Igor V. Babich

Role of the support nature in chemisorption of Ni(acac)2 on the surface of silica and alumina

Abstract Nickel acetylacetonate surface species which are formed on silica and alumina supports in the result of chemisorption of Ni(acac)2 from the gas phase were characterized by FTIR, TG/DSC and chemical analysis. Nickel acetylacetonate is found to be covelently bound to the supports since one acetylacetonate ligand in the initial Ni(acac)2 molecule undergoes substitution with the oxygen atom of surface hydroxyl group. In the case of alumina, acetylacetone which is evolved reacts with coordinatively unsaturated Al3+ ions of the support surface that results in the appearance of the aluminum acetylacetonate surface species. Oxidation of acetylacetonate ligands coordinated to both nickel and aluminum atoms in the surface species was observed at 300–350°C.

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.

Synthesis and characterization of molybdenum(VI) oxo-species on the surface of fumed alumina and silica

Abstract Synthesis of molybdenum(VI) oxo-species on the surface of alumina and silica supports was carried out by their chemical modification with a dichloromethane solution of MoOCl 4 followed by hydrolysis of the anchored groups ( -O) n MoOCl 4− n and subsequent thermal treatment. In the case of alumina, the formation of monomeric molybdenum(VI) oxo-species which strongly interact with the support surface is observed. Mo 6+ ions in these species are found to be tetrahedrally coordinated. On the silica surface, at least two types of molybdenum(VI) oxo-species are detected. Aggregated molybdenum(VI) oxo-species in which Mo 6+ ions have an octahedral coordination appear to be predominant.

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.

Production of Monosugars from Lignocellulosic Biomass in Molten Salt Hydrates: Process Design and Techno-Economic Analysis

ZnCl2 hydrate, the main molten salt used in biomass conversion, combined with low concentration HCl is an excellent solvent for the dissolution and hydrolysis of the carbohydrates present in lignocellulosic biomass. The most recalcitrant carbohydrate, cellulose, is dissolved in a residence time less than 1 h under mild conditions without significant degradation. This technology is referred to as BIOeCON-solvent technology. Separation of the sugars from the solution is the main challenge. The earlier conclusion regarding the potential of zeolite beta for selective adsorption has been used as the basis of a scale-up study. The technology of choice is continuous chromatographic separation (e.g., simulated moving bed, SMB). The sugar monomers are separated from the sugar oligomers, allowing the production of monosugars at high yield, using water as an eluent. Results of a pilot plant study are presented showing a stable operation at high selectivity. Several process designs are discussed, and the techno-economic performance of the BIOeCON-solvent technology is demonstrated by comparison with the state-of-the-art technology of NREL (National Renewable Energy Laboratory), which is based on enzymatic conversion of cellulose. It is concluded that the BIOeCON-solvent technology is technically and economically viable and is competitive to the NREL process. Because the BIOeCON-solvent process is in an early stage of development and far from fully optimized, it has the potential to outperform the existing processes.

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.