Abstract: The preparation of high-strength inorganic fibers by coal fly ash is an important method to achieve its high-value utilization. Due to high content of SiO2 and Al2O3 in coal fly ash, it is necessary that Ca-Fe flux should be added to decrease melting temperature of coal fly ash during homogenization of slag and avoid crystallization behavior during preparation of fibers. In this paper, the influence mechanism of Ca-Fe flux on the fusibility and crystallization behavior of coal fly ash under air atmosphere was investigated. The results show that calcium oxide (CaO) and iron oxide (Fe2O3) does not show synergistic fluxing effect on fusibility of coal fly ash under air atmosphere, moreover, the fluxing effect of CaO on fusibility is more obvious than that of Fe2O3. At high temperature, Fe2O3 cannot react with silicon-aluminum components to form low melting point minerals, while CaO is beneficial to transform refractory mullite into anorthite, which greatly reduces the melting point of fly ash. However, excess CaO (>30%) leads to formation of calcium feldspar, which increases melting point of fly ash obviously. During the cooling process, iron precipitates in the form of hematite while calcium precipitates in the form of anorthite, and the crystallization temperature of hematite is lower than that of anorthite. When content of CaO is 32.46%, the melting point of coal fly ash is the lowest, and there is no crystallization during the cooling process. Therefore, CaO is suitable to adjust fusibility and crystallization behavior of coal fly ash during preparation of inorganic fiber.
Abstract: The effects of oxidative torrefaction on the basic physicochemical, such as composition, torrefaction yield, chemical structure, and microstructure, and gasification properties of corn straw, were studied. The release and transformation of alkali metals during torrefaction and gasification of corn straw were also investigated. The results show that torrefaction can increase the fixed carbon content in corn straw effectively and decrease the values of H/C and O/C. Compared with inert atmosphere torrefaction, oxidative torrefaction has better quality improvement effects, and the best roasting atmosphere is 6% oxygen concentration. Combining H/C, O/C, mass yield and energy yield, it is found that the oxygen concentration of 6% during torrefaction is suitable. The concentration of CO, gas production rate, and gas calorific value of torrefied corn straw increased first and then decreased with the increase of oxygen concentration in the torrefaction atmosphere during gasification. The gasification characteristics were optimal at 6% oxygen concentration, with CO content of 14.73%, gas production rate of 1.09 L/g, and gas calorific value of 4.93 MJ/m3. The alkali metals were enriched in the corn straw during the torrefaction process. The conversion from water-soluble K to ion-exchanged K was also promoted, which helped produce more insoluble K in the gasification process. The oxidative torrefaction promoted the effect more pronounced. The results of the study can provide essential data and technical support for the technological promotion of oxidative torrefaction and gasification of biomass.
Abstract: Carbon nitride (g-C3N4) prepared using thermal condensation of urea was pretreated by H2O2/NH3·H2O and used as support to obtain Fe/g-C3N4 catalyst via impregnation method. The catalytic performance of the catalysts both before and after modification was investigated in CO hydrogenation. Combining detailed characterizations, such as XRD, SEM, TEM, FT-IR, TG, CO2-TPD, CO-TPD, H2-TPR, contact angle measurement, and N2 physical adsorption and desorption, we investigated the effects of surface pretreatment on the texture properties of Fe/g-C3N4 catalysts and the product distribution of CO hydrogenation. The results demonstrate that various pretreatment techniques have significant influences on the textural properties and catalytic performance of the catalysts. The prepared g-C3N4 with a typical honeycomb structure has strong interaction with highly dispersed Fe. Both before and after modification, the materials are hydrophilic, and the hydrophilicity is increased after treatment with H2O2 and NH3·H2O. Treatment with H2O2 enhances surface hydroxyl groups. NH3·H2O treatment improves surface amino groups, promotes CO adsorption, and facilitates the formation of Fe(NCN) phase. The surface basicity of all pretreated catalysts is enhanced. The water gas shift (WGS) reaction activity of the two-step modified catalyst Fe/AM-g-C3N4 was lower, and the CO2 selectivity in CO hydrogenation was reduced to 11.61%. Due to the enhanced basicity of Fe/AM-g-C3N4, the secondary hydrogenation ability of olefins was inhibited to obtain higher olefin selectivity with ${\rm{C}}_2^=-{\rm{C}}_4^=\;s \;{\rm{of}}$ 32.37% and an O/P value of 3.23.
Abstract: Improving the C2+ alcohols yield is highly desirable for the direct synthesis of higher alcohols from syngas. In this work, a series of highly dispersed K-modified NiMoS catalysts with different K contents on ZnAl-mixed oxide support were prepared by the combination of co-precipitation and impregnation method. And their performance in higher alcohols synthesis (HAS) from syngas was investigated. The results show that the introduction of K can modulate the stacking degree of MoS2 slabs, and improve the interaction between NiSx and NiMoS phases. The as-prepared catalyst is conducive to promote the insertion of CHx and non-dissociative CO in HAS, and effectively suppress the generation of hydrocarbons and CO2. The 0.6KNiMoS/ZnAl catalyst exhibits the most double-layer MoS2 slabs (33.7%) and highly synergetic effects between NiSx and NiMoS to achieve the total alcohols selectivity (69.8%) and space-time yield (78.6 mg/(g·h)) of C2+ alcohols.
Abstract: A series of Mo/Sn (1:20, molar ratio) catalysts were prepared by two-step hydrothermal synthesis method, and the effect of calcination temperature of tin precursors on the reaction performance of methanol oxidation to dimethoxymethane (DMM) was investigated. The crystal structure, surface properties, redox property and valence change of molybdenum species of the catalyst were characterized by XRD, Raman, FT-IR, XPS, NH3-TPD and H2-TPR. The results showed that Mo1Sn20-600℃Sn catalyst exhibited better performance than other catalysts, achieving DMM selectivity of 90% with methanol conversion of 30% at 140 ℃. From the characterization results, the surface properties of the tin precursors affected the structure of catalyst, the degree of molybdenum oxide dispersion and valence of molybdenum species, and further influenced the performance of the catalysts. The high temperature calcination of tin precursors is more favorable for the generation of Mo6+ in the Mo1Sn20 catalyst.
Abstract: Cu-Al spinel oxide as a sustained release catalyst gradually releases active metal Cu during the methanol steam reforming reaction, whose catalytic behavior depends strongly on the surface structure of the catalyst. In this context, Cu-Al spinel solid solution is synthesized by a solid phase ball milling method, followed by treating with acidic and basic solutions in order to modulate the surface composition and structure, thereby to further improve the catalytic performance. Nitric acid is effective for the removal of both surface dispersed Cu and Al oxide species, whereas sodium hydroxide is only effective for the removal of Al oxide species, and ammonium hydroxide shows the weakest effect, removing a very small amount of Cu and Al species. Accompanying with the loss of Cu and Al species, the catalyst surface undergoes structural reconstruction, showing a redistribution of Cu species. Consequently, the copper releasing behavior varies drastically. The catalytic testing results show that the nitric acid and ammonium hydroxide treated catalysts present improved activity, where in the former also shows better stability. Sodium hydroxide treatment has a negative effect on the sustained releasing catalytic performance. In combination with the characterization results of the tested catalysts, it is found that both the copper particle dimension and the microstructure strain of sustained released copper play important roles in the catalytic performance. The findings of this report provide a practical method for the improvement of the sustained releasing catalysis.
Abstract: Catalytic combustion is an effective approach to remove volatile organic compounds, in which the development of highly active and durable catalyst is extremely crucial. Herein, a series of CuMnCex/Al2O3/cordierite monolithic catalysts were synthesized by using the ultrasonic-assisted impregnation method. The physicochemical properties were comprehensively characterized via the BET, XRD, SEM, EDX, H2-TPR, O2-TPD, XPS and EPR techniques. The results showed that the catalytic activity of CuMnCex/Al2O3/Cor for toluene combustion was strongly affected by the Ce content. The CuMnCe2/Al2O3/Cor monolithic catalyst showed the best catalytic activity with toluene conversion of 90% at 263 °C under toluene concentration of 1 g/L and space velocity of 78000 mL/(g·h). Meanwhile, the well-dispersed CeO2 in the CuMn matrix not only improved the content of oxygen vacancies and the mobility of oxygen species, but also enhanced the low-temperature reducibility of the catalyst. Moreover, the CuMnCe2/Al2O3/Cor monolithic catalyst exhibited an excellent stability in the long-term test and cycle ability test.
Abstract: To investigate the influence of pore structure on the catalytic activity of catalysts, four catalysts including three-dimensionally ordered macroporous-mesoporous (3DOM-m) CeTiOx, three-dimensionally ordered macroporous (3DOM) CeTiOx, three-dimensionally ordered mesoporous (3DOm) CeTiOx and disordered mesoporous (DM) CeTiOx were synthesized by the sol-gel method. The NH3-SCR denitration testing results show that the performance of the catalysts with different pore structures follows the sequence of 3DOM-m CeTiOx>3DOm CeTiOx>3DOM CeTiOx>DM CeTiOx, and the 3DOM-m CeTiOx shows an excellent catalytic activity, with more than 90% NO conversion in the range of 250–400 ℃ at a GHSV of 60000 h−1 . The characterization of catalysts by XRD, SEM, BET, NH3-TPD and in-situ DRIFTS indicates that the surface area is not the dominant factor determining the catalytic activity of CeTiOx. 3DOM-m CeTiOx has a highly ordered macroporous-mesoporous structure and abundant Bronsted acidic sites, thereby improving the denitrification activity. The NH3-SCR reaction over the 3DOM-m CeTiOx mainly follows the L-H and E-R mechanisms.
Abstract: Formic acid (FA) has received much attention due to its high hydrogen content (4.4%), easy H2 production and synthesis from small platform compounds. γ-Mo2N/C is very selective for the decomposition of FA along the H2 and CO2 pathways, generating very little CO and showing high application value. In this study, γ-Mo2N/C catalysts were prepared using aqueous p-phenylenediamine and ammonium molybdate solutions as precursors, and their FA decomposition performance was evaluated in-situ. The adsorption conformation of FA on the crystalline surface of γ-Mo2N (200) was calculated by DFT, and on this basis, the catalyst performance and the decomposition mechanism of FA on its surface were investigated. The results showed that γ-Mo2N/C exhibited very high catalytic activity at low temperatures and that improving the dispersion of γ-Mo2N on the C carrier was effective in improving the FA conversion. The best catalytic performance was achieved at a molar ratio of 4∶1 between p-phenylenediamine and ammonium molybdate, and the catalyst showed stable performance and high H2 selectivity (N2 40 mL/min, CO<5.0×10−5) in the FA decomposition experiments at 160 ℃ and 100 h. DFT calculations showed that the H atom of the O−H bond in FA was more likely to bind to the N atom on the crystalline surface of γ-Mo2N/C (200), while the O atom of the C=O bond are more likely to bind to Mo atoms on the γ-Mo2N/C (200) crystal plane. The above results help to clarify the mechanism of FA decomposition under the action of γ-Mo2N/C and show the potential application of the non-precious metal catalyst γ-Mo2N/C in the decomposition of FA for H2 production.
Abstract: Photocatalytic mineralization of recalcitrant contaminants such as phenol requires hydroxyl radicals (·OH) for ring-opening reactions. Here, we weaken the adsorption of oxygen species on TiO2 surface by Al doping, which can effectively promote the photoinduced ·OH generation. Besides, Al doping can downshift the conduction band of TiO2. The resulted potential barrier lowering can promote semiconductor-cocatalyst interfacial electron transfer for the reduction half-reaction. Due to the strong correlation between positive and negative charges, the rapid transfer of electrons in the reduction half-reaction can also increase the concentration of holes in the semiconductor and promote the generation of ·OH. By immobilizing the photocatalyst on the light-incident inner wall of the reactor, it can avoid the competitive light absorption by the contaminant. By these virtues, efficient photocatalytic mineralization of low-concentration phenol in wastewater can be realized.
Abstract: In order to enhance the photocatalytic hydrogen production performance of Zn0.5Cd0.5S, Ni-MOF modified Zn0.5Cd0.5S composite photocatalyst was prepared by hydrothermal method. The structure and photoelectrochemical properties of the prepared samples were characterized by XRD, SEM, TEM, XPS and other analytical methods. The results show that Zn0.5Cd0.5S mainly presents a nano particle structure, and Ni-MOF is mainly composed of ultra-thin square sheets with a length of about 10 µm and a width of about 9 µm. When Ni-MOF is combined with Zn0.5Cd0.5S, the Zn0.5Cd0.5S nanoparticles deposit on the surface of the Ni-MOF square sheet, and the particle size is significantly reduced, reducing the aggregation of Zn0.5Cd0.5S nanoparticles. In addition, there is a blue shift in the light absorption range for the composite, but still excellent visible light response ability. In the landfill leachate mixed shale gas flowback wastewater, the 15% Ni-MOF/Zn0.5Cd0.5S shows the best photocatalytic hydrogen production performance. Under simulated sunlight, the hydrogen production after 3 h of illumination is up to 1887 µmol. The hydrogen production process satisfies the zero-level reaction, with a hydrogen production rate of 685.9 µmol/h, which is approximately 5.7 times as high as the hydrogen production rate of Zn0.5Cd0.5S.
Abstract: Carbon dioxide (CO2) is a major anthropogenic greenhouse gas produced by chemical, thermoelectric and steel industries as well as transport sector. The increasing concentration of CO2 in atmosphere is responsible for plenty of environmental problems such as global warming, rising sea levels and increasing global temperatures. However, CO2 could consider as renewable, cheap and non-toxic chemical raw material, using CO2 to produce high value-added chemicals to reduce carbon concentrations is a highly desirable strategy. Five-membered cyclic carbonates have a wide range of applications due to their superior physicochemical properties such as high boiling point, high dipole moment and biodegradability. The synthesis of cyclic carbonates from epoxides and CO2 is by far the most approved method. Nevertheless, due to high thermal stability and kinetic inertness, it is necessary to activate CO2 as feedstock for organic synthesis with large energy, which may result in the release of more CO2 than is actually. Therefore, the use of CO2 as C1 building block is long-term challenged. This paper outlines the progress of research on various types of homogeneous and heterogeneous catalysts for CO2 fixation to generate cyclic carbonates, including organocatalysts, ionic liquids, metal-organic frameworks, and porous organic polymers. Almost all of these catalysts are currently available for the successful fixation of CO2 to terminal epoxides on laboratory scale using pure CO2 at ambient temperatures. For internal epoxides higher reaction conditions are usually required to achieve the desired conversion. It was analyzed three areas of present major challenges in catalyzing multi-substituted epoxides or bio-derived epoxides, diluted CO2 conversion and industrialization, and the directions for future research efforts on the subject were suggested.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
