Abstract: Two gas coals were respectively separated into four components with different vitrinite content using ZnCl2 solution. The carbon structure, composition of coal macerals and minerals, and plastic layer behavior of separating components were characterized by nuclear magnetic resonance spectrometer (13C NMR), coal rock analyzer, X-ray fluorescence spectrometry (XRF) and Gieseler fluidity. Combining with X-ray photoelectron spectroscopy (XPS), effect of different gas coal separation components on sulfur transformation behavior during pyrolysis of high-sulfur coal and distribution of sulfur forms in coke was investigated. The results show that with increase of vitrinite content in gas coal, the relative ratio of aliphatic carbon in coal increases, and the release amount of volatiles increases during pyrolysis; hydrogen free radicals in volatiles promote decomposition of sulfur, stabilize sulfur free radicals in time and release as sulfur-containing gases, and thus sulfur content in coke is reduced. Low density components in gas coal have the largest maximum fluidity and widest plastic range, and stability of plastic layer is the best during co-pyrolysis with high sulfur coal. The basic minerals in gas coal are mainly enriched in high density components, which leads to increase of sulfide sulfur and sulfate sulfur in the coke. For utilization of gas coal in coal-blending pyrolysis, enrichment of vitrinite and selection of coals with easier removal of alkaline minerals are beneficial for reducing sulfur in coke.
Abstract: In order to obtain the mechanism of the effect of CO2 on the NO heterogeneous reduction, density functional theory (DFT) was adopted to investigate the interactions between char and NO with the participation of CO2. The armchair configuration composed with several aromatic ring clusters was selected as the carbonaceous surfaces. Geometric optimizations were carried out at the B3LYP-D3/6-31G(d) level. Energies of optimized geometries were calculated at the B3LYP-D3/def2-TZVP level. The results show that, the surface carbonyl groups produced by the adsorption of CO2 combine with the adsorbed NO to desorb CO2, thereby providing adjacent carbon active sites for subsequent NO adsorption and N2 desorption. Thermodynamic studies show that the exothermic heat of this reaction is 853.9 kJ/mol, and the highest energy barrier is 297.0 kJ/mol without the participation of CO2, but the exothermic heat of this reaction is 593.7 kJ/mol, and the highest energy barrier is 214.1 kJ/mol with the participation of CO2. Kinetic studies show that over the temperature range of 298.15–1800 K, the reaction rate constants of rate-limiting steps are calculated with conventional transition state theory. The rate constant with the participation of CO2 is higher than that without the participation of CO2. In summary, CO2 plays a promoting role in interacting with NO and char and reducing energy barrier to form N2 directly.
Abstract: Three agricultural residues (peanut straw, sorghum stalk and reed) were first pretreated by water washing, with which the pyrolysis experiments were carried out in a fixed bed reactor to investigate how the pyrolysis characteristics are changed by removing the alkali earth metals (AAEMs) and a part of fibrous components by water washing. The result shows that the water washing removes 52.7%–92.6% potassium and approximately half of neutral detergent solute (NDS) from three agricultural residues. The removal of AAEMs and NDS has a complex influence on the pyrolysis of agricultural residues, especially for peanut straw due to its higher contents of both AAEMs and NDS. However, the removal of AAEMs has an inhibitory effect on the reactions such as decarboxylation, decarbonylation, dehydrogenation and polycondensation, and the elution of NDS directly affects the yields and composition of gas and liquid products. For all three agricultural residues, overall, the water washing promotes the production of bio-oil and bio-char, but it lowers the gas yield. The bio-oils generated from the water-washed agricultural residues have higher proportions of oxygenates, especially sugars and furans, with lower proportions of hydrocarbons and nitrogenous compounds. Besides, after washing, the yields of CO2, CO and CH4 with peanut straw decrease significantly, while the proportion of long-chain fatty acids in bio oil increases.
Abstract: Chemical looping methane reforming is a potential route to co-produce syngas and hydrogen by using the oxygen carrier (metal oxide). The oxygen carrier CeO2/LaFeO3 was prepared by sol-gel method, and the structure and oxygen supply capacity of the oxygen carrier were analyzed by X-ray powder diffraction and hydrogen temperature programmed reduction. The influence of CeO2 ratio and reaction temperature on the performance of the oxygen carrier were discussed through fixed bed reaction tests. The content of CeO2 had a significant effect on the oxygen supply capacity of the oxygen carrier. Increasing reaction temperature not only was conducive to methane activation, but also enhanced lattice oxygen migration in the oxygen carrier. A suitable reaction temperature could match methane activation with lattice oxygen migration, thereby improving the selectivity of the oxygen carrier. Experimental results showed that performance of the oxygen carrier was in the optimal when CeO2 content was 10% and reaction temperature was 850 ºC. CH4 conversion rate could reach 94%, H2 selectivity and CO selectivity could reach 90% and 83%, respectively. The oxygen carrier 10%CeO2/LaFeO3 could maintain stable reaction performance and structure in the redox cycles.
Abstract: Conversion of cellulose and starch to furfural was investigated over four zeolites. The zeolites were characterized by X-ray diffraction, 27Al MAS NMR, IR spectra of pyridine adsorption and NH3 temperature-programmed desorption. The roles of acidity and pore structure of zeolites in conversion of cellulose and starch were discussed in detail. The results showed that Hβ zeolite with appropriate Brønsted acid sites, Lewis acid sites and pore structure was effective to produce furfural from cellulose and starch. HY zeolite could not catalyze cellulose reaction with high conversion because of its weak acidity. However, HY zeolite was effective to produce 5-hydroxymethylfurfural (HMF) from starch. H-mordenite and HZSM-5 zeolites with fewer Lewis acid sites could not cause the isomerization reaction from glucose to fructose. So, the further conversion of fructose to furfural or HMF was inhibited. The formation of HMF only depended on the acid properties of zeolites. The formation of furfural was not only determined by the acidity of zeolites, but also by their appropriate pore structure.
Abstract: In this work, a rod-shaped Al2O3 with high specific surface area and rich in unsaturated pentahedral coordination Al3+ sites was synthesized by hydrothermal crystallization method, and the tungsten species was anchored on the surface of the Al2O3 support in the form of oligomeric nanoclusters using the incipient-wetness impregnation method. Then the platinum species were in close contact with the tungsten species in the form of small particle size and high dispersion through high temperature heat treatment. It greatly enhances the degree of interaction between platinum and tungsten species, is conducive to the generation of more active site structures, and significantly improves the catalytic activity of glycerol hydrogenolysis to 1,3-propanediol (1,3-PDO). In a fixed-bed reactor, when the reaction temperature is 160 ℃, the pressure is 5.0 MPa, and the 10% glycerol aqueous solution is continuously added, the catalytic reaction performance evaluation results show that the glycerol conversion of the Pt-WOx/Al2O3 catalyst is 75.2%, and the yield of 1,3-PDO reach 33.1%.
Abstract: Nanocatalysis is facing a technological revolution, which puts forward higher requirements for the accurate control of the size distribution and morphology of metal nanoparticles. Atomic layer deposition (ALD) is proposed as solution to this problem because of its character of accurate controlling metal distribution on atomic level. In this review, the development history, deposition mechanism as well as equipment and technology are summarized. Subsequently, the substrate types and microstructure of obtained catalysts are discussed. In particular, the latest progress of the synthesis and application of metal catalysts prepared by ALD are highlighted. Lastly, the challenges and prospects in ALD are illustrated.
Abstract: Metal-supported zeolite catalysts have been widely used in the NH3 selective catalytic reduction (NH3-SCR) reactions due to their wide temperature window and good hydrothermal stability. In this review, the research progress in the structural characteristics, catalytic performance and reaction mechanism of Cu- and Fe-based zeolite catalysts in NH3-SCR was summarized. In addition, the application of density functional theory (DFT) calculation in clarifying the reaction mechanism of NH3-SCR was introduced. Finally, the reaction kinetics and the apparent kinetic parameters of different metal-based zeolite catalysts in NH3-SCR were compared and discussed. We hope this review could provide new ideas for the study of NH3-SCR reaction mechanism over metal-supported zeolite catalysts.
Abstract: In this work, ZIF-8/Pt/SiO2 catalysts were prepared by combining atomic layer deposition (ALD) and vapor phase conversion methods. First, Pt metal nanoparticles were deposited on SiO2 nanowires by ALD. Then, ZnO was further deposited, also by ALD. Subsequently, the ZnO film was converted into ZIF-8 film by vapor phase crystallization to form a sandwich structure (ZIF-8/Pt/SiO2). The microstructures of the catalysts were characterized by XRD, TEM, BET, IC-MS, XPS, and CO-DRIFT. It was shown that the Pt particles were highly dispersed on the SiO2 nanowires before and after coating with ZIF-8, and the ZIF-8 film was coated continuously on the entire catalyst with high conformity. The performance of the catalyst was studied by using the semi-hydrogenation of 1-heptyne as a probe reaction. The ZIF-8 film induces an electron density increase in the Pt component, leading to an increase of the olefin selectivity from 14% to 70% in the 1-heptyne hydrogenation reaction. A reduced thickness of the ZIF-8 film increases the catalytic activity but does not affect the selectivity of 1-heptylene.
Abstract: A series of modified FER zeolite samples with different acid types, acid density and accessibility were prepared by using different concentrations of ammonium hexafluorosilicate (AHFS) for isomorphous substitution. The texture properties were characterized by XRD and N2 adsorption isotherms. And the acid properties were characterized by NH3-TPD and Py-FTIR. The results showed that when 1-butene and isobutene were respectively used as raw materials, the optimal reaction temperature for skeleton isomerization was 350 ℃, and the side reaction was more obvious when isobutene was used as raw material. During the dealumination process, two new Lewis acid sites with different strength were generated, due to the interaction between the dealumination agent and the extra framework aluminum hydroxyl species on the zeolite. During the reaction, the above two Lewis acid sites promoted the oligomerization-cracking of isobutene, thereby, reducing the selectivity of the main reaction.
Abstract: The LaCoO3/CeO2/cordierite, LaCoO3/γ-Al2O3/cordierite, LaCoO3/SiO2/cordierite monolithic catalysts were synthesized by the suspension coating method and sol-gel method in two steps using cordierite honeycomb ceramic as the substrate and nano-oxides (CeO2, γ-Al2O3, SiO2) as the coating carrier. The phase, microscopic morphology, element composition, redox property, adhesion strength, and texture properties of the samples were characterized and analyzed by XRD, SEM, XPS, H2-TPR, UT and N2 adsorption-desorption techniques. The catalytic activity, high-temperature stability, shutdown/restart cycle stability, and water vapor stability of the monolithic catalyst were evaluated through the catalytic combustion performance of VOCs. Experimental results show that three catalysts exhibit good catalytic activity and stability, and the type of coating can cause a difference in catalytic performance. Among three cattalysts, the LaCoO3/CeO2/cordierite catalyst has the best performance. When the volume fraction of toluene is 0.1% and the space velocity is 18000 mL/(g·h), the tempereratures for the conversion rates of 50% and 90% are 158 and 214 ℃, respectively. The toluene conversion rate is only reduced by 7% after 72 h of stability testing (high temperature, stop/restart cycle, water vapor). Characterization results show that the CeO2 nano-coating helps to form a catalytic layer with a porous and fluffy structure, which makes the catalyst have a higher ratio of adsorbed oxygen, strong low-temperature reducibility and good adhesion.
Abstract: The Fe3O4 loaded ceramic composite microwave absorbents were successfully prepared by recycling the solid waste coal gangue. First, the coal gangue based matrix was obtained by crushing, ball-milling, acid pickling, granulation and sintering process, and then the subsequent experiment involved loading precursor solution as well as in-situ carbothermal reduction. Moreover, the influence of Fe3O4 loading content on the microstructure and electromagnetic performance was also investigated. It was founded that the ceramic composites exhibited excellent microwave absorption when the reduction temperature kept 600 ℃ and the concentration of precursor solution was 1.25−1.5 mol/L, under which the minimum reflection loss value reached −20.1 dB and the effective absorption bandwidth kept 4.7 GHz as the coating thicknesses was 2.0 mm. This was attributed to the better impedance match and attenuation characteristic. The simple technological process provided in this work could offer a novel method for the recycling of coal gangue, and was beneficial for the low-cost of microwave absorbents.
Abstract: In recent years, metal-organic frameworks (MOFs) have gradually been used in the field of oxygen evolution reaction (OER). In order to improve OER performance, MOFs are usually used as precursors to prepare metal oxide/porous carbon composites by pyrolysis at high temperatures in previous studies. Although metal oxide/porous carbon composites show high catalytic activity, they require complicated preparation processes and high temperature. Therefore, it is very significant to find a highly efficient MOFs, which can be directly used as OER without pyrolysis treatment. The results show that when Co-ZIF-67/NF, Ni-MOF-74/NF and Fe-MIL-101/NF are used as OER catalysts in 1 mol/L KOH solution, 377, 383 and 272 mV overpotentials are required to make the current density achieve 10 mA/cm2. The charge transfer resistance (Rct) of Fe-MIL-101/NF is 1.53 Ω, which is smaller than that of Co-ZIF-67/NF (32.40 Ω) and Ni-MOF-74/NF (43.78 Ω). Therefore, the higher of the Rct of the catalyst, the smaller of the charge transfer capacity in the OER process. Thus, the fast charge transfer rate is the main reason for the excellent OER activity of Fe-MIL-101/NF. In addition, the OER activity of Fe-MIL-101/NF (272 mV) without pyrolysis treatment is much higher than that of commercial RuO2/NF (302 mV), indicating that MOFs with fast charge transfer rate can be used as an efficient catalyst for OER without calcination.
Abstract: With H2WO4 and EDA as precursors, WO3/C intermediate was obtained by mechanical stirring and in-situ solid-phase pyrolysis, then WS2/C composite material was obtained by high temperature vulcanization. The WS2/C composite was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and other instrumental analysis methods. At the same time, the electrocatalytic performance of the catalyst was analyzed by the electrocatalytic steady-state polarization curve (LSV), Tafel slope (Tafel), cycle stability (CP), electrochemical impedance (PEIS) and electrochemically active surface area (ECSA) tests of the material. The results show that when the current density of the WS2/C composite is 10 mA/cm2, overpotential is 179 mV, and Tafel slope is 98 mV/dec.
Abstract: Low-cost and high-performance catalyst is crucial for hydrogen generation via the hydrolysis of ammonia borane (NH3BH3, AB) as a chemical hydrogen storage material. In this work, Co-CeOx nanocomposites supported on graphene (Co-CeOx/graphene) were prepared through a facile impregnation and chemical reduction method and used as a catalyst in the hydrolytic dehydrogenation of ammonia borane. The results indicate that the as-prepared Co-CeOx/graphene nanocomposite exhibits superior catalytic activity and recycling stability in the hydrolysis of ammonia borane, owing to the ultra-fine size of Co-CeOx particles, the strong synergistic electronic effect between Co and CeOx, as well as the strong metal-support interaction between Co-CeOx and graphene. For the hydrolysis of ammonia borane over the optimized Co-CeOx/graphene catalyst, the turnover frequency (TOF) reaches 45.1 min−1, with the activation energy (Ea) of 39.5 kJ/mol; such a TOF value is 12 times and 9 times higher than those over Co and Co/graphene, respectively, also much higher than those reported for most noble-metal-free catalysts.
Abstract: The utilization of carbon dioxide as a resource through electrocatalysis is one of the ideal ways to alleviate or solve the current ecological crisis mankind facing. The development of inexpensive and efficient catalysts is the key to promoting the industrialization of electrocatalytic carbon dioxide reduction. CO is an important industrial raw material, as a result, CO2 reduction to CO has important research significance. However, high-active noble metal catalysts that can convert CO2 to CO are difficult to apply in large scale. Zn-based catalysts are potential substitutes. However, the reduction activity of Zn-based catalysts still can not meet the actual needs. In this paper, ZnOHF material is employed in the electrocatalytic CO2 reduction for the first time. ZnOHF nanorods of different sizes are prepared through a simple hydrothermal synthesis method and tested in a Flow-Cell. The large specific surface area of the nanorods and the existence of F atoms on the surface of the material lead to good catalytic activity. The Flow-Cell accelerates the reaction mass transfer process. At –1.28 V (vs. RHE), the R2-ZnOHF nanorods have the highest CO Faraday efficiency of 76.4% with the CO current density of 57.53 mA/cm2.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
