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Abstract: A Cr3+-modified natural zeolite sample from the deposit of Donje Jesenje (Croatia) was structurally studied using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXS), inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The analyses revealed the presence of up to 0.4wt% of chromium in the clinoptilolite crystals. The X-ray photoelectron spectroscopy depth analysis suggested a uniform distribution of chromium from the surface of the crystallites to the depth of 50(3)nm. The study of local environment of chromium by XANES (X-ray absorption near edge structure) showed that chromium cations in the sample were predominantly in the 3+ oxidation state. EXAFS (extended X-ray absorption fine structure) analysis revealed that Cr3+ cations bond to six oxygen atoms at the distance of 1.97(2)Å and two chromium atoms at the distance of 2.54(2)Å suggesting that Cr3+ cations most probably arrange in the zeolite pores in the form of small clusters of CrO6 octahedra. The chromium could not be completely desorbed from the sample after post-treatment with NaCl or HCl solutions thus indicating mostly irreversible sorption of chromium in the zeolite. [Copyright &y& Elsevier]

Abstract: Iron-containing hexagonal mesoporous aluminophosphate (FeHMA) was synthesised hydrothermally in a microwave oven in the presence of cetyltrimethylammonium chloride (CTACl) as a template. The local environment of aluminium and phosphorus forming the aluminophosphate walls was studied by MAS NMR. The local environment of iron incorporated in HMA was investigated by X-ray absorption spectroscopy (XAS). X-ray absorption near edge structure (XANES) studies showed that iron in the as-synthesised and template-free FeHMA was present predominantly in the form of octahedrally coordinated Fe3+ ions. X-ray absorption fine structure (EXAFS) analyses confirmed that iron cations in the as-synthesised and template-free FeHMA were in octahedral coordination with the Fe–O distances of 1.97Å. Mössbauer spectroscopy revealed the presence of octahedrally coordinated Fe3+ and also tetrahedrally coordinated Fe2+ in the template-free FeHMA in the ratio of 4:1, which could not be detected by XANES. After the thermal treatment of template-free FeHMA at 427°C in vacuum the Mössbauer spectra showed that almost half of the iron cations present in the sample were tetrahedrally coordinated. The framework positions of tetrahedrally coordinated Fe2+ and octahedrally coordinated Fe3+ are suggested. [Copyright &y& Elsevier]

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 Mo¨ssbauer 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 Brønsted 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 Brønsted acid sites in the Fe(III) oxidation state. [Copyright &y& Elsevier]

Pure phases of CoAPO-31 and MnAPO-31 were synthesized hydrothermally using di-n-propylamine as a structure-directing 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 31P 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 (Brønsted 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. [Copyright &y& Elsevier]

Zeolite Y was synthesized and modified with EDTA dealumination procedure. The modified zeolites were analyzed by X-ray diffraction, X-ray absorption spectroscopy, chemical analysis and water adsorption measurements. We demonstrated that dealumination with bulk organic acid such as EDTA is able to reduce the original intense water affinity. Furthermore, it was found that dealumination with EDTA, in contrast with steaming and HCl dealumination, provides fully controllable, predictable and secure process of Al removal from the zeolites' frameworks. The shift of the adsorption isotherm in the low partial pressure range represents an interesting result for adsorption-based applications. Image 1 • Zeolite Y dealumination by EDTA reveals "S-shaped" water sorption isotherm. • Bulky EDTA molecule causes dealumination only on particles' surface (silicon-rich shell). • Al XANES reveals significantly less Al(OH) 3 in EDTA-treated than in HCl-treated Y. • Hydrophobic character of EDTA-treated Y interesting for sorption-based applications. [ABSTRACT FROM AUTHOR]

Abstract: An aluminium-free Ti-Beta/SBA-15 composite material was prepared by the post-synthesis incipient wetness-deposition of different amounts of Ti-Beta nanoparticles solution on the SBA-15 matrix. The presence of crystalline nanoparticles in the solution, used for impregnation on SBA-15, was confirmed by HRTEM measurements. The hexagonal arrangement of the mesopores of SBA-15 was proven by XRD and TEM measurements. The presence and the deposition of Ti-incorporated zeolitic nanoparticles on the mesopore walls of SBA-15 were proven by nitrogen sorption analysis, IR spectroscopy and TG analysis. The X-ray absorption spectroscopy analysis of local environment of titanium incorporated in the new composite material showed that the product contained five fold coordinated framework titanium. These Ti sites can be oxidation titanium sites. [Copyright &y& Elsevier]

Abstract: Mesoporous silicate catalyst FeTUD-1 containing only isolated iron was synthesized. Local environment of iron was investigated by X-ray Absorption and Mössbauer spectroscopies. XANES (X-ray Absorption Near Edge Structure) studies show that iron in the as-synthesized and template-free FeTUD-1 is present in the form of Fe3+ ions in coordination geometries posses an inversion center. EXAFS (X-ray Absorption Fine Structure) analyses reveal that iron cations in the as-synthesized sample are coordinated to four oxygens at the distance of 1.87Å and in the template-free sample to one oxygen at 1.86Å and five oxygens at 2.0Å distances. Mössbauer spectroscopy proves the presence of iron in Fe3+ form in template-free sample. Moreover, it determines Fe3+ in two types of distorted octahedral coordinations. [Copyright &y& Elsevier]

Abstract: Thermally stable titanium-containing microporous/mesoporous composite (Ti, Al)-Beta/MCM-48 was synthesised hydrothermally in the presence of structure-directing agents cetyltrimethylammonium bromide (CTABr), polyoxyethylene(8) isooctylhexyl ether (Triton® X-114) and tetraethylammonium hydroxide (TEAOH) in the absence of sodium cations. The presence of both microporous and mesoporous phases was determined by XRD and HRTEM measurements and by the analysis of nitrogen adsorption isotherm based on the α-plot method. The mass percentage (μ) of the microporous material in the composite is approximately 6.5%. NMR investigations showed that acid sites related to framework aluminium were generated by calcination of the as-synthesised (Ti, Al)-Beta/MCM-48. Local environment of titanium incorporated into the microporous/mesoporous silicate material was investigated by X-ray absorption spectroscopy. XANES studies showed the presence of tetrahedrally-coordinated Ti4+ cations in the template-free sample. EXAFS analysis revealed that titanium cations were coordinated to four oxygens in the first coordination shell, to one oxygen at 1.73(1) Å and three oxygens at 1.86(1) Å. In the second coordination sphere three silicon atoms were found at distances 3.18(2) Å and 3.48(2) Å, respectively. These results indicated framework Ti and thus the presence of Ti oxidation centres within the composite material. [Copyright &y& Elsevier]

Abstract: Manganese-modified hexagonal mesoporous aluminophosphate (MnHMA) was synthesized hydrothermally in a microwave oven in the presence of cetyltrimethylammonium chloride (CTACl) as a template. The mesoporous structure was elucidated by HRTEM. Local environment of aluminum and phosphorus forming the mesoporous aluminophosphate framework was studied by MAS NMR. The local environment of manganese incorporated in HMA was investigated by X-ray absorption spectroscopy. XANES studies show that manganese in the as-synthesized and template-free MnHMA is present in the form of Mn2+ and Mn3+ ions in the ratio 40–60%. EXAFS analyses revealed four oxygens in the first coordination sphere of manganese in the as-synthesized and template-free MnHMA at the distances 2.142(5)Å and 2.15(1)Å, respectively. EPR and ESEEM measurements revealed that Mn2+ in both as-synthesized and template-free products was located within the mesoporous aluminophosphate framework. [Copyright &y& Elsevier]

Abstract: Hydrothermally stable titanium containing microporous/mesoporous composite (Ti,Al)-Beta/MCM-41 was synthesized hydrothermally in the presence of structure-directing agents cetyltrimethylammonium bromide (CTABr) and tetraethyl ammonium hydroxide (TEAOH). XRD analysis and analysis of nitrogen adsorption isotherm confirmed the presence of micropores and mesopores in the composite. HRTEM microscopic studies revealed that micro- and mesoporosity of the composite was not due to the mechanical mixture of microporous (Ti,Al)-Beta and mesoporous (Ti,Al)-Beta/MCM-41. The local environment of titanium incorporated into the microporous/mesoporous silicate material was investigated by X-ray absorption spectroscopy. XANES studies showed the presence of tetrahedrally coordinated Ti4+ cations in the template-free sample. EXAFS analysis revealed that titanium cations were coordinated to four oxygens in the first coordination shell at a distance of 1.84Å. In the second coordination sphere one and two silicon atoms were found at the distances 3.12Å and 3.51Å, respectively. These results indicated framework Ti and thus the presence of Ti oxidation centers within the composite material. NMR investigations showed that Brønsted and Lewis acid sites related to framework aluminum were generated by the removal of potassium and sodium ions from the (Ti,Al)-Beta/MCM-41 pores. The new composite material was preliminarily tested in the oxidation reaction. Titanium leaching from the composite was not observed. [Copyright &y& Elsevier]

Abstract: Manganese containing MCM-41 was synthesised by the direct hydrothermal method (DHT) in the presence of cetyltrimethylammonium chloride (CTACl) as a template. The local environment of manganese incorporated in mesoporous silicate MCM-41 was investigated by XAS (X-ray Absorption Spectroscopy). XANES (X-ray Absorption Near Edge Structure) studies showed the coexistence of Mn2+ and Mn3+ cations in both, as-synthesised and template-free MnMCM-41 samples. The major part of manganese cations in the as-synthesised MnMCM-41 was Mn2+, while in the template-free MnMCM-41 the amount of Mn3+ was increased. EXAFS (X-ray Absorption Fine Structure) analyses revealed that major part of manganese cations in the as-synthesised MnMCM-41 were extra-framework with the Mn–O distance of 2.19Å. Manganese cations in the template-free MnMCM-41 were incorporated into the framework and coordinated to three oxygens in the first coordination shell, with two of them at a shorter distance of 1.92Å and one at a longer distance of 2.21Å. Pulsed ESR (Electron Spin Resonance) and ESEEM (Electron Spin-Echo Envelope Modulation) investigations were in agreement with the XANES and EXAFS results. [Copyright &y& Elsevier]

An extra-large pore iron-substituted aluminophosphate molecular sieve FeVPI-5 was synthesized. Elemental analysis indicated isomorphous substitution of aluminum by iron. X-ray absorption spectroscopy (XANES and EXAFS analyses) confirmed the incorporation of Fe(III) into the framework of VPI-5. The acidity tests of FeVPI-5, performed by IR spectroscopy using CO adsorption at low temperature on the oxidized and on the reduced material, gave evidence on redox behavior of framework iron in FeVPI-5. [Copyright &y& Elsevier]

Zinc-, cobalt- and manganese-containing microporous gallophosphates (GaPOs) with the ULM-5 structure have been hydrothermally synthesized in the presence of fluoride ions and 1,6-diaminohexane as the structure-directing agent. X-ray diffraction, elemental and thermogravimetric analyses of ULM-5 and MeULM-5 (Me=Zn, Co, Mn) indicated the incorporation of 2 wt.% for Zn, 1 wt.% for Co and 0.5 wt.% for Mn into the GaPO framework. The UV–VIS spectrum collected on the as-synthesized CoULM-5 sample revealed five-coordinated cobalt(II) in the structure. X-ray absorption spectroscopy (EXAFS) showed that zinc(II), cobalt(II) and manganese(II) substituted gallium on non-tetrahedral sites in the MeULM-5 framework and revealed structural changes of ULM-5 and MeULM-5 in the calcination process. The template-free samples are not thermally stable in the ambient atmosphere. [Copyright &y& Elsevier]