Yuri V. Plyuto

Gas-phase deposition and thermal transformations of Cr(acac)(3) on the surface of alumina supports

Gas-phase deposition and subsequent thermal activation of Cr(acac) 3 on the surface of fumed and precipitated alumina supports have been studied by diffuse reflectance FTIR spectroscopy, TG–DTG, TPO and chemical analysis. It has been found that stabilisation of Cr(acac) 3 on alumina occurs in a molecular form owing to the donor–acceptor interaction of the acetylacetonate ligands with surface hydroxy groups and coordinatively unsaturated Al 3+ ions. Thermally activated processes of removal of acetylacetonate ligands assisted by proton transfer and acetylacetonate ligand pyrolysis have been discriminated.

Thermolysis of Ru(acac)3 supported on silica and alumina

Abstract Precursors of alumina- and silica-supported ruthenium catalysts were prepared by pore volume impregnation of the dehydrated supports with a benzene solution of Ru(acac) 3 . The prepared samples were characterized by diffuse reflectance FTIR and TG/DTG–DTA in order to discriminate Ru(acac) 3 which interacts with the support surface. Weight loss, experimentally observed upon thermolysis of parent and supported Ru(acac) 3 , was compared with that calculated using the proposed reaction stoichiometry. Conditions for activating silica- and alumina-supported Ru(acac) 3 in an oxidizing atmosphere with complete removal of acetylacetonate ligands from the catalyst precursor are recommended.

AlPO4-5 molecular sieve modified with Cr(acac)3

Abstract AlPO 4 -5 molecular sieve was modified by gas phase reaction with Cr(acac) 3 affording Cr/AlPO 4 -5 material with a chromium content not exceeding 0.2 wt.%. Attachment of Cr species to the external surface of AlPO 4 -5 is suggested to result from interaction of surface hydroxyl groups with the acac ligands of Cr(acac) 3 , which is too bulky to enter the AlPO 4 -5 pores. It was shown that the Cr(acac) 3 species which retained their acac ligands predominate on AlPO 4 -5 surface. These ligands are removed by subsequent thermal treatment in air which simultaneously oxidizes Cr (III) ions to give surface-bound Cr (VI) oxo-species.

The Nature of Carbon Vacancies Initiating Graphite Oxidation

The density functional theory (DFT) calculations at the B3LYP/3–21G(d,p) level of C42H16 cluster model were used to mimic the formation of the mono-vacancy defects on the single graphite sheet (graphene) as a result of carbon atom removal due to reaction with molecular oxygen. The formation of the edge mono-vacancy defect (five-membered rings of carbon atoms terminated by CH2 group) appeared to be energetically favourable with energy effect of −263 kJ/mol. In contrast, in the case of basal-plane mono-vacancy defect formation (five- and seven-membered rings of carbon atoms), the respective energy is positive and equal to +362 kJ/mol and the considered process is energetically unfavourable. Similarly, in the temperature interval of 300–1200 K, the reaction of edge mono-vacancy defect formation is energetically favourable since the Gibbs free energy is negative (from −267 to −281 kJ/mol), while the reaction of basal-plane mono-vacancy defect formation is energetically unfavourable as the Gibbs free energy remains positive (from +337 to +314 kJ/mol). The obtained results agree well with the available experimental data which demonstrate the anisotropy of the natural graphite surface to oxidation and confirm that defects at graphite basal plane are most likely associated with the original defect sites and cannot be formed as the result of removal of carbon atoms due to oxidation with molecular oxygen.

Chemical Design of Carbon Coating on the Alumina Support

The developed approach to the synthesis of carbon-coated alumina is described. It includes grafting of 4,4′-methylenebis(phenylisocyanate) (MDI) due to reaction of isocyanate groups (NCO) with hydroxyl groups on the alumina surface via NC bond opening and subsequent pyrolysis of MDI surface species at 700°C in vacuum. Carbon-coated alumina supports with carbon loading up to 17.5 wt.% were synthesised by repetition of grafting–pyrolysis cycles. SEM analysis shows that surface structure of the initial alumina support is retained and no separate carbon phase is observed. It has been found out that carbon coating does not substantially influence the pore structure of the initial alumina support. The mechanism of formation of carbon coating as well as the structure of the synthesised carbon-coated alumina was studied by FTIR, TG/DTG-DTA, XPS, XRD, SEM and adsorption measurements.

Sol-Gel Silica Films Doped with Chromium (III) Acetylacetonate on Aluminium Substrate

Sol-gel silica films doped with Cr(acac)3 and having ca. 100 nm thickness on aluminium substrate were synthesised by dip-coating from the precursor composition prepared by TEOS acidic hydrolysis. It has been found out the that the C = O groups of doping Cr(acac)3 molecules are involved into interaction with silica network terminated with silanol groups. Upon thermal treatment of Cr(acac)3-SiO2 film in air, the ligand elimination from doping Cr(acac)3 molecules took place, resulting in complete thermolysis at 613 K. The latter was accompanied by oxidation of Cr (III) to Cr (VI).

Sol-Gel Template-Free and Template-Structured Silica Films Functionalisation with Methylene Blue Dye and Ag Nanoparticles

Sol-gel derived silica films are promising for application as working elements of sensors for environment control. The goal of the present work was to examine the difference in the post-synthesis functionalisation of nanometer-scale silica films prepared on glass substrates via template and template-free sol-gel routes. The films were prepared by dip-coating from TEOS sol-gel precursor in the absence or presence of CTAB template. It has been found out that the template-structured silica films can be functionalised with Ag nanoparti-cles via [Ag(NH3)2]NO3 ion-exchange or with adsorbed Methylene Blue (MB) cationic dye due to the presence of the well-organised mesopores after template removal. In contrast, only the external geometric surface of the template-free silica films appeared to be accessible for modifier molecules.