Abstract: The fluorescence characteristics of coal macerals can be used as one of the indexes to evaluate the properties of coking coal. In this work, a single-wavelength laser with a wavelength of 360 nm was used as the excitation source to excite the surface of particulate block under a polarizing microscope. Effect of excitation time on fluorescence characteristics of the macerals was studied. The relationship between spontaneous fluorescence intensity and the excitation time of each maceral of six kinds of coking coals show that the fluorescence characteristics of coal macerals are related to the type and metamorphism of coal. The excitation time has a certain effect on the fluorescence parameters of the macerals. By comparing the relative fluorescence intensity values under different excitation times, it is found that the mean relative fluorescence intensity within 15 s can be used as an optical parameter to characterize the structure and metamorphic grade of different macerals. The essence of this method is to express movement of electrons in outer layer of nucleus by macroscopic fluorescence spectrum and relative fluorescence intensity of the initial state value and simplify microscopic complexity into macroscopic and numerical form generally accepted.
Abstract: The effects of silicon oxide additive on the transformation characteristics of sodium and sulfur in coal ash under atmospheric and elevated pressure were investigated in this study. The results indicated that silicon oxide additive significantly inhibited the release of sodium under high pressure. The sodium content in ash with 4% of silicon oxide additive was 3.5% at 0.1 MPa, which was higher than that without additive. However, the sodium content increased to 5.4% without additive and 6.9% with 4% additive at 4 MPa, respectively. The sodium mainly existed in the forms of NaAlSiO4 and NaAlSi3O8 at 0.1 MPa, and the content of NaAlSiO4 increased with increasing additive dosage, which weakened the agglomeration of ash. The decomposition of low melting point mineral CaSO4 was inhibited at 4 MPa, and the formation of Na6Ca2Al6Si6O24(SO4)2 from NaAlSiO4 and CaSO4 was promoted significantly with increasing additive dosage. Furthermore, the inhibition mechanism of sodium and sulfur released from coal ash by silicon oxide under high pressure was proposed.
Abstract: To provide some useful suggestions to the operation of circulating fluidized bed (CFB) gasifier, the effect of gasification temperature, residence time and agent on the release and transformation of sodium was studied by using a fixed bed reactor combined with Factsage software. The results indicated that gasification temperature was the significant factor to the release and transformation of sodium. For the promoting effect of sodium release, it was ascribed to the intense of sodium volatilization and competitive reaction between lime and meta-kaolin. Meanwhile, the high temperature promoted the formation of nepheline and slag. The threshold temperature of latter was near 950 °C. It was interesting to find that the release of sodium could be divided into two stages: coal pyrolysis and char gasification. In coal pyrolysis, part of organic and water-soluble sodium was released. The remainder either combined with char structure, or reacted with minerals. In char gasification, Sodium, combined with char structure, was released along with char gasification. Due to the decrease of melting temperature and the formation of NaOH, steam showed a promoting effect on the sodium release. Oppositely, oxygen and nitrogen presented an inhibiting effect. The former was ascribed to the formation of Na2SO4, while the latter was caused by the chemical binding and physical wrapping effect of char.
Abstract: The effect of flue gas components on the adsorption of PbO on the surface of CaO(001) during sewage sludge combustion was studied by DFT (Density Functional Theory). The calculation results show that O apex on the surface of CaO(001) is the active site of the adsorption of PbO molecules, H2O molecules, SO2 molecules and CO2 molecules. The presences of H2O molecules, SO2 molecules and CO2 molecules increase the adsorption energy of PbO molecules on the surface of CaO(001) by 71.42, 19.589 and 46.431 kJ/mol, respectively. OH group and local Ca(OH)2 surface structure formed by H2O molecules during the adsorption process are conducive to the adsorption of PbO molecules. Density of state orbitals of OS atom in SO2 molecule and Osurf atom on the surface of CaO(001) overlap with the orbitals of Pb atom, making the adsorption of PbO molecules on the surface more stable. CO3 group formed by CO2 molecules pre-adsorbed on the surface of CaO(001) has a strong adsorption effect on PbO molecules, making PbO molecules more stable adsorption on the surface of CaO(001).
Abstract: Fast pyrolysis of biomass is an effective way for biomass conversion and utilization. However, the pyrolysis temperature is usually high because it is a non-catalytic process, resulting in the complicated composition of bio-oil and difficulty to control. Aiming to explore in-situ catalysis in this paper, the fast pyrolysis of lignin, cellulose, corncob and pine wood powder was studied using ZnCl2 as the catalyst. The activation energies of non-catalytic pyrolysis and catalytic pyrolysis were obtained based on kinetic fitting of their thermal gravimetric curves. The variation in pyrolysis oil composition was analyzed. It was found that ZnCl2in-situ catalysis could not only significantly reduce the pyrolysis temperature, but also simplify the resultant bio-oil composition. Even under pyrolysis temperature as low as 350 ℃, fast pyrolysis of pine wood powder could achieve a yield of 47% of bio-oil, which was predominantly composed of the derivatives of cellulose and hemicellulose. ZnCl2in-situ catalysis could significantly decrease the activation energy of cellulose cracking from 304.78 to 112.46 kJ/mol, but has little effect on that of lignin. The carbon residue from ZnCl2-catalyzed pyrolysis was further carbonized at 600 ℃, affording activated carbon with adsorption capacity of phenol up to 165 mg/g. The research work provides guidance and reference for the development of in-situ catalytic pyrolysis technology with high efficiency.
Abstract: The chemical looping gasification (CLG) kinetics of biochars with calcium ferrite as oxygen carriers and the effects of different kinds of calcium ferrite and biochars were investigated by TGA. The properties of biochars and calcium ferrite were analyzed by XRD, SEM, BET, etc. The Škvára-Šesták method was used to determine the kinetic mechanism function. The results show that the reduction reaction rate and the oxygen carrying capacity of oxygen carriers follow the sequence: Ca2Fe2O5 > CaFe2O4 > Fe2O3, and CaFe2O4 > Ca2Fe2O5 > Fe2O3, respectively. The oxygen carriers can be completely reduced to Fe and CaO by biochar. The activation energy of CaFe2O4 reduction is in the range of 167.44–600.83 kJ/mol; and the activation energy of Ca2Fe2O5 reduction is in the range of 413.62–583.51 kJ/mol. The CaFe3O5 generated during the reduction of CaFe2O4 may have a negative influence on the lattice oxygen diffusion. The reduction of CaFe2O4 can be divided into two stages: when the conversion degree α is less than 0.15, the CaFe2O4 is reduced to Ca2Fe2O5 following the random nucleation and nuclei growth model; when α is greater than 0.15, Ca2Fe2O5 is further reduced to CaO and Fe following the 3-D diffusion mechanism. The mechanism function of the reduction of Ca2Fe2O5 is the same as that of the second stage of CaFe2O4 reduction.
Abstract: With carbon dots (CDs) as the reducing agent and support, a PdAg/CDs composite catalyst was prepared by simple light reduction method. The results of XRD, TEM, FT-IR and XPS characterization indicate that the PdAg/CDs composite has an average particle size of about 10.45 nm, where Pd and Ag exist on the surface of CDs mainly in the alloy form of zero valence. The catalytic performance of the PdAg/CDs composite was evaluated in the hydrogenolysis of glucose in water. The results illustrate that the PdAg/CDs composite catalyst is highly active in the glucose hydrogenolysis; after reaction for 3 h under 140 °C, 4 MPa of initial H2 pressure, 100 mg of glucose and 25 mg of catalyst, the conversion of glucose is 68.85% and the yield of acetol reaches 8.36%.
Abstract: In the Fischer-Tropsch synthesis reaction, Fe-based catalysts are widely used in large-scale indirect coal liquefaction industry due to their low price, high activity, and low CH4 selectivity. The catalytic performance is closely related to the catalyst particle size, surface structure and composition. Since reductive carbonization is a key step in the activation of iron-based catalysts, in this work, Fe3O4-O (expose the {111} crystal planes) with different particle size, and similar particle size but exposing different crystal planes, {111} and {110} (Fe3O4-RD), have been prepared to explore the effect of particle size and surface structure on the carbonization process. The results show that the 50 nm Fe3O4-O particles change more significantly than the one with large particle size (2–10 μm) after carbonization. In-situ XRD was used to monitor the phase change of Fe3O4 with exposing different surface planes during carbonization. The results show that 150 nm Fe3O4-O and Fe3O4-RD particles behave differently in carbonization rate and have different iron carbide concentration in the end, which indicates the carbonization process can be affected by exposed crystal planes. TEM analysis reveals that Fe3O4@FexC core-shell structure formed after carbonization.
Abstract: Supported cobalt catalysts (Co@C-ZnZrO2 and Co/ZnZrO2) were prepared through a metal-organic frameworks (MOFs)-mediated synthesis strategy. The influence of MOFs pyrolysis on the structure and Fischer-Tropsch synthesis performance of supported cobalt catalysts was investigated. The crystalline phase and microstructure of supported cobalt catalysts were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), N2 adsorption-desorption and X-ray photoelectron spectroscopy (XPS). The Co/ZnZrO2 showed the CO conversion of 18.1% and the C5 + selectivity of 77.4%, whereas the Co@C-ZnZrO2 exhibited the CO conversion of 8.5% and the C5 + selectivity of 35.2%. The excellent CO conversion for Co/ZnZrO2 was attributed to the more exposure of active Co sites. Meanwhile, the activity of Co sites on Co@C-ZnZrO2 catalyst was restricted by the carbon layer, suppressing the adsorption and activation of syngas on Co sites.
Abstract: Using carbon nanotubes (CNTs) and XC-72R carbon black as the carrier, PtCo/CNTs-C catalyst with high electrochemical activity was prepared by impregnation reduction method. The structure of the catalyst was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The material was used as a catalyst for methanol anodic oxidation, and the effects of different Co doping and temperature on the reaction were investigated. The results showed that PtCo bimetallic alloy was formed in PtCo/CNTs-C nano-catalyst, and the alloy particles were relatively evenly distributed on the surface of the carrier. The introduction of carbon black and metal Co endowed the catalyst with higher catalytic activity. When the mass ratio of Pt∶Co was 94∶6, the catalyst had lower initial potential (−0.651 V (vs SCE)) and higher current density (86.74 mA/cm2) for the catalytic oxidation of methanol, and the chronoamperometric test showed that the catalyst had good stability.
Abstract: MXene (Ti3C2Tx) was prepared by etching MAX (Ti3AlC2) raw material and then ultrathin MXene nanosheets (MXene-NS, namely Ti3C2Tx-NS) was fabricated by using exfoliating method. The morphology, structure and elemental composition of the MXene-NS were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrocatalytic hydrogen evolution reaction (HER) properties of MAX, MXene and MXene-NS were compared by electrochemical tests. The results revealed that compared with MAX and MXene, in 1 mol/L KOH, MXene-NS exhibited the lowest overpotential (190 mV@ −10 mA/cm2), the smallest Tafel slope (168 mV/dec), the smallest charge transfer resistance and the largest electrochemical active surface area. In addition, MXene-NS displayed a good potential response vs. current density. Furthermore, after long-term durability test, the polarization curve of MXene-NS was not notably decayed, which demonstrated the excellent stability for hydrogen evolution. All these results indicated that the exfoliation of MXene could effectively improve its electrocatalytic performance and the as-exfoliated MXene-NS was an excellent alternative for replacing the noble metal catalysts.
Abstract: In this paper, g-C3N4 obtained by calcining melamine at high temperature in static air was used as the carrier, and the precious metal Rh was used as the active component. The Rh nanoparticles were supported on the g-C3N4 support by a simple impregnation reduction method to prepare high activity and high selectivity. Various characterization methods were used to study the microstructure and composition of the catalyst. In addition, the effect of reaction temperature and NaOH concentration on the catalytic decomposition of hydrous hydrazine was also investigated. The results show that the excellent catalytic activity of the catalyst stems from the fact that the g-C3N4 support provides anchor sites for the metal Rh and the support and the strong metal-support interactions. The catalytic activity of the catalyst increases with the increase of the reaction temperature, and the Rh/g-C3N4 catalyst has the highest catalytic activity when the NaOH concentration is 0.75 mol/L. The Rh/g-C3N4 catalyst has an activation energy of 30.7 kJ/mol and TOF value of 1466.4 h−1 for catalyzing the decomposition of hydrous hydrazine for hydrogen production. After 5 cycles, the catalyst still maintains a good catalytic activity, indicating that the catalyst has a good cyclic stability.
Abstract: The carboxylation of C−H bond of terminal alkyne with CO2 to propargylic acid compounds conforms to the concept of green chemistry, which plays an important role in the field of organic and pharmaceutical intermediate synthesis. Under the background of "Carbon peaking and carbon neutrality", this reaction is also an effective way to realize the high value utilization of CO2. At present, this reaction system is mainly carried out through homogeneous catalysis. However, due to the advantages of heterogeneous catalysis system such as easy separation and recovery, heterogeneous catalytic C−H bond carbonylation of alkynes with CO2 has also gradually attracted attention. Based on the activation mechanism of C−H bond and CO2, relevant research has been carried out over coin metal catalysts. Through the synergistic effect of coin metal and carrier, the coupling of C−C bond is promoted to achieve the synthesis of propargylic acid compounds. In this paper, the heterogeneous catalytic C−H bond carbonylation of alkynes with CO2 is systematically reviewed. The activation of the system, the mechanism of carboxylation reaction, and the structural characteristics of the catalyst are analyzed and summarized, which provides a research idea for the development of efficient heterogeneous catalyst for carboxylation and related processes.
Abstract: The application of renewable and clean resources to replace fossil resources such as coal and coke in ironmaking is one of the most important ways for iron and steel companies to achieve "carbon neutrality" and "carbon peaking". Biomass resources such as agricultural and forestry wastes have received a lot of attention in ironmaking because of their low cost and availability, low temperature reducibility and carbon neutrality. In this work, the reaction mechanism, gaseous products and pollutant release characteristics are analyzed in a more systematic way, focusing on the two main thermal utilization methods of biomass, namely pyrolysis and combustion. Subsequently, the process overview, process analysis and pollutant generation mechanism are discussed in detail, by taking blast furnace blowing biomass fuel and biomass reductant for direct reduction ironmaking as representatives. Finally, an economic analysis of the above typical processes based on the utilization of biomass in ironmaking is carried out, as well as an outlook of emission reduction strategies, with a view to providing valuable references for alleviating the contradiction between fossil energy supply and demand, reducing emissions from ironmaking and even the transformation and upgrading of iron and steel industry.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
