CO Pretreatment Research Articles

Promotional effect of CO pretreatment on CuO/CeO2 catalyst for catalytic reduction of NO by CO

The CuO/CeO2 catalysts were investigated by means of X-ray diffraction (XRD), laser Raman spectroscopy (LRS), X-ray photoelectronic spectroscopy (XPS), temperature-programmed reduction (TPR), in situ Fourier transform infrared spectroscopy (FTIR) and NO+CO reaction. The results revealed that the low temperature (<150 °C) catalytic performances were enhanced for CO pretreated samples. During CO pretreatment, the surface Cu+/Cu0 and oxygen vacancies on ceria surface were present. The low valence copper species activated the adsorbed CO and surface oxygen vacancies facilitated the NO dissociation. These effects in turn led to higher activities of CuO/CeO2 for NO reduction. The current study provided helpful understandings of active sites and reaction mechanism in NO+CO reaction.

The enhancement for SCR of NO by NH3 over the H2 or CO pretreated Ag/γ-Al2O3 catalyst

H2 or CO pretreatment had been processed on the Ag/γ-Al2O3 catalyst which significantly enhanced its NH3-SCR activity. The main purpose of this study was to prove that the impacts of pretreatment on silver species caused the enhancement. XRD, UV-vis, XPS, in situ FTIR and NO-TPD results showed the relationship between pretreatment, Ag species, NOX adsorption and NOX conversion. Extra nitrates were adsorbed on the Ag clusters which were produced by the pretreatment, thereby enhancing the activity. The reactivities between NO and NH3 had been studied. The difference between CO-pretreatment and H2-pretreatment had also been discussed. Furthermore, the durability and stability of the pretreated sample were tested. Therefore, a modified Ag2O/Al2O3 catalyst for NH3-SCR was researched.

Synthesis of light olefins from CO hydrogenation over Fe–Mn catalysts: Effect of carburization pretreatment

Effects of carburization during pretreatment with different atmospheres on K promoted Fe–Mn catalysts for CO hydrogenation were investigated. The bulk structure, surface composition and chemical properties of the catalysts before and after pretreatment were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, in situ X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption/oxidation (TPD/TPO) and catalytic activity tests for the selective formation of light olefins. Results indicated that the surface basic sites and CO adsorption were promoted after pretreatment, especially for CO pretreatment. As the formation of iron carbide and elevation of carburization temperature, the surface basicity was significantly enhanced. The catalysts after CO or syngas pretreatment exhibited much higher selectivity to light olefin than that pretreated with H2 due to the basicity change during the pretreatment. The formation of carbide species improved the surface basicity which enhanced the adsorption and dissociation of CO and then decreased the second hydrogenation of primary olefins.

Treatment induced remarkable enhancement of low-temperature activity and selectivity of copper-based catalysts for NO reduction

The poor low-temperature (200–300 °C) activity and N2 selectivity of Cu-based catalysts for NO reduction by CO has driven us to further advance this process. The present work offers a simple but very promising strategy to achieve this goal by CO pre-treatment of the binary CuM/γ-Al2O3 (M = V, Mn, Fe, Co, Ni, Zn) catalysts to tailor the surface active sites. The results demonstrate that CO pre-treatment significantly enhanced the low temperature NO conversion and N2 selectivity of CuM/γ-Al2O3, depending on the type of metal oxides. Among these catalysts, CO pre-treated CuNi/γ-Al2O3 exhibited the highest activity/selectivity (i.e., about 90% at 200 °C) and excellent stability. The activity improvement resulted from the following: 1) the obtainment of oxygen vacancies and more Cu+ species with the suitable ratio of dispersed Cu2+/Cu+, 2) the decrease of apparent activation energy for NO conversion and 3) the more favourable activation and dissociation of NO on the reduced surface, as evidenced by X-ray photoelectron spectroscopy (XPS) and in situ Fourier transform infrared (FTIR) spectroscopy results.

Investigation of surface synergetic oxygen vacancy in CuO–CoO binary metal oxides supported on γ-Al2O3 for NO removal by CO

The influence of CO pretreatment on the properties of CuO–CoO/γ-Al2O3 catalysts was investigated by SEM, TEM, XRD, LRS, XPS, TPR, and in situ FT-IR techniques. And the activities were measured by NO removal by CO. It was shown that the CuO–CoO/γ-Al2O3 catalysts following CO pretreatment exhibited extremely high activity and selectivity. The interaction between copper oxide and cobalt oxide upon the γ-Al2O3 support before and after CO pretreatment was tentatively discussed in the view of incorporation model. According to this model, the dispersed Cu–O–Co species could be reduced to Cu-□-Co species by CO pretreatment, which was considered to be the primary active component for this reaction. FT-IR results suggested that CO was apt to adsorb on Cu+ sites rather than Co2+ while the NO adsorbates could convert to much more stable species with the temperature increasing. Undoubtedly, it was the surface synergetic oxygen vacancy coupled with the adjacent Cu and Co ions that guaranteed the reaction well processing over the CO pretreated samples. As a result, a possible mechanism was tentatively proposed.

Surface morphology of Hägg iron carbide (χ-Fe5C2) from ab initio atomistic thermodynamics

Ab initio atomistic thermodynamics is utilized to achieve the understanding of the surface structure and stability of χ-Fe5C2 under CO and synthesis gas (H2/CO) pretreatment conditions in catalyst activation for Fischer–Tropsch synthesis (FTS). On the basis of the computed surface free energy (γ) as a function of the carbon chemical potential (μC) by considering temperature, pressure, and H2/CO ratios, it is found that CO pretreatment favors stable carbon-rich facets, while small amount of H2 added into CO leads to a large decrease in μC and thus stabilizing carbon-poor facets. The high activity of surface carbon toward hydrogenation might explain the enhanced initial activity of the FTS catalysts activated from CO pretreatment. Moreover, under both CO and H2/CO pretreatments, either low temperature or low pressure can lead to stable carbon-rich facets.

On the interaction of carbon monoxide with ternary Cu/ZnO/Al2O3 catalysts: modeling of dynamic morphological changes and the influence on elementary step kinetics

This paper focuses on gas-phase induced dynamic morphological changes of the catalyst, in particular by carbon monoxide. Those structural changes are studied in terms of hydrogen temperature-programmed desorption (TPD) from carbon monoxide pre-treated surfaces. Modeling the hydrogen TPD from the pre-treated catalyst shows activation of Cu(110) and Cu(100) planes. This is in good agreement with previously shown morphological changes in different gas atmospheres observed from in situ EXAFS and TEM measurements and observed transient maxima of methanol synthesis upon CO pre-treatment which has been reported in the literature. The obtained hydrogen desorption energies for the respective copper surfaces are physically reasonable. This surface heterogeneity is further implemented in a microkinetic model to describe the temperature-programmed surface reaction (TPSR) between carbon monoxide and adsorbed oxygen. It is found that a logarithmic coverage-dependence on adsorbed oxygen is essential for obtaining good agreement between simulation and experiment. For high oxygen loadings the apparent activation energy is essentially constant, which is in good agreement with literature results.

The Effect of CO Pretreatment on Fe/ADM Catalyst for Higher Alcohols Synthesis from Syngas

The catalyst of FeS modified K2CO3/MoS2 (ADM) (Fe/ADM) were prepared and tested for higher alcohols (C2+OH) synthesis (HAS) from synthesis gas(syngas, mixture of H2 and CO). The effects of CO pretreatment on Fe/ADM catalyst and the catalytic performance for HAS were investigated. The ability for C2+OH formation was enhanced and the hydrocarbon selectivity was lowered after CO pretreatment. The XPS spectra revealed that the iron carbide species appeared and the potassium enriched on the surface of CO pretreated Fe/ADM catalyst, which might be responsible for the high activity of higher alcohols and low hydrocarbons synthesis, respectively.

The Remarkable Enhancement of CO‐Pretreated CuOMn2O3/γ‐Al2O3 Supported Catalyst for the Reduction of NO with CO: The Formation of Surface Synergetic Oxygen Vacancy

NO reduction by CO was investigated over CuO/γ-Al2O3, Mn2O3/γ-Al2O3, and CuOMn2O3/γ-Al2O3 model catalysts before and after CO pretreatment at 300 °C. The CO-pretreated CuO-Mn2O3/γ-Al2O3 catalyst exhibited higher catalytic activity than did the other catalysts. Based on X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis diffuse reflectance spectroscopy (DRS), Raman, and H2-temperature-programmed reduction (TPR) results, as well as our previous studies, the possible interaction model between dispersed copper and manganese oxide species as well as γ-Al2O3 surface has been proposed. In this model, Cu and Mn ions occupied the octahedral vacant sites of γ-Al2O3, with the capping oxygen on top of the metal ions to keep the charge conservation. For the fresh CuO/γ-Al2O3 and Mn2O3/γ-Al2O3 catalysts, the -Cu-O-Cu- and -Mn-O-Mn- species were formed on the surface of γ-Al2O3, respectively; but for the fresh CuO-Mn2O3/γ-Al2O3 catalyst, -Cu-O-Mn- species existed on the surface of -Al2O3. After CO pretreatment, -Cu-□-Cu- and -Mn-□-Mn- (□ represents surface oxygen vacancy (SOV)) species would be formed in CO-pretreated CuO/γ-Al2O3 and CO-pretreated Mn2O3/γ-Al2O3 catalysts, respectively; whereas -Cu-□-Mn- species existed in CO-pretreated CuO-Mn2O3/γ-Al2O3. Herein, a new concept, surface synergetic oxygen vacancy (SSOV), which describes the oxygen vacancy formed between the individual Mn and Cu ions, is proposed for CO-pretreated CuO-Mn2O3/γ-Al2O3 catalyst. In addition, the role of SSOV has also been approached by NO temperature-programmed desorption (TPD) and in situ FTIR experiments. The FTIR results of competitive adsorption between NO and CO on all the CO-pretreated CuO/γ-Al2O3, Mn2O3/γ-Al2O3, and CuO-Mn2O3/γ-Al2O3 samples demonstrated that NO molecules mainly were adsorbed on Mn2+ and CO mainly on Cu+ sites. The current study suggests that the properties of the SSOVs in CO-pretreated CuO-Mn2O3/γ-Al2O3 catalyst were significantly different to SOVs formed in CO-pretreated CuO/γ-Al2O3 and Mn2O3/γ-Al2O3 catalysts, and the SSOVs played an important role in NO reduction by CO.

Hydrogen-Promoted Chlorination of RuO2(110)

High-resolution core-level photoemission spectroscopy and temperature-programmed reaction experiments together with density functional theory calculations were used to elucidate on the atomic scale the chlorination mechanism of ruthenium dioxide RuO2(110) by hydrogen chloride exposure. The surface-selective chlorination accounts for the extraordinary stability of the RuO2 catalyst in the Sumitomo process-the heterogeneously catalyzed oxidation of hydrogen chloride by oxygen. The selective replacement of bridging oxygen atoms by chlorine atoms depends on the formation of water molecules serving as leaving groups. Water is produced by the chlorine-assisted recombination of two neighboring surface hydroxyl groups at around 450 K, a temperature where water instantaneously leaves the surface. Finally, the bridging vacancy is rapidly filled in by chlorine atoms, thereby forming bridging chlorine atoms. Preadsorbed hydrogen has shown to facilitate the chlorination process for stoichiometry reasons. The general strategy of transforming bridging O atoms into a good leaving group has been corroborated by the chlorination of RuO2(110) via CO pretreatment with CO2 as the leaving group and subsequent Cl-2 exposure. (Less)

Effect of CO pretreatment on the performance of CuO/CeO 2/γ-Al 2O 3 catalysts in CO + O 2 reactions

The influence of CO pretreatment on the properties of CuO/CeO 2/γ-Al 2O 3 catalysts was investigated using X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). The activities of the treated catalysts were measured in low-temperature CO oxidation reactions (≤200 °C). For this reaction, the activities of CuO/CeO 2/γ-Al 2O 3 catalysts are intimately related to operation temperature, copper oxide loading amount and CO pretreatment. The influence of the first two factors, i.e., operation temperature and copper oxide loading amount, is similar to the previous results of CuO/γ-Al 2O 3 catalysts [H.Q. Wan, Z. Wang, J. Zhu, X.W. Li, B. Liu, F. Gao, L. Dong, Y. Chen, Appl. Catal. B: Environ. 79 (2008) 254–261]. CO conversions are clearly promoted with increasing operation temperatures and the maximum CO conversions are always reached over the catalysts with a copper oxide loading amount of 0.6 mmol Cu 2+/100 m 2 γ-Al 2O 3, at the set operation temperatures. For the third factor, CO conversions over the CO-treated CuO/CeO 2/γ-Al 2O 3 catalysts are slightly lower than those over the fresh catalysts with the same amount of copper oxide. In contrast, the activity was enhanced over the CO-treated CuO/γ-Al 2O 3 catalysts in the previous report. XRD, TPR and XPS results show that CO pretreatment at 250 °C mainly results in the reduction of crystalline CuO to Cu 0 and of partially dispersed Cu 2+ to Cu + and Cu 0 in CuO/CeO 2/γ-Al 2O 3 catalysts. IR results indicate that besides the CO–Cu + adsorption band at ∼2110 cm −1 on the fresh and CO-pretreated catalysts exposed to CO stream when temperatures are above 50 °C, a new adsorption band at 2170 cm −1 is detectable corresponding to CO–Cu 2+ or CO–Cu 0 over the CO-treated CuO/CeO 2/γ-Al 2O 3 catalysts with copper oxide loading amounts of 0.3 and 1.2 mmol/100 m 2γ-Al 2O 3 at the adsorption temperatures beyond 150 °C. The influences of the ceria modification on the generation of copper species in fresh and CO-treated CuO/CeO 2/γ-Al 2O 3 catalysts and their activities in CO oxidation were discussed.

Influence of CO pretreatment on the activities of CuO/γ-Al2O3 catalysts in CO + O2 reaction

The influence of CO pretreatment on the properties of CuO/γ-Al2O3 catalysts was investigated by X-ray diffraction (XRD), temperature programmed reduction (TPR), and infrared spectroscopy (IR). The activities of the treated catalysts were measured in low-temperature CO oxidation reaction (≤200°C). It is shown that CO pretreatment at 250°C mainly results in the reduction of crystalline CuO to Cu0 and dispersed Cu2+ to Cu+. CO–Cu+ interaction is much stronger than those of CO–Cu2+ and CO–Cu0, and as a result, CO molecules adsorbed on Cu+ are the main species on the fresh and CO pretreated catalysts exposed to CO stream at temperatures of 100°C and higher.For the low-temperature CO oxidation reaction, the activities of CuO/γ-Al2O3 catalysts are intimately related to the operation temperature, copper oxide loading amount and CO pretreatment. CO conversions are promoted evidently with increasing operation temperatures. At the set operation temperatures, maximum CO conversions are always reached over the catalysts with a copper oxide loading amount of 0.6mmol Cu2+/100m2 Al2O3, which is close to the dispersion capacity of copper oxide on γ-Al2O3, i.e., 0.75mmol Cu2+/100m2 Al2O3. CO conversions over the catalysts following CO treatment are much higher than those over the fresh catalysts with the same amount of copper oxide. It is concluded that for low-temperature CO oxidation, dispersed copper oxide species are the primary active component, and the dispersed Cu+ species plays a significant role.

Hydrogen Interaction with a Ceria−Zirconia Supported Gold Catalyst. Influence of CO Co-adsorption and Pretreatment Conditions

This work reports on the hydrogen interaction with a 3 wt % Au/Ce0.62Zr0.38O2 (Au/CZ) catalyst prepared by deposition−precipitation. As deduced from X-ray powder diffraction, electron microscopy (scanning transmission electron microscopy−high-angle angular dark field and high-resolution electron microscopy), and CO volumetric/Fourier transform IR (FTIR) adsorption studies, the investigated catalyst shows a good metal dispersion. By combining FTIR spectroscopy and volumetric chemisorption studies, it is shown that upon treating the Au/CZ catalyst with 40 Torr of H2 at room temperature a fast and very intense spillover effect occurs. As determined from the recorded isotherm, very high values of the apparent H/Au ratio (>8.0) and of the atomic hydrogen surface density (>11.0 H/nm2) are reached. In parallel with this observation, the onset of a characteristic IR band at 2133 cm-1 shows the occurrence of significant support reduction with inherent appearance of Ce3+ species. Moreover, the simultaneous growth o...

Characterization of Mo additions in iron-based Fischer–Tropsch catalysts using X-ray absorption spectroscopy and X-ray diffraction

An iron-based Fischer–Tropsch catalyst with a low concentration of molybdenum (90Fe/10Mo/5Cu/17Si) used as a promoter was characterized by X-ray absorption spectroscopy (XAS) and X-ray diffractometry (XRD). The catalyst was prepared using coprecipitation, pretreated in CO, then one sample passivated and one calcined. The XRD data show that after CO pretreatment the calcined and passivated catalysts are almost amorphous with respect to Fe 2O 3 with nanoparticle size of 10 and 100 Å for Fe 3C (only present in the passivated sample). Least squares fitting of the XANES region show that the calcined and passivated samples were similar in the bulk and surface structures, with the calcined samples completely oxidized. As expected, K and L III edges Mo-XANES shows only small molybdenum carbide formation compared to iron carbide.

Phase transformation of unpromoted and promoted Fe catalysts and the formation of carbonaceous compounds during Fischer–Tropsch synthesis reaction

Precipitated Fe catalysts with or without additives (Zn, K, Cu) were prepared, pretreated by CO, and then time-dependent behaviors of their FTS activities were investigated at 503 K and 1.6 MPa in a fixed bed reactor. Over the catalyst without additives, CO conversion showed a maximum at ca. 8 h on stream and then decreased monotonically with increasing time on stream. When Zn, K and/or Cu were added, respectively, similar behaviors were observed. However, an increasing CO conversion was observed during on stream (29 h) when Zn, K and Cu were added simultaneously. X-ray diffraction (XRD) analysis of these catalysts showed the formation of Fe carbides (Fe 5C 2 and Fe x C) after the CO pretreatment irrespective of the catalyst composition. In the case of the catalyst without additives, these carbides were oxidized to Fe 3O 4 during on stream. The oxidation of the carbides was more significant on the catalyst charged near the outlet of the reactor. For the catalyst containing all the additives simultaneously, however, the Fe carbides were only phases detected by XRD analysis even after the long time on stream (29 h). In addition, the formation of amorphous carbonaceous compounds was observed by laser Raman spectroscopy (LRS) for the catalysts after the CO pretreatment and/or the FTS reaction. So-called a graphite-like carbonaceous compound was not observed by LRS, which was considered as one of reasons for the catalyst deactivation in the previous studies. Therefore, it is suggested that the oxidation of the Fe carbides by H 2O vapor is a main reason for the deactivation of the Fe FTS catalyst. Because the Zn, K and Cu containing catalyst showed a higher CO 2 selectivity, the combination of these additives improves the water-gas shift activity, thereby suppresses the oxidation of the Fe carbides.

Ammonia Decomposition Catalyst with Resistance to Coexisting Sulfur Compounds

A cheap and disposal catalyst will be required for the decomposition of ammonia in the presence of sulfur compounds. The possibility of iron ore and red mud as the ammonia decomposition catalyst was investigated using pure or diluted ammonia containing hydrogen sulfide as a reactant. Among the catalysts tested, red mud had the highest catalytic activity for the ammonia decomposition in the presence of hydrogen sulfide. On the other hand, a relatively low conversion of ammonia was observed using a nickel-based commercial catalyst for the ammonia decomposition. The deactivation behavior of an iron ore catalyst caused by sulfur poisoning depended on the pretreatment atmosphere before the reaction; namely, the deactivation was observed for the H2 pretreatment, while the high level of ammonia conversion remained constant for the CO pretreatment. From the X-ray diffraction pattern of the catalysts, the used iron ore catalyst pretreated in the CO atmosphere included FeCx, which was also included in the red mud that was active for the ammonia decomposition. FeCx may be responsible to the sulfur poisoning resistance.

Carbon monoxide (co) downregulates hepatic inducible nitric oxide synthase (inos) by a mitogen-activated protein kinase (mapk) dependent mechanism

Background: Low dose CO is non-toxic and has been shown to possess potent anti-inflammatory properties. We hypothesize that CO would decrease cytokine-stimulated iNOS induction in rat hepatocytes. Methods: Primary hepatocytes from Sprague-Dawley rats were exposed to combinations of cytokines (TNFα, IL-1, IFγ) in the presence or absence of CO pre- and co- treatment at 250 ppm. Protein was harvested for Western blotting at 0, 1 and 6 hours after treatment. Greiss reaction was used to quantify NO production and crystal violet staining was used to measure cell viability. Experiments were performed 2–3 times each and t-test was used to assess significance between groups. Results: CO exposure at 250 ppm did not decrease hepatocyte viability measured by crystal violet staining at 24 hours. Pretreatment with CO resulted in a statistically significant decrease in cytokine mixture (TNFα 500 U/ml, IL-1 200 U/ml, IFγ 100 U/ml) stimulated hepatocyte NO production measured by Greiss reaction (37.8 ± 7.4 to 20.8 ± 5.7 μM, p < 0.05). Western blot 6 hours after stimulation resulted in a similar decrease in iNOS protein in the CO exposed hepatocytes. Pretreatment with CO up-regulated mitogen activated protein kinase phosphatase-1 (MKP-1) protein and decreased TNFα induced c-Jun N-terminal kinase (JNK) activation measured by Western blot. Conclusions: CO pretreatment decreased cytokine stimulated hepatocyte iNOS protein synthesis and NO production. A possible mechanism for this effect is the up-regulation of MKP-1 protein and subsequent decrease in cytokine stimulated JNK activation. The study provides a new mechanism for the anti-inflammatory effects of CO and validates the importance of JNK activation in pro-inflammatory signaling.

The origin of red cell fluorescence caused by hydrogen peroxide treatment

Fluorescence in red cells following hydrogen peroxide treatment has been attributed to lipid peroxidation of the membrane. The putative relationship between lipid peroxidation and fluorescence was questioned by the finding that BHT and α-tocopherol, which are thought to inhibit lipid peroxidation, do not inhibit the fluorescence detected by flow cytometry. Furthermore, lipid peroxidation induced in red cells by the Fe(III)-ADP-ascorbate system did not produce fluorescence. These results require an alternative explanation for the hydrogen peroxide–induced fluorescence. A role for reduced hemoglobin is indicated by the inhibition of fluorescence by pretreatment of cells with CO that binds strongly to ferrohemoglobin and nitrite that oxidizes ferrohemoglobin. Our earlier studies have shown the formation of fluorescent heme degradation products during the reaction of purified hemoglobin with hydrogen peroxide, which was also inhibited by CO and nitrite pretreatment. The fluorescence produced in red cells after the addition of hydrogen peroxide can, therefore, be attributed to fluorescent heme degradation products.

Fischer–Tropsch synthesis. Effect of CO pretreatment on a ruthenium promoted Co/TiO2

The effect of pretreatment, using hydrogen or carbon monoxide, on the activity and selectivity of a ruthenium promoted cobalt catalyst (Ru(0.20 wt%)/Co(10 wt%)/TiO2) during Fischer–Tropsch (FT) synthesis was studied in a continuous-stirred tank reactor (CSTR). The hydrogen reduced catalyst exhibited a high initial synthesis gas conversion (72.5%) and reached steady state after 40 h on stream, after which the catalyst deactivated slightly with time on stream. The carbon monoxide reduced catalyst reached steady state quickly and showed a lower activity and a good stability. Methane selectivity on the carbon monoxide reduced catalyst was 15–20% (carbon base), much higher than that on the hydrogen reduced catalyst (5–10%). Carbon monoxide regeneration increased the activity on the hydrogen reduced catalyst; however, it did not have significant effect on the carbon monoxide reduced catalyst.

Modeling, simulation and optimization of membrane-based gas separation systems

This paper presents various aspects of modeling, simulation, design, and optimization of membrane-based gas separation systems. A model for counter- and crosscurrent membrane modules and an efficient numerical solution procedure based on orthogonal collocation to solve the differential model equations have been developed. The model handles multicomponent mixtures and considers effects of pressure drop and energy balance. The model and solution procedure are combined in a versatile unit which can be conveniently used in a process simulator. The solution procedure allows analytical calculation of sensitivities. The membrane module has been implemented and tested in an external process simulator, OPTISIM, which is based on the equation-oriented approach. The cost optimization features of OPTISIM have then been used to investigate hybrid schemes for CO pretreatment of steam reformer gas. The traditional cold box has been modified with a membrane unit and the results of the cost optimization calculations are presented.