Abstract: Phenol…phenol, phenol…benzene, phenol…oxydibenzene, phenol…quinoline, and benzoic acid…benzoic acid were selected as lignite-related complexes to investigate different hydrogen bonds formed by self-associated OH, OH-π, OH-ether O, OH-N, and COOH-COOH using density functional theory with dispersion correction, respectively. Moreover, the effects of substituents (CH3-, CH3O-, OH-, NH2-, COOH-, and NO2-) in donors on the hydrogen bonds were investigated. Geometry optimization, energy, Mulliken population, and frequency of all the complexes were calculated. It can be seen from optimized structures that there indeed are hydrogen bonds in the different complexes. Bond lengths of all O-H bonds in the different complexes become longer than that of free OH in phenol, which implies that intermolecular interactions exist in all the complexes. Among of them, bond lengths of O-H bonds in benzoic acid…benzoic acid are the longest. In addition, charge transfer can be observed via Mulliken population. Based on frequency analysis, all O-H stretching vibrations have obvious red shift, especially O-H bonds in benzoic acid…benzoic acid and phenol…quinoline, which gives evidence of using the infrared spectroscopy to analyze hydroxyl groups of coals. According to bond energies, the strength of the different hydrogen bonds decreases in the order: COOH-COOH > OH-N > self-associated OH ≈ OH-ether O > OH-π, which is consistent with the reported experimental results. Different substituents have distinct effects on the hydrogen bonds.
Abstract: The carbon quantum dots (CQDs) were prepared by HNO3 pretreatment combined with ball milling and oxidative stripping by hydrogen peroxide with medium temperature coal tar pitch as the carbon source. In order to determine the suitable reaction conditions, the effects of oxidation time and the amount of hydrogen peroxide on the structure and properties of CQDs were investigated with the yield of CQDs and fluorescence quantum yield as targets. Under the optimum condition with an operating reaction time of 6 h and a H2O2 dosage of 100 mL, the respectively highest yield of CQDs and fluorescence quantum yield of 6.3% and 11.2% is obtained, and the prepared sample is denoted as c-CQDs. Meanwhile, the sample particle size is uniform and in the range of 4-14 nm. When the reaction time is extended to 8 h, the carbon quantum dots (a-CQDs) grow larger because of agglomeration. As the amount of H2O2 increases to 120 mL, the size of carbon quantum dots (b-CQDs) becomes smaller and disorder due to excessive oxidation. Then, the effects of reaction conditions on the structure of CQDs were investigated by XPS, TG-DTG, 13C NMR, Raman and XRD. The results show that the carbon content follows the order of a-CQDs > b-CQDs > c-CQDs, while the content of oxygen is b-CQDs > c-CQDs > a-CQDs. According to XPS analysis, the major form of carbon in CQDs is the aromatic carbon. It is noted that the maximum amount of C=O and O-C=O is obtained with the c-CQDs, while the higest value of C-O appears with the b-CQDs. The Xb characterized by 13C NMR characterization illustrates that the average aromatic ring size is about 0.5, and correspondingly, the average number of aromatic rings is about 3.
Abstract: A copper-modified attapulgite (Cu3-ATP) catalyst with both mercury oxidation and ammonia oxidation activities was prepared by an improved wet impregnation method. Several characterization including SEM, H2-TPR and NH3-TPD were performed on it, and its mercury oxidation and ammonia oxidation performance were tested at 150-400 ℃. The results show that the copper species is successfully loaded on ATP surface, which significantly improves the redox ability of the catalyst, increases the strong acid sites and partial strong acid sites on the surface, and thus promotes the oxidation of Hg0 and NH3. HCl plays an important role in Hg0 oxidation. High temperature is not conducive to the Hg0 oxidation reaction, but can promote the oxidation of NH3. At 350 ℃, the oxidation efficiencies of Hg0 and NH3 over Cu3-ATP are both above 90%. Experiments on the influencing factors show that NH3 has an obvious inhibitory effect on mercury oxidation at high space velocity, while low concentrations of Hg0 and HCl have no significant influence on ammonia oxidation. When the gas hourly space velocity (GHSV) is lower than 5×104 h-1, Cu3-ATP can simultaneously oxidize NH3 and Hg0. In addition, the mercury oxidation reaction shows good sulfur resistance and water resistance, but SO2 has a certain inhibitory effect on ammonia oxidation.
Abstract: Influence of heating temperatures on the component distribution of distillates distilled from walnut shell bio-oils was studied. Meanwhile, distillates were further separated into water-soluble and water-insoluble fraction to characterize product distribution. The results showed that distillate fraction yield increased with strengthening heating temperature from 120 to 300 ℃. Aromatic hydrocarbons (e.g. naphthalene) and carboxylic acids (e.g. acetic acid) significantly concentrated in water-insoluble fraction as heating temperatures were below 240 ℃. Notably, the relative concentration of aromatic and carboxylic compounds in the water-insoluble fraction derived from 300 ℃ was 13.86 and 3.15 times higher than that of crude bio-oil, respectively. Large amounts of phenols such as phenol and guaiacol was distilled as heating temperatures exceeded 240 ℃, which induced enhanced yield of water-insoluble fraction. Moreover, the moisture of all the water-soluble fractions was higher than 60%, which demonstrated the water-soluble fraction remarkably concentrated moisture. In addition, undetected components (e.g. butyl 2-ethylacetate and cyclopentanone) in crude bio-oil surprisingly existed in distillates and the total moisture of distillates was higher than that of crude bio-oils, which proved esterification and polycondensation reactions occurred in bio-oil distillation process. Furthermore, the component distribution of distillates also indicated modifying heating temperatures effectively enriched commodity chemicals. Note that water-insoluble fraction distilled from 300 ℃ exhibited relative concentration of phenol, guaiacol, 4-methyl-2-methoxyphenol, 4-ethyl-2-methoxyphenol and 4-propyl-2-methoxyphenol was 109%, 160%, 84%, 53% and 444% higher than that in crude bio-oil, respectively.
Abstract: A Fenton solution with different H2O2 concentrations was used to pretreat an alkali lignin (AL), and combined with fast pyrolysis, the change in the content of phenolic compounds containing methoxy group in light bio-oil was explored, also, the influence of the Fenton solution on the structure of the alkali lignin was also studied. The results show that the peak area of phenolic compounds containing methoxy groups in light bio-oil decreases from 7.3×109 with AL (untreated alkali lignin) to 5.2×109 with 13-FML (pretreated alkali lignin with Fenton solution at a concentration of 13 mL/g H2O2), decreasing by about 29%. While the peak area of phenolic compounds containing methyl groups and ethyl groups increases from 3.9×109 with AL to 7.2×109 with 13-FML, increasing by about 1.85 times. At the same time, the yield of light bio-oil increases from 22.4% to 28.7%. Through FT-IR, 1H NMR and 13C NMR analysis, it is found that Fenton pretreatment can destroy the condensational structural units of lignin and reduce the content of methoxy, thus providing favorable conditions for subsequent fast pyrolysis to produce bio-oil with low methoxy content.
Abstract: Emission of NOx from stationary and mobile sources had caused many environmental problems. NH3 selective catalytic reduction technology (NH3-SCR) is one of the most effective technologies to eliminate NOx based on developing high-efficient catalysts. In this review, the catalytic activity for NH3-SCR, hydrothermal stability and deactivation mechanism of metal-based zeolite catalysts (mainly Cu- and Fe-based zeolite catalysts) employed in NH3-SCR were summarized. The main factors affecting the hydrothermal stability of Cu- or Fe-based zeolite catalysts in NH3-SCR, such as Si/Al ratio, zeolite topological structure, metal content, particle size and preparation methods of catalysts, were systematically reviewed. The modification approaches addressed in recent researches which could effectively improve the hydrothermal stability of metal-based zeolites in NH3-SCR, such as element modification using phosphorus, second active metal, alkali (earth) metal, and surface modification, were discussed. Hopefully, this review could provide a fundamental understanding of the deactivation behaviors of Cu- and Fe-based zeolite catalysts and pave the way towards the improvement of hydrothermal stability of zeolite catalysts in NH3-SCR.
Abstract: A series of copper-cerium composite oxide molecular sieve catalysts (Cu-Ce/SAPO-34) were prepared by impregnation method, and the effects of Ce loading on the hydrothermal stability of Cu/SAPO-34 catalyst were discussed. The reasons for the difference in activity and stability of different catalysts were analyzed by XRD, SEM, H2-TPR, XPS, and NH3-TPD. The present study showed that hydrothermal aging at 750 ℃ did not cause the chabazite (CHA) framework of Cu-Ce/SAPO-34 catalyst to collapse, but destroyed part of the pore structure and acid sites, and reduced the crystallinity of the catalyst surface. Hydrothermal aging promoted tensile distortion of the catalyst lattice, causing Cu2+ to migrate to the catalyst surface, and Cu2+ and Ce4+ clustered to form CuO and CeO2, which resulted in the reduction of the Cu active species and the decrease of the oxygen hole concentration of the catalyst. Therefore, the performance of Cu-Ce/SAPO-34 for the selective catalytic reduction of NOx by NH3 (NH3-SCR) decreased. Ce doping could increase the amount of Cu2+ and Cu+ active species on the surface of Cu/SAPO-34 catalyst, reduce Cu species clusters to form CuO, and improve the distribution of active Cu species on the catalyst surface. Increasing the loading of Ce could stabilize the structure of Cu-Ce/SAPO-34 catalyst and maintain the medium and weak acid sites, thereby improving its hydrothermal stability. The results indicated that the Cu/Ce mass ratio of 4:5 had the best hydrothermal stability among the series of Cu-Ce/SAPO-34 catalysts in this study.
Abstract: A series of monolithic cordierite supported Cu-SSZ-13 catalysts (Cu-SSZ-13/Cordierite) was prepared by coating the Cu-SSZ-13 molecular sieves on the cellular cordierite through ultrasonic dispersion with polyvinyl alcohol (PVA) or pseudo boehmite powder (SB) as assisting agent and used in the selective catalytic reduction of NOx with NH3 (NH3-SCR). With the help of XRD, nitrogen sorption, SEM and H2-TPR characterization techniques, the influence of coating assistant agent on the firmness of the Cu-SSZ-13 layer, catalytic activity in the NH3-SCR of NO, hydrothermal stability and resistance against SO2 poisoning was then investigated. The results indicate that by using PVA as the coating assistant agent, a firm layer of Cu-SSZ-13 can be formed on the surface of monolithic Cu-SSZ-13/Cordierite catalyst. Moreover, the Cu-SSZ-13(PVA)/Cordierite exhibits high catalytic activity in the NH3-SCR of NOx (close to that of the pristine Cu-SSZ-13 molecular sieve), high hydrothermal stability and good tolerance to SO2, displaying great potential as a practicable catalyst for the removal of NOx from exhausts of both the mobile and the stationary sources.
Abstract: The promoting effect of a typical transition metal Ti in the Ti-modified γ-Fe2O3 catalyst on its performance in the selective catalytic reduction (SCR) of NO with ammonia was investigated by density functional theory (DFT) calculation. Various doping models of single Ti and double Ti at different Fe sites on the γ-Fe2O3(001) surface were constructed; the surface doping formation energy was calculated, the adsorption characteristics of O2, NO and NH3 molecules on γ-Fe2O3 (001) surface before and after Ti doping were compared, and the reaction mechanism was analyzed. The results illustrate that single Ti atom tends to be doped at octahedral Feoct site, whereas two Ti atoms at two Feoct sites. The adsorption of O2 onto the catalyst surface can be enhanced through the Ti doping; moreover, the enhancement increases with an increase in the doping content of Ti. Both single Ti and double Ti doping inhibit the N-terminal adsorption of NO on the catalyst surface. Ti can enhance the Lewis acid sites and promote the adsorption of NH3, which is beneficial to SCR reaction. The doping of Ti increases the energy barrier of NO2 formation and reduces the SCR reaction of γ-Fe2O3 at low temperature. The doping of Ti can inhibit the formation of NH and N, avoid the excessive oxidation of NH3, and improve the utilization of NH3, which are beneficial to the SCR reaction by suppressing the N2O produced by the E-R mechanism and enhancing the selectivity to N2. As a result, the Ti doping can significantly improve catalytic performance of γ-Fe2O3 in the NH3-SCR of NO.
Abstract: Based on the quantum chemical density functional theory(DFT), the mechanism of heterogeneous reduction of NO2 on carbonaceous surface was studied. For zigzag and armchair carbonaceous surfaces, M06-2X method and 6-311G(d) basis set were used to optimize the geometry configuration and energy of all stagnation points under different reaction paths, and the reaction paths were analyzed and compared from thermodynamics and kinetics. The role of CO in the heterogeneous reduction of NO2 was deeply investigated, and the effects of carbon surface and reaction temperature on the heterogeneous reaction were also investigated. The results show that the heterogeneous reduction process of NO2 on the carbon surface can be divided into two stages: the reduction stage of NO2 and the desorption stage of carbon oxide. By comparing the reactions without CO molecules, it can be seen that the CO molecules involved in the reaction can reduce the reaction energy barrier of each stage and accelerate the reaction rate of each stage. In the presence of CO molecule, the reaction energy barrier at the reduction stage of NO2 is reduced, which promotes the heterogeneous reaction process of NO2 reduction to NO. CO molecules participating in the reaction can combine with the residual oxygen atoms on the surface to form and release CO2 molecules, which reduces the reaction energy barrier in the release stage of carbon oxides, thus promoting the overall reduction reaction. In addition, the energy barrier of NO2 heterogeneous reduction reaction on zigzag surface is lower and the reaction rate is faster than that on armchair surface, which indicates that the heterogeneous reduction reaction of NO2 is easier on Zigzag carbonaceous surface. Finally, the reaction kinetics analysis shows that the reaction rate of each stage increases with the increase of temperature, which indicates that increasing temperature can promote the heterogeneous reduction of NO2 on the carbonaceous surface.
Abstract: A series of MoSn catalysts doped with different Ce loadings were prepared by hydrothermal method and their catalytic performance in the selective oxidation of dimethyl ether (DME) to methyl formate (MF) was investigated. The results indicate that the introduction of 0.5% Ce can significantly improve the activity of the MoSn catalyst over the 0.5%Ce-MoSn catalyst, the conversion of DME reaches 11.8% at 130 ℃, with a selectivity of 92.2% for MF. The MoSn catalysts were characterized by nitrogen sorption, XRD, NH3-TPD, CO2-TPD, H2-TPR, XPS and in situ-IR; the results illustrate that a small amount of Ce in the MoSn catalyst can obviously increase the quantity of Mo5+, though it has little effect on the structure of the MoSn catalyst.
Abstract: A serious of robust Au/TS-1 catalysts were prepared by modifying with various alkali carbonates including Na2CO3, K2CO3, Rb2CO3 and Cs2CO3 via the ultrasonic impregnation. The alkali carbonate-modified Au/TS-1 catalysts were characterized by XRD, ICP, XPS, UV-vis, FT-IR, NH3-TPD and HAADF-STEM and their catalytic activity and stability in the gas-phase epoxidation of propene were investigated in a fixed-bed reactor in the presence of H2 and O2. The results indicate that the modification with alkali carbonates can decrease the surface acidity and inhibit the aggregation of Au particles; moreover, Rb2CO3 and Cs2CO3 can even reduce the content of extra-framework Ti in Rb-Au/TS-1 and Ce-Au/TS-1. The catalytic activity and stability of Au/TS-1 in the gas-phase epoxidation of propene are significantly improved after the modification with alkali carbonates. In particular, Cs2CO3-modified Cs-Au/TS-1 catalyst exhibits the best performance, with a propene conversion of 6.2%, selectivity of 86.2% to propene oxide (PO) and H2 utilization efficiency of 26.2%. The results suggest that alkali carbonate modification could be a novel strategy to enhance the catalytic activity and stability of Au/TS-1 in propene epoxidation.
Abstract: In this study, a novel BiOBr/HPW/Au photocatalyst was prepared via hydrothermal method followed by photo-reduction method. The characterization results indicated the successful introduction of HPW and Au in BiOBr. BiOBr/HPW/Au exhibited excellent photocatalytic activity in RhB degradation. The degradation rate constant of BiOBr/HPW/Au was 3.55 times higher than that of BiOBr. Radical scavenger experiments showed that ·O2- was the dominant reactive radical species. A possible mechanism of the enhanced photocatalytic activity was attributed to the synergistic effect of BiOBr, HPW and Au, which resulted in enhanced quantum efficiency and high light harvesting efficiency.
Abstract: Carbon nanofibers (CNFs) were synthesized by ethanol catalytic combustion method and FeCoNiB was loaded on the CNFs by electroless plating (chemical deposition) method. The effect of electroless plating condition on the particle size, dispersion, composition and structure of FeCoNiB was then investigated, to establish the process for the controllable synthesis of carbon nanofibers with plated FeCoNiB (FeCoNiB/CNFs). In addition, the electrocatalytic performance of FeCoNiB/CNFs was evaluated for the hydrogen evolution reaction (HER) in alkaline environment. The results illustrate that the FeCoNiB/CNFs shows a low overpotential of 366 mV at 100 mA/cm2 and a quite low Tafel slope value of 41 mV/dec, as well as a stable potential without attenuation during the stability test for 10 h, displaying a stable and high catalytic performance that is comparable to that of noble metal catalysts. This study is probably helpful for the development of efficient non-noble metal catalyst for HER as well as the application of large-scale electrolytic water hydrogen production in industry.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
