Current Articles

2024, Volume 52,  Issue 3

Display Method:
2024, 52(3): 1-8.
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A series of Cu-Mn-Zn/ZrO2 catalysts with different Zn contents were prepared by sol-gel method and characterized by XRD, BET, TPR, N2O-adsorption, XPS, TPD and in-situ DRIFTS. It was found that by increasing a certain amount of Zn, the catalytic activity for CO2 hydrogenation increased. Among all samples, Cu3MnZn0.5Zr0.5 (CMZZ-0.5) possessed the best CO2 conversion (6.5%) and methanol selectivity (73.7%) at 250 °C and 5 MPa. Characterization results showed that Zn entered the Cu1.5Mn1.5O4 spinel structure, forming ZnOx and thus more surface OH groups. This increased the content of Cu0 and Cuα+, which improved the activation of H2 and CO2. The pathway of CO2 to methanol was also clarified through in-situ DRIFTS.
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The massive emission of the greenhouse gas CO2 has caused problems such as global warming and ecological damage. How to effectively utilize CO2 as a resource and create economic benefits has attracted much attention in recent years. In this paper, a series of La-doped ZnO catalysts were designed and synthesized targeting the synthesis of ethylene carbonate (EC) from CO2 and ethylene glycol (EG), which could modulate the Lewis acid-base sites on the ZnO surface, and the catalyst activity was investigated under additive-free conditions. La-ZnO-1%-550℃ had the best catalytic activity with 0.54% conversion of EG, 7.326 mmol/(h∙g) and 99% space-time yield and selectivity of EC at 130 ℃, 4 MPa CO2, and 1 h with good stability. Combined with the analysis of the crystal structure, morphology and surface acid-base of the catalysts, the results showed that La was uniformly distributed in the ZnO hollow nanosheets, and the surface of the La-doped ZnO calcined at 550 ℃ had the most Lewis acid-base sites, and the catalytic activity of the catalysts increased with the increase of moderate to strong Lewis acid-base sites.
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Methane dry reforming reaction is a promising route for the valorization of both CO2 and CH4. However, the catalysts usually suffered from the coking deactivation and the sintering of active phase under the harsh reaction conditions. In this paper, the Mg-Al spinel support with different Mg content prepared by the solvent evaporation-induced self-assembly method was investigated. With this support, Ni/MgAl2O4 was used as the catalyst for methane dry reforming to syngas. XRD, BET and TEM results showed that the addition of appropriate amount of magnesium (10%−15%) was beneficial to the formation of highly stable ordered mesoporous magnesia spinel support with large specific surface area, which can confine the Ni particles in the pore structure and thus enhance the nickel dispersion and improve the resistance of coke formation under high temperature. H2-TPR and XPS analysis indicated the addition of 10%−15% magnesium can promote the interaction between Ni and MgAl2O4, inhibiting the agglomeration of Ni and the coke formation with the active surface-adsorbed oxygen species. Detailed activity tests showed that Ni/MgAl2O4 catalysts with 10%−15% magnesium content has high CH4 and CO2 conversion. During the long-term test for 180 h, the Ni/15-MAO catalyst exihibited the CH4 and CO2 conversions of 92.6% and 92.5%, respectively. The coke deposition percentage was only 0.89% and the grain size of Ni was maintained after reaction.
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The reaction mechanism of methanol/dimethyl ether (DME) carbonylation catalyzed by isomorphously substituted B-, Al-, and Ga-MOR zeolites (B/Al/Ga-MOR) was comparatively investigated by the density functional theory (DFT) calculations. The commonalities and differences between methanol and dimethyl ether as the reactant as well as among various MOR zeolites in the catalytic reaction pathways were disclosed, where one Si atom was substituted by B, Al or Ga at the 8-ring side pockets T3 sites or the 12-ring channels T4 sites of MOR. The results indicate that the insertion of CO into methoxy group to form acetyl groups follows the SN2 mechanism and is the rate-determining step in the carbonylation reactions. Under 473 K, either methanol or dimethyl ether is used as feedstock, the formed acetyl group prefers to interact with CH3O in methanol to form methyl acetate. The T3 sites show better carbonylation selectivity, whereas T4 sites display better trimethoxonium ions selectivity which favors the generation of aromatics and leads to the catalyst deactivation. Comparing with Al-MOR, the introduction of Ga and B at the T3 sites increases the free energy barriers of carbonylation, whereas the introduction of Ga and B in particular at the T4 sites can substantially increase the energy barriers of generating trimethyloxonium ions, which can effectively suppress the side reaction and improve the catalyst stability. This work contributes to the understanding of the catalytic roles of various acidic sites in different channels of the MOR zeolites and provides certain theoretical support for tailoring and designing efficient MOR zeolite catalysts for methanol/dimethyl ether carbonylation.
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Dimethyl carbonate (DMC) is an important and environmentally friendly chemical intermediate to meet the growing demand for a clean and sustainable energy supply. Among several routes for DMC synthesis, the oxidative carbonylation of methanol has attracted much attention with the advantages of a high utilization rate of carbon source, moderate operating conditions and environmental benefits. More importantly, the oxidative carbonylation of methanol is an important development route of modern coal chemical industry in China, and the key lies in the design of highly efficient catalysts. Copper-based catalysts have been used extensively in this reaction. Problems, such as reactor corrosion and catalyst deactivation, occur with chlorine-containing catalysts. The development of chlorine-free catalysts is the focus of current research. Recently, Cu-based catalysts supported on carbon materials have been used extensively in DMC synthesis because of its high activity, high selectivity and facile preparation process. However, the carbon-supported Cu catalysts suffer from the leaching and aggregation of Cu nanoparticles (NPs) in the harsh reaction conditions of high temperature, high pressure as well as severe stirring, leading to the deactivation. It has become a key scienctific problem that needs to be addressed urgently. In our previous studies, several strategies have been attempted to solve the deactivation problem caused by these reasons. For instance, encapsulating Cu NPs with hollow porous carbon spheres or mesoporous carbon materials. Besides, the introduction of N species in the carbon framework or sulfonic acid groups and oxygen-containing groups on the surface of carbon materials leads to an anchoring effect on Cu NPs. Great progress has been made via these methods, yet still unsatisfactory. Supported metal clusters have adjacent metal sites, countable numbers of atoms in each clusters, and limited size range (normally smaller than 2 nm). Benefiting from these distinct geometric and electronic structures, supported metal clusters can trigger synergistic effects among every metal atom, and thus exhibiting enhanced catalytic activity and selectivity in catalysis. Besides, the strong metal-support interaction on supported metal clusters improve the stability of metal clusters, enhancing the catalytic stability. To prevent the aggregation of metal clusters, the metal loading of supported metal clusters catalysts are generally kept at a low level (≤1%). However, catalysts with insufficient numbers of active sites always lead to compromised mass-activity, which greatly restrict them from industrial applications. Hence, the synthesis of supported metal clusters with high metal loading and high stability is a great challenge. In this study, the Cu clusters catalysts with high Cu loading were synthesized via liquid phase reconstruction method under the condition of water and CO. The optimal 15Cu/NCNS-12-CO exhibited superb activity with STYDMC of 3520 mg/(g·h) and stability with the loss rate of 28% after 10 cycles. A series of characterization showed that the strongly reducing CO not only resulted in the partial reconstruction of copper nanoparticles (from ~9.7 nm to ~1.34 nm), but also effectively maintained the existence of Cu0 species, improving the catalytic activity and stability. Further investigation showed that the reconstruction of Cu nanoparticles was dependent on the interaction of atmosphere-metal-support, and was reversible under the oxidation and reducing atmosphere.
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Hydrodeoxygenation of lignin bio-oil to prepare liquid fuels is a very promising route. In this paper, a series of catalysts (Ru/CeO2, Ru/Nb2O5, Ru/ZrO2, Ru/Al2O3 and Ru/CeOx) supported on metal oxides were prepared by incipient wetness impregnation method, which were used to study the upgrading and hydrogenation of lignin-derived phenolic compounds phenol to cyclohexanol. By means of X-ray crystal diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), the structure and physical and chemical characteristics of the prepared catalyst were characterized. It was found that the oxygen vacancies contained in Ru/CeOx could adsorb the raw materials with oxygen groups well, which was beneficial to the efficient hydrogenation of phenol. At the same time, XPS showed that the effective active centers in Ru/CeOx, RuO2 and Ru0, were active sites for catalytic hydrogenation. Therefore, the combined action of oxygen vacancies and metal active sites made the catalyst have good hydrogenation activity. The effects of reaction temperature, pressure and time on hydrogenation were also investigated. It was found that the catalyst could completely convert phenol at a mild temperature (140 ℃) and the yield of cyclohexanol was 90.2%. The cycle characteristics of the catalyst were investigated, and it was found that the catalyst still showed excellent hydrogenation activity after being recycled for 4 times. At the same time, the intermediate products in the hydrogenation process were detected by GC-MS, and then the reaction path of phenol hydrogenation process was deduced.
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Fe-Al-Ti oxygen carriers have good cycling stability and good properties of anti-carbon deposition in the chemical looping hydrogen generation (CLHG) process. However, the formation of FeAl2O4 reduces hydrogen yield and increases sintering. To weaken the formation of FeAl2O4 and to promote properties, the core-shell oxygen carriers of Fe@Al-Ti were prepared by self-assembly template combustion method, which took TiO2 as the inter-layer to separate Fe2O3 and Al2O3. The effect of multi-layer core-shell structure on reaction performance was evaluated on a fixed bed. The results indicated that the inter-layer of Fe@Al-Ti oxygen carriers effectively weakened the contact between Fe2O3 and Al2O3, thus reducing the formation of FeAl2O4 and improving properties of anti-sintering. The Fe@Al-Ti oxygen carriers significantly prevented carbon deposition and surface agglomeration, and had great cycling stability during the CLHG cycles. The core-shell oxygen carrier with a molar ratio of Al∶Ti=3.5∶1 got the highest carbon conversion rate and H2 yield, and oxygen storage capacity in a single cycle, with 57.4%, 75.0%, and 6.01 mmol/g, respectively, which were 28.4%, 30.0%, and 26.9% higher than those of non core-shell Fe-Al-Ti oxygen carriers.
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Red mud is a solid waste in aluminum industry and has been proven to be an efficient alternative to NOx selective catalytic reduction (SCR) catalysts. Acid washing treatment to red mud can improve its alkalinity and surface properties, and increase the conversion rate of NOx. In this paper, Cu, Ce, and Cu/Ce was supported on acid washed red mud and NOx catalytic conversion performance on metal modified red mud catalysts was studied. The research results indicate that Cu+ and Cu2+ in the Cu supported catalyst effectively promote NO conversion rate of red mud in low-temperature (200−300 ℃) flue gas, reaching a maximum of 90.7%; Ce3+ and Ce4+ in Ce supported catalysts effectively promote the NO conversion rate of red mud in flue gas at 200–400 ℃, reaching a maximum of 94.0%; Cu/Ce supporting exhibits better NO conversion rate than single metal supported catalysts at low-temperatures, the optimal Cu∶Ce ratio for supporting is 1∶1; and also exhibits better NO conversion rate than Cu supported catalysts at high-temperature (300−400 ℃), reaching a maximum of 95.5%. The reason may be that under the synergistic effect of Cu/Ce, ACRM-Cu1Ce1 has stronger low-temperature redox ability, higher weak acidic peaks, higher average oxidation state of Fe ions, and higher Cu+ content.
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A series of Cu(x)Co(y)Ce(z)-LDH precursors were synthesized by one-step hydrothermal method, and Cu(x)Co(y)Ce(z)O mixed metal oxide catalysts were prepared after calcination and used to study the selective catalytic reduction of NO by C3H6 (C3H6-SCR) with a fixed bed micro-reactor. Due to the strong synergy between Cu, Co and Ce, Cu(0.21)Co(0.48)Ce(0.31)O achieves 95% NO conversion and 90% N2 selectivity at 225 ℃. In addition, ICP, XRD, TEM, XPS, H2-TPR were used to characterize the basic physical-chemical properties of the catalysts to investigate the relationship between physicochemical properties and catalytic reduction abilities. XRD results show that solid solutions are formed between Cu, Co and Ce, which promotes the dispersion of active metals. XPS and H2-TPR further demonstrate that redox reactions occur between Cu and Co, promoting the formation of oxygen vacancies, thereby improving their catalytic reduction capacity.
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An AgY molecular sieve modified by Ag+ ion was characterized by XRD, FT-IR and N2 adsorption and desorption and used to the adsorption denitrogenation from model fuels containing pyridine, aniline and quinoline basic nitrides. The adsorption capacity for N with the AgY molecular sieve was obviously better than that with the NaY molecular sieve. The effects of adsorption temperature and adsorption time on the adsorption capacity of three kinds of nitrides by AgY molecular sieve were investigated. The experimental results show that the adsorption capacity for N is aniline>quinoline>pyridine. To study the adsorption mechanism of AgY, the 12T cluster model of AgY molecular sieve was established by Materials Studio software and the adsorption of three kinds of nitride molecules on the AgY molecular sieve was simulated at 303 K, 323 K and 343 K. The adsorption energy, the distance between the active center and pyridine, aniline and quinoline molecules, the frontier orbit, the isodensity distribution, the radial distribution function and other relevant parameters were calculated. The calculated results show that the adsorption of aniline by AgY molecular sieve is better than that of quinoline and pyridine, which is consistent with the experimental results. Moreover, the adsorption is mainly the chemical adsorption, and the S and W sites of AgY molecular sieve are the main adsorption sites. The results of isothermal adsorption show that the adsorption of pyridine on the AgY follows the Langmuir-Freundlich mixed adsorption model, and the adsorption of aniline and quinoline follows the Freundlich adsorption model. The results of adsorption kinetics and thermodynamics show that the adsorption of pyridine on the AgY molecular sieve conforms to the quasi-second-order kinetic model, while the adsorption of aniline and quinoline conforms to the quasi-first-order kinetic model, and all adsorption processes are spontaneous entropy increasing process.
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Ni-based catalysts were prepared by mechanochemical method with SAPO-11 zeolite as the carrier, and W was introduced to adjust the electronic structure, grain size and morphology of Ni particle, as well as pore structure, acidity, and acid amount of the catalyst. The effect of NiW ratios on catalyst properties and the hydro-isomerization properties of n-eicosane (n-C20), which is a model compound for coal tar hydrogenation tail oil, was explored by XRD, TEM, BET, NH3-TPD and Py-FTIR. The results show that the specific surface area of Ni/SAPO-11 increases with the addition of W, and reaches the maximum value of 149 m2/g at the W addition of 0.5%. The average particle size of Ni decreases with the addition of W, and reaches to the minimum value of 4.43 nm at the W addition of 1%, which is 36% less than that of Ni/SAPO-11. At this time, the content of Ni0 and the amount of surface acid are the highest. In addition, W promotes the reduction of Ni, causing the reduction peak temperature to move toward lower temperature. XPS results show that with the increase of W content, the binding energy of Ni0 decreases while that of W5+ increases. The isomers distribution of eicosane (n-C20) shows that the conversion of n-C20 and the yield of i-C20 are the highest in the presence of 3Ni1W/SAPO-11, which are 88.23% and 75.72%, respectively. It is mainly the mono-i-C20 with a yield of 71.65%. The on-line sampling results show that n-C20 generates the mono-branched isomer under the action of metal site and acid function. With the reaction, the mono-branched isomer is transformed into the multi-branched isomer, and the unstable multi-branched isomer is cracked into small molecule alkanes.
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Coal pitch, a byproduct of coal coking, is an ideal precursor for preparing conductive carbon fillers because of its rich aromatics and high yield of carbonization products. In this paper, coal pitch-based carbon materials with controllable morphology and structure were prepared by carbonization using coal pitch and multi-walled carbon nanotubes as raw material and structure-directing agent, respectively. The effect of carbon nanotubes on the structure and electrothermal properties of carbon materials was investigated. The results show that the doping of multi-walled carbon nanotubes results in an increase in the lattice arrangement order, a decrease in lattice spacing, and an increase in graphitization degree of conductive fillers, which leads to a significant increase in the carrier concentration of the carbon film and thus its conductivity. The doping of 2% carbon nanotubes can increase the carrier concentration of coal pitch-based carbon film by 3.2 times and reduce the resistance of coal pitch-based carbon film by 67%. At 5, 10 and 15 V, the heating temperature of the coal pitch-based carbon film can reach 44, 88 and 165 ℃, respectively, which is enhanced 7, 22 and 70 ℃ compared with the undoped carbon film, showing great application prospect.
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Constructing S-scheme heterojunction is an effective strategy to form photocatalytic materials with strong reduction property and improve photocatalytic performance. In this paper, NiTiO3/CdS photocatalytic materials with S-scheme heterostructures were prepared by a simple hydrothermal method. The photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), specific surface area analysis and Ultraviolet-visible diffuse reflection spectroscopy (UV-vis DRS). The hydrogen production performance was tested by the photocatalytic hydrogen production experiment from shale gas flowback water. The results showed that NiTiO3 and CdS were successfully compounded. In addition, 15% NiTiO3/CdS showed the optimum hydrogen production performance (1568.9 µmol/(g·h)), and excellent recycling potential. This work is of great significance for the exploration of efficient and stable photocatalysts with S-scheme heterojunctions, the efficient utilization of wastewater and the alleviation of energy shortages.
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Hydrazine hydrate is the most promising hydrogen storage material with a hydrogen content of 8.0%. In this paper, after Ti2O3 support was prepared by H2 reduction, NiPt/Ti2O3 nanocatalyst was prepared by wet chemistry impregnation reduction method and used to catalyze hydrazine hydrate. The research shows that an alloy is formed between Ni and Pt during the preparation of the catalyst, and the formation of the alloy increases the catalytic activity of the catalyst. The interaction between Ti2O3 and NiPt alloy is helpful for the catalytic performance and cyclic stability of the catalyst. The TOF value of the Ni5Pt5/Ti2O3 catalyst for hydrogen production from hydrazine hydrate is 1076.1 h−1, which is superior to the reported catalyst performance.
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In this paper, layered porous carbon sheet (LPCS) was obtained through high temperature calcination under argon atmosphere by using coal pitch as carbon material, sodium chloride as template agent and potassium carbonate as activator. Then, the active component Ru was loaded onto the LPCS support by impregnation to synthesize Ru/LPCS catalyst whose catalytic performance for hydrogen production by hydrolysis of ammonia borane was studied. The results showed that in the presence of light, the maximum value of the turnover frequency (TOF), 334.8 min−1, was obtained at a calcination temperature of 1123 K and a loading of 2% of Ru which is 1.38 times higher than that in the absence of light. The activation energy (Ea) of the catalyst decreased from 90.60 to 70.33 kJ/mol in the presence of light. The hydrogen production rate order with respect to ammonia borane concentration was 0.75, which is first-order relation to the amount of the catalyst.
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Biomass energy is recognized as a zero carbon renewable energy source, and the efficient utilization of biomass has become the key to address the energy and environmental crises. It is of great important for China to achieve the goals of “carbon peaking” and “carbon neutrality”. The co-catalytic pyrolysis technology (co-CFP) of biomass and waste plastics can not only produce the value-added hydrocarbon-rich liquid fuels, but achieve the goal of “treating waste with waste” as well, thereby achieving efficient resource utilization of biomass and waste plastics. From the perspective of high value utilization of biomass and waste plastics, this work reviewed the research progress of the co-CFP of biomass and waste plastics to produce hydrocarbon-rich liquid fuels. First, the basic chemical characteristics of cellulose biomass and waste plastics were introduced. The influence of the catalytic pyrolysis temperature, the types of waste plastics, the types of catalyst, the mass ratio of feedstock-to- catalyst on the yield and quality of bio-oil during the co-CFP of biomass and waste plastics was systematically discussed. The synergistic reaction mechanism between biomass and waste plastics was elucidated. Finally, the work forecasted the future development direction of the co-CFP of biomass and waste plastics, and provided reference and ideas for the high value-added utilization of biomass and waste plastics.
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Molecular dynamics simulation (MD) has become an indispensable means to study the adsorption mechanism of dispersants/surfactants on the surface of coal particles. In this paper, the basic principle of MD is described in terms of force field, geometry optimization, Newton equation of motion, periodic boundary condition, ensemble, temperature and pressure control method, step size and step number. At present, there are three methods for constructing coal macromolecules: classical model, self-constructing model, the graphene layer modified by oxygen-containing functional groups. In the results of MD, the image information of adsorption configuration can directly observe the adsorption status and adsorption process, and the quantitative results, including density distribution curve, root mean square displacement of water, and adsorption energy, can reveal the adsorption mode of dispersant/surfactant. MD combined with experimental methods can shed light on the adsorption mechanism of dispersants/surfactants on the surface of coal particles from both microscopic and macroscopic perspectives, which will provide important theoretical support for the development and application of the dispersant and flotation agent.