dehydration reactions in subduction zones and in the upper mantle. Our results have important implications in understanding the nature and composition of fluids in Earth’s interior and would be helpful to model the tectonic and deep geochemical processes in both early and modern conditions in planetary interiors.

Complete catalytic reaction of mercury oxidation on CeO2/TiO2 (001) surface: A DFT study

CeO2/TiO2 catalyst is a promising material for realizing the integration of denitrification and mercury removal to reduce mercury emissions. Oxidation mechanism of Hg0 on CeO2/TiO2 (001) surface in the presence of HCl and O2 was studied by density functional theory (DFT). The results indicated that Hg0 was physically adsorbed on CeO2/TiO2 (001) surface. As an important intermediate, HgCl was adsorbed on the surface of CeO2/TiO2 (001) utilizing enhanced chemisorption, while the adsorption energy of HgCl2 was only −57.05 kJ/mol. In the absence of HCl, mercury oxidation followed the Mars-Maessen mechanism with a relatively high energy barrier, and the product (HgO) was difficult to desorb, which hindered the reaction process. When HCl existed, reactive chlorine (Cl*) would be produced by the dissociation of HCl, and the mercury oxidation would follow the Langmuir-Hinshelwood mechanism. The co-existence of HCl and O2 had no significant effect on the adsorption of Hg0, but reduced the reaction energy barrier and the final product (HgCl2) was more easily desorbed from the catalyst surface. In addition, two complete cyclic reaction pathways for catalytic oxidation of Hg0 on CeO2/TiO2 (001) surface were constructed to clarify the detailed reaction process.

Is Dissociation of HCl in DMSO Clusters Bistable?

Dissociation of HCl embedded in dimethyl sulfoxide (DMSO) clusters was investigated by projecting the solvent electric field along the HCl bond using B3LYP-D3/6-31+G(d) and MP2/6-31+G(d,p) levels of theory. A large number of distinct structures (about 1500) consisting of up to five DMSO molecules were considered in the present work for statistical reliability. The B3LYP-D3 calculations reveal that the dissociation of HCl embedded in DMSO clusters requires a critical electric field of 138 MV cm-1 along the H-Cl bond. However, a large number of exceptions wherein the electric field values much higher than the critical electric field of 138 MV cm-1 did not result in dissociation of HCl were observed, in addition to several cases wherein the HCl dissociates with an electric field less than the critical electric field. On the other hand, the MP2 level calculations reveal that the critical electric field for HCl dissociation is about 181 MV cm-1 with almost no exceptions. A comparison of calculations carried out using the MP2 and the B3LYP-D3 levels suggests that the dissociation of HCl embedded in DMSO clusters is bistable at the B3LYP-D3 level, which is an artifact, suggesting that care must be exercised in interpreting the processes of proton transfer. The answer to the question raised as the title of this paper is NO.

Highly Efficient Activation of HCl Dissociation on Au(111) via Rotational Preexcitation.

The probability for dissociation of molecules on metal surfaces, which often controls the rate of industrially important catalytic processes, can depend strongly on how energy is partitioned in the incident molecule. There are many example systems where the addition of vibrational energy promotes reaction more effectively than the addition of translational energy, but for rotational pre-excitation similar examples have not yet been discovered. Here, we make an experimentally testable theoretical prediction that adding energy to the rotation of HCl can promote its dissociation on Au(111) 20 times more effectively than increasing its translational energy. In the underlying mechanism, the molecule’s initial rotational motion allows it to pass through a critical region of the reaction path, where this path shows a strong and nonmonotonic dependence on the molecular orientation.

Radical Mechanism of Ir III /Ni II -Metallaphotoredox-Catalyzed C(sp 3 )–H Functionalization Triggered by Proton-Coupled Electron Transfer: Theoretical Insight

Photoredox catalysis can be induced to activate organic substrates or to modulate the oxidation state of transition-metal catalysts via unique single-electron transfer processes, so as to achieve c...

A novel approach for metal extraction from metal sulfide ores with NH4Cl: A combined DFT and experimental studies

Chalcocite (Cu2S) is the main source for metallurgical production of copper worldwide but it usually co-exist with nickel sulfide in nature. To develop an efficient and green process for the separation and extraction of valuable metals from high-grade matte, we performed density functional theory (DFT) calculations and experimental studies to elucidate chlorination mechanism of Cu2S with ammonium chloride (NH4Cl). First, NH4Cl can react with Cu2S directly in the absence of O2, leading to the formation of H2S and NH3 with negative adsorption energies. Second, O2 can promote the chlorination process by providing adsorbed O and promoting the dissociation of HCl decomposed from NH4Cl, leading to the formation of H2O and CuCl species eventually. Besides, SO2 generated at the Cu2S surface after O2 dissociative adsorption, may leading to the generation of Cl2. Finally, the chlorination can also be achieved by the interaction between Cu2S and Cl2, which is favored thermodynamically and kinetically. Based on the computational results, low-temperature roasting experiments were performed. Cu2S was successfully converted into the corresponding metal chloride (CuCl) by NH4Cl in the absence of O2, but the chlorination process is incomplete with unreacted Cu2S. However, the conversion from Cu2S to CuCl is complete under air atmosphere, consistent with our computational results. Furthermore, metallic copper was successfully obtained at the cathode through electrodeposition with CuCl. The present study reveals detailed reaction mechanism between Cu2S and NH4Cl, and shows the chlorination of Cu2S by NH4Cl followed by electrodeposition of the resulting CuCl as a highly efficient and green process.

Dissociation of HCl in water nanoclusters: an energy decomposition analysis perspective.

As known, small HCl-water nanoclusters display a particular dissociation behaviour, whereby at least four water molecules are required for the ionic dissociation of HCl. In this work, we examine how intermolecular interactions promote the ionic dissociation of such nanoclusters. To this end, a set of 45 HCl-water nanoclusters with up to four water molecules is introduced. Energy decomposition analysis based on absolutely localized molecular orbitals (ALMO-EDA) is employed in order to study the importance of frozen interaction, dispersion, polarization, and charge-transfer for the dissociation. The vertical ALMO-EDA scheme is applied to HCl-water clusters along a proton-transfer coordinate varying the amount of spectator water molecules. The corresponding ALMO-EDA results show a clear preference for the dissociated cluster only in the presence of four water molecules. Our analysis of adiabatic ALMO-EDA results reveals a push-pull mechanism for the destabilization of the HCl bond based on the synergy between forward and backward charge-transfer.