Study of intrinsic sulfidation behavior of Fe2O3 for high temperature H2S removal

Iron-based sorbent was preferable for desulfurization from coal-derived gas due to economic consideration and favorable dynamic property. The intrinsic behavior of Fe-based sorbent should be primarily understood in the sulfidation process for improving its performance. A series of tests were carried out with Fe₂O₃, Fe and other compounds containing-Fe (FO) made from the same precursor FeC₂O₄·2H₂O in H₂S-N₂ mixture in this study. The formation of H₂ was observed with Fe and FO as sorbents. While SO₂ was detected with FO and Fe₂O₃ as sorbents, its concentration in outlet was gradually decreased. The crystal phase and surface chemical state of fresh and sulfided Fe₂O₃ with different reaction times were characterized by XRD and XPS measurements. The result suggested that the intrinsic H₂S removal by Fe₂O₃ would produce multi-phase of sulfides. The possible mechanism of sulfidation reaction was discussed.     

Partial oxidation of ethanol over Pd/CeO2 and Pd/Y2O3 catalysts

The effect of the support nature on the performance of Pd catalysts during partial oxidation of ethanol was studied. H₂, CO₂ and acetaldehyde formation was favored on Pd/CeO₂, whereas CO production was facilitated over Pd/Y₂O₃ catalyst. According to the reaction mechanism, determined by DRIFTS analyses, some reaction pathways are favored depending on the support nature, which can explain the differences observed on products distribution. On Pd/Y₂O₃ catalyst, the production of acetate species was promoted, which explain the higher CO formation, since acetate species can be decomposed to CH₄ and CO at high temperatures. On Pd/CeO₂ catalyst, the acetaldehyde preferentially desorbs and/or decomposes to H₂, CH₄ and CO. The CO formed is further oxidized to CO₂, which seems to be promoted on Pd/CeO₂ catalyst.     

Catalytic syngas production from greenhouse gasses: Performance comparison of Ru-Al2O3 and Rh-CeO2 catalysts

In this work, 3% Ru-Al₂O₃ and 2% Rh-CeO₂ catalysts were synthesized and tested for CH₄-CO₂ reforming activity using either CO₂-rich or CO₂-lean model biogas feed. Low carbon deposition was observed on both catalysts, which negligibly influenced catalytic activity. Catalyst deactivation during temperature programmed reaction was observed only with Ru-Al₂O₃, which was caused by metallic cluster sintering. Both catalysts exhibited good stability during the 70 h exposure to undiluted equimolar CH₄/CO₂ gas stream at 750 °C. By varying residence time in the reactor during CH₄-CO₂ reforming, very similar quantities of H₂ were consumed for water formation. Reverse water-gas shift (RWGS) reaction occurred to a very similar extent either with low or high WHSV values over both catalysts, revealing that product gas mixture contained near RWGS equilibrium composition, confirming the dominance of WGS reaction and showing that shortening the contact time would actually decrease the H₂/CO ratio in the syngas produced by CH₄-CO₂ reforming, as long as RWGS is quasi equilibrated. H₂/CO molar ratio in the produced syngas can be increased either by operating at higher temperatures, or by using a feed stream with CH₄/CO₂ ratio well above 1.     

Corrosion mechanisms of Al2O3/MgAl2O4 by V2O5, NiO, Fe2O3 and vanadium slag

The effects of V₂O₅, NiO, Fe₂O₃ and vanadium slag on the corrosion of Al₂O₃ and MgAl₂O₄ have been investigated. The specimens of Al₂O₃ and MgAl₂O₄ with the respective oxides above mentioned were heated at 10 °C/min from room temperature up to three different temperatures: 1400, 1450 and 1500 °C. The corrosion mechanisms of each system were followed by XRD and SEM analyses. The results obtained showed that Al₂O₃ was less affected by the studied oxides than MgAl₂O₄. Alumina was only attacked by NiO forming NiAl₂O₄ spinel, while the MgAl₂O₄ spinel was attacked by V₂O₅ forming MgV₂O₆. It was also observed that Fe₂O₃ and Mg, Ni, V and Fe present in the vanadium slag diffused into Al₂O₃. On the other hand, the Fe₂O₃ and Ca, S, Si, Na, Mg, V and Fe diffused into the MgAl₂O₄ structure. Finally, the results obtained were compared with those predicted by the FactSage software.     

Selective synthesis of mixed alcohols from syngas over catalyst Fe2O3/Al2O3 in slurry reactor

The Fe₂O₃/Al₂O₃ catalyst was studied to selectively synthesize mixed alcohols from syngas in a continuously stirred slurry reactor with the oxygenated solvent Polyethylene Glycol-400 (PEG-400). The selectivity of mixed alcohols in the products reached as high as 95 wt.% and the C₂₊ alcohols (mainly ethanol) was more than 40 wt.% in the total alcohol products at the reaction conditions of 250 °C, 3.0 MPa, H₂/CO = 2 and space velocity = 360 ml/g_cat h. The hydrogen temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) measurements of the catalyst confirmed that the FeO phase was responsible for the high selectivity to mixed alcohols in the process. And the oxygenated solvent PEG-400 was also necessary for the selective synthesis of mixed alcohols in the reaction system.     

Mechanism and kinetics of Al2O3 nanoparticles formation by reaction of bulk Al with H2O and CO2 at sub- and supercritical conditions

Oxidation of bulk samples of 〈Al〉 by water and H₂O/CO₂ mixture at sub- and supercritical conditions for uniform temperature increase and at the injection of H₂O (665 K, 23.1 MPa) and H₂O/CO₂ (723 K, 38.0 MPa) fluids into the reactor has been studied. Transition of 〈Al〉 into AlOOH and Al₂O₃ nanoparticles has been found out. Aluminum samples oxidized by H₂O and H₂O/CO₂ fluids at the injection mostly consist of large particles (300-500 nm) of α-Al₂O₃. Those oxidized for uniform temperature increase contain smaller particles (20-70 nm) of γ-Al₂O₃ as well. Mechanism of this phenomenon is explained by orientation of oxygen in H₂O polar molecules to the metal in the electric field of contact voltage at Al/AlOOH and Al/Al₂O₃ boundary. Addition of CO₂ to water resulted in CO, CH₄, CH₃OH and condensed carbon, increase in size of Al₂O₃ nanoparticles and significant decrease in time delay. In pure CO₂ 〈Al〉 oxidation resulted in oxide film. Using temperature and time dependences of gaseous reactant pressure and Redlich-Kwong state equation, kinetics of H₂ formation has been described and oxidation regularities determined. At aluminum oxidation by H₂O and H₂O/CO₂ fluids, self-heating of the samples followed by oxidation rate increase has been registered. The samples of oxidized aluminum have been studied with a transmission electronic microscope, a thermal analyzer and a device for specific surface measurement. The effect of oxidation conditions on the characteristics of synthesized nanoparticles has been found out.     

Oxy-CO2 reforming of methane to syngas over CoOx/MgO/SA-5205 catalyst

The oxy-CO₂ methane reforming reaction (OCRM) has been investigated over CoO_x supported on a MgO precoated highly macroporous silica–alumina catalyst carrier (SA-5205) at different reaction temperatures (700–900 °C), O₂/CH₄ ratios (0.3–0.45) and space velocites (20,000–100,000 cc/g/h). The reaction temperature had a profound influence on the OCRM performance over the CoO/MgO/SA-5205 catalyst; the methane conversion, CO₂ conversion and H₂ selectivity increased while the H₂/CO ratio decreased markedly with increasing reaction temperature. While the O₂/CH₄ ratio did not strongly affect the CH₄ and CO₂ conversion and H₂ selectivity, it had an intense influence on the H₂/CO ratio. The CH₄ and CO₂ conversion and the H₂ selectivity decreased while the H₂/CO increased with increasing space velocity. The O₂/CH₄ ratio and the reaction temperature could be used to manipulate the heat of the reaction for the OCRM process. Depending on the O₂/CH₄ ratio and temperature the OCRM process could be operated in a mildly exothermic, thermal neutral or mildly endothermic mode. The OCRM reaction became almost thermoneutral at an OCRM reaction temperature of 850 °C, O₂/CH₄ ratio of 0.45 and space velocity of 46,000 cc/g/h. The CH₄ conversion and H₂ selectivity over the CoO/MgO/SA-5205 catalyst corresponding to thermoneutral conditions were excellent: 95% and 97%, respectively with a H₂/CO ratio of 1.8.     

Influence of the Type of Reducing Agent (H2, CO, C3H6 and C3H8) on the Reduction of Stored NOX in a Pt/BaO/Al2O3 Model Catalyst

In this investigation, a comparative study for a NO _X storage catalytic system was performed focusing on the parameters that affect the reduction by using different reductants (H₂, CO, C₃H₆ and C₃H₈) and different temperatures (350, 250 and 150 °C), for a Pt/BaO/Al₂O₃ catalyst. Transient experiments show that H₂ and CO are highly efficient reductants compared to C₃H₆ which is somewhat less efficient. H₂ shows a significant reduction effect at relatively low temperature (150 °C) but with a low storage capacity. We find that C₃H₈does not show any NO _X reduction ability for NO _X stored in Pt/BaO/Al₂O₃ at any of the temperatures. The formation of ammonia and nitrous oxide is also discussed.     

Reduction of NO by CO on Cu/ZrO2/Al2O3 catalysts: Characterization and catalytic activities

ZrO₂, γ-Al₂O₃ and ZrO₂/γ-Al₂O₃-supported copper catalysts have been prepared, each with three different copper loads (1, 2 and 5 wt%), by the impregnation method. The catalysts were characterized by nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) with H₂, Raman spectroscopy and electronic paramagnetic resonance (EPR). The reduction of NO by CO was studied in a fixed-bed reactor packed with these catalysts and fed with a mixture of 1% CO and 1% NO in helium. The catalyst with 5 wt% copper supported on the ZrO₂/γ-Al₂O₃ matrix achieved 80% reduction of NO. Approximately the same rate of conversion was obtained on the catalyst with 2 wt% copper on ZrO₂. Characterization of these catalysts indicated that the active copper species for the reduction of NO are those in direct contact with the oxygen vacancies found in ZrO₂.     

Sequential production of H2 and CO over supported Ni catalysts

Methane decomposition into H₂ and carbon nanofibers at 823 K and subsequent gasification of the carbon nanofibers with CO₂ into CO at 923 K were performed over supported Ni catalysts (Ni/SiO₂, Ni/TiO₂ and Ni/Al₂O₃). Supported Ni catalysts were deactivated for CH₄ decomposition with time on stream due to deposition of a large amount of carbon nanofibers. Subsequent contact of CO₂ with carbon nanofibers on the deactivated catalysts resulted in the formation of CO with a conversion of the carbons higher than 95%. In addition, gasification with CO₂ regenerated the activity of supported Ni catalysts for CH₄ decomposition, indicating that H₂ formation through CH₄ decomposition and CO formation through gasification with CO₂ could be carried out repeatedly. Conversions of carbon nanofibers into CO were kept higher than 95% in the repeated gasification over all the catalysts, while change in the catalytic activity for CH₄ decomposition with the repeated cycles depended on the kind of catalytic supports. Catalytic activity of Ni/SiO₂ for CH₄ decomposition was high at early cycles, however, the activity decreased gradually with the repeated cycles. On the other hand, Ni/TiO₂ and Ni/Al₂O₃ showed high activity for CH₄ decomposition and the activity was kept high during the repeated cycles. These changes of catalytic activities for CH₄ decomposition could be explained by changes in particle sizes of Ni metal, i.e. Ni metal particles in Ni/SiO₂ aggregated into ones larger than 150 nm with the repeated cycles, while the particle sizes of Ni metal in Ni/TiO₂ and Ni/Al₂O₃ remained at an effective range for CH₄ decomposition (60-100 nm).     

Synthesis of a TiO2 ceramic membrane containing SrCo0.8Fe0.2O3 by the sol-gel method with a wet impregnation process for O2 and N2 permeation

A SrCo_0.8Fe_0.2O₃ impregnated TiO₂ membrane (TiO₂-SrCo_0.8Fe_0.2O₃ membrane) was successfully prepared using a sol-gel method in combination with a wet impregnation process. The membrane was subjected to a single gas permeance test using oxygen (O₂) and nitrogen (N₂). The TiO₂ membrane was immersed in the SrCo_0.8Fe_0.2O₃ solution, dried and then calcined to affix SrCo_0.8Fe_0.2O₃ into the membrane. The effect of the acid/alkoxide (H⁺/Ti⁴⁺) molar ratio of the TiO₂ sol on the TiO₂ phase transformation was investigated. The optimal molar ratio was found to be 0.5, which resulted in nanoparticles with a mean size of 5.30 nm after calcination at 400 °C. The effect of calcination temperature on the phase transformation of TiO₂ and SrCo_0.8Fe_0.2O₃ was investigated by varying the calcination temperature from 300 to 500 °C. X-ray diffraction spectroscopy (XRD) and Fourier transform infrared (FTIR) analysis confirmed that a calcination temperature of 400 °C was preferable for preparing a TiO₂-SrCo_0.8Fe_0.2O₃ membrane with fully crystallized anatase and SrCo_0.8Fe_0.2O₃ phases. The results also showed that polyvinyl alcohol (PVA) and hydroxypropyl cellulose (HPC) were completely removed. Field emission scanning electron microscopy (FESEM) analysis results showed that a crack-free and relatively dense TiO₂ membrane (∼0.75 μm thickness) was created with a multiple dip-coating process and calcination at 400 °C. The gas permeation results show that the TiO₂ and TiO₂-SrCo_0.8Fe_0.2O₃ membranes exhibited high permeances. The TiO₂-SrCo_0.8Fe_0.2O₃ membrane developed provided greater O₂/N₂ selectivity compared to the TiO₂ membrane alone.     

Synthesis of magnetic Pb/Fe3O4/SiO2 and its catalytic activity for propylene carbonate synthesis via urea and 1,2-propylene glycol

To facilitate the recovery of Pb/SiO₂ catalyst, magnetic Pb/Fe₃O₄/SiO₂ samples were prepared separately by emulsification, sol-gel and incipient impregnation methods. The catalyst samples were characterized by means of X-ray diffraction and N₂ adsorption-desorption, and their catalytic activity was investigated in the reaction for synthesizing propylene carbonate from urea and 1,2-propylene glycol. When the gelatin was applied in the preparation of Fe₃O₄ at 60°C and the pH value was controlled at 4 in the preparation of Fe₃O₄/SiO₂, the Pb/Fe₃O₄/SiO₂ sample shows good catalytic activity and magnetism. Under the reaction conditions of a reaction temperature of 180°C, reaction time of 2 h, catalyst percentage of 1.7 wt-% and a molar ratio of urea to PG of 1:4, the yield of propylene carbonate attained was 87.7%.     

Kinetic modeling of storage and reduction with different reducing agents (CO, H2, and C2 H4) on a Pt–Ba/-Al2O3 catalyst in the presence of CO2 and H2O

In this paper a global reaction kinetic model is used to understand and describe the NO_x storage/reduction process in the presence of CO₂ and H₂O. Experiments have been performed in a packed bed reactor with a Pt–Ba/γ-Al₂O₃ powder catalyst (1 wt% Pt and 30 wt% Ba) with different lean/rich cycle timings at different temperatures (200, 250, and ) and using different reductants (H₂, CO, and C₂H₄). Model simulations and experimental results are compared. H₂O inhibits the NO oxidation capability of the catalyst and no NO₂ formation is observed. The rate of NO storage increases with temperature. The reduction of stored NO with H₂ is complete for all investigated temperatures. At temperatures above , the water gas shift (WGS) reaction takes place and H₂ acts as reductant instead of CO. At , CO and C₂H₄ are not able to completely regenerate the catalyst. At the higher temperatures, C₂H₄ is capable of reducing all the stored NO, although C₂H₄ poisons the Pt sites by carbon decomposition at . The model adequately describes the NO breakthrough profile during 100 min lean exposure as well as the subsequent release and reduction of the stored NO. Further, the model is capable of simulating transient reactor experiments with 240 s lean and 60 s rich cycle timings.     

Reactivity of a NiO/Al2O3 oxygen carrier prepared by impregnation for chemical-looping combustion

The reactivity of a Ni-based oxygen carrier prepared by hot incipient wetness impregnation (HIWI) on α-Al₂O₃ with a NiO content of 18 wt% was studied in this work. Pulse experiments with the reduction period divided into 4-s pulses were performed in a fluidized bed reactor at 1223 K using CH₄ as fuel. The number of pulses was between 2 and 12. Information about the gaseous product distribution and secondary reactions during the reduction was obtained. In addition to the direct reaction of the combustible gas with the oxygen carrier, CH₄ steam reforming also had a significant role in the process, forming H₂ and CO. This reaction was catalyzed by metallic Ni in the oxygen carrier and H₂ and CO acted as intermediate products of the combustion. No evidence of carbon deposition was found in any case. Redox cycles were also carried out in a thermogravimetric analyzer (TGA) with H₂ as fuel. Both tests showed that there was a relation between the solid conversion reached during the reduction and the relative amount of NiO and NiAl₂O₄ in the oxygen carrier. When solid conversion increased, the NiO content also increased, and consequently NiAl₂O₄ decreased. Approximately 20% of the reduced nickel was oxidized to NiAl₂O₄, regardless ΔX_s. NiAl₂O₄ was also an active compound for the combustion reaction, but with lower reactivity than NiO. Further, the consequences of these results with respect to the design of a CLC system were investigated. When formation of NiAl₂O₄ occurred, the average reactivity in the fuel reactor decreased. Therefore, the presence of both NiO and NiAl₂O₄ phases must be considered for the design of a CLC facility.     

Effect of TiO2 supporting layer on Fe2O3 photoanode for efficient water splitting

For an electrochemical water splitting system, titanate nanotubular particles with a thickness of ∼700 nm produced by a hydrothermal process were repetitively coated on fluorine-doped tin oxide (FTO) glass via layer-by-layer self-assembly method. The obtained titanate/FTO films were dipped in aqueous Fe solution, followed by heat treatment for crystallization at 500 °C for 10 min in air. The UV–vis absorbance of the Fe-oxide/titanate/FTO film showed a red-shifted spectrum compared with the TiO₂/FTO coated film; this red shift was achieved by the formation of thin hematite-Fe₂O₃ and anatase-TiO₂ phases verified using X-ray diffraction and Raman results. The cyclic voltammetry results of the Fe₂O₃/TiO₂/FTO films showed distinct reversible cycle characteristics with large oxidation–reduction peaks with low onset voltage of I–V characteristics under UV–vis light illumination. The prepared Fe₂O₃/TiO₂/FTO film showed much higher photocurrent densities for more efficient water splitting under UV–vis light illumination than did the Fe₂O₃/FTO film. Its maximum photocurrent was almost 3.5 times higher than that obtained with Fe₂O₃/FTO film because of the easy electron collection in the current collector. The large current collection was due to the existence of a TiO₂ base layer beneath the Fe₂O₃ layer.     

Catalytic steam reforming of ethane and propane over CeO2-doped Ni/Al2O3 at SOFC temperature: Improvement of resistance toward carbon formation by the redox property of doping CeO2

Ni/Al₂O₃ with the doping of CeO₂ was found to have useful activity to reform ethane and propane with steam under Solid Oxide Fuel Cells (SOFCs) conditions, 700-900 °C. CeO₂-doped Ni/Al₂O₃ with 14% ceria doping content showed the best reforming activity among those with the ceria content between 0 and 20%. The amount of carbon formation decreased with increasing Ce content. However, Ni was easily oxidized when more than 16% of ceria was doped. Compared to conventional Ni/Al₂O₃, 14%CeO₂-doped Ni/Al₂O₃ provides significantly higher reforming reactivity and resistance toward carbon deposition. These enhancements are mainly due to the influence of the redox properties of doped ceria. Regarding the temperature programmed reduction experiments (TPR-1), the redox properties and the oxygen storage capacity (OSC) for the catalysts increased with increasing Ce doping content. In addition, it was also proven in the present work that the redox of these catalysts are reversible, according to the temperature programmed oxidation (TPO) and the second time temperature programmed reduction (TPR-2) results.During the reforming process, in addition to the reactions on Ni surface, the gas-solid reactions between the gaseous components presented in the system (C₂H₆, C₃H₈, C₂H₄, CH₄, CO₂, CO, H₂O, and H₂) and the lattice oxygen (O_x) on ceria surface also take place. The reactions of adsorbed surface hydrocarbons with the lattice oxygen (O_x) on ceria surface (C_nH_m+O_x→nCO+m/2(H₂)+O_x−n) can prevent the formation of carbon species on Ni surface from hydrocarbons decomposition reaction (C_nH_m⇔nC+m/2H₂). Moreover, the formation of carbon via Boudard reaction (2CO⇔CO₂+C) is also reduced by the gas-solid reaction of carbon monoxide (produced from steam reforming) with the lattice oxygen (CO+O_x⇔CO₂+O_x−1).     

Improvement of coke resistance of Ni/Al2O3 catalyst in CH4/CO2 reforming by ZrO2 addition

This work investigates the improvement of Ni/Al₂O₃ catalyst stability by ZrO₂ addition for H₂ gas production from CH₄/CO₂ reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO₂ loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH₄:CO₂ ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al₂O₃ was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO₂, as it enhances dissociation of CO₂ forming oxygen intermediates near the contact between ZrO₂ and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO₂–Al₂O₃ composite and the plugging of Al₂O₃ pore by ZrO₂. The 15% Ni/10% ZrO₂/Al₂O₃ co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made.     

Supported Rh catalysts for methane partial oxidation prepared by OM-CVD of Rh(acac)(CO)2

The organometallics chemical vapour deposition (OM-CVD) technique, using Rh(acac)(CO)₂ as a precursor, was employed for the preparation of heterogeneous Rh catalysts supported on low surface area refractory oxides (α-Al₂O₃, ZrO₂, MgO and La₂O₃). Prepared systems were tested in the methane catalytic partial oxidation (CH₄-CPO) reaction in a fixed bed reactor and compared to a reference catalyst prepared from impregnation of Rh₄(CO)₁₂.Catalysts supported on Al₂O₃, ZrO₂ and MgO show better or comparable performances with respect to the reference system.Complete decomposition of Rh precursor during formation of the metal phase under reductive conditions was investigated by TPRD and confirmed by infrared and mass spectrometry data.Supported Rh phase was characterized by CO and H₂ chemisorption, CO-DRIFT spectroscopy and HRTEM microscopy in fresh and aged selected samples. Rh(I) isolated sites and Rh(0) metal particles were found on fresh catalysts; after ageing an extensive reconstruction occurs mainly consisting in a sintering of Rh isolate sites to metal particles but without large increase in mean particles size.Catalytic performances and Rh species balance were found to be dependent on the support material.     

Reduction of lean NOx by ethanol over Ag/Al2O3 catalysts in the presence of H2O and SO2

The reduction of lean NOx using ethanol in simulated diesel engine exhaust was carried out over Ag/Al₂O₃ catalysts in the presence of H₂O and SO₂. The Ag/Al₂O₃ catalysts are highly active for the reduction of lean NOx by ethanol but the reaction is accompanied by side reactions to form CH₃CHO, CO along with small amounts of hydrocarbons (C₃H₆, C₂H₄, C₂H₂ and CH₄) and nitrogen compounds such as NH₃ and N₂O. The presence of H₂O enhances the NOx reduction while SO₂ suppresses the reduction. The presence of SO₂ along with H₂O suppresses the formation of acetaldehyde and NH₃. By infrared spectroscopy, it was revealed that the reactivity of NCO species formed in the course of the reaction was greatly enhanced in the presence of H₂O. The NCO species readily reacts with NO in the presence of O₂ and H₂O at room temperature, being converted to N₂ and CO₂ (CO). Addition of SO₂ suppresses the formation of NCO species and lowers the reactivity of the NCO species. However, the reduction of NOx is still kept at high conversion levels in the presence of H₂O and SO₂ over the present catalysts. About 80% of NOx in the simulated diesel engine exhaust was removed at 743 K. This revised version was published online in July 2006 with corrections to the Cover Date.