Alcohol Synthesis from Syngas over K2CO3/CoS/MoS2 on Activated Carbon

Supported K₂CO₃/Co–MoS₂ on activated carbon was prepared by a co-impregnation technique and has been characterized by X-ray diffraction (XRD) and BET. Active ingredients ranged from 39 to 66% and included molysulfide and cobalt sulfide. XRD analysis indicates that cobalt and molybdenum sulfides are found in the Co₃S₄ and Co₉S₈ phases. These catalysts were performance tested in a fixed-bed reactor under higher alcohol synthesis conditions, 2000–2400 psig and 270–330°C. Active chemicals on the carbon extrudates decreased the surface area dramatically, as measured by BET. Surprisingly, at the high level of active chemicals, alcohol productivity and selectivity were decreased. An increase in the reaction temperature led to a decrease in the selectivity of methanol and an increase in selectivity of hydrocarbons. Total alcohol productivity was also increased as gas hourly space velocity (GHSV) was increased. Co₉S₈ may play a role in the catalyst aging process. In prolonged reaction periods (140 h), sulfur is lost from the surface, possibly as H₂S. The quantity of Co₉S₈ on the surface appears to increase as the catalyst ages.     

Polyethylene glycol as an efficient and reusable solvent medium for the synthesis of thiohydantoins using K2CO3 as catalyst

Polyethylene glycol was found to be an inexpensive, non-toxic, recyclable and an effective medium for the synthesis of thiohydantoin derivatives in the presence of K₂CO₃ as the catalyst. The procedure is operationally simple and environmentally benign.     

Preparation and characterization of gel polymer electrolyte based on PVA-K2CO3

ABSTRACT

In this study, electrolyte materials were synthesized by mixing a highly conducting salt (K₂CO₃) with the poly(vinyl alcohol) (PVA) in different proportions (from 10 to 50 wt.%). The synthesized electrolyte was characterized using Fourier transform infrared (FTIR) spectroscopy, field-emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) for their functional groups, morphology, thermal stability, glass transition temperature (T_g ), ionic conductivity, and potential window, respectively. Characterization results show that the complex formation between PVA and K₂CO₃ salt has been established by FTIR spectroscopic study, which indicates the detailed interaction between PVA and the salts in PVA-K₂CO₃ composites while the amorphous nature of the electrolyte after incorporation of the salts has been confirmed by FESEM analysis. Similarly, TGA and DSC analysis revealed that both decomposition temperature and T_g of the synthesized electrolytes decrease with the addition of K₂CO₃ due to the strong plasticizing effect of the salt. The results confirm that the electrolytes have sufficient thermal stability for supercapacitor operation, as well as an amorphous phase to effectively deliver high ionic conductivity. The highest ionic conductivity of 4.53 × 10^?3 S cm^?1 at 373 K and potential window of 2.7 V was exhibited by PK30 (30 wt.% K₂CO₃), which can be considered as high value for solid-state electrolytes which are superior to those electrolytes from PVA salts earlier reported. The results similarly show that the prepared electrolyte is temperature-dependent as conductivity increase with increase in temperature. Based on these properties, it can be imply that the PVA-K₂CO₃ gel polymer electrolyte (GPE) could be a promising electrolyte candidate for EDLC applications. The results indicate that the PVA-K₂CO₃ as a new electrolyte material has great potential in practical applications of portable energy-storage devices.     

Hydrotalcites for adsorption of CO2 at high temperature

Adsorption of carbon dioxide by hydrotalcites was investigated by using a gravimetric method at 450 ‡C. Hydrotalcites possessed higher adsorption capacity of CO₂ than other basic materials such as MgO and Al₂O₃. Two different preparation methods of hydrotalcite with varying Mg/Al ratio were employed to determine their effects on the adsorption capacity of CO₂. In addition, varying amounts of K₂CO₃ were impregnated on the hydrotalcite to further increase its adsorption capacity of CO₂. The hydrotalcite prepared by the high supersaturation method with Mg/Al=2 showed the most favorable adsorption-desorption pattern with high adsorption capacity of CO₂. K₂CO₃ impregnation on the hydrotalcite increased the adsorption capacity of CO₂ because it changed both the chemical and the physical properties of the hydrotalcite. The optimum amount of K₂CO₃ impregnation was 20 wt%. The hydrotalcite prepared by the high supersaturation method with Mg/Al=2 and 20 wt% K₂CO₃ impregnation has the highest adsorption capacity of CO₂ with 0.77 mmol CO₂/g at 450 ‡C and 800 mmHg.     

Comparing Molecular Mechanisms in Solar NH3 Production and Relations with CO2 Reduction

Molecular mechanisms for N₂ fixation (solar NH₃) and CO₂ conversion to C2+ products in enzymatic conversion (nitrogenase), electrocatalysis, metal complexes and plasma catalysis are analyzed and compared. It is evidenced that differently from what is present in thermal and plasma catalysis, the electrocatalytic path requires not only the direct coordination and hydrogenation of undissociated N₂ molecules, but it is necessary to realize features present in the nitrogenase mechanism. There is the need for (i) a multi-electron and -proton simultaneous transfer, not as sequential steps, (ii) forming bridging metal hydride species, (iii) generating intermediates stabilized by bridging multiple metal atoms and (iv) the capability of the same sites to be effective both in N₂ fixation and in CO_x reduction to C2+ products. Only iron oxide/hydroxide stabilized at defective sites of nanocarbons was found to have these features. This comparison of the molecular mechanisms in solar NH₃ production and CO₂ reduction is proposed to be a source of inspiration to develop the next generation electrocatalysts to address the challenging transition to future sustainable energy and chemistry beyond fossil fuels.     

Dehydrogenation of Propane in the Presence and Absence of CO2 Over β-Ga2O3 Supported Chromium Oxide Catalysts

The dehydrogenation of propane to propene in the presence and absence of CO₂ over β-Ga₂O₃ supported chromium oxide catalysts has been studied. The effect of chromium content and feed composition on the dehydrogenation of propane has been investigated. It has been found that deposition of chromium oxide enhances the dehydrogenation activity and resistance to coke deposition. Moreover, it has been shown that CO₂ promotes the dehydrogenation of propane above 848 K. At that temperature in the presence of CO₂ both the yield of propene and conversion of propane were higher than in the inert gas atmosphere.     

Adsorption of CH3 and its reactions with CO2 over TiO2

The adsorption, decomposition of CH₃ and its reactions with CO₂ were followed by means of Fourier transform infrared spectroscopy combined with mass spectrometry. Methyl radicals were produced by the pyrolysis of azomethane. Absorption bands, observed at room temperature adsorption, were attributed to adsorbed CH₃ and CH₃O species. The decomposition of adsorbed CH₃ in vacuum started above 400 K and was accelerated by CO₂. In the study of the interaction of methane with titania, activated in different ways, we found no convincing spectroscopic evidence for the activation of methane at 300 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of supports on catalytic activity of chromium oxide-based catalysts in the dehydrogenation of propane with CO2

Dehydrogenation of propane in the presence and absence of CO₂ over CrO_x/SiO₂ and CrO_x/Al₂O₃ catalysts with Cr loading between 0.7–20.4 wt% was discussed. It was found that the nature of support strongly effects on the catalytic performance in the dehydrogenation with CO₂. Over the CrO_x/SiO₂ catalyst CO₂ enhance the propene yield, whereas over the CrO_x/Al₂O₃ catalyst the yield and selectivity of propene in the presence of CO₂ strongly decrease. The effect of steam on catalytic performance of the tested catalysts was also discussed.     

A Fourier-transform infrared study of CO2 and CO2/H2 interactions with caesium-doped copper catalysts

FTIR spectra are reported of CO₂ and CO₂/H₂ on a silica-supported caesium-doped copper catalyst. Adsorption of CO₂ on a “caesium”/silica surface resulted in the formation of CO₂ ⁻ and complexed CO species. Exposure of CO₂ to a caesium-doped reduced copper catalyst produced not only these species but also two forms of adsorbed carboxylate giving bands at 1550, 1510, 1365 and 1345 cm⁻¹. Reaction of carboxylate species with hydrogen at 388 K gave formate species on copper and caesium oxide in addition to methoxy groups associated with caesium oxide. Methoxy species were not detected on undoped copper catalyst suggesting that caesium may be a promoter for the methanol synthesis reaction. Methanol decomposition on a caesium-doped copper catalyst produced a small number of formate species on copper and caesium oxide. Methoxy groups on caesium oxide decomposed to CO and H₂, and subsequent reaction between CO and adsorbed oxygen resulted in carboxylate formation. Methoxy species located at interfacial sites appeared to exhibit unusual adsorption properties.     

Pressure-Swing Adsorption Separation of H2S from CO2 with Molecular Sieves 4A, 5A,and 13X

The separation of bulk quantities of H₂S from CO₂ was investigated through a series of pressure-swing adsorption experiments utilizing 4A, 5A, and 13X molecular sieves. High selectivity of H₂S over CO₂ was encountered for all sieves, particularly for the 13X and 5A. Practically pure CO₂ was produced in the adsorption stage with fresh 5A and 13X sieves, at high product recovery rates. Efficient H₂S purification was obtained with fresh 5A and regenerated 4A zeolites. The experimental results were in line with theoretical predictions of the literature.     

Methanol Synthesis from CO2 Using Skeletal Copper Catalysts Containing Co-precipitated Cr2O3 and ZnO

Skeletal Cu-Cr₂O₃-ZnO catalysts have been prepared by leaching CuAl₂ alloy particles at 273 K using 6.1 M aqueous NaOH solutions containing sodium chromate (Na₂CrO₄) and sodium zincate (Na₂Zn(OH)₄). The presence of sodium chromate and sodium zincate in the caustic solution was found to affect the pore structure and surface areas of the resulting catalysts. Both BET and Cu surface areas were increased by increasing the concentration of Na₂CrO₄ and of Na₂Zn(OH)₄.Increasing the Na₂CrO₄ level from 0 to 0.06 M in a 6.1M NaOH solution containing 0.2M Na₂Zn(OH)₄ caused the content of ZnO in the catalyst to decrease from 8.8 to 3.0 wt% whilst increasing the Cr₂ O₃ content from 0 to 1.7 wt%, indicating that the presence of Na₂CrO₄ in the leach liquor not only resulted in deposition of a Cr compound but also inhibited precipitation of zinc hydroxide onto skeletal Cu catalysts. On the other hand, increasing the concentration of Na₂Zn(OH)₄ from 0 to 0.6 M in a 6.1 M NaOH solution containing 0.008 M Na₂ CrO₄ resulted in increasing the ZnO loading from 0 to 8.9wt% with an almost constant content of Cr₂ O₃ (1.3 ± 0.2%) in the catalysts, revealing that sodium zincate only led to precipitation of zinc hydroxide and did not suppress Cr₂O₃ formation.Hydrogenation of CO₂ was studied using a gas mixture of 24% CO₂ in H₂ at a total pressure of 4MPa, space velocities up to 210000L kg^-1h^-1 and temperatures in the range 493-533K. The catalysts were found to be both highly active and selective for methanol synthesis. This study confirms the role of ZnO in promoting the activity of copper for methanol synthesis from CO₂ and improving the selectivity by inhibiting the reverse water-gas shift reaction. The role of Cr₂O₃ is to improve the structural development of high surface area skeletal copper.     

Development of new alumina-modified sorbents for CO2 sorption and regeneration at temperatures below 200 °C

A new regenerable alumina-modified sorbent was developed for CO₂ capture at temperatures below 200 °C. The CO₂ capture capacity of a potassium-based sorbent containing Al₂O₃ (KAlI) decreased during multiple CO₂ sorption (60 °C) and regeneration (200 °C) tests due to the formation of the KAl(CO₃)(OH)₂ phase, which could be converted into the original K₂CO₃ phase above 300 °C. However, the new regenerable potassium-based sorbent (Re-KAl(I)) maintained its CO₂ capture capacity during multiple tests even at a regeneration temperature of 130 °C. In particular, the CO₂ capture capacity of the Re-KAl(I)60 sorbent which was prepared by the impregnation of Al₂O₃ with 60 wt.% K₂CO₃ was about 128 mg CO₂/g sorbent. This excellent CO₂ capture capacity and regeneration property were due to the characteristics of the Re-KAl(I) sorbent producing only a KHCO₃ phase during CO₂ sorption, unlike the KAlI30 sorbent which formed the KHCO₃ and KAl(CO₃)(OH)₂ phases even at 60 °C. This result was explained through the structural effect of the support containing the KAl(CO₃)(OH)₂ phase which was prepared by impregnation of Al₂O₃ with K₂CO₃ in the presence of CO₂.     

SOLUBILITY OF CO2AND H2S IN A MIXED SOLVENT

Mixed solvents are a combination of chemical and physical solvents and have some advantages over traditional treating solvents for the removal of acid gases from gas streams. The solubility of H₂S and CO₂in a mixed solvent consisting of AMP (2-amino-2-methyl-l-propanol), sulfolane, and water has been measured at 40 and 100°C at partial pressures of the acid gas to 6000 kPa. The solubility in the mixed solvent was compared with the solubility in an aqueous solution of equivalent amine concentration. At solution loadings less than 1 mol acid gas/mol amine, the solubility of the acid gas is lower in the mixed solvent than in the corresponding amine solvent. At higher loadings, the trend is reversed and the solubility is greater in the mixed solvent. The results are rationalized in terms of the effect of the physical solvent component on the chemical reaction and physical vapor-liquid equilibria. The solubility model of Deshmukh and Mather was used to correlate the data.     

Hydrothermal synthesis of Ag2CO3-TiO2 loaded reduced graphene oxide nanocomposites with highly efficient photocatalytic activity

Abstract

In this work, a growth of Ag₂CO₃-TiO₂ NPs over GO sheets and reduction of GO were simultaneously achieved by the hydrothermal process at 130 °C for 4?h. The photocatalytic activity of the as-prepared Ag₂CO₃-TiO₂ NPs decorated reduced graphene oxide (Ag₂CO₃-TiO₂/rGO) composite was studied by the degradation of methylene blue (MB) solution under visible light irradiation. A remarkable enhancement in the photocatalytic activity of the TiO₂ was achieved after sensitizing with Ag₂CO₃ and loading in rGO sheets which is attributed to the reduced charge recombination, enhanced dye adsorption, and the improvement in the light harvesting capacity of the composite.     

EFFICIENT DESULFURIZATION IN O2/CO2 COMBUSTION: DEPENDENCE ON COMBUSTION CONDITIONS AND SORBENT PROPERTIES

Based on experiments on desulfurization, CaSO₄ decomposition, and a system approach using theoretical analysis, efficient in-furnace desulfurization in O₂/CO₂ combustion was investigated. The influence of combustion conditions and sorbent properties on system desulfurization efficiency was clarified. The global desulfurization efficiency was found to increase with O₂ purity. The global desulfurization efficiency in a dry recycle was higher than that in a wet recycle. The global efficiency of in-furnace desulfurization decreased with initial O₂ concentration. As the temperature increased, the global desulfurization efficiency increased first and then decreased due to the decomposition of CaSO₄. In the temperature range investigated, the global desulfurization efficiency in O₂/CO₂ coal combustion was much higher than that of conventional coal combustion in air. The global desulfurization efficiency decreased with sorbent size. When the particle radius decreased to one quarter, the global desulfurization efficiency doubled, becoming as high as 80%. The global desulfurization efficiency was very different among the three sorbents investigated, whether in O₂/CO₂ combustion or in conventional air combustion. The global desulfurization efficiency increased in the order of Ca(OH)₂, scallop, and limestone in O₂/CO₂ combustion, but in the order of scallop, Ca(OH)₂, and limestone in conventional air combustion. Nevertheless, all three sorbents demonstrated much higher desulfurization efficiency in O₂/CO₂ combustion than in conventional air combustion.     

Improvement of Pt/ZrO2 by CeO2 for high pressure CH4/CO2 reforming

CH₄/CO₂ reforming over Pt/ZrO₂, Pt/CeO₂ and Pt/ZrO₂ with CeO₂ was investigated at 2 MPa. Pt/ZrO₂, which shows stable activity under 0.1 MPa, and Pt/CeO₂ showed gradual deactivation with time at the high pressure. The deactivation was suppressed drastically on Pt/ZrO₂ with CeO₂ prepared by different impregnation order (co-impregnation of Pt and CeO₂ on ZrO₂, and consecutive impregnation of Pt and CeO₂ on ZrO₂). The amount of coke deposition was found insignificant and similar among all the catalysts (including Pt/ZrO₂ and Pt/CeO₂). Catalytic activity after the reaction for 24 h was in agreement with Pt particle size after the reaction for same period, indicating that the difference of the catalytic stability is mainly dependent on the extent of Pt aggregation through catalyst preparation, H₂ reduction, and the CH₄/CO₂ reforming. Pt aggregation and the amount of coke deposition were least pronounced on (Pt–Ce)/ZrO₂ prepared by impregnation of CeO₂ on Pt/ZrO₂ and the catalyst showed highest stability.     

A study of the oxidative coupling of methane over SrO-La2O3/CaO catalysts by using CO2 as a probe

20%SrO-20%La₂O₃/CaO catalyst (SLC-2), prepared by impregnation, has shown 18% CH₄ conversion and 80% C₂-selectivity for the oxidative coupling of methane (OCM) at 1073–1103 K with CH₄O₂ molar ratio=91 and total flow rate of 100 ml/min. Addition of SrO onto La₂O₃/CaO (LC) catalyst strengthens the surface basicity and leads to an increase in CH₄ conversion and C₂-selectivity. Meanwhile, the reaction temperature required to obtain the highest C₂-yield increases with increasing SrO content. The formation of carbonate on the catalyst surface is the main reason for the deactivation of LC and SLC catalysts. If the amount of CO₂ added into the feed is appropriate and the reaction temperature is high enough, there is no deactivation at all. In such case, the added CO₂ will suppress the formation of CO₂ produced via the OCM reaction, therefore, improves the C₂-selectivity. The FT-IR spectra of CO₂ adspecies recorded at different temperatures show that CO₂ interacts easily with the catalyst surface to form different carbonate adspecies. Unidentate carbonate is the main CO₂ adspecies formed on the catalyst surface. On the LC catalyst surface, the unidentate carbonate was first formed on Ca²⁺ cations at room temperature. If the temperature is higher than 473 K, it will form on La³⁺ cations. On the SLC catalyst surface, if the temperature is lower than 573 K, only the unidentate carbonate formed on Ca²⁺ cations could be observed. When the temperature is higher than 673 K, it will then form on Sr²⁺ cations. This suggests that the unidentate carbonate can migrate on the LC and SLC catalyst surface on one hand, and on the other hand, that the surface composition of SLC catalysts is dynamic in nature. On the basis of both the decomposition temperatures of the carbonate species, and the temperature dependence of the value which is the difference of symmetric and asymmetric stretching frequencies of surface carbonates, the in situ FT-IR technique offered two approaches to measure the surface basicity of the SLC catalyst. The results thus obtained are in good agreement with that of CO₂-TPD. The role of the surface basicity of the SLC catalyst is also discussed.     

CO Adsorbed Infrared Spectroscopy Study of Ni/Al2O3 Catalyst for CO2 Reforming of Methane

CO adsorbed infrared spectroscopy study was conducted in this work in order to better understand the significantly improved anti-coke performance of Ni/Al₂O₃ catalyst obtained via argon glow discharge plasma treatment. The present study revealed a significant decrease of linear to bridge (L/B) adsorbed CO for glow discharge plasma treated Ni/Al₂O₃, compared to that for untreated Ni/Al₂O₃, indicating an enhancement of close packed plane concentration. This structure change leads to lower methane turnover frequency (TOF) and better balance of carbon formation-gasification, resulting in better anti-coke property of Ni/Al₂O₃ for CO₂ reforming of methane.     

Modification of ABS Membrane by PEG for Capturing Carbon Dioxide from CO2/N2 Streams

Carbon dioxide capture and storage (CCS) has been propounded as an important issue in greenhouse gas emissions control. In this connection, in the present article, the advantages of using polymeric membrane for separation of carbon dioxide from CO₂/N₂ streams have been discussed. A novel composition for fabrication of a blend membrane prepared from acrylonitrile-butadiene-styrene (ABS) terpolymer and polyethylene glycol (PEG) has been suggested. The influence of PEG molecular weight (in the range of 400 to 20000) on membrane characteristics and gas separation performance, the effect of PEG content (0–30 wt%) on gas transport properties, and the effect of feed side pressure (ranging from 1 to 8 bar) on CO₂ permeability have been studied. The results show that CO₂ permeability increases from 5.22 Barrer for neat ABS to 9.76 Barrer for ABS/PEG20000 (10 wt%) while the corresponding CO₂/N₂ selectivity increases from 25.97 to 44.36. Furthermore, it is concluded that this novel membrane composition has the potential to be considered as a commercial membrane.     

Study of the Supported K2MoO4 Catalyst for Methanethiol Synthesis by One Step from High H2S-Containing Syngas

ESR and XPS are used to study the Mo-based catalysts MoO₃/K₂CO₃/SiO₂ and K₂MoO₄/SiO₂ prepared with two kinds of precursors, (NH₄)₆Mo₇O₂₄4H₂O and K₂MoO₄. The catalytic properties of the catalysts for methanethiol synthesis from high H₂S-containing syngas are explored. The activity assay shows that the two catalysts have much the same activity for the reaction. By the ESR characterization of both functioning catalysts, the resonant signals of oxo-Mo(V) (g=1.93), thio-Mo(V) (g=1.98) and S (g=2.01 or 2.04) can be detected. In the catalyst MoO₃/SiO₂ modified with K₂CO₃, as increasing amounts of K₂CO₃ are added, the content of oxo-Mo(V) increases, but thio-Mo(V) decreases. The XPS characterization indicates that Mo has mixed valence states of Mo⁴⁺, Mo⁵⁺ and Mo⁶⁺, and that S includes three kinds of species: S^2– (161.5 eV), [S–S]^2– (162.5 eV) and S⁶⁺ (168.5 eV). Adding K₂CO₃ promoter to the catalysts, the Mo species of high valence state is easily sulphided and reduced to Mo₂S and oxo-M(V), and the derivation of [S–S]^2– and S^2– species from S is promoted simultaneously. The methanethiol synthesis is favored if the mole ratio of (Mo⁶⁺ + Mo⁵⁺)/Mo⁴⁺ 0.8 and S^2–/[S–S]^2– is kept at a value of about 1.