Abstract: In the process of gasification for different size of coal particles, there are remarkable differences in the cracking mode, behavior of volatile removal and coke-slag interaction. These differences lead to the discrepancies in structural characteristics and reaction behavior for fine slag. Therefore, it is considered that the study on relationship between structure, properties and size distribution of fine slag from entrained flow gasification can provide vital guidance for analyzing the formation mechanism of fine slag and optimizing the size of coal particles for gasification. For this purpose, the fine slag from Ningdong typical GSP technology in Ningxia Province was selected as a raw material. After drying, crushing and sieving, three kinds of samples with size of <0.125, 0.125–0.250 and >0.250 mm were prepared, and called small, medium and large size samples respectively. The nitrogen adsorption, XRD, Raman spectroscopy and TGA were applied to clarify the physicochemical structure and combustion reactivity of samples. It is found that there are huge differences in the composition, structure or reactivity of the samples in different size. Precisely, three types of samples account for 22%, 46%, and 32% respectively. All the fine slag contains a large number of spherical particles and irregular particles. The sample with the middle size particles, which has the most content of residual carbon (19%) and the lowest graphitization degree (30%), shows the slightest gasification degree. It also presents the largest specific surface area (87.8 m2/g), and the optimal combustibility index regardless of the heating rate. While, the above properties of the sample with large size particles are completely opposite. Apparently, coal gasified sufficiently tends to form fine slag in large particle size, while coal gasified insufficiently is more likely to form slag in middle particle size. To some degree, all these findings can supply a certain basis to the study of gasification process. Meanwhile, the medium-sized fine slag with the most content in fine slag has low gasification degree, large content of carbon, and large specific surface area and porosity, which still has a certain potential utilization value for the treatment and disposal of the fine slag.
Abstract: Interactions of potassium-based catalysts with Shenfu (SF) char during catalytic gasification was observed by an in-situ heating stage microscope. The effects of the gasification temperature (800−900 °C) and the catalyst loading (4.4%, 10%) on the reactivity of coal char were investigated. The heating stage microscopy was used to visualize the catalytic gasification process of coal char particles and the fractal theory was introduced to analyze the surface structure of coal char particles to reveal the gasification reactivity. The experimental results show that the fractal dimension of coal char particles is positively correlated with the carbon conversion rate, and the fractal dimension increases by increasing the gasification temperature and the catalyst loading. The relationship between the initial gasification reaction rate and the fractal dimension of coal char particles is consistent with that between the carbon conversion rate and the fractal dimension of coal char particles. There is an exponential relation between the fractal dimension of coal char and the char angle; the fractal dimension increases with the increase of coal char particle angle; and the fractal dimension of coal char particles can be used in the study of coal char catalytic gasification process.
Abstract: High-temperature coal tar foaming phenolic resins and phenolic foams were prepared by partially displacing petroleum-based phenol. High-temperature coal tar and the phenolic foams were analyzed with gas chromatograph/mass spectrometer and infrared spectroscopy. Morphology and performance of the phenolic foams including compression strength, slag rate, thermal stability, flame resistance, and thermal insulation were characterized with optical microscope, thermogravimeter, limited oxygen index instrument, and thermal conductometer. The results show that compression strength of the phenolic foams slightly decreases and slag rate reduces, which indicates the enhancement of toughness. Moreover, the phenolic foams possess good thermal stability, flame resistance, and thermal insulation. When the substitution rate is 10%−15%, it has the maximum limited oxygen index of 36.1% and minimum thermal conductivity of 0.034 W/(m·K). The aforementioned results suggest that high-temperature coal tar can be used to partially substitute phenol to prepare phenolic foams with good performance, which provides a new route for high value-added utilization of high temperature coal tar.
Abstract: The conversion of CO2, an abundant carbon resource, into high value-added chemicals or liquid fuels is an attractive way to mitigate carbonemissions, which is also a sustainable approach for the cyclic utilization of carbon resources. However, the selective activation and controllable conversion of CO2 is challenging because of the inertness of CO2 and high C–C coupling barrier. In recent years, some obvious breakthroughs on CO2 hydrogenation to high value-added chemicals or liquid fuels have been made by construction of a tandem catalytic system. For the tandem catalysis, the matching of Fe-based catalyst or metal oxides and zeolites, the assembly between the two active sites, the pore structure and acidity of the zeolites, as well as the reaction conditions and atmosphere all have important effects on the product distribution. Herein, the critical factors affecting the CO2 activation and conversion and the formation of the target products, as well as the stability over the tandem catalysts are summarized. Finally, an outlook is provided.
Abstract: In the industrial circumstances, sulfur-containing species are frequently present simultaneously in the exhaust gas, containing methane, ethane and volatile organic compounds (VOCs). These species may occupy the active sites on the catalyst surface during the oxidation reaction, causing temporary physical deactivation of the catalyst. Moreover, permanent deactivation might occur when sulfur-containing species react with the active sites, which thereby causes the poisoning and invalidation of the catalysts. This paper reviewed the anti-toxicity properties of precious metals, composite metal oxides and perovskite-type catalysts adopted in the catalytic combustion of exhaust gas. The detailed poisoning mechanism of the catalysts was discussed, and the way to improve the anti-toxicity of the catalyst was also proposed accordingly. This review may provide some insight into the development of catalysts with high resistance to sulfur poisoning.
Abstract: As a typical saturated bicyclic compound, decalin is normally used as a probe molecule of saturated cycloalkanes for the mechanism study of selective ring-opening reaction during the hydrogenation of light cycle oil. In this review, the molecular structure and reaction characteristics of cis-decalin and trans-decalin are introduced. The mechanism of the selective ring-opening reaction of decalin based on different catalytic systems is systematically analyzed, including the carbocation mechanism on monofunctional acid catalysts, the hydrogenolysis reaction mechanism on monofunctional metal catalysts, and the bifunctional ring-opening reaction mechanism on acid-metal bifunctional catalysts. In addition, the effect of the process conditions, such as reaction temperature, support acidity and zeolite pore size, on the performance of selective ring-opening reaction of decalin are summarized. Finally, the shortcomings of current research are put forward, and the urgent and deserved research topics are proposed.
Abstract: The way of CO dissociation, as a crucial step in the Fischer-Tropsch (F-T) synthesis process, has been a subject of intense debate in literature. In order to understand the F-T synthesis reaction behavior of cobalt catalysts with different crystal planes, the CO dissociation behavior over three cobalt catalysts with different crystal facets during F-T reaction was investigated by excluding the influence of support, promoter and particle size. The catalysts were characterized by temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), in-situ Raman and Chemical Transient Kinetics (CTK). The results show that CO on the Co(10-11) is activated by direct dissociation, among which small amount of carbonaceous species generated by CO dissociation forms carbon depositing on the catalyst surface under F-T reaction condition, and a large amount of carbonaceous species are hydrogenated to CHx species. The CO on the Co(0001) crystal surface is activated predominantly by hydrogen-assisted dissociation, a large fraction of CO is dissociated into carbon deposition and a tiny fraction of CO is hydrogenated into CHx. CO is directly dissociated on the Co(11-20) plane. The weak dissociation of CO on this catalyst results in a trace amount of carbon deposition, and a trace amount of CHx intermediate in the presence of hydrogen.
Abstract: Titanium subgroup nanometallic oxides (TiO2, ZrO2 and HfO2), prepared via supercritical method, were combined with ZSM-5 and quartz to obtain bifunctional catalysts (Ti/HZ, Zr/HZ, Hf/HZ) and metal oxide catalysts (Ti/Si, Zr/Si, Hf/Si) respectively. The effect of crystal structure, surface oxygen vacancy and syngas adsorption of metal oxides on the catalytic CO hydrogenation was investigated. The results show that the bifunctional catalysts could directly catalyze the syngas to aromatics. The oxygen vacancy concentration, oxygen electron properties and the H/C ratios (the adsorption ratio of CO to H2) of the metal oxides synergistically determine the type of intermediates on the metal oxide surface. The CHxO* species generated on the surface of ZrO2 is beneficial for Zr/HZ catalyst to obtain higher aromatic selectivity (71.15%), while CH3* on TiO2 and HfO2 leads to higher CH4 selectivity for Ti/HZ and Hf/HZ catalysts. The results of this research could provide a valuable reference for design of syngas aromatization catalyst.
Abstract: The activation of C−H bonds of CH4 is a key step for the conversion of methane to chemical commodities. Loading Ni onto ZrO2 is regarded as a relatively efficient way to harness the beneficial electronic property and the fine dispersion of the Ni catalyst for CH4 dissociation. Herein we demonstrate the crucial role of Ni13 catalyst supported on ZrO2 for the dissociation of CH4. The density functional theory (DFT) results show that the ZrO2 supported Ni13 stabilizes all species better and facilitates CH4 activation. The stepwise dehydrogenations of CH4 on Ni13-ZrO2(111) exhibits longer C−H bond lengths of ISs , lower Ea, and smaller displacements between the detaching H and the remaining CHx fragment in TSs . In addition, they are also thermodynamically more feasible. However, without the ZrO2 support on Ni13, the opposite results are obtained. Consequently, the ZrO2 modified Ni13 is more superior to the original Ni13 in CH4 dehydrogenation. The electronic analysis combining DFT calculations confirmed that the larger overlap between C 2p and Ni 3d, and the electron transfer of Ni→C cause the weaker C 2p−H 1s hybridization. In addition, the reduction of electron transfer of H→C leads to a stronger interaction between Ni and C along with a weak C−H bond. Hence, the ZrO2 support serves as the d-band electron reservoir at Ni13 and it is benefit to the activation of C−H bonds in CH4 dehydrogenation.
Abstract: The technology of alkylation of toluene with methanol to p-xylene has attracted much attention due to the high selectivity of p-xylene and low energy consumption in product separation unit. Twin HZSM-5 molecular sieve has the characteristics of large coverage proportion of zigzag channels on the surface and less aluminum distribution on the outer surface. It shows high selectivity for p-xylene in the alkylation of toluene and methanol. In this paper, silicalite-1 (S-1) was grown epitaxially on the surface of twin HZSM-5 molecular sieve by hydrothermal crystallization, and twin HZSM-5@Silicalite-1 core-shell catalyst was obtained. Compared with twin HZSM-5, HZSM-5@40Silicalite-1 core-shell catalyst shows excellent catalytic performance in toluene methanol alkylation. Under the reaction conditions of 470 ℃, 0.1 MPa and hydrogen atmosphere, the conversion of toluene is 8.5% and the selectivity of p-xylene is 98.4%. Then, the effect of solid-liquid mass ratio of nuclear HZSM-5 and silicalite-1 shell precursors on the growth of silicalite-1 crystal was further studied, and the effect of silicalite-1 on the catalytic performance of twin HZSM-5 was investigated. The pore structure and acid properties of core-shell materials were studied in detail by SEM, XRD, XRF, liquid static adsorption, N2 adsorption desorption, NH3-TPD and Py-FTIR.
Abstract: A bifunctional catalyst of Ru5/ASA-TiO2 was prepared by using a novel silicon-aluminum (ASA)-TiO2 amorphous composite, which was synthesized by a steam-assisted method, as the support. X-ray diffraction (XRD), pyridine adsorption infrared (Py-FTIR), ammonia-temperature-programmed desorption (NH3-TPD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and other methods were used to characterize the structure and the acidity of the prepared catalyst. Using diphenyl ether as the lignite-related model compound, the reaction activity of the Ru5/ASA-TiO2 for the catalytic hydrogenolysis of 4–O–5 type ether bonds was investigated under a mild condition. The results show that the weak acid and/or the Lewis acid rather than the strong Brønsted acid mainly contribute to improve the conversion rate and the benzene yield of the catalytic hydrogenolysis of diphenyl ether. The reaction temperature can influence the relative content of various types of acids to significantly affect the selectivity of the hydrogenolysis products of diphenyl ether. The conversion rate of diphenyl ether is greater than 98% while the benzene yield is 67.1%.
Abstract: As ammonia slip becomes more serious with the traditional deNOx application, ammonia-free technologies have received more and more attention recently. Cu-K bimetal loaded activated carbon catalysts were prepared by equivalent-volume impregnation method for the direct reduction of NO and showed good NO reduction performance in a wide temperature range under temperature-programmed surface reactions (TPSRs) conditions in aerobic and anaerobic environments. The catalysts were characterized by BET, SEM, XRD, XPS, H2-TPR, Raman and FT-IR techniques and the NO reduction mechanism was analyzed. Experimental results show that the active functional groups formed on the surface of activated carbon are the important intermediate products and play a key role in the reduction reaction. The presence of O2 greatly promotes the formation of the intermediate, C(O) (Oxygen-containing functional groups on the carbon surface), leading to the increase reduction rate of NO. The bimetallic oxides catalysts are obviously effective to directly reduce NO. When the ratio of copper: potassium is 2∶1, the NO reduction efficiency is about 90% at 300 °C. The catalytic activity mainly depends on the redox cycle of CuO/Cu2O, and the potassium inhibits the agglomeration of copper on the surface of carbon materials and enhances the catalytic reactivity of Cu.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
