Abstract: Meihuajing coal and Yangchangwan coal from Ningdong, China are chosen as raw materials to study char gasification reactivity using thermogravimetric analyzer and in-situ heating stage microscope, and typical gasification coal-Shenfu bituminous coal char is used as reference char sample. The char physicochemical properties are systematically characterized. The results show that the order for gasification reactivity of 3 chars at the same gasification temperature is Yangchangwan char > Meihuajing char > Shenfu char. In-situ study of heating stage microscope shows that with the progress of char-CO2 gasification, most of char particles react with CO2 as shrinking particle mode, and the particle reaction form changes from shrinking particle mode to shrinking core mode at high carbon conversion level. Additionally, it can be found from the results of shrinkage ratio variation of the particle projected area during gasification that Yangchangwan char shows the largest shrinkage area when undergoes the same reaction time, followed by Meihuajing char and Shenfu char. The difference in gasification reactivity is mainly attributed to the difference of physicochemical properties of chars. i.e., Yangchangwan char shows the largest specific surface area and the total contents of K, Na and Ca and the lowest order degree of carbon structure, followed by Meihuajing char and Shenfu char.
Abstract: This work aims to investigate the structural evolution of the char during gasification under a single or mixed atmosphere of H2O and/or CO2 with the synchronized investigation of the effect of the varying char structure on the gasification reactivity. The experimental char was prepared from a bituminous coal at 1000℃. The changes of the char structure along with the progress of the carbon conversion during gasification were characterized using N2 adsorption, SEM, and Raman spectroscopy. The results revealed that H2O showed a more dramatically change on the char structure than CO2 and two reactants had different reaction pathways. The different pathways of reactants affected the evolution manners of the char structure and different gasification reactivity of char was related to structural evolution. The specific reaction rate between the char and CO2 decreased monotonously with increasing carbon conversion. However, the opposite trends are observed when H2O exist, either H2O alone or the mixtures of H2O and CO2. The char gasification reactivity was under the common effect of physical and chemical structure. In terms of the mixture of H2O and CO2, the significant specific surface area caused by H2O provided more active sites for CO2. The interactions between H2O and CO2 promoted reaction between C and CO2 (C + CO2 → CO) in mixtures of H2O and CO2, leading to higher amount of CO and higher specific reaction rate than calculated.
Abstract: The effect of dispersibility of Fe on coal chars with different specific surface areas on the catalytic hydrogasification performance was studied in a pressurized fixed bed reactor. The chars and catalysts were characterized by XRD, BET, H2-TPR, FT-IR, TEM and Raman spectroscopy. The results show that the active site and graphitization degree of coal char are not the only factors affecting the catalytic gasification reaction, but the dispersion of catalyst has a greater impact on the reaction. The larger the specific surface area of coal char is, the more uniform the Fe catalyst disperses on the surface of coal char and the smaller the average grain size of the active component of catalyst is, which can promote the formation of the catalytically hydrogenated mesophase product Fe3C and methane yield. For 900-char with higher specific surface area, the methane yield can reach 53% when the hydrogen pressure is 2 MPa, the temperature is 750℃ and the Fe loading is 5%. The effect of Fe catalyst loading on the catalytic hydrogasification was investigated with 900-char. It is found that the methane yield increases first and then decreases, and the Fe loading has a saturation point.
Abstract: A Shengli lignite from Inner Mongolia was selected as the research object, with which the low-temperature oxidation experiments were carried out at different temperatures (200-300℃) in a fixed bed reactor. The structure of coal samples after oxidation treatment was characterized by FT-IR, Raman and XPS. The effects of low-temperature oxidation at different temperatures on the microstructure and mass change of lignite were investigated and the combustion performance was determined by TGA. The results show that the temperature has a significant influence on mass change rate of Shengli lignite during low-temperature oxidation. The mass change rate of lignite is very limited when temperature is below 220℃ and it changes obviously when the temperature is higher than 220℃. Especially at 220-230℃, the mass change rate of coal samples is changed from 5.80% (220℃) to 42.55% (230℃). The FT-IR/Raman/XPS characterization results show that the analogous benzoquinone structure forms after oxidized at 220℃, and these lead to the stretching vibration absorption peak of the aromatic C=C shift to lower wavenumber. In Raman spectra, the position of the D peak shifts, and the distance between the peaks of D and G increases. The content of C-O-and C=O on the surface of coal samples increases at oxidation temperature lower than 220℃. It is speculated that the jump of mass change rate of coal samples at 220-230℃ is mainly related to the oxidative decomposition of analogous benzoquinone structure.
Abstract: The effect of vermiculite on the slagging characteristics of high-sodium and high-calcium Zhundong coal was studied by a drop-tube furnace and with ash fusion tester. The results show that with the increase of the amount of vermiculite blended, the ash melting point temperature first decreases and then increases. When the ratio of blending is 6%, the ash fusion point temperature is the lowest. The higher the blending ratio is, the more obvious the improvement of the slagging condition of Zhundong coal is. When the ratio of blending is 4%, the slag sample becomes loose and porous, the texture turns to be brittle, and the adhesion between the slag sample and the deposition probe is weak, being easy to be removed by soot blowing. It is recommended that the amount of vermiculite blended should be 4%. The original mineral in coal ash is mainly composed of quartz, gehlenite and low fusion point minerals of pyroxene. After blending vermiculite, the omphacite, sodium-containing minerals, is converted into pargasite, and the iron-bearing minerals such as augite and hematite are converted into forsterite ferroan, and the minerals in the slag sample are mainly forsterite, which has a high fusion point. Sodium can be captured by vermiculite. With the sampling temperature decreasing and the vermiculite blending ratio increasing, the effect of sodium capture becomes more and more obvious.
Abstract: With terephthalic acid (H2BDC) as ligand and cobalt acetate as Co source, metal-organic frameworks (Co-BDC MOFs) were synthesized in water by co-precipitation; after that, core-shell Co@C catalysts were prepared by chemical vapor deposition (CVD) of Co-BDC MOFs in acetylene and Ar atmosphere. The structure, composition and properties of Co@C catalysts were characterized by XRD, nitrogen physisorption, SEM, TEM, XPS, TGA and Raman spectroscopy and their catalytic performance in Fischer-Tropsch synthesis (FTS) were investigated in a fixed-bed tubular reactor. The results demonstrated that the carbonization atmosphere has an important influence on the graphitization degree of carbon shell, whereas has little effect on the phase and size of Co core. The pore of graphite shell is significantly improved by CVD in acetylene, which can enhance the selectivity to heavier hydrocarbons (C5+) for CO hydrogenation; in particular, the Co@C-C2H2 catalyst shows a high selectivity of 82.66% to the C5+ hydrocarbons. As the carbon shell can effectively inhibit the cobalt nanoparticles from migration and agglomeration during the FTS reaction, the Co species were well distributed in both the fresh and spent catalysts and no significant sintering and deactivation are observed for the Co@C catalysts upon the FTS tests. During the FTS reaction, the active phase changes from metallic Co to a mixture of metallic Co and Co2C, whilst the catalytic activity of Co@C-C2H2 keeps almost unchanged, suggesting that Co2C may also be an active phase for the Fischer-Tropsch synthesis.
Abstract: A series of fused iron (FI) catalysts promoted with biomass ash were prepared by physical mixing method and characterized by X-ray diffraction, transmission electron microscopy and Mossbauer spectroscopy. The catalytic performance of CO2 hydrogenation to higher hydrocarbons was evaluated in a fixed bed reactor. The results show that compared with the catalyst without biomass ash (B-ash), the fused iron catalysts promoted with biomass ash have smaller particle size and narrower size distribution, and the four phases of Fe3O4, Fe5C2, Fe3C as well as α-Fe coexist in synergy. Thus, the tandem reaction of reverse water gas shift (RWGS) and C-C coupling proceed efficiently, and the selectivity of higher hydrocarbons is significantly improved while methane formation is effectively suppressed. Among the products, C4-18 hydrocarbons are dominant. The C4-18 hydrocarbons' selectivity in all hydrocarbons reaches 73.9% at the conditions of 300℃, 1.0 MPa, 4800 h-1, H2/CO2=3.0 as well as the additive amount of the promoter is 5% (mass ratio).
Abstract: Y-Co3O4 catalysts with Y/Co molar ratio of 0.03 were prepared by several methods, such as one-step hydrothermal, two-step hydrothermal, and impregnation methods, to catalyze the decomposition of N2O. Among these catalysts, the one prepared by one-step hydrothermal method exhibited the highest activity, and then the Y-Co3O4 catalysts with various molar ratios of Y/Co were synthesized by one-step hydrothermal method. Subsequently, the optimized 0.03Y-Co3O4 was impregnated by K2CO3 solution to prepare K-modified catalyst and named as 0.02K/0.03Y-Co3O4. These catalysts were characterized by X-ray diffraction (XRD), nitrogen physisorption, hydrogen temperature-programmed reduction (H2-TPR), oxygen temperature-programmed desorption (O2-TPD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques. The results show that both Co3O4 and Y-Co3O4 exhibit spinel structure, however Y-doped Co3O4 catalysts are more active than bare Co3O4. After further modified by potassium, the 0.02K/0.03Y-Co3O4 reveals higher activity due to the more active sites (Co2+) and easier desorption of surface oxygen species than un-modified 0.03Y-Co3O4. In detail, the temperatures of N2O full conversion over 0.02K/0.03Y-Co3O4 catalyst are 325, 350, 375℃, under the reaction atmospheres of 1%N2O+Ar, 1%N2O+2%O2+Ar, 1%N2O+2%O2+8.2%H2O+Ar, respectively. In addition, over 90% conversion of N2O can be maintained at 350℃ after continuous reaction for 50 h in the co-presence of oxygen and steam on K-modified Y-Co3O4 catalyst. There is a dynamic compensation effect between apparent activation energy (Ea) and pre-exponential factor (A) in N2O decomposition over Y-Co3O4 and K-modified catalysts.
Abstract: In this paper, Co3O4 catalysts were prepared by the liquid precipitation method, and further was subjected to reduction-oxidation pretreatment to obtain Co3O4-RO. The catalysts were characterized by XRD, N2-physisorption, Raman, H2-TPR, XPS and O2-TPD. Their catalytic activities in N2O decomposition were tested on a fixed-bed continuous flow microreactor. The results show that both the crystallinity and the crystallite size of Co3O4-RO decrease in comparison with Co3O4. Especially the structural reconstruction resulted from the reduction-oxidation pretreatment weakens the Co-O bond and enhances the oxygen desorption capacity on the catalyst surface, which endows the Co3O4-RO a lower activation energy. Thus the catalytic activity of the Co3O4-RO in N2O decomposition increases significantly. At the same time, Co3O4-RO shows strong resistance to O2 (2% in feed)and H2O (2.3% in feed).
Abstract: A series of CuO/ZrO2 catalysts were prepared by a deposition-precipitation method using ZrO2 calcined at various temperatures (120, 250, 350 and 450℃) as supports. The water-gas shift (WGS) reaction was carried out on these catalysts using H2 rich reactant gas (15% CO, 55% H2, 23% N2, 7% CO2). It was shown that the catalytic activity of the catalysts increased at first and then decreased with increasing calcination temperature of ZrO2. The catalyst supported on ZrO2 calcined at 250℃ showed the highest catalytic activity. The structure and reducibility of CuO/ZrO2 catalysts were studied by various techniques, such as XRD, N2-physisorption, N2O titration, H2-TPR and CO-TPR-MS. The results show that the Cu dispersion and the proportion of catalytically active Cu-[O]-Zr species ("[]" represents an oxygen vacancy on ZrO2 support) decrease with the increase of ZrO2 calcination temperature. The calcination of ZrO2 at higher temperature leads to an improvement of the reducibility of Cu-[O]-Zr species and hydroxyl groups on the CuO/ZrO2 catalysts, resulting in an easier onset of the surface WGS reaction between surface hydroxyl groups and CO reductant. The two factors reach a balance for the catalyst supported on ZrO2 calcined at 250℃ (moderate temperature), as is thought to be responsible for the highest WGS activity of this catalyst.
Abstract: The Al-MCM-41 zeolites with different Al contents were prepared by post-grafting method and characterized by means of XRD, N2 adsorption-desorption, NH3-TPD, and Py-FTIR. The adsorptive performance of thiophene on these samples was investigated in a fixed bed by using micro coulombmeter and GC-SCD technique. The thiophene adsorption capacity was correlated with the acid properties and texture properties of the molecular sieve, and the effect of olefin on the adsorption desulfurization mechanism of active species in Al-MCM-41 was investigated. The results show that the introduction of lower content aluminum species is conducive to the formation of B (Brønsted) acid center and L1 (Lewis) acid center, while higher content aluminum species is conducive to the formation of L2 (Lewis) acid center. L2 acid center exhibits a far stronger thiophene adsorption ability than L1 acid center that has a slightly stronger thiophene adsorption ability than B acid center. Competitive adsorption and catalytic conversion of olefin and thiophene take place on the B acid center, and the catalytic reaction is dominated. The existence of L2 acid center greatly promotes the catalytic conversion reaction on the B acid center. The adsorption of macromolecular sulfide instead of thiophene increases the saturated adsorption capacity of Al-MCM-41 zeolites.
Abstract: A series of solid super acid catalysts, S2O82-/ZrO2, S2O82-/ZrO2-CuO and S2O82-/ZrO2-CoO, were synthesized by coprecipitation impregnation method with zirconium nitrate, copper nitrate and cobalt nitrate as the metal sources and with ammonium persulfate as the impregnation solution. The catalysts were characterized by XRD, FT-IR and NH3-TPD. The characterization shows that the S2O82-/ZrO2-CoO catalyst has the most super acid sites among the three catalysts. S2O82-/ZrO2-CoO as the catalyst and hydrogen peroxide as the oxidant were used for oxidative desulfurization of FCC gasoline, and the effects of reaction temperature, catalyst dosage, reaction time and oxidant dosage on the desulfurization of FCC gasoline were studied. The optimal conditions were determined as:FCC gasoline of 15 mL, reaction temperature of 70℃, reaction time of 1.5 h, oxidant dosage of V(H2O2):V(oil)=7.5:1, and catalyst dosage of 0.02 g/mL. Moreover, the reaction product was extracted with N, N-dimethylformamide. When the volume ratio of extractant to gasoline is 1:1, the sulfur removal efficiency and recovery of FCC gasoline reach to 85.34% and 94.45%, respectively. The catalyst exhibits a relatively stable catalytic activity.
Abstract: A packed-bed dielectric barrier discharge (DBD) reactor was developed to investigate the removal of biomass tar in fuel gas atmosphere, and benzene was used as the tar surrogate. The effects of fuel gas composition, packing materials, reaction temperature and reduction methods of catalysts on the removal efficiency of benzene were investigated. The results indicate that the benzene removal efficiency of air-gasification fuel gas is close to that of steam-gasification fuel gas at low temperatures, but the presence of O2 in the fuel gas leads to a large drop in the removal efficiency. In addition, the enhancement of the plasma discharge power and the use of packing materials with higher permittivity, specific surface area and pore volume can improve the benzene removal efficiency. For the plasma-catalytic process, the combination of DBD plasma and Ni/γ-Al2O3 (C) shows a significant benzene removal potential. The benzene removal efficiency decreases with temperature from 230-330℃, reaching a minimum value of 11.6%, and then notably increases to 85.4% at 430℃. Furthermore, the combination of plasma and Ni/γ-Al2O3 (P), which is reduced by plasma under H2 atmosphere, has a similar tendency of benzene removal behavior within the temperature range of 230-430℃, reaching a maximum removal efficiency of 90.0% at 430℃ due to higher specific surface area and nickel dispersion of Ni/γ-Al2O3 (P). Moreover, the increased CH4 concentration induced by the methanation of the fuel gas and the slightly decreased heating value of the fuel gas are obtained in the plasma-catalytic process.
Abstract: A new composite photocatalyst, viz., BiVO4/MIL-53(Fe), was prepared through a simple hydrothermal approach and characterized by means of X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, Fourier transform infrared spectroscopy, N2 absorption-desorption and UV-visual diffuse reflectance spectroscopy. The photocatalytic activity of prepared BiVO4/MIL-53(Fe) catalysts was investigated in the degradation of RhB as a simulated pollutant and a possible reaction mechanism for the photocatalytic degradation of RhB was then proposed. The results indicate that after modifying BiVO4 with metal-organic frameworks (MOFs), the surface area of BiVO4/MIL-53(Fe) is improved greatly; moreover, the BiVO4/MIL-53(Fe) composite also exhibits much higher photocatalytic activity than pristine BiVO4 and MIL-53(Fe). In particular, the photocatalytic activity of BF-2 composite is about 5.2 and 8.1 times higher than those of pure MIL-53 (Fe) and BiVO4, respectively. In addition, BiVO4/MIL-53(Fe) composite photocatalyst is rather stable and can keep its photocatalytic activity and structure after four recycling tests.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
