Nataša Novak Tušar

MnO(x) nanoparticles supported on a new mesostructured silicate with textural porosity.

A two-step synthesis of a novel mesostructured silicate, KIL-2, and its manganese-containing analogue, Mn/KIL-2, has been developed. KIL-2 possesses interparticle mesopores with pore dimensions between 5 and 60 nm and a surface area of 448 m(2). The mesopores are formed by the aggregation of silica nanoparticles, which creates a network with interparticle voids. The particle size and the pore diameters depend on the temperature of the ageing step (first step) and on the solvothermal treatment in ethanol (second step), respectively. Mn/KIL-2 contains octahedrally coordinated Mn(3+) (80%) and tetrahedrally coordinated Mn(2+) (20%) ions. Mn(3+) ions are present in the extra-framework MnO(x) nanoparticles with typical dimensions of 2 nm, which are homogeneously distributed throughout the material. Mn(2+) ions occur as isolated manganese framework sites. The material is also able to retain its structure characteristics after the hydrothermal treatment in boiling water. Because of its non-toxic nature and cost-effective synthesis, Mn/KIL-2 thus exhibits properties that are needed for an environment-friendly catalyst.

A zinc-rich CHA-type aluminophosphate

Abstract Zinc(II)-substituted chabazite-like aluminophosphate ZnAPO-34 of excellent phase purity and a high amount of incorporated zinc was synthesized hydrothermally in the presence of tetraethylammonium hydroxide (TEAOH). The characterization of the product indicates that 20% of framework aluminum is replaced by zinc and shows that template is located at the center of the unit cell, in the large interstitial cavity of the chabazite framework. 27 Al and 31 P MAS n.m.r. results are consistent with the X-ray structural determination. Extended X-Ray Absorption Fine Structure (EXAFS) spectroscopic analysis proves the isomorphous substitution of zinc for aluminum in the framework.

Framework cobalt and manganese in MeAPO-31 (Me = Co, Mn) molecular sieves

Pure phases of CoAPO-31 and MnAPO-31 were synthesized hydrothermally using di-n-propylamine as a structuredirecting agent. The incorporation of manganese(II) and cobalt(II) into framework aluminum sites of AlPO4-31 was suggested from elemental, thermogravimetric and X-ray powder diffraction analysis. Isomorphous aluminum substitution with cobalt(II) was confirmed from static 31 P NMR spectra. UV–VIS and XANES spectra revealed a partial oxidation of framework cobalt(II) and manganese(II) into cobalt(III) and manganese(III) in the calcined MeAPO-31 and thus the presence of redox centers in the products. The generation of acid sites (Bronsted and Lewis) in MeAPO-31 was supported by IR measurements of pyridine and by ammonium adsorption/desorption. The strength of the acid sites in the catalysts studied decreased in the following order: MnAPO-31 > CoAPO-31 > AlPO4-31.

Photocatalytic degradation of gaseous toluene by using immobilized titania/silica on aluminum sheets

PurposeThe aim of this study was to prepare a highly active immobilized titania/silica photocatalyst and to test its performance in situ toward degradation of toluene as one of the major toxic indoor contaminants.MethodsIn this work, two different titania layers immobilized on Al sheets were synthesized via low temperature sol–gel method employing presynthesized highly active titania powders (Degussa P25 and Millennium PC500, mass ratio 1:1): (a) with a silica/titania binder and a protective layer and (b) without the binder. The photocatalysts were characterized by X-ray diffraction, nitrogen sorption measurements, scanning electron microscopy (SEM), infrared spectroscopy, and UV–vis diffuse reflectance spectroscopy (DRS). The in situ photocatalytic degradation of gaseous toluene was selected as a probe reaction to test photocatalytic activity and to verify the potential application of these materials for air remediation.ResultsResults show that nontransparent highly photocatalytically active coatings based on the silica/titania binder and homogeneously dispersed TiO2 powders were obtained on the Al sheets. The crystalline structure of titania was not altered upon addition of the binder, which also prevented inhomogeneous agglomeration of particles on the photocatalyst surface. The photoactivity results indicate that the adsorption properties and photocatalytic activity of immobilized photocatalysts with the silica/titania binder and an underlying protective layer were very effective and additionally, they exhibited considerably improved adhesion and uniformity.ConclusionWe present a new highly photocatalytically active immobilized catalyst on a convenient metallic support, which has a potential application in an air cleaning device.

Manganese‐Containing Porous Silicates: Synthesis, Structural Properties and Catalytic Applications

Porous silicates are often used as catalysts or catalyst supports for many chemical reactions. The immobilization of metals by their incorporation into silicate frameworks is an important strategy for generating catalytically active sites. The catalytic properties of metal‐modified porous silicates depend on the structure type and on the location and nature of the incorporated metal. Recently, manganese‐containing porous silicates have received considerable attention as catalysts for various chemical conversions. Herein, an overview on the synthesis, structure characterization, and catalytic applications of manganese‐containing porous silicates is presented. The particular suitability of these materials to address major challenges in environmentally benign catalysis is outlined.

EXAFS and NMR investigation of zinc, manganese and cobalt substituted aluminophosphates with the chabazite structure

Abstract Zinc, manganese and cobalt containing aluminophosphates with the chabazite (CHA) structure type (MeAPO-34, MeZn, Mn and Co) have been synthesized hydrothermally in the presence of tetraethylammonium hydroxide. All samples showed a very high crystallinity without impurity phases, as evidenced by X-ray diffraction and scanning electron microscopy. The results of EXAFS spectroscopy on as-synthesized samples show that the metals possess 4 oxygen atoms in the first coordination shell which is an indication for a tetrahedral coordination in the lattice. The decrease of the EXAFS amplitude for some samples upon calcination is in agreement with the presence of Lewis acid sites, as previously reported. 31P NMR confirmed the incorporation of metals in the AlPO4-34 structure. For Zn and Mn, the 31P NMR spectra show various lines attributed to different P(nAl, 4-nMe) units and the calculation of the fraction of metal in the samples after deconvolution of the spectra is in very good agreement with elemental analysis. Comparison of the relative intensities of the lines with those obtained by a binomial theorem showed that metals randomly substitute Al in the AlPO4-34 framework. Incorporation of Co in the samples was suggested by a strong decrease in both T1 and T2 relaxation times with respect to SAPO-34 or ZnAPO-34, thus confirming EXAFS data.

Glycerol acetylation on mesoporous KIL-2 supported sulphated zirconia catalysts

Zirconia nanomaterials were prepared by impregnation of KIL-2 type silica with 4, 8 and 12 wt.% ZrO2 and were modified by sulphate groups in order to vary the type and strength of acidity. Samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and N2 physisorption methods. Acidic properties of adsorbed pyridine were investigated by FT-IR spectroscopy. The catalytic performance of ZrKIL-2 and SO42−/ZrKIL-2 in glycerol esterification with acetic acid was studied and compared to that of pure zirconia varieties. It was found that silica-supported zirconia samples are more active than pure zirconia ones. With increasing ZrO2 content, KIL-2-supported catalysts showed increasing catalytic activity and selectivity in producing valuable fuel additives, di- and triacetyl glycerols. Sulphated analogues showed even higher activity and selectivity compared to non-sulphated ones due to their strong Bronsted acidity.

Monitoring the crystallization process of a zeolite structure on SBA-15 mesopore walls

Hierarchical materials based on crystallization of the MFI structure on mesoporous Al-SBA-15 have been synthesized by a hydrothermal procedure in water. The effect of the crystallization temperature and time as well as the proportion of zeolite template has been investigated. In addition to XRD, TEM and N2 sorption measurements, the structural and textural properties of the materials have also been studied by hyperpolarized (HP) 129Xe NMR and FTIR. These techniques emphasized that the main issue during the synthesis procedure is to find the optimal parameters (time, temperature and concentrations) in order to maintain the structure of the Al-SBA-15 mesoporous solids under the conditions required for zeolite crystallization. Embryonal MFI crystals have been identified on SBA-15 walls which remained ordered for materials obtained with TPABr : Al molar ratio of 0.7 : 1 after 8 h of hydrothermal treatment at 180 °C. Evidence for these zeolite nanocrystals has been obtained for the first time by hyperpolarized 129Xe NMR spectroscopy. Moreover, this was corroborated by the appearance of an IR absorption band at 542 cm−1 due to the asymmetric stretching vibration of the double five-membered rings present in ZSM-5.

In situ Generation of Ni Nanoparticles from Metal–Organic Framework Precursors and Their Use for Biomass Hydrodeoxygenation

So far, in situ-generated Ni nanoparticles have been reported to be efficient catalysts for tar cracking during wood liquefaction by pyrolysis. Herein, their performance in further bio-oil conversion steps is evaluated. Nanoparticles were generated for the first time from a Ni-containing metal-organic framework, MIL-77, during the hydrotreatment of glycerol-solvolyzed lignocellulosic (LC) biomass. Reactions were conducted at 300 °C and the H2 pressure was 8 MPa in a slurry reactor. The catalytic activity and selectivity of the deoxygenation and hydrocracking reactions for real biomass-derived feedstock using in situ-generated nanoparticles was compared with Ni nanoparticles dispersed on a silica-alumina support (commercial Ni/SiO2 -Al2 O3 catalyst). The mass activity of the in situ-generated nanoparticles for hydrogenolysis was more than ten times higher in comparison to their commercial analogues, and their potential for the use in LC biorefinery is discussed.

Synthesis and characterization of triclinic MeAPO-34 (Me ¼ Zn, Fe) molecular sieves

Triclinic ZnAPO-34 and triclinic FAPO-34 were synthesized by hydrothermal crystallization from zinc(II)- and iron(II)-containing gels. The products are thermally stable up to 900 °C. XANES and EXAFS analyses were applied to study the local environment of zinc in the ZnAPO-34 samples, while XANES analysis and Mossbauer spectroscopy were performed on the iron-substituted samples. Zn(II) remains in the same oxidation state during synthesis and after thermal treatment, while iron exhibits Fe(II) and Fe(III) oxidation states. Analysis of the local structure showed that Zn(II) is located on tetrahedral sites of the framework, while Fe(II) and Fe(III) are present on octahedral sites. Infrared study of carbon monoxide adsorption at 100 K showed the presence of strong Bronsted acid sites on the Zn and Fe(II) samples, indicating the substitution of the metals in the framework. Rhombohedral FAPO-34 can be reversibly oxidized in the infrared cell, evidencing the disappearance of the Bronsted acid sites in the Fe(III) oxidation state.