Abstract: A series of Cu/SiO2 catalysts modified with lanthanum (La) (30Cu-nLa/SiO2, n=0, 0.5, 1 and 2) were synthesized using the ethanol (EtOH)-assisted ammonia-evaporation method; their catalytic performance in the gas-phase hydrogenation of methyl acetate (MeOAc) to produce ethanol (EtOH) was investigated. The results indicate that the catalytic performance of Cu/SiO2 can be greatly enhanced by La modification. In particular, the 30Cu-0.5La/SiO2 catalyst exhibits excellent performance in the MeOAc hydrogenation; under 230 °C, 2 MPa H2, an LHSV of 2 h−1 and an H2/MeOAc molar ratio of 20, the MeOAc conversion reaches 98.5%, with a total EtOH yield of 97.0%. The N2-sorption, XRD, ICP-OES, H2-TPR, FT-IR, TEM, XPS, and AES characterization results reveal that the introduced La metal has a strong interaction with Cu, which can promote the dispersion of the copper species on the SiO2 support. Moreover, the content of Cu+ is increased significantly, which can enhance the electronic interaction with MeOAc via the acyl and methoxide groups and thus promote the hydrogenation of MeOAc to EtOH.
Abstract: A bifunctional catalyst was prepared by physical mixing of ZnZrOx metal oxide and SAPO-34 zeolite for the one-step conversion of synthesis gas to light olefins (STO) reaction. The effects of triethylamine, tetramethylammonium hydroxide and tetraethylammonium hydroxide solutions and different concentrations of triethylamine solution on the texture, structure and acidity of SAPO-34 zeolite were investigated. XRD, SEM, N2 adsorption and desorption, NH3-TPD were used to characterize the SAPO-34 zeolite and the STO reaction performance of the catalyst after alkali treatment was investigated. The results show that all three kinds of organic base with 0.06 mol/L post-treatment can etch some hierarchical channels on the surface of SAPO-34 zeolite, thus accelerating the diffusion of intermediate transition species formed on the surface of metal oxides into the channels of SAPO-34 zeolite in STO reaction, improving the CO conversion rate in STO reaction. At the same time, all three kinds of alkali treatments can reduce the acid amount and acid strength of SAPO-34 zeolite, thereby improving the selectivity for light olefins in the STO reaction. The treatment of SAPO-34 zeolite with 0.02−0.10 mol/L triethylamine resulted in the formation of hierarchical pores etched on the surface of SAPO-34 zeolite, which improved the conversion rate of CO in the STO reaction. Moreover, the acid strength and acidity of SAPO-34 zeolite treated with 0.02 and 0.06 mol/L triethylamine solutions decreased, inhibiting the formation of methane and the hydrogenation of light olefins. Therefore, as the concentration of alkali treatment gradually increased from 0, 0.02 to 0.06 mol/L, the selectivity for light olefins gradually increases. Under the reaction conditions of 400 ℃, 3.0 MPa and GHSV=3600 mL/(g·h), the CO conversion rate increased from 24.0% to 26.4%, and the selectivity of light olefins increased from 78.2% to 84.7% on the bifunctional catalyst composed of 0.06 mol/L triethylamine-treated SAPO-34 compared to untreated SAPO-34 zeolite, and the modified bifunctional catalyst had good catalytic stability.
Abstract: In this work, the reaction mechanism of DRM catalyzed by NiCo diatomic cluster was studied by density functional theory. Based on our studied that the minimum energy reaction path was found for four steps: CH4 dissociation, CO2 dissociation, oxidation of intermediates C* and CH*, and generation of H2 and H2O. Finally, the energetic span model was applied in the cycle reaction to obtain some kinetic information. At 298 K, it is hard to generate C* during the methane dehydrogenation process. At 913 K, the determining intermediate changes from IM1-1 to IM6-1, and the determining transition state changes from TS78-1 to TS56-1 of dehydrogenation of methane; Because of the reduction of energy spans, the elimination of C* and CH* are accelerated. This work can understand the mechanism of DRM catalyzed by NiCo diatomic clusters, which can provide theoretical reference for the experimental development.
Abstract: A series of Ce modified CuLDH-Cex catalysts were synthesized by adding different amounts of Ce to CuMgAl hydrotalcite (CuLDH) catalysts. The physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD), N2 adsorption-desorption (BET), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), etc. The results showed that the addition of Ce changed the hydrotalcite structure of CuLDH catalyst, and an appropriate amount of Ce increased the surface area of the catalyst and improved the dispersion of Cu particles. At the same time, an appropriate amount of Ce was beneficial for increasing the density of strong alkaline sites and the number of oxygen vacancies on the catalyst surface, promoting the adsorption and conversion of CO2. Ce was beneficial for adjusting the Cu+/Cu0 ratio on the catalyst surface, and a higher Cu+/Cu0 ratio was conducive to the formation of methanol. When the Ce/Cu ratio was 0.3, the catalyst exhibited higher activity with 7.5% CO2 conversion, 78.4% methanol selectivity and 362.8 g/(kg·h) spatiotemporal yield at 240 ℃ under 2.5 MPa with a GHSV=9000 mL/(g·h). It was proved by in-situ DRIFTS that CuLDH-Ce0.3 catalyst followed HCOO* reaction path during CO2 hydrogenation for methanol.
Abstract: A series of Cu1−xZrxO2 bimetallic oxides with different Cu-Zr molar ratios for glycerol carbonate synthesis from glycerol and CO2 were prepared by hydrothermal method. The results found that the performance was significantly affected by the Zr doping amounts. Under the optimal reaction conditions, the Cu0.99Zr0.01O2 catalyst had the best catalytic performance. The conversion of glycerol and the selectivity of glycerol carbonate reached 64.1% and 85.9%, respectively. Cu1−xZrxO2 complex oxide exhibited better activity than pure CuO and pure ZrO2. The structures, morphologies and surface properties of the catalysts were characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption and desorption, Temperature programmed reduction (H2-TPR), Temperature programmed desorption (TPD) and Fourier Transform Infrared Spectroscopy (FT-IR). It is speculated that the high activity is related to the degree of dispersion of Zr on the surface of CuO, the surface content of oxygen species and the number of acidic-basic sites. In addition, catalytic activity did not change significantly after six cycles, indicating the excellent stability of the catalyst.
Abstract: The Co3O4@MnOx monolithic catalyst with nanorod morphology was synthesized on nickel foam by a two-step hydrothermal process and characterized by XRD, EDS-mapping, H2-TPR, XPS, Raman and Soot-TPR. The catalytic soot combustion activities of the catalysts were investigated in a fixed-bed micro-reactor and the intrinsic activities of the catalysts were investigated by the isothermal kinetic experiments. The results reveal that the Co3O4@MnOx catalyst shows a core-shell structure with Co3O4 as the core and MnOx as the shell. Compared with Co-NW, there exist more high-valent state species of Mn4+ and Mn3+ and oxygen vacancies on the Co3O4@MnOx catalyst surface due to the interaction between Co3O4 and MnOx, which improve the redox performance of Co3O4@MnOx. Compared with Co-NW, the active oxygen species amount of Co3O4@MnOx is increased by two times, and Co3O4@MnOx shows enhanced activity, which lowers the ignition temperature by 148 ℃ in the presence of NO. Also, compared with Co-NW, Co3O4@MnOx decreases the activation energy of soot combustion reaction from 113.6 to 102.2 kJ/mol, and its intrinsic activity is increased by two times.
Abstract: Mn/TiO2 has good low temperature NH3 selective catalytic reduction (SCR) activity for NOx. The presence of alkali metals in the flue gas can physically and chemically poison the catalyst leading to toxic deactivation of the Mn/TiO2 catalyst. This study investigated the mechanism of K-poisoning in Mn/TiO2 low temperature SCR catalysts by preparing K-poisoning Mn/TiO2 catalysts using exposed {101} surface TiO2 as a carrier. It was found that the denitrification efficiency of the Mn/TiO2 catalyst decreased with increasing K-poisoning concentration. Experimental characterisation and DFT calculations showed that the NH3-SCR reaction on the surface of the fresh Mn/TiO2 catalyst was controlled by both E-R and L-H mechanisms. K adsorption led to a reduction in the catalyst specific surface area, a decrease in the ratio of Mn4+ and chemisorbed oxygen on the catalyst surface and a decrease in the number of acidic sites on the surface, resulting in a decrease in denitrification activity; at the same time, K was more likely to adsorb near the Mn top site as well as the bridging O site, resulting in the activation of NO adsorption was severely curtailed and the adsorption of NH3 was weakened, making the L-H mechanism blocked and the E-R mechanism the main control.
Abstract: Biomass has a wide range of sources and is porous, and it is a raw material for the preparation of adsorbents with high application value. The adsorption effect of metal oxide-modified biochar on CO2 and acetone can be significantly improved, but the together/competitive relationship and adsorption mechanism of metal oxide-modified biomass-based adsorbent for simultaneous adsorption of multiple components are not clear. Based on this, the co-adsorption relationship between CO2 and C3H6O on the surface of metal oxide-doped nitrogen-rich biochar was carried out, which is of great significance for the multi-component synergistic adsorption and removal of biomass-based adsorbents. In this study, the adsorption mechanism of CO2 and C3H6O (CO2&C3H6O) on the surface of different metal oxide-coupled pyrrole biochar (CN5@MOx, MOx=ZnO, CaO, Na2O) was explored by comparing the adsorption capacity, adsorption energy, state density and charge differential density analysis. Firstly, the adsorption capacity and adsorption energy of CO2/C3H6O single component were calculated from the CN5@MOx surface, and the calculation results show that at 333 K and 100 kPa, the adsorption capacity of CO2/C3H6O on the surface of the CN5@Na2O is 3.65 and 15.34 mmol/g, and the adsorption energy is −145.86 and −132.47 kJ/mol, respectively, which are higher than that of CO2/C3H6O on the surface of CN5@CaO and CN5@ZnO. It was concluded that Na2O-doped pyrrole-nitrogen biochar had the best adsorption effect on CO2/C3H6O one-component adsorption. The common/competitive adsorption of CO2&C3H6O on the CN5@MOx surface was further studied. The calculation results show that there are critical temperatures for the adsorption of CO2&C3H6O on the surface of CN5@Na2O, CN5@CaO and CN5@ZnO (333, 353 and 393 K, respectively), and the adsorption capacity of CO2&C3H6O coexistence system on the CN5@MOx surface is higher than that of CO2/C3H6O single component after the critical temperature. The adsorption energy of CO2&C3H6O on the surface of CN5@Na2O, CN5@CaO and CN5@ZnO was at least 141.59, 112.77 and 31.75 kJ/mol higher than that of CO2 or C3H6O single-component adsorption, respectively, and the adsorption of CO2 and C3H6O on the CN5@MOx surface showed a synergistic promotion effect, and the CN5@Na2O had the best co-adsorption effect on CO2&C3H6O. Finally, the electron density difference and density of state were used to analyze the mechanism of synergistic adsorption of CO2&C3H6O on the CN5@MOx surface, and it was concluded that the adsorption force of CO2 was generated by the indirect interaction between C3H6O and CO2, and the electron cloud of Na and C3H6O in Na2O overlapped, and charge transfer occurred, which enhanced the interaction force between the two. The binding energy of the main formant of C3H6O and CN5 in the p orbital on the CN5@Na2O surface is 3.43 eV lower than that of CN5@ZnO, making the most stable adsorption of C3H6O on the CN5@Na2O surface.
Abstract: The reasonable matching of zeolite and matrix is one of the most effective strategies to increase the yield of light olefins in naphtha catalytic cracking. However, the influence of the surface Lewis acidity within the matrix on the cracking reactions has remained ambiguous. Therefore, in present study, boron and zinc co-modified γ-Al2O3 and tin modified mesoporous silica KIT-6 with tuned surface Lewis acidity were applied to evaluate the cracking reactivity of n-heptane and 1-hexene to light olefins, in which the matrix was used alone and coupled with ZSM-5 zeolite in different packed modes. The effects of the modifiers on the textural properties and surface acidity of γ-Al2O3 and KIT-6 were investigated by XRD, TEM, N2 physical absorption-desorption, and NH3-TPD. The results showed that B doping reduced the Lewis acidity (both in the amount and acid strength) of γ-Al2O3, while the incorporation of Zn doping led to increased Lewis acidity. In addition, the Lewis acidity of ordered mesoporous KIT-6 increased as Sn doping rose. While for pure matrix, the ascend in conversions of n-heptane and 1-hexene was consistent with the increased Lewis acidity of the B and Zn co-modified γ-Al2O3 and xSn/KIT-6 rose, along with decreased activation energy. In contrast, when coupled with ZSM-5 zeolite, the highest conversion was achieved in the dual-bed manner of matrix and zeolite, and the conversion increased concomitantly with the increase in the Lewis acidity of the matrix. However, excessive Lewis acidity can accelerate the hydrogen transfer rate while diminishing the selectivity of light olefins.
Abstract: An Fe-based hydrodesulfurization (HDS) catalyst modified by Y zeolite was developed using Fe as the main active metal and Zn as a promoter. The change of morphology, pore structure, dispersity, reducibility, electronic defect structure and acidity of the Fe-based catalysts before and after modification were investigated using low-temperature nitrogen physical adsorption, X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), NH3-temperature programmed desorption (NH3-TPD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and pyridine infrared spectroscopy (Py-IR). Meanwhile, the HDS performance of the Fe-based catalyst was evaluated using a fixed-bed reactor. The results showed that the introduction of Y zeolite provided the Brønsted (B) acid sites, which increased the sulfur removal rates of Fe based catalysts by 10.7% −34.1%. Meanwhile, the B acid sites improved the selectivity of the direct desulfurization (DDS) reaction pathway. In addition, the B acid sites not only promoted the increase of DDS selectivity but also inhibited further deep hydrogenation of tetrahydrodibenzothiophene (THDBT) and hexahydrodibenzothiophene (HHDBT) in the hydrogenation (HYD) reaction pathway, thereby ensuring an increase in desulfurization efficiency while reducing hydrogen consumption. The fundamental reason was that the introduction of Y zeolite enhanced the acidity of the modified catalyst, especially the interaction between B acid sites and active metal promoted electron transfer, which adjusted the Fe species electronic defect structure, resulting in the improvement of HDS performance.
Abstract: Using strong-caking coking coal as raw material, coal-based carbon foam (NCF) was prepared by constant pressing and self-foaming method and used as carbon base to produce coal-based active carbon foamed (HPCs) together with KOH activator, which was used as electrode material for double-layer capacitor. The effects of KOH added by mechanical mixing, aqueous solution impregnation and ethanol solution impregnation methods on microstructure and electrochemical properties of the prepared materials were studied. The results show that formation of pore structure, crystal structure, surface chemistry and electrochemical performance of HPCs are significantly affected by KOH dispersion and adhesion. The NCF itself has a three-dimensional connected bubble pore structure, which is conducive to the activator (KOH) penetrating into the bubble pore and providing a large number of attachment sites, thus increasing the contact area between the activator and the carbon matrix and resulting in efficient activation. The good fluidity of KOH solution can make K+ more effectively interspersed in the bubble structure of NCF, act on the defect site during activation, and generate more micropores and mesoporous structures on the internal matrix of carbon matrix, effectively amplifying the activation effect. ACF-W obtained by KOH aqueous impregnation has the highest specific surface area (3098.35 m2/g), total pore volume (1.68 cm3/g), mesoporous volume ratio (59.13%). It shows excellent specific capacitance (310 F/g) and cycle stability when used as electrode material.
Abstract: Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are important reactions for rechargeable Zinc-air batteries (RZABs). Unfortunatly, OER holds a high thermodynamic equilibrium potential and complex reaction path, which require an large votage to derive this reaction and greatly hinder its commercial application. Herein, α-MnO2 was successfully achieved and as the bifunctional ORR/iodide oxidation reaction (IOR) electrocatalyst. In alkline media, α-MnO2 exhibits fast kinetics and low oxidation potential for IOR. Expectedly, α-MnO2 exhibits remarkable IOR activity in 1.0 mol/L KOH with 0.5 mol/L KI. Compared with potential at 10 mA/cm2 for OER (1.709 V vs. RHE), the potential at 10 mA/cm2 reduce 398 mV (1.311 V vs. RHE) for α-MnO2 during IOR process. α-MnO2 also provides small Tafel slope of 57.5 mV/dec. Additionly, α-MnO2 represents outsanding ORR performances with respect to Pt/C. As an air electrode for RZAB, the fabricated RZAB delivers excellent performances. To be specific, at 5 mA/cm2, the voltage gap between charging and discharging reduces from 0.97 V to 0.61 V, energy efficiency increses from 54.9% to 66.2%. This work provide an unique strategy to construct bifunction ORR/IOR electrocatalysts and promote the commercialization of RZABs.
Abstract: Oxidized carbon nitride nanosheets (o-CN NSs) was prepared by oxidative stripping with bulk carbon nitride (CN) as the precursor, and then reduced carbon nitride nanosheet (r-CN NSs) was prepared via reduced o-CN NSs. The thickness of o-CN NSs and r-CN NSs are both about 2 nm and retain the heptazine ring skeleton structure of pure CN. Compared with o-CN NSs, r-CN NSs has a smaller band gap (2.62 eV), wider photoresponse range (485 nm) and higher H2 evolution rates (1700 μmol/(g·h)). The H2 evolution rates of r-CN NSs is 8.5 times of CN and 2.1 times of o-CN NSs. After a 20 h cycle test, the photocatalytic hydrogen production efficiency of r-CN NSs has no attenuation, has well photocatalytic stability. Experimental and theoretical analyses reveal that r-CN NSs is nanosheet structure with amino group at the edge. The introduction of amino group improves the crystallinity of nanosheets, improves the separation efficiency of electrons and holes, broadens the photoresponse range of nanosheets, thus resulting in the enhanced photocatalytic performance.
Abstract: Zeolite-based catalysts have been widely used in the field of heterogeneous catalysis, but it is still difficult to control the structure and location of active sites on zeolite, which also confronts with great challenge both from academia and industry. Atomic layer deposition (ALD) is an advanced thin film deposition technique, owing to its advantages of self-limiting surface reactions, which can precisely tailor the growth process of metallic particles in atomic scale. In this review, we present a comprehensive summary of regulating the location of active sites on zeolite, modifying the framework structure and regioselective depositing of metal on special sites to engineering the surface structures of zeolites via ALD method. The design and regulation the structures of active component by ALD technology are beneficial to the development of zeolite-based catalysts. However, due to the complex of zeolite channels and the existence of defects, it is still challenging for the ALD technology to design, regulate and apply with large-scale for zeolite-based catalysts, and it will be the focus in the future research.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
