Evidence of liquid water formation during methane hydrates dissociation below the ice point

Dissociation of small methane hydrate samples formed from water droplets of size 0.25-2.5 mm has been investigated below the ice melting point in the temperature range of 240-273 K, where the self-preservation effect is observed for bulk hydrates. The experiments included optical microscopy observations combined with P-T measurements of the dissociation conditions for the methane hydrates. For the first time, the formation of supercooled liquid water during the hydrate dissociation was reliably detected in the temperature range of 253-273 K. The formation of the liquid phase was visually observed. The induction time of the ice nucleation for the metastable liquid water depended from the dissociation temperature and a size of water droplets formed during the hydrate dissociation. It was found that in the temperature range of 253-273 K values of the dissociation pressure for the small hydrate samples fall on the extension of the water-hydrate-gas equilibrium curve into the metastable region where supercooled water exist. The average molar enthalpy of 51.7 kJ/mol for the dissociation of the small methane hydrate samples in the temperature range of 253-273 K was calculated using Clausius-Clapeyron equation. This value agrees with the enthalpy of dissociation of bulk methane hydrates into water and gas at temperatures above 273 K.     

Metastable states during dissociation of carbon dioxide hydrates below 273 K

In this study, the dissociation of isolated carbon dioxide hydrate particles of sizes in the range 0.25–2.5 mm was investigated. It was found that below the ice melting point, the hydrates dissociated into supercooled water (metastable liquid) and gas. The formation of the liquid phase during CO₂ hydrate dissociation was visually observed, and the pressures of the hydrate dissociation into supercooled water and gas were measured in the temperature range 249–273 K. These pressures agreed well with the calculated data for the supercooled water–hydrate–gas metastable equilibrium (Istomin et al., 2006). In the P–T area on the phase diagram bounded by the ice–hydrate–gas equilibrium curve and the supercooled water–hydrate–gas metastable equilibrium curve, hydrates could exist for a long time because the metastable phase and their stability are not connected to the self-preservation effect. The growth of the metastable CO₂ hydrate film on the surface of supercooled water droplets formed during the hydrate dissociation was observed at pressure above the three-phase supercooled water–hydrate–gas metastable equilibrium pressure but still below the three-phase ice–hydrate–gas equilibrium pressure. It was found that the growth rate of the metastable CO₂ hydrate film was higher by a factor of 25 and 50 than that for methane hydrate and propane hydrate, respectively.     

Stability and growth of gas hydrates below the ice–hydrate–gas equilibrium line on the P–T phase diagram

Using a previously developed experimental technique, the behavior of small methane and propane hydrate samples formed from water droplets between 0.25 and 2.5 mm in size has been studied in the pressure–temperature area between the ice–hydrate–gas equilibrium line and the supercooled water–hydrate–gas metastable equilibrium line, where ice is a stable phase. The unusual persistence of the hydrates within the area bounded by these lines and the isotherms at T=253 K for methane hydrate or at T=263 K for propane hydrates was observed. This behavior has not previously been reported. For example, in the experiment carried out at 1.9 MPa and 268 K, the methane hydrates existed in a metastable state (the equilibrium pressure at 268 K is 2.17 MPa) for 2 weeks, then immediately dissociated into liquid supercooled water and gas after the pressure was isothermally decreased slightly below the supercooled water–hydrate–gas metastable equilibrium pressure. It was found that dissociation of metastable hydrate into supercooled water and gas was reversible. The lateral hydrate film growth rates of metastable methane and propane hydrates on the surface of supercooled water at a pressure below the ice–hydrate–gas equilibrium pressure were measured. The temperature range within which supercooled water formed during hydrate dissociation can exist and a role of supercooled water in hydrate self-preservation is discussed.     

Preparation of highly dispersed SiO2 and Pt particles in Nafion112 for self-humidifying electrolyte membranes in fuel cells

We have developed preparation protocol of practically large size self-humidifying polymer electrolyte membranes (PEMs) with highly dispersed nanometer-sized Pt and/or SiO₂ for fuel cells. The Pt particles were expected to catalyze the recombination of H₂ and O₂, leading to a suppression of the chemical short-circuit reaction at the electrodes, while the SiO₂ particles were expected to adsorb the water produced at the Pt particles together with that produced at the cathode reaction. Stable SiO₂ particles were formed in a commercial PEM (Nafion^®112) via in situ sol-gel reactions at 70 °C. It was found by SAXS that the hydrophilic cluster size increased by water adsorbed SiO₂, which may contribute to the increase in the proton conductivity once SiO₂ adsorbed water. Pt particles were uniformly dispersed in a Na⁺-form normal-PEM or SiO₂-PEM by an ion-exchange reaction with [Pt(NH₃)₄]Cl₂, followed by a reduction with 1-pentanol at 125 °C. The newly prepared Pt-SiO₂-PEM was found to perform a self-humidifying operation in a standard-size PEFC (25 cm² electrode area) with H₂ and O₂ humidified at 30 °C. The performance of the Pt-SiO₂-PEM cell operated with the low humidity reactant gases was as high as the normal-PEM cell fully humidified, because the ohmic resistance of the former cell was as low as the latter cell.     

Characteristics of subzero startup and water/ice formation on the catalyst layer in a polymer electrolyte fuel cell

This work experimentally explores the fundamental characteristics of a polymer electrolyte fuel cell (PEFC) during subzero startup, which encompasses gas purge, cool down, startup from a subfreezing temperature, and finally warm up. In addition to the temperature, high-frequency resistance (HFR) and voltage measurements, direct observations of water or ice formation on the catalyst layer (CL) surface have been carried out for the key steps of cold start using carbon paper punched with microholes and a transparent cell fixture. It is found that purge time significantly influences water content of the membrane after purge and subsequently cold-start performance. Gas purge for less than 30 s appears to be insufficient, and that between 90 and 120 s is most useful. After gas purge, however, the cell HFR relaxation occurs for longer than 30 min due to water redistribution in the membrane-electrode assembly (MEA). Cold-start performance following gas purge and cool down strongly depends on the purge time and startup temperature. The cumulative product water measuring the isothermal cold-start performance increases dramatically with the startup temperature. The state of water on the CL surface has been studied during startup from ambient temperatures ranging from −20 to −1 °C. It is found that the freezing-point depression of water in the cathode CL is 1.0 ± 0.5 °C and its effect on PEFC cold start under automotive conditions is negligible.     

A study of rubber liquefaction in supercritical water using DAC-stereomicroscopy and FT-IR spectrometry

Phase behavior and liquefaction of styrene-butadiene rubber (SBR) in supercritical water (SCW) were studied with a diamond anvil cell (DAC) technique coupled with optical microscopy and FT-IR spectroscopy. Apparent concentrations were calculated using digital imaging analysis. When SBR+H₂O+H₂O₂ systems (15.0-28.8 wt% SBR) were rapidly heated at a rate of 2.7-9.7°C s⁻¹ at pressures ranging from 809 to 1038 MPa, SBR particle began dissolving at 542-546, 196 and 201°C with 0, 5, and 10 wt% H₂O₂ concentration, respectively. Solubility increased with H₂O₂ concentration. After solubility reached the maximum at 521-558°C, a non-dissolved particle expanded and changed to reddish volatile compounds at 535-585°C, which underwent liquefaction and then carbonization as temperature increased to 686°C. The dissolved compounds in water, inhibited formation of char. For the isothermal runs at 450°C and 395-721 MPa, liquefaction started at 1628, 663, and 53 s with 0, 5, and 10 wt% H₂O₂ concentration, respectively. The results show conclusively that the SBR can dissolve in SCW while non-dissolved residue undergoes liquefaction. Addition of H₂O₂ promoted the liquefaction process.     

Batch testing of solid fuels with ilmenite in a 10 kWth chemical-looping combustor

Batch experiments were conducted in a 10 kW_th chemical-looping combustor for solid fuels using ilmenite, an iron titanium oxide, as the oxygen carrier with two solid fuels: a petroleum coke from Mexico and a bituminous coal from South Africa. The purpose of these batch tests was to attain detailed information on fuel conversion, complementary to previous continuous operation of the unit. At steady-state, a fuel batch of typically 25 g was introduced in the fuel reactor and gas concentrations were measured at the outlet of both air and fuel reactors. The fuel reactor was fluidized with steam and the amount of bed material was typically 5 kg. The fuel introduced devolatilizes rapidly while the remaining char is gasified and the resulting syngases H₂ and CO react with the oxygen carrier. Operation involved testing at different fuel reactor temperatures from 950 to 1030 °C, and investigation of the influence of particle circulation between air and fuel reactors.The fuel conversion rate was increased at higher temperature: at 950 °C the instantaneous rate of conversion for petroleum coke averaged at 17.4%/min while at 1030 °C, the value was 40%/min. For the much more reactive South African coal, the averaged rate at 970 °C was 47%/min and increased to 101%/min at 1000 °C. For petroleum coke testing with particle circulation, the oxygen demand - defined as oxygen lacking to fully convert the gases leaving the fuel reactor - was typically 12-14% for the gasified char including H₂S, in line with previous experiments with the same unit and fuel. If only syngases are considered, the oxygen demand for char conversion was 8.4-11%. Similar or even lower values were seen for the char of South African coal. This is in line with expectations, i.e. that it is possible to reach fairly high conversion, although difficult to reach complete gas conversion with solid fuel. It was also seen that the volatiles pass through the system essentially unconverted, an effect of feeding the fuel from above. Moreover, the oxygen demand for char conversion decreased with increasing temperature. Finally, the CO₂ capture - defined as the proportion of gaseous carbon leaving the fuel reactor to total gaseous carbon leaving the system - decreased at higher particle circulation and a correlation between capture and circulation index was obtained.     

Heteropolyacid in glass electrolytes for the development of H2/O2 fuel cells

The scope of the present work was to investigate and evaluate the electrochemical activity of H₂/O₂ fuel cells based on the influence of a heteropolyacid glass membrane with a Pt/C electrode at low temperature. A new trend of sol-gel derived PMA (H₃PMo₁₂O₄₀) heteropolyacid-containing glass membranes inherent of a high proton conductivity and mechanical stability, was heat treated at 600 °C and implemented to H₂/O₂ fuel cell activities through electrochemical characterization. Significant research has been focused on the development of H₂/O₂ fuel cells using optimization of heteropolyacid glasses as electrolytes with Pt/C electrodes at 30 °C. A maximum power density of 23.9 mW/cm² was attained for operation with hydrogen and oxygen, respectively, at 30 °C and 30% humidity with the PMA glass membranes (4-92-4 mol%). Impedance spectroscopy measurements were performed on a total ohmic cell resistance of a membrane-electrode-assembly (MEA) at the end of the experiment.     

Carbonation of fly ash in oxy-fuel CFB combustion

Oxy-fuel combustion of fossil fuel is one of the most promising methods to produce a stream of concentrated CO₂ ready for sequestration. Oxy-fuel FBC (fluidized bed combustion) can use limestone as a sorbent for in situ capture of sulphur dioxide. Limestone will not calcine to CaO under typical oxy-fuel circulating FBC (CFBC) operating temperatures because of the high CO₂ partial pressures. However, for some fuels, such as anthracites and petroleum cokes, the typical combustion temperature is above 900 °C. At CO₂ concentrations of 80-85% (typical of oxy-fuel CFBC conditions with flue gas recycle) limestone still calcines, but when the ash cools to the calcination temperature, carbonation of fly ash deposited on cool surfaces may occur. This phenomenon has the potential to cause fouling of the heat transfer surfaces in the back end of the boiler, and to create serious operational difficulties. In this study, fly ash generated in a utility CFBC boiler was carbonated in a thermogravimetric analyzer (TGA) under conditions expected in an oxy-fuel CFBC. The temperature range investigated was from 250 to 800 °C with CO₂ concentration set at 80% and H₂O concentrations at 0%, 8% and 15%, and the rate and the extent of the carbonation reaction were determined. Both temperature and H₂O concentrations played important roles in determining the reaction rate and extent of carbonation. The results also showed that, in different temperature ranges, the carbonation of fly ash displayed different characteristics: in the range 400 °C < T ? 800 °C, the higher the temperature the higher the CaO-to-carbonate conversion ratio. The presence of H₂O in the gas phase always resulted in higher CaO conversion ratio than that obtainable without H₂O. For T ? 400 °C, no fly ash carbonation occurred without the presence of H₂O in the gas phase. However, on water vapour addition, carbonation was observed, even at 250 °C. For T ? 300 °C, small amounts of Ca(OH)₂ were found in the final product alongside CaCO₃. Here, the carbonation mechanism is discussed and the apparent activation energy for the overall reaction determined.     

Anhydrous proton conducting polymer electrolytes based on poly(vinylphosphonic acid)-heterocycle composite material

The development of anhydrous proton conducting membrane is important for the operation of polymer electrolyte membrane fuel cell (PEMFC) at intermediate temperature (100-200 °C). In this study, we have investigated the acid-base hybrid materials by mixing of strong phosphonic acid polymer of poly(vinylphosphonic acid) (PVPA) with the high proton-exchange capacity and organic base of heterocycle, such as imidazole (Im), pyrazole (Py), or 1-methylimidazole (MeIm). As a result, PVPA-heterocycle composite material showed the high proton conductivity of approximately 10⁻³ S cm⁻¹ at 150 °C under anhydrous condition. In particular, PVPA-89 mol% Im composite material showed the highest proton conductivity of 7×10⁻³ S cm⁻¹ at 150 °C under anhydrous condition. Additionally, the fuel cell test of PVPA-89 mol% Im composite material using a dry H₂/O₂ showed the power density of approximately 10 mW cm⁻² at 80 °C under anhydrous conditions. These acid-base anhydrous proton conducting materials without the existence of water molecules might be possibly used for a polymer electrolyte membrane at intermediate temperature operations under anhydrous or extremely low humidity conditions.     

Electrochemical behaviour of propane-fed solid oxide fuel cells based on low Ni content anode catalysts

Two different low Ni content (10 wt.%) anode catalysts were investigated for intermediate temperature (800 °C) operation in solid oxide fuel cells fed with dry propane. Both catalysts were prepared by the impregnation of a Ni-precursor on different oxide supports, i.e. gadolinia doped ceria (CGO) and La_0.6Sr_0.4Fe_0.8Co_0.2O₃ perovskite, and thermal treated at 1100 °C for 2 h. The Ni-modified perovskite catalyst was mixed with a CGO powder and deposited on a CGO electrolyte to form a composite catalytic layer with a proper triple-phase boundary. Anode reduction was carried out in-situ in H₂ at 800 °C for 2 h during cell conditioning. Electrochemical performance was recorded at different times during 100 h operation in dry propane. The Ni-modified perovskite showed significantly better performance than the Ni/CGO anode. A power density of about 300 mW cm⁻² was obtained for the electrolyte supported SOFC in dry propane at 800 °C. Structural investigation of the composite anode layer after SOFC operation indicated a modification of the perovskite structure and the occurrence of a La₂NiO₄ phase. The occurrence of metallic Ni in the Ni/CGO system caused catalyst deactivation due to the formation of carbon deposits.     

Eggshell-membrane-templated synthesis of hierarchically-ordered NiO–Ce0.8Gd0.2O1.9 composite powders and their electrochemical performances as SOFC anodes

Hierarchically-ordered NiO-Ce_0.8Gd_0.2O_1.9 (GDC) composite anode powders were synthesized using eggshell membranes as biotemplates. The morphology of the as-synthesized powders depended on the kind of Ni precursor and the use of EDTA as a chelating agent. Hierarchically-ordered anode powders were obtained from Ni chloride and Ni acetate precursors with EDTA. The Ni–GDC anode synthesized from Ni chloride precursor with EDTA exhibited the lowest polarization resistance at 800 °C and an activation energy of 0.01 Ω cm² and 0.74 eV, respectively, in humidified H₂. In accordance with the polarization resistance results, the 0.5-mm thick GDC electrolyte-supported single cell with the Ni–GDC anode synthesized from Ni chloride precursor with EDTA showed a maximum power density of 0.34 W cm⁻² at 800 °C with humidified H₂ fuel.     

Determination of the eutectic solubility lines of the ternary system NaHCO3–Na2CO3–H2O

A crystallizer was built and a procedure developed to accurately measure the eutectic solubility lines where ice and salt coexist in equilibrium with the solution, for potential application of Eutectic Freeze Crystallization. The eutectic solubility lines of the ternary system NaHCO₃–Na₂CO₃–H₂O were determined experimentally and calculated with the extended UNIQUAC model. The extended UNIQUAC model describes the experimental data quite well. Anhydrous NaHCO₃ and Na₂CO₃·10H₂O were the only two types of crystals present in equilibrium with ice crystals in the ternary system. At the quadruple point NaHCO₃ and Na₂CO₃·10H₂O are in equilibrium with a solution of about 4.34 wt% of Na₂CO₃ and 4.77 wt% of NaHCO₃ at −3.32 °C. The anhydrous NaHCO₃ crystals were needle shaped with lengths between 5 and 10 μm, that were agglomerated into particles of about 100–300 μm, while the Na₂CO₃·10H₂O crystals were hexagonally shaped with sizes between 100 and 500 μm.     

Dry catalytic partial oxidation of diesel-fuel distillates into syngas

Volatile compounds distilled below 205 °C from diesel fuel are reformed into synthesis gas by dry catalytic partial oxidation using porous membrane reactors, eliminating complex liquid-fuel injectors and fuel-air mixers, greatly simplifying reformers for applications with solid-oxide fuel cells and NO_x traps. For distillates utilizing 20 wt% of the diesel fuel, 88 mol% of the carbon is converted into CO and 75 mol% of the hydrogen into H₂. Rationale is as follows: Long-chain n-alkanes such as n-hexadecane, with normal boiling point, 286.5 °C, but autoignition temperature, 205 °C, are the least thermally stable hydrocarbons in diesel fuel. If attempts are made to vaporize diesel fuel under oxygen-lean conditions without precautions, long-chain n-alkanes crack at autoignition temperatures forming radicals that initiate polymerization. By eliminating more troublesome compounds by distillation, and by effusing cooler air through porous ceramic membranes to react radicals with oxygen, carbon deposition is largely suppressed. A perovskite catalyst, fed pre-heated air at >900 °C, provides a reservoir of mobile lattice oxygen to react with adsorbed carbon. In continuous runs of 72 h, carbon deposition was negligible in the reactor, on the catalyst, and in the exhaust, except for minor graphite deposited onto walls near the catalytic hot zone.     

CO tolerance and CO oxidation at Pt and Pt-Ru anode catalysts in fuel cell with polybenzimidazole-H3PO4 membrane

CO tolerance of H₂-air single cell with phosphoric acid doped polybenzidazole (PA-PBI) membrane was studied in the temperature range 140-180 °C using either dry or humidified fuel. Fuel composition was varied from neat hydrogen to 67% (vol.) H₂-33% CO mixtures. It was found that poisoning by CO of Pt/C and Pt-Ru/C hydrogen oxidation catalysts is mitigated by fuel humidification. Electrochemical hydrogen oxidation at Pt/C and Pt-Ru/C catalysts in the presence of up to 50% CO in dry or humidified H₂-CO mixtures was studied in a cell driven mode at 180 °C. High CO tolerance of Pt/C and Pt-Ru/C catalysts in FC with PA-PBI membrane at 180 °C can be ascribed to combined action of two factors—reduced energy of CO adsorption at high temperature and removal of adsorbed CO from the catalyst surface by oxidation. Rate of electrochemical CO oxidation at Pt/C and Pt-Ru/C catalysts was measured in a cell driven mode in the temperature range 120-180 °C. Electrochemical CO oxidation might proceed via one of the reaction paths—direct electrochemical CO oxidation and water-gas shift reaction at the catalyst surface followed by electrochemical hydrogen oxidation stage. Steady state CO oxidation at Pt-Ru/C catalyst was demonstrated using CO-air single cell with Pt-Ru/C anode. At 180 °C maximum CO-air single cell power density was 17 mW cm⁻² at cell voltage U = 0.18 V.     

Formation of LiNi0.5Co0.5VO4 nano-crystals by solvothermal reaction

LiNi_0.5Co_0.5VO₄ nano-crystals were solvothermally prepared using a mixture of LiOH·H₂O, Ni(NO₃)₂·6H₂O, Co(NO₃)₂·6H₂O and NH₄VO₃ in isopropanol at 150–200 °C followed by 300–600 °C calcination to form powders. TGA curves of the solvothermal products show weight losses due to evaporation and decomposition processes. The purified products seem to form at 500 °C and above. The products analyzed by XRD, selected area electron diffraction (SAED), energy dispersive X-ray (EDX) and atomic absorption spectrophotometer (AAS) correspond to LiNi_0.5Co_0.5VO₄. V–O stretching vibrations of VO₄ tetrahedrons analyzed using FTIR and Raman spectrometer are in the range of 620–900 cm⁻¹. A solvothermal reaction at 150 °C for 10 h followed by calcination at 600 °C for 6 h yields crystals with lattice parameter of 0.8252 ± 0.0008 nm. Transmission electron microscope (TEM) images clearly show that the solvothermal temperatures play a more important role in the size formation than the reaction times.     

Catalytic activity of titanium oxide for oxygen reduction reaction as a non-platinum catalyst for PEFC

A non-platinum cathode electrocatalyst must have the stability and catalytic activity for the oxygen reduction reaction (ORR) in order to be used in polymer electrolyte fuel cells (PEFCs). Titanium oxide catalysts as the non-platinum catalyst were prepared by the heat treatment of titanium sheets in the temperature range from 600 to 1000 °C. The prepared catalysts were chemically and electrochemically stable in 0.1 mol dm⁻³ H₂SO₄. The titanium oxide catalysts showed different catalytic activities for the ORR. The ORR of the catalysts heat-treated at around 900 °C occurred at the potential of about 0.65 V versus RHE. It is considered that the deference in the catalytic activity for the ORR of the heat-treated titanium oxide catalysts was due to the fact that the heat-treatment condition changed the material property of the catalyst surface. In particular, it was found that the catalytic activity for the ORR of the Ti oxide catalysts increased with the increase in the specific crystalline structure, such as the TiO₂ (rutile) (1 1 0) plane and the work function. It is considered that a surface state change, such as the crystalline structure and work function, might affect the catalytic activity for the ORR.     

A proton-conducting composite membrane: Sn0.95Al0.05P2O7 and polystyrene-b-poly(ethylene/propylene)-b-polystyrene

An anhydrous proton conductor, Sn_0.95Al_0.05P₂O₇ (SAPO), composed of polystyrene-b-poly(ethylene/propylene)-b-polystyrene (SEPS), was developed and characterized using morphological, structural, and electrochemical analyses. In the composite membrane with 20 wt% SEPS, a homogeneous distribution of SAPO particles in the matrix was obtained in the thickness range of 65-90 μm, yielding a proton conductivity of 3.4 × 10⁻³ S cm⁻¹ at 200 °C, tensile strength of 4.6 MPa and an elongation at break of 711.0% at room temperature. Fuel cell tests verified that the open-circuit voltage was maintained at a constant value of approximately 1 V between 100 and 250 °C. The peak power densities achieved with unhumidified H₂ and air were 77.0 mW cm⁻² at 100 °C, 121.0 mW cm⁻² at 150 °C, and 163.1 mW cm⁻² at 225 °C.     

Ca-α SiAlON hollow spheres prepared by carbothermal reduction–nitridation from different SiO2 powders

The formation process of hollow spheres composed of nanosized Ca-α SiAlON particles was investigated using SiO₂ starting powders with different characteristics in particle size, shape and crystalline state. TEM observations showed Ca-α SiAlON hollow spheres composed of a large number of nanosized particles in the products prepared at 1450 °C for 120 min in nitrogen. In all systems, the Ca-α SiAlON hollow spheres were always produced through an intermediate Si–Al–Ca–O liquid phase in the same mechanism, regardless of the characteristics of SiO₂ starting powders used. Spherical solid particles consisted of amorphous phase containing Si, Al, Ca, O and a small amount of N were generated at the initial stage of carbothermal reduction–nitridation. These spherical solid particles changed into hollow particles with the progression of the reaction from the liquid phase to the crystalline Ca-α SiAlON with increasing temperature.     

Characteristics of the removal of mercury vapor in coal derived fuel gas over iron oxide sorbents

The characteristics of a novel method for Hg removal using H₂S and sorbents containing iron oxide were studied. Previously, we have suggested that this method is based on the reaction of Hg and H₂S over the sorbents to form HgS. However, the reaction mechanism is not well understood. In this work, the characteristics of the Hg removal were studied to clarify the reaction mechanism. In laboratory made sorbents containing iron oxide were used as the sorbent to remove mercury vapor from simulated coal derived fuel gases having a composition of Hg (4.8 ppb), H₂S (400 ppm), CO (30%), H₂ (20%), H₂O (8%), and N₂ (balance gas). The following results were obtained: (1) The presence of H₂S was indispensable for the removal of Hg from coal derived fuel gas; (2) Hg was removed effectively by the sorbents containing iron oxide in the temperature range of 60-100 °C; (3) The presence of H₂O suppressed the Hg removal activity; (4) The presence of oxygen may play very important role in the Hg removal and; (5) Formation of elemental sulfur was observed upon heating of the used sample.