Mesoporous molecular sieve-based materials for catalytic oxidation of VOC: A review.

As the main contributor of the formation of particulate matter as well as ozone, volatile organic compounds (VOCs) greatly affect human health and the environmental quality. Catalytic combustion/oxidation has been viewed as an efficient, economically feasible and environmentally friendly way for the elimination of VOCs. Supported metal catalyst is the preferred type of catalysts applied for VOCs catalytic combustion because of the synergy between active components and support as well as its flexibility in the composition. The presence of support not only plays the role of keeping the catalyst with good stability and mechanical strength, but also provides a large specific surface for the good dispersion of active components, which could effectively improve the performance of catalyst as well as decrease the usage of active components, especially the noble metal amount. Mesoporous molecular sieves, owing to their large surface area, unique porous structures, large pore size as well as uniform pore-size distribution, were viewed as superior support for dispersing active components. This review focuses on the recent development of mesoporous molecular sieve supported metal catalysts and their application in catalytic oxidation of VOCs. The effect of active component types, support structure, preparation method, precursors, etc. on the valence state, dispersion as well as the loading of active species were also discussed and summarized. Moreover, the corresponding conversion route of VOCs was also addressed. This review aims to provide some enlightment for designing the supported metal catalysts with superior activity and stability for VOCs removal.

Application of MCM-48 with large specific surface area for VOCs elimination: synthesis and hydrophobic functionalization for highly efficient adsorption.

MCM-48 molecular sieve with a large specific area (1470.87 m2/g) was hydrothermally synthesized for VOCs elimination by the adsorption method. The dynamic adsorption behaviors of toluene on this material were evaluated via breakthrough curves under both dry and wet conditions. A high toluene adsorption capacity of 171.13 mg/g was observed under dry conditions; however, in the presence of water vapor (20% RH), the adsorption capacity greatly decreased to 58.88 mg/g due to the competitive occupation of adsorption sites between water molecules and toluene molecules. To improve the affinity to toluene, functionalized MCM-48 materials were obtained by the co-condensation method and grafting method, respectively. It was found that co-M48(1:5)-100/48 sample by co-condensation method presents the highest dynamic adsorption capacity at both dry condition (194.62 mg/g) and 20% RH (122.42 mg/g), which has a significant advantage in the same type of adsorbent. This could be ascribed to the conjugated π-electrons effect between aromatic rings of phenyl groups uniformly distributed in MCM-48 skeleton and toluene molecules, which was qualitatively confirmed by FTIR. Moreover, cycle tests confirmed that this adsorbent possesses superior stability. The Yoon-Nelson model was successfully employed to describe the dynamic adsorption behavior of toluene over the organofunctionalized MCM-48 adsorbents, and the adsorption force of toluene was explained. Finally, a diagram describing the effect of different functionalization methods on the hydrophobicity and organophilicity of MCM-48 was given for a better understanding.

Fe-modified Ce-MnOx/ACFN catalysts for selective catalytic reduction of NOx by NH3 at low-middle temperature.

A series of MnOx/ACFN, Ce-MnOx/ACFN, and Fe-Ce-MnOx/ACFN catalysts on selective catalytic reduction (SCR) of NOx with NH3 at low-middle temperature had been successfully prepared through ultrasonic impregnation method, and the catalysts were characterized by SEM, XRD, BET, H2-TPR, NH3-TPD, XPS, and FT-IR spectroscopy, respectively. The results demonstrated that the 15 wt% Fe(1)-Ce(3)-MnOx(7)/ACFN catalyst achieved 90% NOx conversion (100~300 °C), good water resistance, and stability (175 °C). The excellent catalytic performance of the Fe(1)-Ce(3)-MnOx(7)/ACFN catalyst was mainly attributed to the interaction among Mn, Ce, and Fe. The doping of Fe promoted the dispersion of Ce and Mn and the formation of more Mn4+ and chemisorbed oxygen on the surface of a catalyst. This work laid a foundation for the successful application of active carbon fiber in the field of industrial denitrification, especially in the aspect of denitrification moving bed. Graphic abstract.

Supramolecular architecture of tetrathiafulvalene-bridged bis(ß-cyclodextrin) with porphyrin and its electron transfer behaviors.

A bridged bis(ß-cyclodextrin) 3 with a tetrathiafulvalene (TTF) linker was synthesized by an electrophilic reaction of mono-6-deoxy-6-iodo-ß-cyclodextrin 1 with 6,7-bis(methylsulfanyl)-2,3- bis(2-cycanoethylsulfanyl)tetrathiafulvalene 2 under the alkaline condition. Benefiting from the good solubilizing ability of the ß-cyclodextrin unit, the solubility limit of 3 in water could reach 1.0 × 10(-3) M, i.e. 0.4 mg mL(-1) calculated as TTF residue. The conformational changes during the inclusion complexation process of 3 with 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrin 4 were investigated by UV/Vis and 2D NMR spectroscopy. Significantly, the photo-induced electron transfer (PET) process between the TTF moiety in 3 and the porphyrin unit in 4 would take place within the 3/4 supramolecular complex under the light irradiation, leading to the highly efficient quenching of the fluorescence of 4, and could then be recovered by the formation of TTF cations in the presence of H(2)O(2). Furthermore, taking advantage of the high affinity between 3 and 4, the linear nanoarchitectures were achieved and comprehensively characterized by using transmission electron microscopy (TEM) and atomic force microscopy (AFM). These observations indicated that the strong complexation was a crucial and basic factor to achieve the PET process in the non-covalently constructed assemblies.