氮化SBA-16负载镍基催化剂的制备及其对甲烷二氧化碳重整反应的催化性能

通过软模板法合成了SBA-16分子筛,采用高温氨气氮化的方法使有序介孔硅材料中的氧原子部分被氮原子取代,得到氮化的SBA-16载体(SBA-16-N)。采用满孔浸渍法制备了镍基催化剂,并将制得的Ni/SBA-16和Ni/SBA-16-N催化剂用于甲烷二氧化碳重整反应。通过透射电镜、氮气物理吸附、X射线衍射、X射线光电子能谱和二氧化碳程序升温脱附等手段研究了载体和催化剂的结构,并利用热重分析对反应之后回收催化剂进行了表征。结果表明,高温氮化后的分子筛中掺入了氮元素,增加了载体的碱性,改善了载体对反应气体的吸附活化能力,增强了载体与金属之间的相互作用,从而提高了催化剂的活性和抗积炭性能。     

Sorption equilibria of CO2 on silica-gels in the presence of water

The sorption equilibria of carbon dioxide on three types of silica gel (SG) with different pore size distributions in the presence of water were studied experimentally using a volumetric method at 275?K with pressures from 0 to 3.7?MPa. Both the pore size distribution of the silica gel and the quantity of pre-sorbed water impact the formation of the CO₂ hydrates. For wet silicon gel A(SG-A) with water loading ratio of 0.75, the highest CO₂ sorption was about 2.5?mmol of CO₂ per gram of dry sorbent at 275?K. Similarly, the highest sorption was about 2.7?mmol for wet SG-B with R _w =0.81. However, CO₂ hydrate did not form on the wet surface of SG-C due to its large pore sizes.     

Tailoring the Pore Size,Basicity, and Binding Energy of Mesoporous C3N5 for CO2 Capture and Conversion

We investigated the CO₂ adsorption and electrochemical conversion behavior of triazole-based C₃N₅ nanorods as a single matrix for consecutive CO₂ capture and conversion. The pore size, basicity, and binding energy were tailored to identify critical factors for consecutive CO₂ capture and conversion over carbon nitrides. Temperature-programmed desorption (TPD) analysis of CO₂ demonstrates that triazole-based C₃N₅ shows higher basicity and stronger CO₂ binding energy than g-C₃N₄. Triazole-based C₃N₅ nanorods with 6.1 nm mesopore channels exhibit better CO₂ adsorption than nanorods with 3.5 and 5.4 nm mesopore channels. C₃N₅ nanorods with wider mesopore channels are effective in increasing the current density as an electrocatalyst during the CO₂ reduction reaction. Triazole-based C₃N₅ nanorods with tailored pore sizes exhibit CO₂ adsorption abilities of 5.6–9.1 mmol/g at 0 °C and 30 bar. Their Faraday efficiencies for reducing CO₂ to CO are 14–38% at a potential of −0.8 V vs. RHE.     

Investigation of Mg modified mesoporous silicas and their CO2 adsorption capacities

CO₂ adsorption properties on Mg modified silica mesoporous materials were investigated. By using the methods of co-condensation, dispersion and ion-exchange, Mg²⁺ was introduced into SBA-15 and MCM-41, and transformed into MgO in the calcination process. The basic MgO can provide active sites to enhance the acidic CO₂ adsorption capacity. To improve the amount and the dispersion state of the loading MgO, the optimized modification conditions were also investigated. The XRD and TEM characteristic results, as well as the CO₂ adsorption performance showed that the CO₂ adsorption capacity not only depended on the pore structures of MCM-41 and SBA-15, but also on the improvement of the dispersion state of MgO by modification. Among various Mg modified silica mesoporous materials, the CO₂ adsorption capacity increased from 0.42 mmol g⁻¹ of pure silica SBA-15 to 1.35 mmol g⁻¹ of Mg–Al–SBA-15-I1 by the ion-exchange method enhanced with Al³⁺ synergism. Moreover, it also increased from 0.67 mmol g⁻¹ of pure silica MCM-41 to 1.32 mmol g⁻¹ of Mg–EDA–MCM-41-D10 by the dispersion method enhanced with the incorporation of ethane diamine. The stability test by 10 CO₂ adsorption/desorption cycles showed Mg–urea–MCM-41-D10 possessed quite good recyclability.     

Correlation between pore-expanding and dye adsorption of platelet C/SBA-15 prepared by carbonization and oxidation of P123-TMB/SBA-15 composites

Platelet SBA-15 with significantly shortened and larger mesopores were prepared with different dosage of trimethylbenzene (TMB) in the assembly process, and then functionalized with acidic oxygen groups by oxidation of carbon layer that obtained by carbonization of P123-TMB organic species occluded in the silica pores. The preparation procedure involved three steps, namely, (a) synthesis platelet SBA-15 with larger mesopores, (b) carbonization, using P123 in the pore directly as the carbon source, and (c) oxidation with K₂S₂O₈. The resulting oxidation and carbonization of platelet SBA-15 (CST-ox, where C = carbon, S = SBA-15, T = trimethylbenzene, and ox refers to oxidation) composites contained of carbonaceous matter with acid oxygen groups (e.g. –COOH, –C=O and –OH) attached onto the deposited carbon layer. The structural characteristics of the parent silica were retained in the oxidized composite materials, which exhibit high surface area, large pore volume and well-ordered porosity. The oxygen-functionalized CST-ox composites with larger mesopores were found to be excellent adsorbents towards methylene blue. Especially, the adsorption equilibrium time was significantly reduced from 60 to 20 min, and the maximum adsorption capacity was increased from 379 to 420 mg/L, for which may be closely associated with the larger pore size, highly shortened meso-channels and the functionalized carbon layers. The adsorption kinetic data were analysed using pseudo-first-order, pseudo-second-order and Weber’s intraparticle diffusion models. Also equilibrium data were fitted to the Langmuir, Freundlich isotherm models and isotherm constants were determined. Thermodynamic parameters such as changes in the free energy of adsorption (ΔG ⁰), enthalpy (ΔH ⁰) and entropy (ΔS ⁰) were calculated.     

Adsorption and desorption of toluene on nanoporous TiO2/SiO2 prepared by atomic layer deposition (ALD): influence of TiO2 thin film thickness and humidity

Adsorption and desorption of toluene on bare and TiO₂-coated silica with a mean pore size of 15 nm under dry and humid conditions were studied using toluene breakthrough curves and temperature programmed desorption (TPD) of toluene and CO₂. Two TiO₂/silica samples (either partially or fully covered with TiO₂) were prepared with 50 and 200 cycles of TiO₂ atomic layer deposition (ALD), respectively. The capacity of silica to adsorb toluene improved significantly with TiO₂-thin film coating under dry conditions. However, toluene desorption from the surface due to displacement by water was more pronounced for TiO₂-coated samples than bare samples under humid conditions. In TPD experiments, silica with a thinner TiO₂ film (50-ALD cycled) had the highest reactivity for toluene oxidation to CO₂ both in the absence and presence of water. Toluene adsorption and oxidation reactivity of silica can be controlled by modifying the silica surface with small amount of TiO₂ using ALD.     

Organo-modified mesoporous silica for sorption of carbon dioxide

Abstract  

Organo-modified mesoporous silica SBA-15 has been studied for sorption of carbon dioxide (CO₂). The SBA-15 sample was functionalized with a branched chain polymer, polyethylenimine (PEI), of different molecular weights (1,300 and 2,000 g mol⁻¹). Surface modification was carried out by impregnation of silica by PEI or by grafting with (3-chloropropyl)triethoxysilane, followed by substitution of chlorine atoms by PEI ligands. The prepared modified mesoporous materials were characterized by nitrogen adsorption/desorption at 77 K, high-resolution transmission electron microscopy, small-angle X-ray scattering, and thermal methods. Sorption of CO₂ was studied by gravimetric method at 303 K. The total amount of sorbed CO₂ varied between 0.19–0.67 mmol/g for respective samples. Regeneration of the materials after adsorption was achieved by thermal treatment at 343 K.     

Amino-functionalized pore-expanded SBA-15 for CO2 adsorption

The adsorption of CO₂ on pore-expanded SBA-15 mesostructured silica functionalized with amino groups was studied. The synthesis of conventional SBA-15 was modified to obtain pore-expanded materials, with pore diameters from 11 to 15 nm. Post-synthesis functionalization treatments were carried out by grafting with diethylenetriamine (DT) and by impregnation with tetraethylenepentamine (TEPA) and polyethyleneimine (PEI). The adsorbents were characterized by X-ray diffraction, N₂ adsorption–desorption at 77 K, elemental analysis and Transmission Electron Microscopy. CO₂ capture was studied by using a volumetric adsorption technique at 45 °C. Consecutive adsorption–desorption experiments were also conducted to check the cyclic behaviour of adsorbents in CO₂ capture. An improvement in CO₂ adsorption capacity and efficiency of amino groups was found for pore-expanded SBA-15 impregnated materials in comparison with their counterparts prepared from conventional SBA-15 with smaller pore size. PEI and TEPA-based adsorbents reached significant CO₂ uptakes at 45 °C and 1 bar (138 and 164 mg CO₂/g, respectively), with high amine efficiencies (0.33 and 0.37 mol CO₂/mol N), due to the positive effect of the larger pore diameter in the diffusion and accessibility of organic groups. Pore-expanded SBA-15 samples grafted with DT and impregnated with PEI showed a good stability after several adsorption–desorption cycles of pure CO₂. PEI-impregnated adsorbent was tested in a fixed bed reactor with a diluted gas mixture containing 15 % CO₂, 5 % O₂, 80 % Ar and water (45 °C, 1 bar). A noteworthy adsorption capacity of 171 mg CO₂/g was obtained in these conditions, which simulate flue gas after the desulphurization step in a thermal power plant.     

改性中孔分子筛SBA-16薄膜的合成及表征

在酸性条件下, 以导电玻璃(ITO)为基底合成了SBA-16分子筛膜. 所制备的SBA-16膜孔径均匀, 具有体心立方结构(属于Im3m空间群), SBA-16膜的晶胞参数为18.6 nm. TEM, SEM和XRD等技术研究表明, 加入少量的AlCl₃盐于形成膜的母液并且采用RSiX₃对导电玻璃基底进行处理, 能够明显改善SBA-16膜的连续性而不影响孔结构. 红外(FTIR)研究结果表明, SBA-16膜的表面硅羟基和结晶水很少, 膜很稳定. XPS研究表明, 加入少量MnCl₂对SBA-16膜进行改性, 可以提高膜的导电性.     

Graphene Oxide Membranes with Heterogeneous Nanodomains for Efficient CO2 Separations

Achieving high membrane performance in terms of gas permeance and carbon dioxide selectivity is an important target in carbon capture. Aiming to manipulate the channel affinity towards CO₂ to implement efficient separations, gas separation membranes containing CO₂‐philic and non‐CO₂‐philic nanodomains in the interlayer channels of graphene oxide (GO) were formed by intercalating poly(ethylene glycol) diamines (PEGDA). PEGDA reacts with epoxy groups on the GO surface, constructing CO₂‐philic nanodomains and rendering a high sorption capacity, whereas unreacted GO surfaces give non‐CO₂‐philic nanodomains, rendering low‐friction diffusion. Owing to the orderly stacking of nanochannels through cross‐linking and the heterogeneous nanodomains with moderate CO₂ affinity, a GO‐PEGDA500 membrane exhibits a high CO₂ permeance of 175.5 GPU and a CO₂/CH₄ selectivity of 69.5, which is the highest performance reported for dry‐state GO‐stacking membranes.     

Effect of the amine type on thermal stability of modified mesoporous silica used for CO2 adsorption

In this study, the preparation by grafting of amino-functionalized SBA-15 molecular sieves was carried out. Amino-functionalized molecular sieves were synthesized using a silane coupling agent and different types of amination reagents which react with modified SBA-15. These composites were characterized by FT-IR spectroscopy, X-ray diffraction at low angles, nitrogen physisorption at 77 K, and evaluated by the adsorption of CO₂ and its temperature-programmed desorption—TPD. Thermal stability was investigated by TGA and DTA methods. In the view of a possible use of these amino-functionalized molecular sieves as sorbents for CO₂ removal, their adsorption–desorption properties towards CO₂ were also investigated by the TPD method. The mass loss of amino-functionalized molecular sieves above 215 °C was due to the oxidation and decomposition of amino propyl functional groups. This means that these composites could be used for adsorption of CO₂ at temperatures below 215 °C. The adsorption of CO₂ and its temperature programmed desorption using thermogravimetry were studied for amino-functionalized molecular sieves at 60 °C. The evolved gases during the adsorption–desorption of CO₂ on amino-functionalized molecular sieves were identified by online mass spectrometry coupled with thermogravimetry. CO₂ adsorption isotherms of functionalized samples at 60 °C showed that both the adsorption capacity (mg CO₂/g adsorbent) and the efficiency of amino groups (mol CO₂/mol NH₂) depend on the type of amination reagents and the amount of organic compound used.

     

CO_2 capture over molecular basket sorbents: Effects of SiO_2 supports and PEG additive

The objective of this work is to study the influences of silica supports and PEG additive on the sorption performance of molecular basket sorbent(MBS) for CO_2 capture consisting of polyethylenimine and one of the following supports: SBA-15(2-D structure), TUD-1(3-D sponge-like structure) and fumed silica HS-5(3-D disordered structure). Effects of the supports regarding pore structures and pore properties, the PEI loading amount as well as the sorption temperature were examined. Furthermore, polyethylene glycol(PEG) was introduced as an additive into the sorbents and its effect was investigated at different PEI loadings and sorption temperatures. The results suggest that the pore properties of MBS(after PEI loading) play a more important role in the CO_2 sorption capacity, rather than those of the supports alone.MBS with 3D pore structure exhibits higher CO_2 sorption capacity and amine efficiency than those with 2D-structured support. Among the sorbents studied, fumed silica(HS-5) based MBS showed the highest CO_2 sorption capacity in the temperature range of 30-95 °C, probably due to its unique interstitial pores formed by the aggregation of polymer-loaded SiO_2 particles. It was found that the temperature dependence is directly related to the PEI surface coverage layers. The more PEI surface coverage layers, the higher diffusion barrier for CO_2 and the stronger temperature dependence of CO_2 capacity. 3D MBS exceeds 2D MBS at the same PEI coverage layers due to lower diffusion barrier. Adding PEG can significantly enhance the CO_2 sorption capacity and improve amine efficiency of all MBS, most likely by alleviating the diffusion barrier within PEI bulk layers through the inter-molecular interaction between PEI and PEG.     

Restrictive Regulation of Ionic Liquid Quaternary Ammonium Salt in SBA-15 Pore Channel for Efficient Carbon Dioxide Conversion

Herein, the synthesis of a new type of catalyst, SBA−M (Schiff complex of different metal types grafted on SBA-15) based on a quaternization reaction, is described. Various amounts of ionic liquid were grafted into the pore channels of SBA-15 using the post-grafting method, which allowed the ionic liquid to be grafted into the pore channels restrictively. Notably, over six cycles, SBA−Mn (0.2) has been shown to maintain its catalytic activity and stability. In addition, a reaction mechanism for the cycloaddition of CO₂ with epoxides based on density-functional theory is proposed. The cycloaddition reaction of CO₂ and epoxides is an efficient way of carbon fixation. It is demonstrated that the metal coordinated with the oxygen atom of the epoxides and that a halogen attacked the carbon of epoxides. Moreover, theoretical calculations and synthesis strategy provide a new approach for CO₂ conversion.     

Polyol-modified layered double hydroxides with attenuated basicity for a truly reversible capture of CO2

Dendrimers bearing hydroxyl groups supported by layered double hydroxides (CO₃–LDH) with Mg/Al ratio ranging from 1:1 to 5:1 showed improved properties for the reversible capture of carbon dioxide (CO₂). The adsorption capacity of the starting LDH was due to the intrinsic base-like behavior, and was found to depend on the Mg/Al ratio. When contacted with polyol dendrimers in aqueous media, no intercalation took place. This was explained in terms of low exfoliation grade of LDH and hydrophobic character of the dendrimer molecules. The latter rather adsorb on the external surface of the LDH stacks for low dendrimer loadings, or aggregate into organic clusters for higher contents. Analyses through thermal programmed desorption of CO₂ revealed that dendrimer incorporation advantageously attenuates the basicity strength of the starting LDH support, by lowering the desorption temperature. The OH groups of the organic moiety were found to display an amphoteric character, and act as the main adsorption sites. The weak interactions with CO₂ facilitate easier release of the major part of adsorbed CO₂ at temperature not exceeding 80–100 °C. On polyol organo-LDHs, the reversible CO₂ retention was discussed herein in terms of acid–base interactions. This concept allows envisaging the capture of diverse pollutants and other greenhouse gases by modifying the chemical groups on the dendritic moiety.     

Metallic nickel supported on mesoporous silica as catalyst for hydrodeoxygenation: effect of pore size and structure

Catalytic hydrodeoxygenation (HDO) of anisole, a methoxy-rich lignin-derived bio-oil model compound, was carried out over a series of Ni-containing (5, 10, 20, and 30 wt%) catalysts with commercial silica and ordered mesoporous silica SBA-15 as support. Both supports and catalysts were characterized by N₂ adsorption–desorption isotherms, X-ray diffraction, CO chemisorption, and transmission electron microscopy (TEM). Catalytic reaction was performed at 250 °C and 10 bar H₂ pressure. Depending on the catalyst support used and the content of active metal, the catalytic activity and product distribution changed drastically. Increase of the nickel loading resulted in increased anisole conversion and C₆ hydrocarbon (benzene and cyclohexane) yield. However, loading more Ni than 20 wt% resulted in a decrease of both conversion and C₆ yield due to agglomeration of Ni particles. In addition, Ni/SBA-15 samples exhibited much stronger catalytic activity and selectivity toward C₆ hydrocarbon products compared with Ni/silica catalysts. The differences in catalytic activity among these catalysts can be attributed to the effect of the pore size and pore structure of mesoporous SBA-15. SBA-15 can accommodate more Ni species inside channels than conventional silica due to its high pore volume with uniform pore structure, leading to high HDO catalytic activity.     

Carbon dioxide reforming of methane over Ni/Mo/SBA-15-La2O3 catalyst: Its characterization and catalytic performance

The Ni/Mo/SBA-15 catalyst was modified by La2O3 in order to improve its thermal stability and carbon deposition resistance during the CO2 reforming of methane to syngas. The catalytic performance, thermal stability, structure, dispersion of nickel and carbon deposition of the modified and unmodified catalysts were comparatively investigated by many characterization techniques such as N2 adsorption, H2-TPR, CO2-TPD, XRD, FT-IR and SEM. It was found that the major role of La2O3 additive was to improve the pore structure and inhibit carbon deposition on the catalyst surface. The La2O3 modified Ni/Mo/SBA-15 catalyst possessed a mesoporous structure and high surface area. The high surface area of the La2O3 modified catalysts resulted in strong interaction between Ni and Mo-La, which improved the dispersion of Ni, and retarded the sintering of Ni during the CO2 reforming process. The reaction evaluation results also showed that the La2O3 modified Ni/Mo/SBA-15 catalysts exhibited high stability.     

Epoxy-functionalized large-pore SBA-15 and KIT-6 as affinity chromatography supports

Mesoporous silica supports are proposed as an alternative to polymeric stationary phases for fast affinity chromatography due to their better mechanical strength compared to polymers. Ideal supports should combine high surface area and large pore size to allow a high loading capacity of large molecules, such as proteins, and favor their accessibility. Increasing the pore size of large-surface area micelle-templated silicas (SBA-15, KIT-6) has been achieved by swelling the micelles by the addition of organic molecules and increasing synthesis time and temperature. The pore size of hexagonal silica mesostructured SBA-15 has been increased up to 35 nm. These materials could find therefore application as affinity chromatography for immunoextraction.     

Electrocatalytic Reduction of CO2 to Acetic Acid by a Molecular Manganese Corrole Complex

The controlled electrochemical reduction of carbon dioxide to value added chemicals is an important strategy in terms of renewable energy technologies. Therefore, the development of efficient and stable catalysts in an aqueous environment is of great importance. In this context, we focused on synthesizing and studying a molecular Mn^III‐corrole complex, which is modified on the three meso‐positions with polyethylene glycol moieties for direct and selective production of acetic acid from CO₂. Electrochemical reduction of Mn^III leads to an electroactive Mn^II species, which binds CO₂ and stabilizes the reduced intermediates. This catalyst allows to electrochemically reduce CO₂ to acetic acid in a moderate acidic aqueous medium (pH 6) with a selectivity of 63 % and a turn over frequency (TOF) of 8.25 h^?1, when immobilized on a carbon paper (CP) electrode. In terms of high selectivity towards acetate, we propose the formation and reduction of an oxalate type intermediate, stabilized at the Mn^III‐corrole center.     

Effect of synthesis conditions on the mesoscopical order of mesoporous silica SBA-15 functionalized by amino groups

Mesoporous amine-functionalized SBA-15 silica has been synthesized directly by the co-condensation of tetraethyl orthosilicate (TEOS) and aminopropyl-trimethoxysilane (APTMS) under acidic conditions with an APTMS/(APTMS + TEOS) molar ratio of 10%. The effect of synthesis conditions, including TEOS pre-hydrolysis, as well as the heating temperature and time, on the mesoscopical order and pore structure of the functionalized SBA-15 have been studied in detail by means of powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, infrared spectra and solid state ²⁹Si nuclear magnetic resonance. A functionalized SBA-15 silica with a highly ordered two-dimensional P6 mm hexagonal symmetry and a narrow pore size distribution centered at 6 nm can be obtained if TEOS is allowed to pre-hydrolyze for 2 h. For the sample with TEOS pre-hydrolysis time of 4 h, aging at 50°C or 150°C leads to a more ordered pore arrangement compared to 100°C and also a narrower pore size distribution with larger pore volume. Increasing aging time is in favor of the formation of mesoscopically ordered structure, but fails to obtain a superior pore structure.     

Temperature Dependence in the Synthesis of SBA-16-Type Mesoporous Silica with Pluronic F68 Block Copolymer

By adjusting the local effective surfactant packing parameter through synthesis temperature, highly ordered SBA-16-type mesoporous silica materials have been synthesized by templating with a nonionic triblock copolymer Pluronic F68 in strongly acidic conditions at temperature 30～40°C with the addition of K₂SO₄. The prepared SBA-16-type mesoporous silica materials having Im3m cubic mesostructure were proved by the well-defined x-ray diffraction patterns combined with transmission electron microscopy. Scanning electron microscopy indicated that a transformation from faced-sphere to faced-polyhedron shape morphologies could be induced with increasing of the synthesis temperature. The nitrogen adsorption–desorption analysis revealed that the mean pore size (5.50～6.13 nm) of the prepared materials increased with increasing synthesis temperature. However, when the synthesis temperature exceeded 46°C, only disordered mesoporous silca was obtained. Our synthesis strategies by adjusting the local effective surfactant packing parameter through synthesis condition, even in a narrow range, would be used not only to optimize the synthesis conditions of reported mesoporous silca, but also to fabricate new mesoporous silica materials with well-ordered channel and anticipated morphologies.