Selective catalytic reduction of NO by ammonia using mesoporous Fe-containing HZSM-5 and HZSM-12 zeolite catalysts: An option for automotive applications

Mesoporous and conventional Fe-containing ZSM-5 and ZSM-12 catalysts (0.5–8 wt% Fe) were prepared using a simple impregnation method and tested in the selective catalytic reduction (SCR) of NO with NH₃. It was found that for both Fe/HZSM-5 and Fe/HZSM-12 catalysts with similar Fe contents, the activity of the mesoporous samples in NO SCR with NH₃ is significantly higher than for conventional samples. Such a difference in the activity is probably related with the better diffusion of reactants and products in the mesopores and better dispersion of the iron particles in the mesoporous zeolite as was confirmed by SEM analysis. Moreover, the maximum activity for the mesoporous zeolites is found at higher Fe concentrations than for the conventional zeolites. This also illustrates that the mesoporous zeolites allow a better dispersion of the metal component than the conventional zeolites. Finally, the influence of different pretreatment conditions on the catalytic activity was studied and interestingly, it was found that it is possible to increase the SCR performance significantly by preactivation of the catalysts in a 1% NH₃/N₂ mixture at 500 °C for 5 h. After preactivation, the activity of mesoporous 6 wt% Fe/HZSM-5 and 6 wt% Fe/HZSM-12 catalyst is comparable with that of traditional 3 wt% V₂O₅/TiO₂ catalyst used as a reference at temperatures below 400 °C and even more active at higher temperatures.     

Fabrication and application of silicalite-1 and TS-1 hollow fibers with polyethylene imine (PEI) fibers as substrates

Silicalite-1 and titanium containing silicalite-1 (TS-1) hollow fibers were fabricated with polyethylene imine (PEI) fibers as substrates. The acid treated PEI fibers were positively charged and can be effectively coated with silicalite-1 or TS-1 nanocrystals from their colloidal solution. The adsorbed silicalite-1 or TS-1 nanocrystals grew up and became more compact upon two days of vapor phase Ostwald ripening in autoclave. Silicalite-1 and TS-1 hollow fibers were obtained after calcination at 400 °C in air. The shell thickness of the hollow fibers is ～1 μm. Hydroxylation of phenol with H₂O₂ was investigated over TS-1 based catalysts in order to compare influences of nanocrystals composed macrostructure and Al₂O₃ binder on the catalytic activities.     

A magnetically recyclable TS-1 for ammoximation of cyclohexanone

In this paper, Fe₃O₄ nanoparticles coated with titanium silicalite-1 (designated Fe₃O₄@TS-1) were successfully prepared and used as catalysts for ammoximation of cyclohexanone. Characterizations demonstrated that the magnetic catalyst was coated with a thin TS-1 layer of ~ 30 nm in thickness. The catalyst still displayed excellent catalytic activity after introducing Fe₃O₄ core. Recovery experiments revealed that Fe₃O₄@TS-1 catalyst could be easily recovered by adding an external magnetic field. Moreover, no appreciable catalytic deactivation was observed after four times of recycling. This work provided a promising way to overcome the recycle problem during the application of TS-1.     

Production of high-quality biodiesel fuels from various vegetable oils over Ti-incorporated SBA-15 mesoporous silica

Ti-incorporated SBA-15 mesoporous silica (shortly termed Ti-SBA-15) was a highly efficient and recyclable solid acid to synthesize high-quality biodiesel fuel (BDF) derived from various vegetable oils at moderate reaction condition, in comparison to siliceous SBA-15 and commercial TiO₂ catalysts with different anatase sizes, where the catalytically active sites mainly related to the tetrahedral-coordinated Ti(IV) species with weak Lewis acid nature. The TOF values of Ti-SBA-15 catalysts were around 18–166 h^− 1, an order of magnitude larger than those of commercial TiO₂ catalysts. A high-quality BDF containing more than 98.4 mass% of fatty acid methyl ester (FAME), which met with international fuel standard, was obtained over 3Ti-SBA-15 catalyst at 200 °C using a methanol/oil ratio of 108. Most importantly, the 3Ti-SBA-15 catalyst showed extremely high water and free fatty acid (FFA) tolerance levels, which were several ten times better than homogeneous and heterogeneous catalysts in conventional BDF production technology.     

Synthesis of ordered mesoporous manganese titanium composite oxide catalyst for catalytic ozonation

In this account, highly ordered mesoporous MnO_x/TiO₂ composite catalysts with efficient catalytic ozonation of phenol degradation were synthesized by the sol–gel method. The surface morphology and properties of the catalysts were characterized by several analytical methods, including SEM, TEM, BET, XRD, FTIR, and XPS. Interestingly, Mn doping was found to improve the degree of order, and the ordered mesoporous structure was optimized at 3% doping. Meanwhile, MnO_x was highly dispersed in the ordered mesoporous materials to yield good catalytic ozonation performance. Phenol could completely be degraded in 20 min and mineralized at 79% in 60 min. Thus, the catalyst greatly improved the efficiency of degradation and mineralization of phenol when compared to single O₃ or O₃ + TiO₂. Finally, the reaction mechanism of the catalyst was discussed and found to conform to pseudo-first-order reaction dynamics.     

Preparation,characterization and testing of Cr/AlSBA-15 ethylene polymerization catalysts

Ethylene polymerization catalysts have been prepared by grafting chromium(III) acetylacetonate onto AlSBA-15 (Si/Al = ∞, 156, 86 and 30) mesoporous materials. A combination of XRD, nitrogen adsorption, TEM, ICP-atomic emission spectroscopy, H₂-TPR, TGA, UV–vis and FT-IR spectroscopy, were used to characterize the prepared Cr–AlSBA-15 catalysts. By reducing the Si/Al ratio of the AlSBA-15 supports increases the amount of chromium anchored, promotes the stabilization of chromium species as chromate and decreases the reduction temperature of Cr⁶⁺ ions determined by H₂-TPR. Attachment of Cr species onto AlSBA-15 surface results from the interaction of hydroxyl groups with the acetylacetonate ligands through H-bonds. On the contrary, a ligand exchange reaction may occur over siliceous SBA-15.The polymerization activity of Cr–AlSBA-15 catalysts is significantly improved by increasing aluminium content of the AlSBA-15 supports. Particularly, the chromium catalyst prepared with AlSBA-15 (Si/Al = 30) support is almost four times more active than a conventional Cr/SiO₂ Phillips catalyst. Polymers obtained with all the catalysts showed melting temperatures, bulk densities and high load melt indexes indicating the formation of linear high-density polyethylene.     

Desilication of TS-1 zeolite for the oxidation of bulky molecules

A series of modified TS-1 samples have been produced by desilication of the original TS-1 (4 wt.% Ti) using a chemical treatment with NaOH. Desilicated TS-1 zeolites exhibit a large BET surface area together with a well-developed mesoporosity. The hierarchical catalysts from desilication of TS-1 zeolite show a good catalytic activity for the oxidation of small molecules and a significantly higher activity for the oxidation of bulky molecules.     

Reforming of methane with carbon dioxide over supported bimetallic catalysts containing Ni and noble metal: I. Characterization and activity of SiO2 supported Ni–Rh catalysts

Cobalt catalysts supported on silica aerogel have been prepared using sol–gel chemistry followed by drying under supercritical ethanol conditions. Three different loadings of cobalt were synthesized: 2, 6, and 10% by weight. Transmission electron micrographs indicate that the metallic cobalt exists as discrete particles 50–70 nm in diameter for the 2 and 6% loadings. The 10% catalyst shows long needles of cobalt. BET and BJH measurements indicate that the catalysts retain the silica aerogel properties of high surface area (∼800 m²/g), large pore volume (∼5 cm³/g), and an average pore diameter in the mesoporous regime (∼25 nm). The catalysts were evaluated for Fischer–Tropsch activity in a laboratory-scale packed bed reactor. All three catalysts were active with the 10% Co catalyst achieving more than 20% CO conversion which corresponds to a rate of 1.53 g CO per g-cat per hour. The catalysts were selective for the C₁₀₊ hydrocarbons with more than 50% of the carbon contained within this fraction. A significant portion of the C₉–C₁₅ hydrocarbon product was observed as 1-olefins which reflects the enhanced mass transport within the very porous aerogel support.     

Synthesis and characterization of new Mg–O–F system and its application as catalytic support

The Mg–O–F system (MgF₂–MgO) with different contents of MgF₂ (100–0%) and MgO is tested as support of iridium catalysts in the hydrogenation of toluene as a function of the MgF₂/MgO ratio. Mg–O–F samples have been prepared by the reaction of magnesium carbonate with hydrofluoric acid. The MgF₂–MgO supports, after calcination at 500 °C, are classified as mesoporous of surface area (34–135 m²·g^− 1) depending on the amount of MgO introduced. The Ir/Mg–O–F catalysts have been tested in the hydrogenation of toluene. The highest activity, expressed as TOF, min^− 1, was obtained for the catalyst supported on Mg–O–F containing 75 mol%MgF₂.     

Electrospun mesoporous zirconia ceramic fibers for catalyst supporting applications

Mesoporous zirconia has been widely used as supporting materials, absorption materials, catalysts and high temperature insulating materials. While seldom has taken a consideration of the mesoporous fiber structure. In the present work, mesoporous zirconia ceramic fibers were fabricated by electrospinning method with CTAB as the template. The thermal decomposition and crystallization process of the mesoporous zirconia fibers were fully studied by TG/DSC, IR spectra and XRD. The highest surface area of the mesoporous zirconia fibers was about 120 m²/g. With mesoporous zirconia fibers as the supporting materials, tungstate supported on zirconia fibers catalyst showed that the specific activity of bromination of phenol red was 1.26 mmol h^?1 g^?1. The results confirmed that zirconia fibers with the mesoporous structure would be a promising candidate as a supporting material.     

Highly mesoporous LaNiO3/NiO composite with high specific surface area as a battery-type electrode

This study reports the fabrication and characterization of mesoporous LaNiO₃/NiO composite with a very high specific surface area for a battery-type electrode. The mesoporous LaNiO₃/NiO composite was synthesized via a sol–gel method by using silica gel as a template, the colloidal silica gel was obtained by the hydrolysis and polymerization of tetraethoxysilane in the presence of La and Ni salts. We investigated the structure and the electrochemical properties of mesoporous LaNiO₃/NiO composite in detail. The mesoporous composite sample showed a specific surface area of 372 m² g⁻¹ with 92.7% mesoporous area and displayed remarkable electrochemical performance as a battery-type electrode material for supercapacitor. The specific capacity values were found to be 237.2 mAh g⁻¹ at a current density of 1 A g⁻¹ and 128.6 mAh g⁻¹ at a high current density of 20 A g⁻¹ in 1 M KOH aqueous electrolyte. More importantly, this mesoporous composite also showed an excellent cycling performance with the retention of 92.6% specific capacitance after 60,000 charging and discharging cycles.     

Hydrothermal synthesis of mesoporous titanosilicate with the aid of amphiphilic organosilane

Mesoporous MFI-type titanosilicates (TS-1) were hydrothermally synthesized with the aid of amphiphilic organosilane and the effects of the amphiphilic organosilane on the structural and textural properties of the resultant materials were investigated. The physicochemical properties of the samples were characterized by various techniques and their catalytic performance was investigated by the epoxidation of cyclohexene with hydrogen peroxide. The content of organosilane added was essential for the formation of uniform mesopore in TS-1, and greatly influenced the crystallinity. Highly crystallined TS-1 with uniform mesopores of 3.7 nm diameter was successfully synthesized. The mesoporous TS-1 preserved tetrahedrally coordinated Ti ions in the framework, but it was featured with more hydrophobic surface and less defect sites in comparison to conventional TS-1. Mesoporous TS-1 showed a higher conversion for the epoxidation of cyclohexene owing to an easier access of bulky molecules to the catalytic active sites. Mesoporous TS-1’s higher hydrophobicity made its epoxide selectivity two times as much as that of conventional TS-1.     

Effect of graphene thickness on the morphology evolution of hierarchical NiCoO2 architectures and their superior supercapacitance performance

The rational design of electrode materials with special hierarchical architectures which possess both high surface area and conductivity is significant to enhance the performance of supercapacitors. Herein, hierarchical NiCoO₂ architectures assembled by ultrathin mesoporous nanosheets are in-situ grown on graphene@Ni foam (G@NF) by a template-free solvothermal route and subsequent annealing process, which is used as self-supported and binder-free supercapacitor electrodes. The effect of graphene thickness on morphology evolution of NiCoO₂ is investigated. Benefiting from the synergistic effect between graphene with remarkable conductivity and hierarchical NiCoO₂ architectures with high specific capacity, the NiCoO₂/G@NF electrodes show greatly improved electrochemical performance compared to NiCoO₂@NF and G@NF. The optimized NiCoO₂/G@NF has a specific capacitance of 1220 F/g at 1 A/g. While the NiCoO₂@NF and G@NF are only 565 and 151 F/g, respectively. The optimized NiCoO₂/G@NF remains 840 F/g at 20 A/g, revealing a remarkable rate performance (69% capacity retention from 1 to 20 A/g). Moreover, an outstanding cyclic stability of 80% capacitance retention can be obtained after 5000 charge/discharge cycles at 10 A/g, whereas the NiCoO₂@NF is only 46.5%. These results suggest that the hierarchical NiCoO₂ architectures/graphene hybrids are good candidates as effective electrode materials for supercapacitors.     

HDS of thiophene over CoMo/AlMCM-41 with different Si/Al ratios

A series of AlMCM-41 molecular sieves with different Si/Al ratios were synthesized followed by the deposition of cobalt and molybdenum oxides on these mesoporous supports by co-impregnation. Such materials were further calcined and catalysts with 15 wt.% of cobalt and molybdenum and a Co/(Co + Mo) atomic ratio of 0.30 were obtained. These materials were characterized by X-ray diffraction (XRD), transmission electron microscopy and selected area electron diffraction (TEM/SAED), X-ray fluorescence (XRF), and nitrogen adsorption. Hydrodesulphurisation (HDS) of thiophene was carried out at 350 °C in a fixed bed continuous flow micro reactor coupled on line to a gas chromatograph. The main XRD peaks of MCM-41 phase were observed in all samples and peaks due to MoO₃ and CoMoO₄ phases were also identified from XRD results. It was found that the as-synthesized catalysts presented reasonable conversion results for HDS of thiophene, when compared to other supported catalysts. The main products of HDS of thiophene were H₂S, isobutene, 1-butene, n-butane, 2-butene-trans, and 2-butene-cis. It was observed that the reactivity of the as-synthesized catalysts is a direct function of the Si/Al ratio, nature and concentration of the active species on the mesoporous supports.     

Synthesis of hierarchical mesoporous titania with interwoven networks by eggshell membrane directed sol–gel technique

Hierarchical mesoporous titania with interwoven networks was successfully prepared through a surface sol–gel process followed by a calcination treatment and using eggshell membrane (ESM) as the biotemplate. The biotemplating synthesis was systematically investigated by controlling calcination temperature (550–800 °C), heating rate (1–35 °C/min), impregnant pH value (1–3), and so on. Different from traditional immersion techniques, the nucleation, the growth, and the assembly of mesoporous TiO₂ in our work depended more on some reactions involving ESM biomacromolecules. As-prepared ESM-morphic TiO₂ was composed of intersectant fibers assembled by 6 nm nanocrystallites at 3D with hierarchical pores from 2 nm up to 8 μm.     

Catalytic conversion of glucose to 5-hydroxymethylfurfural over nano-sized mesoporous Al2O3–B2O3 solid acids

A series of nano-sized mesoporous Al₂O₃–B₂O₃ catalysts with different molar ratios of Al/B were prepared from aluminum isopropoxide and boric acid through an evaporation-induced self-assembly (EISA) process, and were characterized by ICP-AES, FTIR (pyridine adsorption), XRD, NH₃-TPD, SEM, TEM, and N₂ adsorption–desorption. These catalysts were further used as solid acids in the catalytic conversion of glucose to 5-hydroxymethylfurfural (HMF). An optimized HMF yield of 41.4% was obtained within 120 min at 140 °C over Al₂O₃–B₂O₃ (Al/B = 5:5). It was demonstrated that catalysts with the presence of Lewis acid sites were more favorable for the formation of HMF.     

Mesoporous Li2FeSiO4@ordered mesoporous carbon composites cathode material for lithium-ion batteries

The mesoporous Li₂FeSiO₄@ordered mesoporous carbon (CMK-3) has been firstly synthesized by a sol–gel method. The structural properties of the samples are characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and nitrogen adsorption–desorption. The composite is then evaluated as a cathode material for lithium ion batteries. It exhibits greatly improved electrochemical performance compared with bulk Li₂FeSiO₄ and shows an excellent rate capability (160, 148, 129, 110, 90, 66 and 50 mAh g⁻¹ at 0.1, 0.2, 0.5, 1, 2, 5 and 10 C, respectively) with significantly enhanced cycling performance. The greatly enhanced lithium storage properties of the Li₂FeSiO₄@CMK-3 composites may be attributed to the interpenetrating conductive carbon network, ordered mesoporous structure, and small uniform Li₂FeSiO₄ nanocrystallites that increase the ionic and electronic conduction throughout the electrode.     

Triton X-100 directed synthesis of mesoporous γ-Al2O3 from coal-series kaolin

Mesoporous γ-Al₂O₃ has been successfully synthesized by using calcined coal-series kaolin as raw material and Triton X-100 (TX-100) as template. The effect of TX-100/Al^3 + ratio on the structural and textural properties of mesoporous γ-Al₂O₃ was investigated. Physical properties of obtained samples were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption, transmission electron microscopy (TEM), thermogravimetric analysis (TG), scanning electron microscopy (SEM) with energy-dispersive X-ray analysis (EDAX) and Fourier transform infrared spectroscopy (FTIR). The results indicated that the amount of TX-100 influenced the structure and porous properties of mesoporous γ-Al₂O₃ significantly. When TX-100/Al^3 + ratio was in the range of 0.03–0.15, all samples had mesoporous structures with BET surface area of 193.0–261.0 m²/g and pore size of 5.04–6.71 nm. In addition, the reaction mechanism involved in the process was proposed and discussed.     

Efficient catalysis of mesoporous Al-MCM-41 for Mukaiyama aldol reactions

Mesoporous aluminosilicates, Al-MCM-41 (Si/Al = 20 and 50), efficiently catalyzed Mukaiyama aldol reaction of benzaldehyde with 1-(trimethylsiloxy)cyclohexene in CH₂Cl₂ at 0 °C to afford the corresponding β-trimethylsiloxy ketone in quantitative yield. On the other hand, mesoporous silica (MCM-41), amorphous SiO₂–Al₂O₃, and H–Y and H-ZSM-5 zeolites barely catalyzed the reaction. Additionally, the less ordered Al-MCM-41 prepared by mechanical compression exhibited much lower catalytic activity compared with Al-MCM-41, indicating that the presence of the ordered mesoporous structure in aluminosilicates is crucial for the catalysis. The Al-MCM-41 catalyzed Mukaiyama aldol reaction was applicable to a wide range of aldehydes and silyl enol ethers. Furthermore, the Al-MCM-41 catalyst could be recycled at least three times without any loss in the yield. Thus, mesoporous aluminosilicates are promising heterogeneous catalysts for fine chemicals synthesis.     

Simultaneous catalytic removal of NOx and soot particulates over CuMgAl hydrotalcites derived mixed metal oxides

A series of CuMgAl hydrotalcites derived oxides were prepared by co-precipitation and calcination methods and tested for the simultaneous catalytic removal of NOx and soot. The obtained samples were characterized by XRD, N₂ adsorption-desorption, H₂-TPR and ICP-AES techniques. The crystal phases, porous structures and redox properties of the catalysts were strongly influenced by Cu substitution contents and calcination temperatures. The CuMgAl mixed oxides with mesoporous properties exhibit high activity for the simultaneous NOx-soot removal. Among the tested catalysts, 3.0Cu-800 sample shows the best performance with the ignition temperature of soot = 260 °C and the total amounts of N₂ = 6.0 × 10^− 5 mol. Based on the experimental work, a primitive kinetics analysis was carried out from the non-steady (dynamic) TPR measurements. Linear Arrhenius plots of rates of CO₂, N₂ and N₂O formation were observed around the onset of formation curves where the substantial amount of the soot still remains in the soot/catalyst mixture and the effective area of the soot/catalyst contact can be regarded as constant. Finally, a compensation effect was found for the formation of CO₂, N₂ and N₂O over CuMgAl mixed oxides with CuO as the predominant phase.