Margarita Popova

Methanol conversion to light alkenes over SAPO-34 molecular sieves synthesized using various sources of silicon and aluminium

Depending on the various sources of Si and Al used for the synthesis, SAPO-34 materials with different degrees of crystallinity and density of acid sites, as shown by TPD of ammonia and TPD-TGA of 1-propanamine have been prepared. The effect of the different acidities on the activity, selectivity and lifetime of the catalysts in the reaction of methanol conversion to light alkenes has been studied.

Carboxylic modified spherical mesoporous silicas аs drug delivery carriers.

The present study deals with the development and functionalization of mesoporous silica nanoparticles as drug delivery platforms. Spherical MCM-41 and SBA-15 silicas with different pore sizes (2.7 nm and 5.5 nm, respectively) were post-synthesis modified applying a new, two step process. The initial step was the modification with 3-amino-propyltriethoxysilane, and the next was the reaction with succinic anhydride in toluene in order to obtain carboxylic modified mesoporous carriers. The carboxylic-functionalized mesoporous materials were characterized by XRD, nitrogen physisorption, TEM, ATR FT-IR spectroscopy. The successful carboxylic functionalization was proved by the changes of the zeta potential of the mesoporous materials before and after modification. The parent and the carboxylic-modified MCM-41 and SBA-15 materials showed high adsorption capacity (approximately 50 wt.%, except for non-functionalized MCM-41) for sulfadiazine that possesses amino functional groups. Mesoporous structure peculiarities lead to different adsorption capacities on the carriers. In vitro release studies showed slower release rate of sulfadiazine from carboxylic modified MCM-41 and SBA-15 mesoporous particles compared to the non modified ones. Both non loaded and drug-loaded silica materials demonstrated no cytotoxicity on Caco-2 cell line. The functionalized mesoporous systems are appropriate drug delivery platforms due to their biocompatibility and the possibility to modify drug release.

Toluene oxidation on titanium- and iron-modified MCM-41 materials

Iron- and titanium-modified MCM-41 materials, prepared by direct synthesis at ambient temperature or wet impregnation technique, were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), UV-vis diffuse reflectance, Mössbauer and FT-IR spectroscopies. Their catalytic behavior was studied in total oxidation of toluene. Materials with high surface area and well-ordered pore structure were obtained. The increase of the titanium content (up to 50%) in the bisubstituted, iron and titanium containing materials leads to partial structure collapse of the silica matrix. Finely dispersed anatase particles were also formed during the impregnation procedure. The catalytic activity of the bisubstituted materials was influenced by the method of their preparation, but higher catalytic stability could be achieved, compared to iron monosubstituted one. The nature of the catalytic active sites is discussed.

Transalkylation of toluene with cumene over zeolites Y dealuminated in solid-state: Part II. Effect of the introduced Lewis acid sites

The effects of the introduced Lewis acid sites of different kind (InO+ or AlO+) and the variation of InO+ concentration on the catalytic behavior of dealuminated in solid-state HY zeolites in the reaction of cumene–toluene transalkylation have been studied. The catalysts, indium modified HY(3.7) and ultra stable zeolite USY(3.4), containing essentially equivalent amounts of framework aluminum and Lewis acid sites (InO+ and AlO+, respectively), have been compared to the initial HY(3.7), not containing any extra-framework aluminum (EFAl). Strictly controlled conditions were used for the formation of Lewis acid sites: through reductive solid-state ion exchange (RSSIE) for InO+ or by steaming in the case of AlO+. The ratio between the Lewis and Broensted acid sites was varied by progressive replacement of the protons by InO+ cations in HY(5.6) zeolite. The zeolites modified by monovalent (InO+ and AlO+) have, as a result, an enhanced catalytic activity in comparison with HY(3.7). This effect is mainly due to intense side reactions of dealkylation, oligomerization, cracking and re-alkylation at the expense of the cymenes formation. The data for the distribution of the reaction products suggest a highly preferred mechanism of dealkylation/alkylation with the increase of the Lewis/Broensted acid site ratio. The presence of cation-connected Lewis acid sites is supposed to be responsible for the fast samples’ deactivation.

Silver- and sulfadiazine-loaded nanostructured silica materials as potential replacement of silver sulfadiazine

Silver sulfadiazine (AgSD) is the leading topical antibacterial agent for the treatment of burn wound infections. Antibacterial effect of AgSD is limited by its poor aqueous solubility, and antibacterial activity develops only by decomposition of AgSD to silver ions and sulfadiazine. In this study, it is for the first time that application of silver-modified nanoporous silica carriers (MCM-41 or SBA-15) loaded with sulfadiazine (SD), instead of silver sulfadiazine, overcoming the abovementioned disadvantages has been demonstrated. By direct or post synthesis methods, 5-15 nm sized silver nanoparticles can be stabilized in the channels or on the outer surface of nanoporous silica supports; moreover, the empty channels can be loaded by SD molecules. The SD-loaded, silver-modified materials show sustained release properties and similar or even better antimicrobial properties than AgSD. Adsorption of AgSD on nanoporous silica particles significantly improves its water solubility.

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.

Influence of the Lewis acidity of indium-modified beta zeolite in the m-xylene transformation

Abstract The catalytic performance of NH4-beta zeolite containing different amounts of indium, introduced as In+ cations by the method of reductive solid-state ion exchange (RSSIE), has been studied in the m-xylene conversion. It has been shown that In cations regarded as coordinatively unsaturated species possessing Lewis acidity substantially change the catalyst stability and the selectivity of the reaction when performed in an inert atmosphere. An acceleration of the side reactions of disproportionation and coking has been observed on the In-modifications of zeolite beta and a mechanism of hydride ion abstraction and faster benzylic cation formation on them have been supposed. In presence of H2 these reactions are strongly suppressed at the expense of the main reaction of isomerisation. On the completely In-exchanged beta zeolite a partial bimolecular mechanism of isomerisation is suggested.

Iron‐Functionalized Silica Nanoparticles as a Highly Efficient Adsorbent and Catalyst for Toluene Oxidation in the Gas Phase

Catalytic oxidation is one of the most important industrially applicable processes for the decomposition of volatile organic compounds (VOCs) in polluted air. The advanced VOC removal process is composed of an adsorption unit and a catalytic incinerator. Many efforts have been made to design a combined adsorption–catalytic unit with optimal activity and selectivity. We demonstrate that iron‐functionalized silica nanoparticles with interparticle mesoporosity (FeKIL‐2) act as highly efficient adsorbents and catalysts with optimal Fe/Si molar ratios of 0.01 in toluene oxidation as model VOCs in the gas phase. By using UV/Vis, FTIR, and Mössbauer spectroscopic techniques, we prove that the enhanced activity of the catalyst is attributed to iron incorporated into the silica matrix, which depends on the iron content. The iron content with Fe/Si≤0.01 leads to the formation of stable Fe3+ ions in the silica matrix, which ensures easier oxygen release from the catalyst (Fe3+/Fe2+ redox cycles). The increase in the iron content with Fe/Si>0.01 leads to the formation of oligonuclear iron complexes. The material thus introduces a promising, environmentally friendly, cost‐effective, and highly efficient catalyst with combined adsorption and catalytic properties for the removal of low‐concentration VOC from polluted air.

Autoreduction of Copper on Silica and Iron‐Functionalized Silica Nanoparticles with Interparticle Mesoporosity

Copper‐supported catalysts are of industrial importance in many catalytic processes. Mesoporous silica materials are of particular interest as green heterogeneous catalyst supports. In the present study we demonstrate the nature and reduction properties of copper oxide species, which are influenced by the peculiarity of the silica nanoparticles with interparticle mesoporosity (KIL family) and the presence of a second metal (iron) in the silica matrix. The copper‐containing KIL‐2 and FeKIL‐2 samples are prepared by incipient wetness impregnation. The reduction of copper oxide species is easier on the FeKIL‐2 supported sample in comparison to its KIL‐2 supported analogue, whereas the copper‐containing KIL‐2 sample shows higher catalytic activity in total toluene oxidation. The presence of iron in the FeKIL‐2 structure leads to autoreduction of copper followed by the redispersion and oxidation of metallic copper in the reaction medium; this results in the formation of different types of finely dispersed copper oxide species (<100 nm). The later species possess lower catalytic activity in toluene oxidation in comparison to species that are 100 nm in size and formed on KIL‐2.

Preparation of efficient quercetin delivery system on Zn-modified mesoporous SBA-15 silica carrier

Mesoporous silica material type SBA-15 was modified with different amounts of Zn (2 and 4wt.%) by incipient wetness impregnation method in ethanol. The parent, Zn-modified and quercetin loaded samples, were characterized by XRD, N2 physisorption, TEM, thermal gravimetric analysis, UV-vis and FT-IR spectroscopies and in vitro release of quercetin at pH5.5 which is typical of dermal formulations. By this loading method anhydrous quercetin was formed on the silica carrier It was found that the different hydrate forms of quercetin (dihydrate, monohydrate, anhydrite) significantly influence the physico-chemical properties of the delivery system. It was found that hydrate forms of quercetin can be differentiated by XRD and by FT-IR spectroscopic methods. Thus, by evaluating the interaction of the drug with the silica carrier the changes due to its hydration state always have to be taken into account. Formation of Zn-quercetin complex was evidenced on zinc modified SBA-15 silica by FT-IR spectroscopy. High quercetin loading capacity (over 40wt.%) could be achieved on the parent and Zn-containing SBA-15 samples. The in-vitro release process at pH=5.5 showed slower quercetin release from Zn-modified SBA-15 samples compared to the parent one. Additionally, the comparative cytotoxic experiments evidenced that quercetin encapsulated in Zn-modified silica carriers has superior antineoplastic potential against HUT-29 cells compared to free drug. Zn-modified SBA-15 silica particles could be promising carriers for dermal delivery of quercetin.