Porous Carbon Spheres Derived from Hemicelluloses for Supercapacitor Application

With the increasing demand for dissolving pulp, large quantities of hemicelluloses were generated and abandoned. These hemicelluloses are very promising biomass resources for preparing carbon spheres. However, the pore structures of the carbon spheres obtained from biomass are usually poor, which extensively limits their utilization. Herein, the carbon microspheres derived from hemicelluloses were prepared using hydrothermal carbonization and further activated with different activators (KOH, K₂CO₃, Na₂CO₃, and ZnCl₂) to improve their electrochemical performance as supercapacitors. After activation, the specific surface areas of these carbon spheres were improved significantly, which were in the order of ZnCl₂ > K₂CO₃ > KOH > Na₂CO₃. The carbon spheres with high surface area of 2025 m²/g and remarkable pore volume of 1.07 cm³/g were achieved, as the carbon spheres were activated by ZnCl₂. The supercapacitor electrode fabricated from the ZnCl₂-activated carbon spheres demonstrated high specific capacitance of 218 F/g at 0.2 A/g in 6 M KOH in a three-electrode system. A symmetric supercapacitor was assembled in 2 M Li₂SO₄ electrolyte, and the carbon spheres activated by ZnCl₂ showed excellent electrochemical performance with high specific capacitance (137 F/g at 0.5 A/g), energy densities (15.4 Wh/kg), and good cyclic stability (95% capacitance retention over 2000 cycles).     

Conversion of Poly(Ethylene Terephthalate) Waste into Activated Carbon: Chemical Activation and Characterization

Due to its high carbon content, low impurities, low cost and easy availability, poly(ethylene terephthalate) (PET) waste is considered as a suitable precursor for the production of activated carbon. The chemical activation of PET wastes using different chemical agents such as H₃PO₄, H₂SO₄, ZnCl₂, and KOH was investigated. KOH‐ and ZnCl₂‐activated PET were found to be the best choices for the adsorption of small and large molecules. The capacities of the adsorbents towards I₂, methylene blue, N₂, CH₄, and CO₂ followed the order KOH‐PET >H₃PO₄‐PET > ZnCl₂‐PET > H₂SO₄‐PET; however, in the molasses uptake and selective adsorption of CO₂ compared to CH₄, ZnCl₂‐PET performed better than the other adsorbents.     

Well-Defined Highly Active Heterogeneous Catalyst System for the Coupling Reactions of Carbon Dioxide and Epoxides

The poly(4-vinylpyridine)-supported zinc halide catalysts, prepared from a reaction of ZnX₂ and poly(4-vinylpyridine), exhibit high selectivity and activity for the coupling reaction of CO₂ and ethylene oxide or propylene oxide. Solid NMR characterization of the poly(4-vinylpyridine)-supported ZnBr₂ catalyst and its reaction product with propylene oxide and/or CO₂ show that a pyridinium-alkoxy ion-bridged zinc bromide complex is functioning as an active species, such as in the homogeneous catalysis with L₂ZnBr₂ (L = pyridine or methyl-substituted pyridine).     

emf Studies of zinc halides ln concentrated aqueous NH4NO3CA(NO3)2 solutions

The formation constants of the species ZnC⁺, ZnCl₂, ZnBr⁺ and ZnBr₂ were determined from emf measurements in suitable concentration cells. Mixtures of NH₄NO₃Ca(NO₃)₂ with a molar ratio 0.844/0.156 containing variable amounts of water (from 0 to 1.2 moles per mol of salt) were used as a solvent. The bromide complexes were found to be more stable than the chloride complexes in the anhydrous melt, while the opposite was found in the concentrated aqueous solutions. The results are discussed on the basis of models for chemical equilibria in molten salts and aqueous melts.     

Incorporation of Metal Ions into Silica-Grafted Imidazolium-Based Ionic Liquids to Efficiently Catalyze Cycloaddition Reactions of CO<Subscript>2</Subscript> and Epoxides

Abstract  

A variety of imidazolium-based ionic liquids (ILs) have been widely developed to effectively catalyze the cycloaddition reactions of CO₂ and epoxides. To further improve the catalytic performance of those IL catalysts, we incorporated various metal chlorides (CoCl₂, NiCl₂, CuCl₂, ZnCl₂, and MnCl₂) into silica-grafted 1-methyl-3-[(triethoxysilyl)propyl] imidazolium chloride to produce a series of heterogeneous catalysts. Catalytic reaction tests demonstrated that the incorporation of such metal ions can significantly enhance the catalytic reactivity of the silica-grafted ILs towards cycloaddition reactions of CO₂ and epoxides that produce cyclic carbonates in solvent-free conditions. In addition, the effects on the catalytic reactivity of reaction parameters including reaction time, reaction temperature and CO₂ pressure were investigated.     

Synthesis of diphenyl carbonate from compressed carbon dioxide and phenol without use of organic solvent

Diphenyl carbonate (DPC) was synthesized from CO₂ and phenol catalyzed by Lewis acids. Compressed CO₂ was used as reactant and solvent. It was found that the conversion of phenol and the yield of DPC are dependent on the metal center of Lewis acids, and zinc halides have better catalytic performance than aluminum halides. The reaction of CO₂ with phenol is sensitive to pressure, temperature, and reaction time, and it is improved using triethylamine as acid acceptor. A 31.7% DPC yield was obtained under optimized reaction conditions: 9 MPa at 100 °C for 3 h.     

Highly selective synthesis of dimethyl carbonate from urea and methanol catalyzed by ionic liquids

Direct synthesis of dimethyl carbonate from methanol and urea using ionic liquids, such as Et₃NHCl–FeCl₃, Et₃NHCl–ZnCl₂, Et₃NHCl–CuCl₂, Et₃NHCl–SnCl₂ and emimBr–ZnCl₂, as catalysts were investigated. Among the ionic liquids, Et₃NHCl–ZnCl₂ or emimBr–ZnCl₂ exhibited higher activity for the synthetic reaction and surprisingly high selectivity to DMC. The effects of the various reaction conditions, i.e. reaction temperature, molar ratio of methanol to urea, and amount and composition of catalysts, on the synthesis of DMC were discussed in a systematic way. The reaction mechanism and the reasons why raised activity and high selectivity of the catalyst are maintained were explored.     

NaY ZEOLITE–SUPPORTED POTASSIUM SALT CATALYSTS FOR DIPROPYL CARBONATE SYNTHESIS FROM TRANSESTERIFICATION ROUTE

The catalytic synthesis of dipropyl carbonate (DPC) from transesterification of dimethyl carbonate and propyl alcohol over NaY zeolite–supported potassium salt catalysts was investigated at atmospheric pressure. K₂CO₃/NaY and KOH/NaY catalysts exhibited better catalytic activity than other potassium salt catalysts. From infrared resonance (IR), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), it could be concluded that K₂CO₃/NaY and KOH/NaY catalysts showed preferable order degree of zeolite structure, which was associated with higher dispersal of the active species K₂O and extraction for part of the non-framework silicon and aluminum of the system after alkali treatment. And the partial extraction of the non-framework silicon and aluminum allowed the reactants and the products to pass through the pore of the catalysts easily and facilitated catalytic performance for DPC synthesis.     

Carbon dioxide pressure induced heterogeneous and homogeneous Heck and Sonogashira coupling reactions using fluorinated palladium complex catalysts

The Heck reaction of iodobenzene and methyl acrylate was investigated with CO₂-philic Pd complex catalysts having fluorous ponytails and the organic base triethylamine (Et₃N) in the presence of CO₂ under solventless conditions at 80 °C. The catalysts are not soluble in the organic phase in the absence of CO₂ and the reaction occurs in a solid-liquid biphasic system. When the organic liquid mixture is pressurized by CO₂, CO₂ is dissolved into the organic phase and this promotes the dissolution of the Pd complex catalysts. As a result, the Heck reaction occurs homogeneously in the organic phase, which enhances the rate of reaction. This positive effect of CO₂ pressurization competes with the negative effect that the reacting species are diluted by an increasing amount of CO₂ molecules dissolved. Thus, the maximum conversion appears at a CO₂ pressure of around 4 MPa under the present reaction conditions. The catalysts are separated in the solid granules by depressurization and are recyclable without loss of activity after washing with n-hexane and/or water. When the washing is made with hexane alone, the catalytic activity tends to increase on the repeated Heck reactions, probably due to the accumulation of such a base adduct as Et₃NHI on the catalysts. When the washing is further made with water, however, the base adduct is taken off from the catalysts and they show similar activity levels in the repeated runs. The potential of CO₂ pressure tunable heterogeneous/homogeneous reaction system has also been investigated for Sonogashira reactions of iodobenzene and phenylacetylene under similar conditions.     

Copolymerization of carbon dioxide and propylene oxide with neodymium trichloroacetate-based coordination catalyst

The copolymerizations of carbon dioxide (CO₂) and propylene oxide (PO) were performed using new ternary rare-earth catalyst. It was found that the rare-earth coordination catalyst consisting of Nd(CCl₃COO)₃, ZnEt₂ and glycerine was very effective for the copolymerization of PO with CO₂. The effects of the relative molar ratio and addition order of the catalyst components, copolymerization reaction time, and operating pressure as well as temperature on the copolymerization were systematically investigated. At an appropriate combination of all variables, the yield could be as high as 6875 g/mol Nd per hour at 90 °C in a 8 h reaction period.     

Relationship between Pyrite in the Precursor and the Pore Structure of High‐Surface Area Activated Carbon Preparations

High‐surface area activated carbons (HAC) were prepared from analogous sulfur‐containing precursors by using KOH chemical activation. The relationship between pyrite (FeS₂) in the precursor and the pore structure of the as‐prepared HAC was investigated comprehensively. The results suggest that FeS₂ in the precursor reacts with KOH, producing K₂SO₄, K₂S₂O₃, K₂S, thioether (R‐S‐R'), and Fe₃O₄, which reduce the actual amount of KOH used to develop the porosity. As a result, the existence of the by‐product Fe₃O₄ further clarifies that FeS₂ in the precursor can consume some amount of KOH, which leads to the decrease in the specific surface area and pore volume of HAC. Interestingly, part of the inorganic sulfur from FeS₂ in the precursor can be transformed into organic sulfide R‐S‐R'.     

Pd[tBuNH(S)NHP(O)(OiPr)2-S]2Cl2 Complex as Air- and Moisture-Stable Catalyst for Palladium Catalyzed Suzuki Cross-Coupling Reaction

A highly efficient Suzuki cross-coupling reaction between phenyl bromide and phenylboronic acid catalyzed by the palladium complex Pd[tBuNH(S)NHP(O)(OiPr)₂-S]₂Cl₂ in acetonitrile, toluene, THF or DMF has been investigated. The bases we have employed for this reaction were Na₂CO₃, K₂CO₃ or Cs₂CO₃. It was established that using DMF and K₂CO₃ at 100 °C shows excellent yields of the product at the catalyst amount of 0.1 mmol. The cross-coupling reactions of iodo- and chloro-benzene with phenylboronic acid were also investigated. The influence of the halide nature was as expected.     

Suzuki Cross-Coupling Reaction Catalyzed by the Palladium Complex Pd[N-MorphC(S)NP(O)(OiPr)2-O,S]2

Suzuki cross-coupling reaction between phenyl bromide and phenylboronic acid, catalyzed by the palladium complex Pd[N-MorphC(S)NP(O)(OiPr)₂-1,5-O,S)]₂ in acetonitrile, toluene, THF or DMF has been investigated. Bases employed for the reaction were Na₂CO₃, K₂CO₃ or Cs₂CO₃. Varying largely the experimental conditions we found that excellent yields of the product were obtained using toluene and K₂CO₃ at 100 °C at the catalyst amount of 0.02 mmol.     

Steam gasification of coal char using alkali and alkaline-earth metal catalysts

The catalytic effect of alkali and alkaline-earth metal salts or oxides on the gasification of Chinese Linnancang coal char was investigated at atmospheric pressure and a temperature of 800 °C. The order of catalytic activity is K₂SO₄ or K₂CO₃ Na₂CO₃ KCl NaCl CaCl₂ or CaO. The effect of amount of catalysts added on catalytic activity was studied. The distribution of K₂CO₃ or CaO catalysts on the coal char surface for different methods of catalyst loading was examined by an electron microprobe analyser. The relation between the catalytic activity and distribution of catalysts were illustrated. The loading method of K₂CO₃ has little effect on its catalytic activity but that of CaO influences the activity significantly.     

The Influence of Supercritical Carbon Dioxide (SC‐CO2) on Electrolytes and Hydrogenation of Soybean Oil

The electrochemical hydrogenation of soybean oil with supercritical carbon dioxide (SC‐CO₂) has been studied to seek ways for substantial reduction of the trans fatty acids (TFA). The solubility of CO₂ in electrolytes and the conductivity of electrolytes were investigated using a self‐made electrochemical hydrogenation reactor. The optimum hydrogenation parameters were assessed. Both the solubility of CO₂ in electrolytes and the conductivity of electrolytes increased with increasing CO₂ pressure. When the pressure reached a critical point of CO₂, the solubility of CO₂ expressed as a mole fraction was 0.42 in cathode electrolyte and 0.1 in anode electrolyte. At 8 MPa, the conductivity of electrolytes was 1.5 times higher than that at 2 MPa. When the pressure was higher than the critical point of CO₂, the solubility of CO₂ in electrolytes and the conductivity of electrolytes reached a stable value. The optimum condition for electrochemical hydrogenation of soybean oil in SC‐CO₂ were reaction pressure (8 MPa), reaction temperature (48 °C), current (125 mA), agitation speed (300 rpm), and reaction time (8 h). Fatty acid profile, iodine value, and TFA content were evaluated at the optimum parameters. This investigation showed that the electrochemical hydrogenation of soybean oil in SC‐CO₂ was improved. The reaction time was shortened by 4 h, and TFA content was reduced by 35.8% compared to traditional hydrogenation process.     

SiCl3CCl3 as a novel precursor for chemical vapor deposition of amorphous carbon films

Amorphous carbon films, characterized by XRD, AFM, SEM and Raman, were deposited from SiCl₃CCl₃ on quartz substrates at 773-1273 K by low pressure chemical vapor deposition using a hot-wall reactor. XPS studies showed that the films grown at 773 K contained 90% C and 10% Cl, while the films grown at 1273 K contained 100% C. SiCl₄, CCl₄ and Cl₂CCCl₂ were detected by on-line FT-IR studies. The extrusion of dichlorocarbene, :CCl₂, from SiCl₃CCl₃ should provide the source of carbon in the reaction. On Si substrates, an etching process at the film-substrate interface assisted the lift-off of the films from the substrates. The C films curled and formed rolls.     

The absorption of CO2 by amine-potash solutions

CO₂ has been absorbed in a stirred vessel into aqueous solutions of MEA and DEA containing K₂CO₃, K₂SO₄ and Na₂SO₄ at 25° and 11°C. While electrolytes in general appear to increase the rate of reaction between CO₂ and both MEA and DEA, K₂CO₃ increases the rate of reaction of DEA much more than that of MEA. The addition of K₂CO₃ to solutions of DEA increases the absorption rate, in spite of the decrease in the solubility and diffusivity of CO₂. The observations help to explain why DEA is an effective promoter for the absorption and desorption of CO₂ by hot, concentrated potash solutions.     

Catalytic combustion of trichloroethene over Ru/Al2O3: Reaction mechanism and kinetic study

The performance of 0.5% Ru/Al₂O₃ for the deep oxidation of trichloroethene (1000–2500 ppmV, WHSV = 55 h⁻¹) in air was studied in this work. Experiments were carried out both at dry and wet (20,000 ppmV of H₂O) conditions. Catalytic performance was studied in terms of activity and selectivity for the different reaction products (CO₂, HCl, Cl₂, C₂Cl₄, CCl₄ and CHCl₃). Both the activity and the selectivity for total combustion are higher than other catalysts suggested in the literature for this process (especially Pd and Pt).The main organic by-products are CCl₄ and CHCl₃, whereas in all the other catalysts tested in the literature, tetrachloroethene is the main organic by-product. This fact suggests that the mechanism of the combustion reaction, involving a double-bond scission, is essentially specific for this catalyst.Kinetic data was fit to a pseudo-first order kinetic expression, providing fairly good fit.     

CO2 Adsorption Kinetics of K2CO3/Activated Carbon for Low‐Concentration CO2 Removal from Confined Spaces

K₂CO₃ supported on activated carbon (K₂CO₃/AC) is a promising means to remove low‐concentration CO₂ from confined spaces. In this removal process, physical adsorption plays an important role but it is difficult to quantify the amount of CO₂ adsorbed when both H₂O and CO₂ are present. The linear driving force mass transfer model is adopted to study the CO₂ adsorption kinetic characteristics of K₂CO₃/AC by analyzing the experimental data. The effect of K₂CO₃ and H₂O on the adsorption of CO₂ in K₂CO₃/AC was also evaluated. K₂CO₃ loaded on the support is found to increase the mass transfer resistance but decrease the activation energy required for the physical adsorption process. The presence of water vapor is disadvantageous to achieve high physical adsorption capacity since it enhances the chemical sorption in the competitive dynamic sorption process.     

Activated Carbon Preparation from Lignin by H3PO4 Activation and Its Application to Gas Separation

Activated carbons were produced from corn straw lignin using H₃PO₄ as activating agent. The optimal activation temperature for producing the largest BET specific surface area and pore volume of carbon was 500 °C. The maximum BET specific surface area and pore volume of the resulting carbon were 820 m²g^–1 and 0.8 cm³g^–1, respectively. The adsorption isotherm model based on the Toth equation together with the Peng‐Robinson equation of state for the determination of gas phase fugacity provide a satisfactory representation of high pressure CO₂, CH₄ and N₂ adsorption. The kinetic adsorption results show that the breakthrough difference between CO₂ and CH₄ is not obvious, indicating that its kinetic separation performance is limited.