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[Display omitted] • Mesoporous ordered silica materials were used as supports for catalysts. • Aluminum and cobalt were grafted on silica surface. • The catalysts showed poor activity in N 2 O decomposition and N 2 O reduction by CO. • The catalysts were significantly more active in CO oxidation. • SBA + Co showed the highest catalytic activity in CO oxidation. Three different ordered mesoporous silica materials, such as MCM-41, Al incorporated into the silica framework MCM-41 (mass ratio Si/Al = 9) and SBA-15, were prepared. Furthermore, aluminum was grafted on the surface of MCM-41 (mass ratio Si/Al = 16) and SBA-15 (mass ratio Si/Al = 23) by the molecular designed dispersion (MDD) method. In a next step, cobalt (Co = 10–12 wt%), as an active metal for redox reactions, was introduced by the MDD technique. The prepared catalysts were characterized by atomic absorption spectroscopy, microwave plasma-atomic emission spectroscopy, N 2 physisorption, thermogravimetric analysis, X-ray diffraction, diffuse reflectance UV–vis spectroscopy, infrared and Raman spectroscopies, transmission electron microscopy, temperature programmed reduction by hydrogen and their catalytic properties were evaluated for two model reactions: N 2 O decomposition and CO oxidation. All prepared catalysts showed poor activity in the reaction of N 2 O decomposition and the use of reducing agent (carbon monoxide) improved it only little. Contrary to this, all catalysts were significantly more active for CO oxidation by oxygen. The highest activity was reached over the SBA + Co catalyst which is proposed to be due to the smallest size of tetrahedral Co(II) species on SBA-15 silica support. [ABSTRACT FROM AUTHOR]

Electron tomography is an essential imaging technique for the investigation of morphology and 3D structure of nanomaterials. This method, however, suffers from well-known missing wedge artifacts due to a restricted tilt range, which limits the objectiveness, repeatability and efficiency of quantitative structural analysis. Discrete tomography represents one of the promising reconstruction techniques for materials science, potentially capable of delivering higher fidelity reconstructions by exploiting the prior knowledge of the limited number of material compositions in a specimen. However, the application of discrete tomography to practical datasets remains a difficult task due to the underlying challenging mathematical problem. In practice, it is often hard to obtain consistent reconstructions from experimental datasets. In addition, numerous parameters need to be tuned manually, which can lead to bias and non-repeatability. In this paper, we present the application of a new iterative reconstruction technique, named TVR-DART, for discrete electron tomography. The technique is capable of consistently delivering reconstructions with significantly reduced missing wedge artifacts for a variety of challenging data and imaging conditions, and can automatically estimate its key parameters. We describe the principles of the technique and apply it to datasets from three different types of samples acquired under diverse imaging modes. By further reducing the available tilt range and number of projections, we show that the proposed technique can still produce consistent reconstructions with minimized missing wedge artifacts. This new development promises to provide the electron microscopy community with an easy-to-use and robust tool for high-fidelity 3D characterization of nanomaterials. [ABSTRACT FROM AUTHOR]

A straightforward procedure to synthesize cysteine functionalized materials with tailored support properties has been developed. It allows tuning the hydrophobicity of the material via the incorporation of aliphatics, aromatics or silica in the framework structure. The aldol condensation of 4-nitrobenzaldehyde and acetone, as a probe reaction for the catalytic activity of the produced materials, exhibited a remarkable interplay between the reactant, solvent, traces of water and support hydrophobicity. A selective enrichment in the catalyst pores of specific bulk phase molecules is believed to be the key to achieve the targeted catalyst performance. [ABSTRACT FROM AUTHOR]

Barium titanate (BaTiO 3 ) was produced from an barium-titanate-peroxo-hydroxide precursor material in NaCl-KCl and Na 2 SO 4 -K 2 SO 4 salt mixtures or fluxes at temperatures up to 1080 °C via the molten-salt synthesis (MSS) method. Beside the different salt mixtures several other parameters were studied to determine the effect on the particle morphology. A relatively fast heating rate and a relatively high salt to precursor ratio resulted in a highly faceted morphology. The effect of the salt flux was clearly seen in the morphology of BaTiO 3 obtained by MSS at 1080 °C. Cube-shaped particles were observed for the chloride-flux-grown BaTiO 3 while hexagonal-shaped flat particles were observed for the sulfate-flux-grown BaTiO 3 . BaTiO 3 particles produced in the chloride-flux were either {1 0 1} or {0 0 1} faceted. The hexagonal surface of the sulfate-flux-grown BaTiO 3 was {1 1 1} faceted. [ABSTRACT FROM AUTHOR]

We report the synthesis of M 0.25 Cu 0.25 Mg 0.5 Fe 2 O 4 (where M = Mn, Zn, Co, Ni) nanoparticles using the coprecipitation method in the presence of carboxymethyl cellulose (CMC) as the in-situ surfactant. The crystalline structure and surface morphology were examined by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) and it was established that the average diameter of the magnetic nanoparticles (MNPs) is in the range of 3–10 nm. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) show that the MNPs are activated by the hydrophilic groups of the surfactant, which coat them and enhance their stability. The vibrating sample magnetometry measurements show the superparamagnetic behavior of the nanoparticles. Due to their small crystallite size, which implies large surface area, and their functionalization with organic groups, the obtained nanoparticles could have medical and catalytic applications. [ABSTRACT FROM AUTHOR]

Tetragonal cube-shaped barium titanate (BaTiO 3 ) was produced by the hydrothermal treatment of a peroxo-hydroxide precursor, a single-source amorphous barium titanate precursor, in a highly concentrated sodium hydroxide solution. Phase pure barium titanate with cube-shaped morphology and particle-sizes in the 0.2–0.5 µm range were formed at temperatures above 80 °C. Also, the cube-shaped morphology of the BaTiO 3 product was preceded by spherical- and plate-like morphologies with, respectively, a Ti-excess and Ba-excess. Coinciding with these morphological observations, changes in the reaction product were also observed. The formation of crystalline BaTiO 3 proceeded alongside secondary BaTi 2 O 5 and Ba 2 TiO 4 phases. These secondary phases disappeared as the reaction time was increased leaving only BaTiO 3 as the sole reaction product. Kinetic analysis of the formation of hydrothermal BaTiO 3 crystallization by the Johnson-Mehl-Avrami method showed that BaTiO 3 crystallization is a homogeneous dissolution-precipitation reaction. The mechanism is governed by nucleation and growth in the beginning of the reaction and dissolution-precipitation dominating throughout the hydrothermal reaction process. [ABSTRACT FROM AUTHOR]

Barium titanate powder was processed by slip casting in a rotating strong magnetic field of 9.4 T. The orientation factor of the sintered compact was analyzed by the X-ray diffraction technique and the microstructure (grain-size) was analyzed by scanning electron microscope. The hydrothermally prepared barium titanate was used as matrix material and the molten-salt synthesized barium titanate, with a larger particle-size, was used as template for the templated grain-growth process. Addition of large template particles was observed to increase the orientation factor of the sintered cast (5 vol% loading). Template particles acted as starting grains for the abnormal grain-growth process and the average grain-size was increased after sintering. Increasing the solid loading (15 vol%) resulted in a similar orientation factor with a decrease of the average grain-size by more than half. However, addition of templates to the 15 vol% cast had a negative effect on the orientation factor. The impingement of growing particles was stated as the primary cause of particle misorientation resulting in a low orientation factor after sintering. Different heating conditions were tested and it was determined that a slow heating rate gave the highest orientation factor, the smallest average grain-size and the highest relative density. [ABSTRACT FROM AUTHOR]

Three different ordered mesoporous silica materials, such as MCM-41, Al-containing MCM-41 (with 1.6 wt% of Al incorporated into the silica framework) and SBA-15, were prepared. Furthermore, aluminum (1.8 wt%) was grafted on the silica surface by the molecular designed dispersion method (MDD). In a next step, rhodium (1.4–2.9 wt%), as an active metal for the catalytic reaction of N 2 O decomposition, was introduced by the MDD technique. The following order of the catalytic activity was found under an inert atmosphere: Al(incorporated)-MCM-41 + Rh > MCM-41 + Al(grafted) + Rh > SBA-15 + Rh ≈ MCM-41 + Rh. The influence of textural properties, total acidity and rhodium dispersion on the activity of catalysts was studied. [ABSTRACT FROM AUTHOR]

Highly ordered SBA-15-type ethane-bridged PMOs have been obtained by employing H 3 PO 4 as acid to tune the pH in the presence of copolymer surfactant P123. The effects of the acidity and the addition of inorganic salt on the formation of the mesostructure are investigated. It is found that, compared with HCl, the polyprotic weak acid H 3 PO 4 is preferable for the synthesis of highly ordered SBA-15-type ethane-bridged PMOs with larger pore size and surface areas under mild acidic conditions. Moreover, taking the advantages of the mild acidic condition, vanadium-containing SBA-15-type ethane-bridged PMOs were successfully prepared through a direct synthesis approach. The XRD, N 2 -sorption, UV–Vis and CW-EPR studies of the V-PMO show that part of the vanadium species are present in polymeric (V–O–V) n clusters, while part of the vanadium centers are well-dispersed and immobilized on the inner surface of the mesopores. [ABSTRACT FROM AUTHOR]

Layered double hydroxides (LDHs) containing zinc and titanium in the layers with the cationic ratio of 3 were synthesized by the co-precipitation method at constant pH. The mixed metal oxides (ZnTi-MMO) obtained by the calcination of ZnTi-LDH at different temperatures were characterized together with the precursor material by X-ray diffraction (XRD), N sorption at 77 K, scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and ultraviolet-visible (UV-Vis) spectroscopy techniques. The photocatalytic activity was studied for the phenol degradation in aqueous solution under UV light irradiation. The results point out that the structural transformations of the layered porous clay to the ZnTi-MMO, as a function of the calcination treatment, have an important impact on the photocatalytic performances of the phenol degradation. These results may open new perspectives in tailoring the semiconductor-based capabilities of ZnTi-LDHs based nanoarchitectonics. [ABSTRACT FROM AUTHOR]

[Display omitted] • Solution-pH increased with increased [Fe]. Possibly a surface controlled reaction. • Lower temperatures (T): Consistently higher [H+] and lower Fe-dissolution. • Higher CO 2 -pressures (P): Consistently higher [H+] and higher Fe-dissolution. • At 1 barg P: pH measured ≅ pH modelled. At 10 barg P: pH measured ≅ 1.3 * pH modelled. • Underlying influences of CO 2 -depressurization on experiment and model discussed. FeCO 3 cement can be produced by reacting CO 2(aq) and particulate-Fe(0). Process conditions and solution compositions influence cement properties through kinetics of Fe-dissolution and FeCO 3 -precipitation. This study investigates Fe-dissolution in dilute systems (water(wt.)/Fe(wt.) = 1000) at 30/60 °C, and 1/10 barg CO 2 -pressures. Experimentally, time-evolution of solution composition shows increased [Fe] and solution-pH. As a proxy for high-pressure in-situ experiments, a modeling approach is developed to quantify with [Fe]-increase, the: decreased [ H + ], increased [ HCO 3 - ]/[OH–]/[ CO 3 2 - ], and undisturbed [CO 2(aq) ]/[H 2 CO 3 ]. Fe-dissolution rates increase with: (a) pH-decrease with increased CO 2 -pressure, and (b) faster kinetics at higher temperatures, even with higher pH. Experimental and modeled pH are comparable at 1 bar, two causes are discussed for it being ∼ 1.2 times at 10 barg: CO 2 -depressurization, and Fe-precipitation. Lower CO 2 -mediated dissolution activation energies of ∼ 30 (1 barg) and ∼ 20 kJ/mol (10 barg) compared to strong acids (∼60 kJ/mol) are attributed to buffering action of CO 2(aq). [ABSTRACT FROM AUTHOR]

Highlights: [•] Zeolite β nanoparticles are used in a mesotemplate-free method to obtain bimodal materials. [•] The impact of the nanoparticles synthesis on final material properties is proven. [•] The structure of mesotemplate-free materials is visualised by electron tomography. [•] A TEM study elucidates the relation between temperature and nanoparticle growth. [ABSTRACT FROM AUTHOR]

• Production of highly selective mesoporous CuO/TiO 2 catalysts for CO-PROX. • ADP on a mesoporous support affords ultra-small highly dispersed CuO nanoparticles. • Optimization of CO-PROX performance by Cu loading adjustment. • 5 wt% Cu loading provides the optimum CO-PROX performance. • The 5 wt% Cu/TiO 2 catalyst demonstrates high long-term stability and durability. Supported CuO catalysts onto a highly crystalline mesoporous TiO 2 material are produced via an ammonium driven deposition precipitation method and tested for preferential oxidation of CO in H 2 -rich gases. The effect of Cu loading on the oxidation activity is investigated by producing samples with final Cu content varying between 2.5 and 10 wt%. According to the analysis results, the chemical nature of the CuO species differs in each sample depending on the Cu loading. All materials tested are highly selective towards CO oxidation up to 160 °C. The 5 wt% Cu loaded material demonstrates the optimum CO-PROX performance, which is ascribed to the formation of finely dispersed and easily reducible copper oxide nanoparticles. Stability and durability of the latter sample are assessed by performing multiple testing cycles corresponding to >100hrs on stream as well as by the separate and combined addition of CO 2 and H 2 O in the feeding stream. [ABSTRACT FROM AUTHOR]

Abstract: The control of the formation process during and after self-assembly is of utmost importance to achieve well structured, controlled template-assisted mesoporous titania materials with the desired properties for various applications via the evaporation induced self-assembly method (EISA). The present paper reports on the large influence of the thermal stabilization and successive template removal on the pore structure of a mesostructured TiO2 material using the diblock copolymer Brij 58 as surfactant. A controlled thermal stabilization (temperature and duration) allows one to tailor the final pore size and uniformity much more precise by influencing the self-assembly of the template. Moreover, also the successive thermal template removal needs to be controlled in order to avoid a structural collapse. N2-sorption, TGA, TEM, FT-Raman spectroscopy, and small angle & wide angle XRD have been used to follow the crystal growth and mesostructure organization after thermal stabilization and after thermal template removal, revealing its effect on the final pore structure. [Copyright &y& Elsevier]

Thermogravimetry, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used for the studying of thermally induced structural changes of polyacrylonitrile (PAN) deposited on the surface of SBA-15 type mesoporous silica. Polymer was introduced onto the support by the precipitation polymerization of acrylonitrile in aqueous suspension of SBA-15. Low temperature transformation (to 723 K) of the deposited PAN was analyzed. It was found that at about 523 K, exothermic cyclization of polymer chains to the so-called ladder form of PAN occurred. However, the total cyclization of PAN required higher carbonization temperatures, at which gradual dehydrogenation followed by graphitization was initiated. XPS revealed that the cyclic form of PAN and a relatively large amount of carbonyl species, formed during the carbonization of the PAN/SBA-15 composite at 623 K, were responsible for the high sorption capacity in the methyl-ethyl ketone (MEK) vapor elimination. The efficiency in the MEK adsorption was also influenced by the content of PAN-derived carbon deposited on the SBA-15 surface. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid structures of layered double hydroxides able to incorporate, store and controlled release both Ca(II) and glutamate were fabricated by using the ability of the hydrotalcite-like anionic clay to manifest its “structural memory” in the aqueous solution of calcium glutamate. X-ray diffraction, IR spectroscopy, X-Ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy and thermal analyses evidence the formation of a hybrid system consisting of nanosized clusters of Ca(II) deposited on glutamate intercalated anionic clay. The resultant hybrid released Ca(II) rapidly with almost 80% release within 2h though a profile of a much slower and sustained release, with~54% release within 20h is obtained for glutamate. The kinetic models fitted to the experimental data reveal that the mechanism of Ca(II) release is probably due to the surface and/or intraparticle diffusion while glutamate release is better fitted to the bulk diffusion via ionic exchange. The present findings demonstrate the tremendous promise of layered double hydroxides to develop complex therapeutics by incorporation and controlled delivery of multiply biologically active agents. [Copyright &y& Elsevier]

Abstract: The hydrothermal, mechanical and chemical stability of various mesoporous materials have been studied in detail, using X-ray diffraction and nitrogen sorption. Pure siliceous nanoporous powders (MCM-41 and SBA-15) are evaluated against their hybrid counterparts; namely 2 types of periodic mesoporous organosilicas (benzene and ethane bridged PMOs) and an organosilane grafted MCM-41 material. In primary tests, the stability of the hybrid materials is found to be superior compared to that of the pure siliceous ones. The stability of the materials was correlated to their hydrophobicity via immersion calorimetry, applied for the first time in this context. Based on these results, a clear correlation between the hydrophobicity of a material and its stability has been revealed. In addition, with 29Si-MAS-NMR and vacuum experiments, the mechanism of the structural deterioration in the three different stability treatments could be unambiguously identified as the hydrolyzation of the siloxane bonds. The homogeneity of the hydrophobic groups throughout the entire network was found to be of great importance, irrespective of the hydrophobic nature at the surface as determined by calorimetric measurements. The results reveal that the most stable material can withstand (a) a pressure of 740MPa during 5min, (b) a 2h stirring in a 2M NaOH solution and (c) a 3 day steaming treatment at 393K. [Copyright &y& Elsevier]

Abstract: A novel method was developed for the synthesis of titanate nanosheets with high surface area. A solid-state mixture of NaOH and TiO2 was reacted at 600°C for several minutes. The aqueous dispersion of the resulting melt was aged at room temperature for periods up to 14days. After hydrochloric acid treatment and washing procedures, the reaction product was characterized by X-ray diffraction, Raman spectroscopy, N2-sorption and small-angle X-ray scattering measurements. The titanate compound not subjected to the aging process was amorphous and possessed a microporous framework, while the aged samples displayed nanosheet morphology and high specific surface area (396–509m2 g−1). It was revealed that the very short heat treatment is of crucial importance for the titania-titanate phase transformation, while the aging process is needed for the morphological evolution of the titanate samples. The effects of the aging time on the structure and the morphology are discussed. [Copyright &y& Elsevier]

Abstract: In this paper, the amorphous barium titanate precursor was prepared by the peroxo-hydroxide method and post-treated by various drying procedures, such as: room temperature drying, room temperature vacuum drying and vacuum drying at 50°C. The objective in the latter two treatments was to increase the Ti–O–Ba bonds of the precursor. The post-treated precursors were compared with the untreated (i.e., ‘wet’) precursor. Also, a barium titanate precursor was prepared by an alkoxide route. Afterwards, the precursors were hydrothermally treated at 200°C in a 10M NaOH solution. Vacuum drying of the precursor seemingly promoted the formation of Ti–O–Ti bonds in the hydrothermal end-product. The low Ba:Ti ratio (0.66) of the alkoxide-route prepared precursor lead to a multi-phase hydrothermal product with BaTiO3 as the main phase. In contrast, phase pure BaTiO3, i.e. without BaCO3 contamination, was obtained for the precursor which was dried at room temperature. Cube-shaped and highly crystalline BaTiO3 particles were observed by electron microscopy for the hydrothermally treated peroxo-hydroxide-route prepared precursor. [Copyright &y& Elsevier]

Abstract: In this study the effects of the heating rate and heating time on the formation of crystal-like benzene bridged periodic mesoporous organosilicas (PMOs) are investigated. The time needed to heat up an autoclave during the hydrothermal treatment has shown to be crucial in the synthesis of PMOs, while the total duration of heating gave rise to only minor differences. By choosing a smart heating profile, superior PMO materials can be obtained in a short time. Different heating profiles in a range from one minute to one hour are adopted by microwave equipment and compared with conventional heating methods. The heating rate has a large influence on the porosity characteristics and the uniformity of the obtained particles. Moreover, two new alternative synthetic strategies to adopt the smart heating profile are presented, in order to give some possible solutions for the expensive microwave equipment. [Copyright &y& Elsevier]

Abstract: Ti-SBA-15 was exposed to illumination in the presence of different gas mixtures containing CO or CO2, and H2O or H2, in order to clarify the route to hydrocarbon formation in photocatalytic CO2 reduction over this photocatalyst. A mixture of CO and H2O led to the highest quantities of CH4, C2H4, and C2H6 after 7h of reaction, whereas a mixture of CO2 and H2 lead to the lowest production rate of these products. H2O has been identified as more efficient in activation of CO and CO2 than H2. CH3OH was not detected as significant product, and when fed to the catalyst, did not yield extensive product formation. Formaldehyde was found very reactive over the catalytic system, yielding a product distribution (C1–C2) of similar nature as obtained by CO activation. Finally, backward reactions, i.e., oxidation of hydrocarbon products into CO or CO2, were found significant. Based on the experimental activity profiles, results indicated above, and available literature, a mechanism for photocatalytic CO2 reduction is proposed involving the formation of CO in the initial stages, followed by consecutive formation of formaldehyde, which converts to CH4, C2H4, and C2H6, presumably by reaction with photo-activated H2O (OH radicals). [Copyright &y& Elsevier]

Abstract: Mesoporous silica supports (MCM-41, SBA-15 and silica gel) were modified by the introduction of controlled amounts of polymer-derived carbon. Precipitation polymerization of polyacrylonitrile in the aqueous suspension of a silica material was used as a deposition method. The samples of PAN/silica composites were studied by thermal analysis, performed in air and inert atmosphere, in order to determine the amount of a deposited polymer and its thermal stability. The effect of surface area of a silica support and the monomer concentration in the mother solution on the effectiveness of deposition was revealed. The PAN/silica composites were transformed into C/SiO2 adsorbents by carbonization carried out at 623K. Texture (low-temperature sorption of N2), surface structure (FTIR-DRIFT) and morphology (SEM) of the carbonized samples were investigated. The adsorption tests in the elimination of methyl–ethyl ketone from gas phase were performed under dynamic conditions. The MCM-41-based composites containing highly dispersed carbon layers on the surface appeared to be the most promising adsorbents for a commercial application. Moreover, these materials exhibited a high stability in the adsorption–desorption runs repeated ten times suggesting the possibility of regeneration of the adsorbent bed without a significant loss in the adsorption effectiveness. [Copyright &y& Elsevier]

Abstract: In the field of photocatalytic air purification, the immobilisation of catalyst particles on support surfaces without loss of photon efficiency is an important challenge. Therefore, an immobilisation method involving a one-step suspension coating of pre-synthesised photocatalysts on glass beads was applied. The various benefits are exemplified in the gas phase photodegradation of ethylene. Coating of glass beads is easy, fast, cheap and offers a more efficient alternative to bulk catalyst pellets. Furthermore, this coating procedure allows to use porous, pre-synthesised catalysts to their full potential, as the surface area and morphology of the initial powder is barely altered after coating, in strong contrast to pelletising. With this technique it became possible to study the gas phase photocatalytic activity of commercial titanium dioxide, trititanate nanotubes and mixed phase anatase/trititanate nanotubes in a packed bed reactor towards the degradation of ethylene without changing the catalyst properties. Coating of glass beads with the photocatalyst revealed the superior activity of the as-prepared nanotubes, compared to TiO2 Aerolyst® 7710 in gaseous phase. [Copyright &y& Elsevier]

Abstract: Filtration membrane technology has already been employed to remove various organic effluents produced from the textile, paper, plastic, leather, food and mineral processing industries. To improve membrane efficiency and alleviate membrane fouling, an integrated approach is adopted that combines membrane filtration and photocatalysis technology. In this study, filtration membranes of alumina nanofibers (AF) with pore size of about 10nm (determined by the liquid–liquid displacement method) have been synthesized through an in situ hydrothermal reaction, which permitted a large flux and achieved high selectivity. Silver nanoparticles (Ag NPs) are subsequently doped on the nanofibers of the membranes. Silver nanoparticles can strongly absorb visible light due to the surface plasmon resonance (SPR) effect, and thus induce photocatalytic degradation of organic dyes, including anionic, cationic and neutral dyes, under visible light irradiation. In this integrated system, the dyes are retained on the membrane surface, their concentration in the vicinity of the Ag NPs are high and thus can be efficiently decomposed under light irradiation. Meanwhile, the usual flux deterioration caused by the accumulation of the filtered dyes in the passage pores can be avoided. For example, when an aqueous solution containing methylene blue is processed using an integrated filtration membrane, a large flux of 200Lm−2 h−1 and a stable permeating selectivity of 85% were achieved. The combined visible light photocatalysis and filtration function leads to superior performance of the integrated membranes, which have a potential to be used for the removal of organic pollutants in drinking water. [Copyright &y& Elsevier]

Abstract: The nature of core template has significant influences on the synthesis of hollow silica microspheres via the polystyrene (PS) beads templating route. Our present study indicates that the silica forming medium determines whether a surfactant is needed in the synthesis. It is shown that in a medium which itself gives discrete silica microspheres, hollow silica microspheres can only be templated by PS beads with the addition of cetyltrimethylammonium bromide surfactant. In contrast, in a medium which itself generates highly aggregated silica microspheres, hollow silica microspheres successfully templated by PS beads without any cationic surfactant. A unified mechanism for the formation of hollow silica shells with and without the surfactant is proposed. [ABSTRACT FROM AUTHOR]

This research presents a novel approach for developing noble metal-free three-way catalysts by using ZnAl layered double hydroxide (LDH) co-precipitated with Mn and Ti. Cu was added as the catalytically active metal. Two methods were explored, namely the addition of Cu during the co-precipitation step and a post-synthesis method using the LDH memory effect. In case the starting material had LDH characteristics high amounts of CuO were adsorbed on the support and high dispersion degrees of CuO were obtained. A four-cycle three-way catalysis test was used for evaluation. The smaller CuO particle size resulted in better performance for oxidation reactions. The addition of Mn had a positive effect on the general performance of the catalysts, while the presence of Ti mainly improved the NO conversion. The developed materials showed good stability in consecutive catalytic testing cycles and even show some NO conversion under stoichiometric conditions. The developed CuO-based ZnAl layered double hydroxide-based materials are very promising catalysts for Three-way catalysis, allowing to reduce the precious metal content compared to the classical catalysts composition. [Display omitted] • High loadings of well-dispersed CuO nanoparticles on LDH due to memory effect • Superior catalytic performance due to well-dispersed CuO nanoparticles • Amorphous aluminium oxide in the LDH material works as support dispersing CuO • Increased performance with Mn addition and NO conversion with Ti addition [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: Post-synthesis hydrothermal treatments have been used to improve the quality of MCM-41 materials. In our latest work, merging of surfactant-containing silica microspheres during the hydrothermal treatments was observed. Mechanistic insights and the different stages that are involved in the merging process can be summarized as follows. First, the surfaces of the starting microspheres open up due to the dissolution of silica. Then the dissolved silica species provide mass source for the formation of particle necks connecting two neighboring microspheres. Gradually, surfaces of the starting microspheres are flattened to meet the needs of further growth of the necks. Finally, some chain-like highly-ordered mesoporous structures up to several micrometers are formed. The observed merging of the surfactant-containing microspheres is a re-assembling process, which is under the control of electrostatic force between the dissolved silica species and the surfactant cations. The occluded surfactant cations in the precursor spheres play important roles in the merging process. [Copyright &y& Elsevier]

Abstract: The incorporation of the tetravalent Ti4+ cations into layered double hydroxide (LDH) type materials was studied as a function of the cationic ratio in the brucite-like sheets. Therefore, Zn–Ti-LDHs with different cationic ratio were prepared by the coprecipitation method at constant pH. The X-ray diffraction patterns revealed that only for the cationic ratio of 3, the characteristic layered structure was formed. The presence and the symmetry of the interlayer carbonate anions were investigated with FTIR–PAS spectroscopy. The UV–DR shows the octahedral environment of the Ti4+ cations in the brucite-like sheets. Following the same synthesis procedure, a reference sample containing Zn2+ and Al3+ (cationic ratio of 3) was synthesized. The Zn–Al- and Zn–Ti-LDHs textural features were investigated with N2 adsorption at 77K and scanning electron microscopy. Incorporation of Ti4+ cations in the brucite-like sheets of LDHs lead to a material with much smaller particles, therefore more interparticle porosity and higher volume of N2 adsorbed at high relative pressures was observed. [Copyright &y& Elsevier]

Abstract: Silicalite-1 precursor nanoparticle solutions are prepared from a mixture of TPAOH, H2O and TEOS. Acidification of the clear nanoparticle solution and a consequent hydrothermal treatment results in the formation of a large pore mesoporous material. The use of meso-templates for the formation of the mesopores is no longer required. These materials will be denoted mesosil. The porous characteristics of mesosil materials can be adjusted by controlling synthesis time, temperature and pH. The maximum surface area and pore volume are up to 600m2/g and 1.35cm3/g, respectively. The porosity in these materials originates from the interparticle voids between the nanoparticles (size approximately 5nm) in contrast to the framework porosity of M41S, SBA-15, and similar materials in which mesopores are formed through a templated synthesis route. The material is characterized by N2-sorption, TEM, FT-Raman, DRIFT and TGA measurements. [Copyright &y& Elsevier]

Abstract: The catalytic activity of alkaline and earth alkaline-modified silica-supported metal oxide was investigated for epoxidizing propylene with nitrous oxide. Iron oxide gave the best results, and surprisingly chromium oxide also produced propylene oxide (PO). Unmodified iron oxide catalyst showed low oxidation activity and produced propanal (57% selectivity) in concert with small amounts of acrolein, allyl alcohol, and acetone. After modification, the oxidation rate increased significantly, with PO the principal product. PO selectivities up to 85–90% and space–time yields of 0.25–0.53 mmol PO g−1 h−1 were obtained over supported iron oxide modified with Rb2SO4. A high throughput composition study revealed that other alkali and earth alkali salts were less effective modifiers. Isopropanol decomposition demonstrated that Rb2SO4 severely reduced the acidity of the catalyst. As a result of the neutralization, PO isomerization was drastically reduced. Accordingly, when feeding PO instead of propylene with N2O over the catalyst, a similar reduction of consecutive PO reactions was observed on Rb2SO4 modification. Despite the excellent epoxidation results, a catalytic process remains infeasible due to the restricted service time of the catalyst. Thermogravimetric analyses of a spent catalyst showed carbonaceous residues, suggesting that cokes deactivate the catalyst. Feeding PO indicates that PO itself is a source of cokes. Catalyst regeneration is possible without significant loss of performance. UV–vis DRS and EPR were used to determine the local environment of Fe3+ in the (un)promoted iron oxide catalyst; the findings suggest well-dispersed distorted tetrahedral Fe3+ sites for epoxidation activity. Fe dispersion is ruled by the promoter salts, with both anions and cations being essential. Along with the structural influences, inspection of the catalytic data in concert with XPS and Raman analyses provides evidence of a direct (electronic) promoter effect on the catalytic activity. [Copyright &y& Elsevier]

Abstract: Tens of micrometer-sized hollow silica spheres with thermally stable nanoporous shells were synthesized within 5min, followed by a drying and a calcination step. Most of the nanopores could be retained up to 700°C, and the hollow spherical morphology was remained at least until 950°C. It is proposed that a fast hydrolysis and condensation of tetraethyl orthosilicate take place around multi-lamellar octylamine vesicles. The morphology of the vesicles is then fixed by a quick gelation process, resulting in hollow organo-silica spheres. After the removal of the template by calcination, nanopores are generated in the hollow shells. [Copyright &y& Elsevier]

Abstract: Spherical, irregular and gyroidal MCM-41 were used for the deposition of VO x by the molecular designed dispersion method (MDD), in liquid phase, using vanadyl acetylacetonate. The molecular designed dispersion method using metal complexes on a highly porous support is a suitable method to prepare high quality catalysts. Deposition of VO(acac)2 was carried out at room temperature and with a decreasing temperature gradient. The porous characteristics and coordination environment of the supported vanadium oxide was studied by a combination of different techniques such as N2 adsorption/desorption, FT-Raman and FTIR-PAS. The results show that vanadia is present at the surface of the pore walls. Different morphologies of the support materials has no influence on the reaction mechanism for the VO(acac)2 deposition. However, the vanadium loading is significantly influenced by the morphologies of the support. The spherical MCM-41 gives the highest loading of vanadium, although it has a smaller surface area, pore volume and pore diameter than irregular and gyroidal MCM-41. Dye adsorption experiments prove that MCM-41 with various morphologies have different accessibilities, which is also related to differences in the vanadium loadings. [Copyright &y& Elsevier]

Abstract: The growth of titania nanoparticles within the mesopores of SBA-15 has been controlled by a post-synthesis deposition using the acid-catalyzed sol–gel method (ACSG). The crystal size, the location and the crystalline phase of the titania nanoparticles can be tuned by a careful adjustment of the preparation conditions. The influence of the initial titania amount, the pH and the temperature on the characteristics of titania-SBA-15 catalyst has been studied. The combined data from the structural and chemical analysis demonstrates that titania nanoparticles with different sizes were grafted within the SBA-15 channels. The formation mechanism of the titania nanoparticles within the mesopores is discussed. The photodecomposition of rhodamine 6G (R6G) in aqueous medium was selected as probe reaction to test the photoactivity of the titania-SBA-15 powders and to verify the potential use of these materials for wastewater treatment. It was shown that the preparation method and the structural characteristics of the mesoporous materials are of great importance for the adsorption capacity and the photocatalytic activity. [Copyright &y& Elsevier]

Abstract: Using a quaternary mixture of surfactant F127, demineralized water, HCl and butanol, it is possible to form different sized spheres of SBA-16 only by controlling the amount of siliceous precursor (TEOS) used during the synthesis. These spheres are well ordered and show very high porosity. The size of the spheres can be explained by an agglomeration mechanism of colloidal SBA-16 particles and a consequent filling of the interparticle voids with amorphous silica. The existence of the colloidal particles as well as the formation of partially formed (agglomerated) spheres and the filling of the voids is evidenced by SEM. All materials were characterized using N2-sorption, X-ray diffraction and scanning electron microscopy. [Copyright &y& Elsevier]

Continuous Wave (CW) and pulsed Election Paramagnetic Resonance (EPR) spectroscopy in conjunction with Raman spectroscopy are used to investigate the properties of Vanadium Silicalite-1 (VS-1) nanoparticles dispersed onto the mesoporous walls of SBA-15 silica. The properties of the deposited Zeolite nanoparticles are found to be remarkably different from those of the full grown VS-1 zeolite. Monitoring of the local VO² environment in the noncalcined nanoparticles in SBA-15 reveals that in contrast to the full grown zeolite case, these sites are highly hydrophilic. Also, the stability of the TPAOH template is found to be affected by acidification of the nanoparticles. These results promise to be of great importance in elucidating the formation mechanism of TPAOH-templated zeolitic nanoparticles and their incorporation in mesoporous silica materials. [ABSTRACT FROM AUTHOR]

Abstract: The molecular designed dispersion (MDD) method was used for the modification of SBA-15 with vanadium oxide. Vanadyl acetylacetonate was grafted on the support surface at different VO(acac)2 concentrations in a toluene solution, and then converted into the VO x /SBA-15 catalysts at elevated temperatures. The thermal transformation of surface species was studied by FTIR-PAS spectroscopy. The obtained materials were characterized with respect to their texture (BET), metal dispersion (FT-Raman and UV–vis-DR) and reducibility (H2-TPR). It was found that only isolated V5+ species were present in the samples with a low V loading. The catalyst with the highest V content showed the presence of polymeric V5+ species, which appeared to be easier reducible compared to the isolated form of V. The VO x /SBA-15 samples were tested as catalysts in the oxidative dehydrogenation of ethylbenzene to styrene in the presence of N2O. An increase in the catalytic activity with raising the V content was observed. It was however prove that monomeric V5+ species were considerably more active and selective in the styrene formation than oligomeric ones. [Copyright &y& Elsevier]

Abstract: Modified tin dioxide nanoparticles of enhanced thermal stability were prepared by sol–gel technique. The main point of the procedure is phosphoric acid treatment of the tin oxide hydrate (SnO2·nH2O). During the procedure, the molar ratio of P:Sn was varied in the range of 0.01–3.4. The structure and morphology of the modified SnO2 particles (P-SnO2) and that of two reference samples (SnO2 and SnHPO4/SnP2O7) were studied with various methods. X-ray diffraction (XRD) and diffuse reflectance infrared Fourier transform (DRIFT) measurements reveal that there are various tin phosphate compounds on the surface of SnO2 particles, improving the thermal stability of the original particles. The phosphate-containing shell formed on tin oxide hydrate inhibits sintering of the particles during calcination. The amorphous untreated SnO2 particles undergo crystallization at around 300°C (relatively sharp X-ray (110), (101) and (211) reflection peaks appear), whereas P-SnO2 particles remain amorphous up to 550°C. At 1000°C, the untreated SnO2 continue to crystallize into bulk material, while the crystal growth of P-SnO2 is inhibited: the average SnO2 crystallite size at P:Sn=0.01 molar ratio remains 27.7nm. Increasing phosphoric acid concentrations resulted in decreasing sintering effect during calcination. The band gap energy of the investigated particles was determined from UV–vis–DR measurements. [Copyright &y& Elsevier]

Abstract: TiO x , VO x and TiO x –VO x oxides were highly dispersed at different metal loadings on the mesoporous silica SBA-15 by the molecular designed dispersion (MDD) method. A combination of different techniques (N2-sorption, FT-Raman, TPR, UV–vis-DR) was used to verify the nature of the vanadia and/or titania species on the surface of the mesoporous support. Temperature-programmed desorption (NH3-TPD) was applied to characterise the surface acidity of these catalysts. Vanadia and titania were found to be present as isolated species, even at high metal oxide concentrations. The supported catalysts were tested in the selective catalytic reduction (SCR) of NO with ammonia. Among the studied samples, the highest activity was found for TiO x –VO x mixed oxides on SBA-15. The catalytic activity results were discussed in terms of loading and metal dispersion on the support material. [Copyright &y& Elsevier]

Abstract: The thermal stability of Na2Ti3O7 and Na2Ti6O13, together with that of their protonated forms was investigated. The influence of temperature on the structural behaviour of tri- and hexa-titanates was studied using DTG, XRD, FTIR and FT-Raman. These results were correlated with the nature of the exchangeable cations using elemental analysis and N2-sorption. The tunnel structure of Na2Ti6O13 revealed a higher thermal stability compared to the layered structure of Na2Ti3O7 that shows traces of dimerisation above 800°C. The sodium forms were observed to be more thermally stable compared to their protonated forms. However, analysis show that ‘H2Ti6O13’ is much more thermally stable than the layered H2Ti3O7 which go through structural changes above 250°C and suffer a complete structural collapse into anatase/rutile above 800°C. It was obvious that thermal stability was significantly influenced by the nature of the exchangeable cations and the degree of ion-exchange. [Copyright &y& Elsevier]

Iron species were loaded into the mesopores of MCM-41 spheres by incipient wetness impregnation procedure with Fe(ACAC)3 as the precursor. The magnetism of the samples was studied by vibrating sample magnetometer (VSM), diffuse reflectance ultraviolet–visible (DRUV-vis) spectra and Mossbauer spectra. The results show that the magnetic behavior of the iron-loaded MCM-41 spheres depends on the content of iron loading, valence, and coordination state of iron ions, testing temperature and the atmosphere for the pyrolysis of the iron precursor. [Copyright &y& Elsevier]