Lead removal from flue gas continues to be an important environmental issue. Adding sorbents in the furnace is a reliable method to control lead emission. Modified kaolin sorbent developed by a combined method of thermal pre-activation and phosphate impregnation was first applied to capture lead from flue gas. Modified kaolin exhibited higher PbCl2 removal performance than raw kaolin at 800-1100 ?. The best adsorption performance of raw and modified kaolin was obtained at 1000 ? with adsorption efficiencies of 76.72 % and 85.87 %, respectively. The adsorption capacity of modified kaolin was about 283.51 mg/g at 1000 ?. Lead aluminosilicate and lead phosphate were produced in the adsorption reaction. O-2 was conducive to the conversion of PbCl2 to PbO, and directly participated in the formation of lead aluminosilicatemiddot H2O was in favor of the adsorption reaction, and reduced the energy barrier for dechlorination of PbCl2, and promoted the eutectic melting process. SO2 and NO inhibited PbCl2 removal due to the competitive adsorption between SO2/NO and PbCl2 at the active sites. High concentration of HCl can obviously suppress the reaction of PbCl2 and modified kaolin. Quantum chemistry calculations were conducted to identify the active sites, and to uncover the molecular-level interaction of PbCl2 and modified kaolin. Theoretical results manifested that PbCl2 adsorption was chemisorbed on kaolin (0 0 1) surface. The adsorption energies of PbCl2 on raw kaolin and modified kaolin were - 124.60 and - 205.90 kJ/mol, respectively. Al, O and P atoms of modified kaolin were identified as the active sites for PbCl2 adsorption.

Al2O3 has been considered as an effective sorbent of lead removal from the SO2-containing flue gas. The reaction chemistry between PbCl2 and SO2 over Al2O3 surface was systemically explored by quantum chemistry calculations. The results suggest that the chemisorption mechanism is responsible for PbCl2 and SO2 adsorption over Al2O3 surface. The intense orbital hybridization and overlap are related to strong chemisorption of PbCl2 and SO2 over Al2O3 surface. PbSO4 can be produced from the reaction between PbCl2 and SO3 generated from SO2/SO3 transformation. SO2/SO3 transformation includes three steps: SO2 -> SO2(ads) -> SO3(ads) -> SO3. The reaction pathway between PbCl2 and SO3 over Al2O3 surface contains six steps: O2 adsorption, SO3(ads) -> SO4(ads), PbCl2 -> PbCl2(ads), PbCl2(ads) -> PbSO4(ads), PbSO4 desorption, and Cl2 desorption. The rate-determining step (RDS) of PbSO4 formation over Al2O3 surface is SO2 oxidation due to its larger energy barrier. The activation energy barriers of SO2 oxidation over Al2O3 (001) and Al2O3 (110) surfaces are 114.56 and 416.03 kJ/mol, respectively. Al2O3 (001) surface exhibits higher activity for PbSO4 formation than Al2O3 (110) surface. This study of reaction mechanism can be conducive to better comprehend the transformation of lead species on Al2O3 sorbent in the presence of SO2.

A combination study of density functional theory (DFT) calculation and microkinetic analysis was carried out to investigate A-site tuning effect on formaldehyde (HCHO) oxidation over La-Mn perovskite catalysts (A = Sr, Ag, and Sn). The oxygen mobility of A-doped LaMnO3 catalysts and reaction mechanism of HCHO oxidation on catalyst surfaces were investigated. The microkinetic simulation was performed to quantitatively determine the activity of catalysts toward the HCHO catalytic oxidation. The results indicated that A-site tuning weakens the binding energy of Mn-O bond of LaMnO3 surface and facilitates the formation of surface oxygen vacancy. The presence of dopants can significantly reduce the activation energy of O-2 dissociation, which ascribes to the facilitation of electron transfer between oxygen species and catalyst surfaces. The reaction cycle of HCHO oxidation contains seven steps: HCHO adsorption, HCHO* dehydrogenation, CHO* dehydrogenation, CO2 desorption, H2O desorption, O-2 adsorption and oxygen vacancy recovery. The dopants promote HCHO adsorption and reduce the activation energy of HCHO oxidation. Two elementary steps control the overall reaction rate of HCHO oxidation. CHO* dehydrogenation step has the largest degree of rate control value at low temperature and O-2 adsorption step controls the whole reaction at high temperature

Iron oxide (Fe2O3) has been used as an effective sorbent to remove various heavy metals due to its large adsorption capacity and low cost. The cadmium capture capability of Fe2O3 sorbent was investigated in the simulated flue gas at the temperatures of 700-1100 degrees C. Fe2O3 sorbent exhibited much better Cd adsorption capability than SiO2 and Al2O3 sorbents. The largest Cd adsorption capacity of Fe2O3 sorbent was 86.7 mg/g at 700.C. The XPS analysis demonstrated that Fe3+ might partially participate in the cadmium adsorption process. A large quantity of CdO was generated and adsorbed on the Fe2O3 surface. The density functional theory (DFT) calculations were used to determine the active sites and the involved mechanism of different cadmium species adsorption over Fe2O3 sorbent. Cd, CdCl2, and CdO can be stably adsorbed on the Fe2O3 surface with the adsorption energies of -40.64 kJ/mol, -237.42 kJ/mol, and -375.03 kJ/mol, respectively. The results illustrate that the Fe atoms are the essential active sites for cadmium species adsorption on Fe2O3 surface. The orbital hybridization between cadmium atom and Fe site suggests that the strong interaction occurs during Cd adsorption process. Both physisorption and chemisorption mechanisms were responsible for the cadmium capture by Fe2O3 sorbent.

Al2O3 is regarded as an effective sorbent to capture lead from flue gas. The adsorption behaviors of different species of lead (Pb, PbO, PbCl and PbCl2) on the Al2O3 surfaces were explored based on density functional theory. The results show that the chemisorption mechanism is responsible for the adsorption of lead species on the Al2O3 surface. The high reactivity of Pb adsorption on the ?-Al2O3 (110) surface is mainly attributed to the existence of unsaturated Al atoms. The Al hollow sites are identified as the effectively active sites for Pb adsorption on the (110) surface. The adsorption energies of different species of lead on the Al-terminated (110) surface are in the range of - 4.20 to - 6.30 eV. PbO adsorption at the Al hollow site of the Al-terminated (110) surface shows the highest adsorption energy (- 6.30 eV), suggesting that Al2O3 prefers to capture PbO among different species of lead. The strong interactions of PbO, PbCl and PbCl2 molecules with the unsaturated Al atoms of the ?-Al2O3 (110) surface are responsible for PbO, PbCl and PbCl2 capture by Al2O3. Al2O3 has a good ability to capture different species of lead, and the adsorption capacity follows the order: PbO > Pb > PbCl > PbCl2.

The reaction mechanism of dichloromethane (CH2Cl2) oxidation on LaMnO3 catalyst was investigated using density functional theory calculations. The results showed that CH2Cl2 dechlorination proceeds via CH2Cl2 → CH2ClO → HCHO. The adsorbed Cl∗ and formaldehyde (HCHO) are identified as the important intermediates of CH2Cl2 dechlorination process. The dissociated Cl atoms prefer to adsorb on the surface Mn sites. Surface hydroxyl groups are not directly involved in the CH2Cl2 dechlorination process, but react with the adsorbed Cl∗ to form HCl. The energy barrier of HCl formation is lower than that of Cl2 formation, indicating that hydroxyl groups facilitate the removal of adsorbed Cl∗ species. Three possible pathways of HCHO oxidation with the assist of lattice oxygen, active oxygen atom and hydroxyl groups were investigated. HCHO catalytic oxidation contains four steps: HCHO → CHO → CO → H2O desorption → CO/CO2 desorption. Compared with the HCHO oxidation by lattice oxygen and hydroxyl groups, HCHO oxidation assisted with activated oxygen atom is more thermodynamically favorable. A complete catalytic cycle was proposed to understand the preferable reaction pathway for CH2Cl2 oxidation on LaMnO3 catalyst. The catalytic cycle includes CH2Cl2 dechlorination, HCl formation and HCHO oxidation. The microkinetic analysis indicates that there are four steps controlling the reaction cycle: CH2Cl2∗ + ∗ → CH2Cl∗ + Cl∗, CH2OCl∗ + Cl∗ → CH2O∗ + Cl∗, O2∗ + ∗ → 2O∗, and CHO2∗ + OH∗ → CO2 + H2O∗.

CuFe2O4 is regarded as a promising candidate of catalyst for Hg0 oxidation in industrial flue gas. However, the microcosmic reaction mechanism governing mercury oxidation on CuFe2O4 remains elusive. Herein, experiments and quantum chemistry calculations were conducted for understanding the chemical reaction mechanism of oxygen-assisted mercury oxidation on CuFe2O4. CuFe2O4 shows the optimal catalytic activity towards mercury oxidation at 150 ºC. The reactivity difference of different lattice oxygen species is associated with its atomic coordination environment. The lattice oxygen coordinating with two octahedral Cu atoms and a tetrahedral Fe atom shows higher catalytic activity towards mercury oxidation than other lattice oxygen atoms. The inverse spinel structure of CuFe2O4 is favorable for O2 activation due to the Jahn-Teller effect, thereby promoting mercury oxidation. O2 molecule preferably adsorbs on iron active site and dissociates into active oxygen species. Hg0 oxidation is a three-step reaction process: Hg0 adsorption, Hg(ads) → HgO(ads), and HgO desorption. The energy barrier of mercury oxidation by chemisorbed oxygen is lower than that of mercury oxidation by lattice oxygen. The chemisorbed oxygen preserves higher reactivity towards mercury oxidation than lattice oxygen. Hg(ads) → HgO(ads) is the rate-determining step of mercury oxidation by chemisorbed oxygen because of the higher energy barrier of 116.94 kJ/mol. This work could provide the theoretical guidance for the diversified structure design of highly-efficient catalysts used for elemental mercury oxidation.

Oxygen vacancy (OV) has a close relationship with chlorinated volatile organic compounds catalytic oxidation. The role of OV for methylene chloride (DCM) decomposition over defective La-Mn perovskite catalyst was investigated using Density Functional Theoretical calculations. The adsorption characteristics and dissociation processes of reactants (DCM, O2 and H2O) on perfect and defective surfaces were comparatively studied. In DCM dechlorination process, the unoccupied orbitals of OV interact with binding orbitals of Cl atoms, and thus facilitate Cl abstraction. The dissociated Cl atoms are trapped by the OV on the defective surface. The activation energy of HCl formation (144.31 kJ/mol) with the assistant of hydroxyl groups is lower than that of Cl2 formation (250.86 kJ/mol) over defective LaMnO3 surface. OV (Lewis acid) and its proximal surface hydroxyls (Lewis base) tend to form the frustrated Lewis acid-base pairs, which can capture the dissociated Cl atoms with the assistance of protons into HCl. The surface hydroxyls can be regenerated readily from H2O dissociation at OV sites, thus achieving a sustainable Cl remove. Molecular O2 is easily activated and dissociated into O atoms by OV on defective surface. The atomic O adsorbed on surface Mn sites are the primary oxygen active species for DCM deep oxidation.

Mercury emitted from human activities has received increasing attention because of its extreme toxicity, persistence and bioaccumulation. The development of highly-efficient sorbent with abundant active sites that exhibit high affinity toward Hg0 is the key challenge for elemental mercury capture at low temperature. Herein, Cu-In spinel-type sulfides were synthesized through a hydrothermal synthesis. The Hg0 removal performance of CuxIn2-xS2 sorbents was evaluated in the temperature range of 75 °C to 175 °C. The synthesized CuxIn2-xS2 sorbents showed excellent performance for Hg0 removal at low temperatures, which perfectly matches the optimal temperature of flue gas at the downstream of desulfurization system. Hg0 removal efficiency of CuxIn2-xS2 sorbents significantly improved as the Cu proportion increased. CuInS2 sorbent showed superior mercury removal performance, the mercury removal efficiency reached 99.6% at 125 °C. O2 and NO showed a slight inhibition on Hg0 capture. The coexistence of SO2 and H2O showed no obvious negative effects on Hg0 removal. The CuInS2 sorbent displayed a superior tolerance to SO2 and H2O. TPD and XPS analyses demonstrated that the adsorbed mercury mainly existed in the form of mercuric sulfides (HgS). Hg0 adsorption over CuInS2 sorbent occurred via the Mars-Maessen mechanism. In this mechanism, Hg0 vapor was physically adsorbed on CuInS2 sorbent and then converted to HgS. This study provides future potential for applying CuxIn2-xS2 sorbents to capture gaseous mercury at low temperature.

NOx is widely considered to be one of the most important components in the flue gas. A systematically theoretical study based on density functional theory was conducted to provide an atomic-level understanding of the effects of NOx on Pb adsorption over the Al2O3 surface. The results suggest that the adsorption energies of Pb over Al2O3 (110) surface are larger than those of Pb over Al2O3 (001) surface. Al2O3 (110) surface is more favorable for Pb adsorption than Al2O3 (001) surface. NO and NO2 are adsorbed at the same active adsorption site (surface Al atom). NOx competes with Pb for the active sites on the Al2O3 surface. The notable charge accumulation and depletion are accountable for the intense interaction of Pb and NOx-covered Al2O3 surface. At low concentration of NOx, the adsorption of NO and NO2 over Al2O3 surface increases the Pb adsorption capacity of Al2O3 sorbent through strengthening the activity of its neighbor Al and O sites. The formation of Pb-Al and Pb-N bonds can greatly strengthen Pb adsorption over Al2O3 (110) surface in the presence of NO/NO2. However, the high-concentration NO and NO2 inhibit Pb adsorption over Al2O3 surface due to the competitive adsorption between Pb and NO/NO2.

A series of Cu-Fe spinel-type catalysts were synthesized by sol-gel auto-combustion method for the catalytic combustion of HCHO. A combined experimental and theoretical investigation based on in situ FT-IR and density functional theory (DFT) was performed to uncover the reaction process of HCHO catalytic combustion on Cu-Fe spinel-type catalysts. The results show that CuxFe(3-x)O4 catalysts display the typical pattern of spinel structure. The chemical states of Cu and Fe cations on the catalyst surface include Cu-+,Cu- Cu2+, Fe2+ and Fe3+. Cu0.5Fe2.5O4 exhibits excellent HCHO oxidation efficiency and good water-resistance performance. The superior catalytic performance of Cu0.5Fe2.5O4 catalyst is closely associated with the high crystalline degree of spinel. The flexible valences of metal cations in spinel-type catalysts are beneficial for electron transfer, thus facilitates HCHO adsorption and oxidation. Formate species (HCO2) is the major reaction intermediate during HCHO combustion. The reaction pathway of HCHO catalytic combustion contains eight elementary steps: HCHO adsorption, H2CO2 dehydrogenation, HCO2 dehydrogenation, CO2 desorption, O-2 adsorption, OOH formation, H2O formation and desorption. HCO2 dehydrogenation is identified as the rate-determining step because of the highest energy barrier of 254.80 kJ/mol. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Experiments and density functional theory calculations were conducted to uncover the reaction chemistry of Hg-0 oxidation during SO2/SO3 conversion over V2O5/TiO2 catalyst. The results show that SO2 promotes Hg-0 oxidation over V2O5/TiO2 catalyst with the assistance of oxygen. The promotional effect is dependent on the reaction temperature, and is associated with the bimolecular reaction between Hg-0 and SO3 over V2O5/TiO2 catalyst. SO2 can be oxidized to SO3 which has high oxidation ability for Hg-0 oxidation. SO2/SO3 conversion proceeds through a three-step reaction process in the sequence of SO2 adsorption -> SO2 oxida-tion -> SO3 desorption. SO2 oxidation presents an activation energy barrier of 223.84 kJ/mol. HgSO4 species is formed from the bimolecular reaction between Hg-0 and SO3 over V2O5/TiO2 catalyst. Hg-0 oxidation by SO3 over V2O5/TiO2 catalyst occurs through three reaction pathways, which are energetically favorable for HgSO4 formation. SO2* -> SO3* is identified as the rate-determining step of HgSO4 formation. During Hg-0 oxidation by SO3 over V2O5/TiO2 catalyst, HgSO4 desorption is a highly endothermic reaction process and requires a higher external energy. The proposed skeletal reaction network can be used to well understand the reaction mechanism of Hg-0 oxidation during SO2/SO3 conversion over V2O5/TiO2 catalyst. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Elemental mercury (Hg-0) and hydrogen sulfide (H2S) are two typical toxic pollutants in coal-derived syngas. The specific role of H2S in Hg-0 elimination over CuMn2O4 sorbent and the involved reaction mechanism were systematically studied by experimental and theoretical methods. The synthesized CuMn2O4 sorbent was tested for Hg-0 removal under simulated syngas and exhibited superior Hg-0 capture performance (up to 95.6% at 200 degrees C). In the absence of H2S, both H-2 and CO inhibited Hg-0 removal over CuMn2O4, but the Hg-0 removal efficiency was greatly improved after the introduction of 400 ppm H2S. H2S played a key role in Hg-0 elimination in syngas by generating reactive sulfur species upon CuMn2O4. Density functional theory (DFT) calculations indicated that Hg-0 and HgS were strongly chemisorbed upon CuMn2O4 surface with the adsorption energies of -129.84 and -220.21 kJ/mol, respectively. H2S was dissociatively adsorbed on CuMn2O4 and generated active sulfur species. Both H2S-pretreatment experiments and DFT calculations demonstrated that Hg-0 reaction with H2S over CuMn2O4 occurred via a Langmuir-Hinshlwood mechanism, where chemisorbed Hg-0 reacted with active sulfur species to form surface-bonded HgS. Furthermore, XPS and TPD analyses certified that the formation of active sulfur species and HgS upon the spent CuMn2O4 sorbents.

Co3O4 has been regarded as a potential active catalyst component for Hg oxidation from flue gas with low or no chlorine due to its excellent redox activity, high element abundance, and good thermal stability. The reaction mechanisms of Hg-0 oxidation by different surface oxygens (chemisorbed oxygen and lattice oxygen) on the Co3O4 surface were investigated using density functional theory (DFT) calculations. It is found that Hg-0 and HgO adsorptions on Co3O4(110) are controlled by the chemisorption mechanism. The surface Co3+ atom is determined as the major active adsorption site. O-2 is chemisorbed on Co3O4(110) in perpendicular and parallel orientations with the adsorption energies of -1.00 and -1.20 eV, respectively. The parallelly adsorbed O-2 can be activated after overcoming an energy barrier of 0.87 eV to produce active oxygen atoms. The reaction processes of He oxidation by surface oxygens undergo three steps: (1) Hg-0 -> Hg(ads), (2) Hg(ads) -> HgO(ads), and (3) HgO desorption, in which the HgO formation reaction is the rate-determining step. Hg-0 oxidation by chemisorbed oxygen is thermodynamically and kinetically more beneficial than that by lattice oxygen, and the dissociatively adsorbed O-2 is the most active oxygen for Hg-0 oxidation.

Co3O4 has been considered as promising active catalyst component for mercury control because of its excellent catalytic and long persistent activity. The heterogeneous mechanisms of Hg-0 oxidation by HCl and Cl-2 upon Co3O4 (1 1 0) surface were studied using density functional theory (DFT) calculations. The results demonstrate that both Hg-0 and HgCl2 are chemisorbed upon Co3O4 (1 1 0) with the binding energies of -0.74 and -1.43 eV, respectively. HgCl can be molecularly chemisorbed upon Co(3)O(4)1 1 0) and act as intermediate during Hg(0 )oxidation. HC1 and Cl-2 dissociate on Co3O4 (1 1 0) and convert into active chlorine species. Hg-0 catalytic oxidation by HC1 and Cl-2 on Co3O4(1 1 0) proceeds with Langmuir-Hinshelwood mechanism, in which the chemisorbed Hg-0 interacts with the surface active Cl atoms to produce HgCl2. The optimal oxidation pathway includes four steps: (1) Hg-0 adsorption, (2) HgCl formation, (3) HggCl(2) formation and (4) HgCl 2 desorption. The rate-limiting step is HgCl formation with an energy barrier of 0.67 eV. Hg-0 oxidation by HCl is thermodynamically and kinetically more favorable than that by Cl-2 because the presence of H atoms weakens the interaction between reaction intermediate and Co3O4 surface.

采用实验与量子化学计算相结合的方法研究了烟气中NO对铜-锰尖晶石脱汞性能的影响机理.结果表明,NO在高于250℃时抑制铜-锰尖晶石对Hg0的脱除,主要归因于NO与Hg0之间的竞争吸附作用;而在温度低于250℃时,NO对铜-锰尖晶石的Hg0脱除性能影响较小.吸附剂表面上吸附的汞主要以Cu-Hg合金和Hg(NO3)2的形式存在.铜-锰尖晶石表面上部分NO被氧化成NO2并与吸附态汞反应形成Hg(NO3)2.吸附剂表面上Cu和Mn原子为NO与Hg0的吸附活性位点,NO的吸附能大于Hg0的吸附能;因此,NO与Hg0之间存在竞争吸附.由于Cu、Mn、N原子之间的强烈轨道杂化作用,NO与铜-锰尖晶石吸附剂表面之间具有较强的相互作用.

The capture of Hg-0 in syngas is challenging since the reducing atmosphere is disadvantageous to oxidize Hg-0. Spinel CoxMn3-xO4 sorbents synthesized by a low-temperature sol-gel auto-combustion method were employed for the first time to remove Hg-0 under simulated syngas. The Hg-0 capture performance of CoxMn3-xO4 sorbents increased with Co mole ratio increases. CoMn2O4 showed the highest Hg-0 capture performance among the CoxMn3-xO4 sorbents, attained over 95% Hg-0 removal efficiency at 40-160 degrees C. The characterization results indicated that the mobile-electron environment, higher contents of surface Co and chemisorbed oxygen, larger BET surface area of CoMn2O4 sorbent were responsible for its superior performance. Ten repeated adsorption-regeneration cycles demonstrated that the regenerability of CoMn2O4 sorbent is excellent. Density functional theory (DFT) calculations were performed to determine the active sites of CoMn2O4 and to reveal Hg-0 adsorption mechanism. The results suggested that Hg-0 was chemisorbed on CoMn2O4 with a high adsorption energy (-1.04 eV). The two-fold coordinated surface Co atom was determined as the major active site for Hg-0 adsorption. The strong orbital hybridization between Hg and Co atoms resulted in the strong chemisorption of Hg-0 on CoMn2O4 surface.

CuCl2/TiO2 has been regarded as a highly promising sorbent to remove elemental mercury (Hg0) from flue gas. The density functional theory and periodical model were used to demonstrate mercury adsor...

Hg-0 catalytic oxidation is an attractive approach to reduce mercury emissions from industrial activities. How-ever, the rational design of highly active catalysts remains a significant challenge. Herein, the charge distribution modulation strategy was proposed to design novel catalysts: copper ferrite spinel-type catalysts were developed by introducing Cu2+ cations into octahedral sites to form electron-transfer environment. The synthesized catalysts with spinel-type stoichiometry showed superior catalytic performance, and achieved > 90 % Hg-0 oxidation efficiency in a wide operation temperature window of 150-300 degrees C. The superior catalytic performance was closely associated with the mobile-electron environment of copper ferrite. Hg-0 oxidation by HCl over copper ferrite followed the Eley-Rideal mechanism, in which physically adsorbed Hg-0 reacted with active chlorine species. Density functional theory calculations revealed that octahedral Cu atom is the most active site of Hg-0 adsorption on copper ferrite surface. Both direct oxidation pathway (Hg* -> HgCl2*) and HgCl-mediated oxidation pathway (Hg* -> HgCl* -> HgCl2*) played important role in Hg-0 oxidation over copper ferrite. HgCl2* formation was identified as the rate-limiting step of Hg-0 oxidation. This work would provide a new perspective for the development of admirable catalysts with outstanding Hg-0 oxidation performance.

CuMn2O4 spinet has been experimentally demonstrated to be a kind of promising sorbent for Hg-0 capture from flue gas due to its excellent adsorption performance, regenerability, and recyclability. Theoretical studies based on the state-of-the-art density functional theory (DFT) were performed to gain an understanding of several important aspects of Hg-0 removal by a CuMn2O4 sorbent, including active sites and the reaction mechanism. DFT calculation results show that Hg-0 and HgO adsorption on the CuMn2O4 surface is dominated by the chemisorption mechanism. The stronger interaction between Hg-0 and the CuMn2O4 surface is closely associated with orbital hybridization between the Hg atom and surface metal atoms (Cu and Mn). CuMn2O4 shows an excellent O-2-activation ability due to the lower energy barrier. O-2 dissociation reaction on the CuMn2O4 surface is activated by 6.31 kJ/mol and is exothermic by 101.37 kJ/mol. The chemisorbed oxygen atom produced from molecular O-2 dissociation reacts with adsorbed Hg-0 to form HgO species. O-2* species can also directly react with adsorbed Hg-0. The most favorable pathway for gaseous HgO formation is described by a three-step process, namely He adsorption, Hg-0 oxidation, and HgO desorption. In the comprehensive mercury adsorption-oxidation-desorption process, HgO desorption is predicted to be rate-limiting.