Julita Mrowiec-Białoń

Nickel-alumina composite aerogel catalysts with a high nickel load: a novel fast sol-gel synthesis procedure and screening of catalytic properties

AbstractNickel–aluminacompositeaerogelswithlargenickelloadingweresynthesizedusinganovelcomplexingagent-assisted sol–gel procedure to obtain materials displaying very large and open internal surface area, easily ac-cessible for large molecules and demonstrating excellent catalytic properties. They were tested in the followingreactions:(i)hydrogenationofpropeneand1-butene,(ii)methanizationofcarbondioxide,(iii)isometizationof1-butene,(iv)dehydrogenationofcyclohexane,(v)conversionofequimolarmixtureofCOandNOtoCO 2 andN 2 .Fullconversions and 100% selectivities were obtained in reactions (i), (ii), (iv) and (v) and an equilibrium composi-tioninreaction(iii).ThesecatalystsshowednopyrophoricactivityonexposingtoairevenatNicontentaslargeas50wt%. 2003ElsevierScienceB.V.Allrightsreserved. 1. IntroductionThenickel-basedcatalystsareofconsiderableindustrialinterest,especiallyforreactionssuchashydrogenationofaromaticsandunsaturatedhy-drocarbons, CO 2 =CH 4 reforming and reductionoffunctionalgroups[1–5],andaluminaismostoften used as nickel support. Quite often thesecatalystscontainaconsiderablenickelload,wellinexcessof10%(w/w)[2,5],toensureapropersurfacedensityandsizeofmetalclusters.How-ever,carbondepositionoverthemetallicandtheacidsidesofthesupportandNiparticlelossandsinteringathightemperatures,facilitatedbyhighnickelloadings,leadtocatalystsdeactivation.Itis well documented that this carbon depositiondecreaseswiththeincreaseinbasestrengthofthecatalystsandtheadditionoflantanium,magne-sium or molybdenium oxides has been foundparticularlyusefultodiminishthiseffect[3,6,7].

Thermostability and esterification activity ofMucor javanicus lipase entrapped in silica aerogel matrix and in organic solvents

The lipase ofMucor javanicus (nowM. circinelloides) entrapped in silica matrix by the sol-gel method esterified primary and secondary alcohols with conversions ranging from 30 to 35% and 10 to 15%, respectively. Loss in activity of the preparations after incubation at 100°C for 1 h with petroleum ether, dodecane, 1-heptanol or oleyl alcohol was about half of that observed for the native lipase.

Alkaline lipase from Pseudomonas fluorescens non-covalently immobilised on pristine versus oxidised multi-wall carbon nanotubes as efficient and recyclable catalytic systems in the synthesis of Solketal esters

In order to produce effective and recyclable catalysts for enantioselective transesterification in the industrial applications, alkaline lipase from Pseudomonas fluorescens was non-covalently immobilised (ca. 6 wt%) on pristine multi-wall carbon nanotubes (MWCNTs) and oxidised MWCNTs (O-MWCNTs) using an adsorption technique. Mesoporous silica modified with n-octyl groups was used as a reference support. Irreversible transesterifications of three vinyl esters (acyl donors) by racemic Solketal with a chromatographically (GC) traced kinetics were selected as model reactions. The undertaken comparative studies revealed that different morphology and chemical functionalisation of the supports led to various enzyme loadings, catalytic activities and enantioselectivities. MWCNT-lipase emerged as the exceptionally active (yield up to 98%, t=1h, 1320 Ug(-1), i.e. 9 times more active than native enzyme) whereas lipase immobilised on O-MWCNTs as the most enantioselective system, particularly for longer acyl chain esters (e.e. up to 72% after 30 min at yield of 20%, 340 Ug(-1)). Moreover, the activity of all nanotube-based catalysts after 10 cycles of transesterification remained practically unchanged. The differences in performance of MWCNTs and O-MWCNTs as solid supports were found to be based on geometry of pores, dominating hydrophobic interactions and absence/presence of the surface polar groups. Due to an excellent activity and reusability of the nanotube-lipase catalysts one can propose (O-)MWCNT as supports of a prospective industrial relevance.

Two-component aerogel adsorbents of water vapour

Abstract Two-component SiO2–CaCl2 or SiO2–LiBr aerogels exhibit outstanding adsorption capacities of water vapour, in the range of 0.9–1.1 kg H2O/kg adsorbent. Adsorption properties remain stable during repeated adsorption/desorption cycles.

New MCF type supports for platinum — characterization of Pt/MCF and Pt/NbMCF and comparison with Pt/MCM-41

Abstract We prepared the siliceous and niobiosilica mesostructured cellular foams (MCF) as supports for 1wt% of platinum loaded via the wetness impregnation method. For the comparison the Pt/MCM-41 and Pt/NbMCM-41 materials were investigated. Niobium was introduced by two methods, co-precipitation with siliceous source and the impregnation of siliceous MCF. The method of Nb introduction determines the surface properties and finally the catalytic activity of platinum containing catalysts. The efficiency of Nb introduction and activity in acetonylacetone transformation (test reaction) and NO, O2, C3H6 interaction (studied by FTIR) are discussed in this work.

Water-tolerant solid Lewis-acid sites: Baeyer–Villiger oxidation with hydrogen peroxide in the presence of gallium-based silica catalysts

The Baeyer–Villiger oxidation of a model cyclic ketone, 2-adamantanone, using H2O2 as the oxidizing agent, was systematically studied in the presence of two types of heterogeneous catalysts based on gallium(III) triflate as a hydrolytically stable Lewis acid precursor. Active-phase silica with a bimodal pore-size distribution of mesopores was used as a solid carrier. The first type of catalyst was prepared by post-synthesis treatment with gallium(III) triflate using an impregnation procedure, while the second type assumed the use of gallium(III) triflate as a source of Ga catalytic centres incorporated into a silica structure in a one-pot synthesis. The structural parameters of both catalysts were determined. The extremely high activity of both catalysts in promoting the oxidation, allowing full conversion of the ketone with lactone formation in a very short time (20 min to 90 min, molar ratio ketone : 60 wt% aq. H2O2 = 1 : 2 at 70 °C), is reported for the first time. In the case of the use of the catalysts for oxidation in a one-pot synthesis, the amount of the catalyst was low (a ratio of 2.64 mol% of gallium to the ketone), but the second catalyst from post-synthesis treatment was used in truly catalytic amounts (0.132 mol%). The superactivity of this catalyst (very high TON 711) is related to the availability of all catalytic centres on the surface of the catalyst. Lewis and Bronsted acid sites in the described catalysts were found, and the participation of both in the conversion of the ketone was postulated. To show the application potential, the recycling studies of the catalysts were demonstrated.

Ellipsometric study of porosity distribution in hybrid silica-based sol-gel films

This chapter describes ellipsometric investigation of porosity distribution in hybrid silica-based sol–gel films. The surface of silicon wafers was not hydrophilized, unlike that of glass slides, and this appeared to affect the film structure, especially in the near substrate region. The values of refractive index from films, especially the older ones, supported on silicon were somewhat lower, an indicative of larger porosity (30–35%). They fluctuated somewhat with a rise in distance from the substrate and even attained a maximum value at some distance from its surface. On the whole the mean value of porosity in the investigated coatings was estimated to be in the range of 15–30%. The analysis of hybrid thin films obtained by a dip-coating sol–gel method showed that porosity within films markedly changes as a function of distance from the substrate surface. As can be inferred from the refractive index profiles, the porosity profiles in films may be quite complex, depending on the coating sol structure and its condensation as well the substrate surface properties and the pretreatment. If highly condensed sols are used the profiles of porosity increase from the minimum values at the substrate surface to level out with a rise in distance from the substrate surface.

SAXS studies on porous inorganic dry gels

The small-angle X-ray scattering method is shown to be very useful tool in studies of nanoporous materials. The correlation between the profiles of SAXS curves and the structure of dry gels is analysed in detail. The scattering methods afford the ability to obtain quantitative data on nanomorphology not available by other means. Investigations focus on conventional dry gels, sol-gel xerogels and aerogels.

Preparation effects on titania-sulfate aerogel morphology

Abstract Institute of Chemical and Process Engineering, Faculty of Chemistry, Silesian Technical University, 44–100 Gliwice, Ks. M. Strzody 7, Poland The presence of sulfate ions markedly affects the nanopore structure of titania-sulfate aerogels. In TiO 2 -SO 4 2− materials, unlike in zirconia-sulfate aerogels, the larger sulfate load stimulates formation of a more consolidated structure. The XRD analysis shows that even a crystalline phase (anatase) may be present in fresh, dry aerogels, which, perhaps, is the first observation of this phase in sol-gel titania obtained from the low temperature drying process.

Effective sol-gel adsorbents of water vapor prepared using ethyl silicate 40 as a silica precursor

Abstract Effective composite sol-gel adsorbents of water vapor can be prepared in a one-step procedure using ethyl silicate 40 as a cost-effective silica precursor. Adsorption properties exhibited by the materials thus obtained are comparable with those of the samples obtained from the more complex procedure developed previously which made use of tetraethoxysilane.