Alexander A. Khassin

Bio: Alexander A. Khassin is an academic researcher from Novosibirsk State University. The author has contributed to research in topics: Catalysis & Hydrogen. The author has an hindex of 14, co-authored 28 publications receiving 690 citations. Previous affiliations of Alexander A. Khassin include Russian Academy of Sciences.

Metal-support interactions in cobalt-aluminum co-precipitated catalysts: XPS and CO adsorption studies

Abstract: Cobalt-aluminum catalysts were prepared using either the precipitation of Co2+ in the presence of freshly prepared Zn-Al hydrotalcite (the promoted sample) or the co-precipitation of Co2+ and Al3+ (the unpromoted samples). The evolution of the initial hydrotalcite-like structure was monitored during its calcination and the reductive treatment by means of XPS. It was shown that at 480°C the reduction of the calcined samples results in the formation of Co0 species, the further reduction at 650°C results in an increase of the amount of the Co0 species. The samples reduced at 650°C chemisorb readily carbon monoxide at 77 K, while the sample reduced at 480°C does not chemisorb CO at 77 K. At elevated temperatures, all reduced samples are found to be able to chemisorb CO. Terminal CO moieties as well as monodentate carbonates, formates and carboxyl species were detected at the surface of the reduced samples at their exposure to the CO medium at the elevated temperature. The intensity of the IR absorption bands of chemisorbed CO are found proportional to the surface fraction of the Co0 species, measured by XPS. The apparent red shift of the IR absorption bands is observed for CO adsorbed on the samples reduced at 480°C. The obtained data correlate with the catalytic properties of the Co-Al samples in hydrogenation reactions. The conclusion on the existence of a strong metal–support interaction in the samples under the study is made.

Coprecipitated iron-containing catalysts (Fe-Al2O3, Fe-Co-Al2O3, Fe-Ni-Al2O3) for methane decomposition at moderate temperatures: I. Genesis of calcined and reduced catalysts

Abstract: Genesis of the composition and structure of the active component of coprecipitated iron containing catalysts (Fe-Al 2 O 3 , Fe-Co-Al 2 O 3 , Fe-Ni-Al 2 O 3 ) with high metal loadings (>50 wt.%) for methane decomposition at moderate temperatures (600–650 °C) has been investigated by XRD, EXAFS, radial electron density distribution (REDD), TEM, FTIR and Mossbauer spectroscopy. The main stages of the catalyst genesis during drying, thermal decomposition and reduction have been studied. For bimetallic systems (Fe-Co-Al 2 O 3 , Fe-Ni-Al 2 O 3 ) intermediate spinel phases with a composition (M II , Fe) 3 O 4 (M=Co, Ni) have been shown to form during heat treatment and reduction. This leads to a decrease of the reduction temperature for iron oxides. Reduced bimetallic catalysts (Fe-Co-Al 2 O 3 , Fe-Ni-Al 2 O 3 ) are composed of alloys. The structure and parameters of their crystal lattices depend on the type and concentration of the added metal. Alumina has been shown to behave as a structural promoter. A model of the reduced catalysts consisting of highly dispersed (20–50 nm) metal and alumina particles with a spinel phase at their interface has been suggested.

Cobalt–aluminum co-precipitated catalysts and their performance in the Fischer–Tropsch synthesis

Abstract: Cobalt–aluminum catalysts were prepared using either Co2+ precipitation onto freshly prepared Mg–Al or Zn–Al hydrotalcite (promoted samples) or co-precipitation of Co2+ and Al3+ (non-promoted samples). The evolution of initial hydrotalcite structure was monitored during its calcination and reductive treatment. It has been shown that, at moderate temperatures, hydrotalcites results decomposition yields a Co oxide phase supported by a highly defective inverted spinel-like structure. Cations Co2+ enter the support structure, and occupy both tetrahedral and octahedral positions. Octahedron coordinated Co species are reduced at 580–620°C. After the reduction at 470–480°C catalyst phase composition shows Co0 supported on inverted spinel-like structure, which contains Co2+ in the octahedral coordination. Further reduction at 600°C transforms the support to ‘ideal’ spinel, which contains no octahedron coordinated Co2+. Chemical properties of the Co–Al catalysts, including their performance in the Fischer–Tropsch synthesis (FTS), were found to depend on the catalyst reduction temperature, and thus on the support structure. Metal-support interaction is supposed to explain the observed properties of metallic cobalt.

Dynamic Cu/Zn Interaction in SiO2 Supported Methanol Synthesis Catalysts Unraveled by in Situ XAFS

Abstract: In situ X-ray absorption spectroscopy XAFS at the Cu and Zn K-edge has been used to unravel the Cu/Zn interaction and identify the possible active site of Cu-based methanol synthesis catalysts in the Cu/ZnO/SiO2 ternary system. These highly dispersed silica supported catalysts, whose activity increases sharply as a function of the reduction temperature, were studied calcined, reduced at 200, 300, and 400 °C, and for each reduction temperature under passivation/rereduction and methanol synthesis conditions. Results showed that the calcined form consists mainly of a mixed Cu/Zn hydrosilicate that is progressively transformed as the reduction temperature increases into (i) Cu metal particles, (ii) increasingly dispersed ZnO species on SiO2, and (iii) finally a Zn metallic phase forming segregated bimetallic Cu–Zn α-brass alloy particles. These different structures and Cu/Zn interfaces may correspond to different active phases and activities in methanol synthesis. After reduction at 200 and 300 °C, Cu0 is lik...

Dehydrogenation of methanol over copper-containing catalysts

Abstract: The catalytic properties in methanol dehydrogenation of copper metal formed as a result of reduction by hydrogen of copper-containing oxides with different structure: copper chromite (tetragonally distorted spinel), copper hydroxysilicate (Chrysocolla), and copper-zinc hydroxysilicate (Zincsilite) have been studied. This process proceeds via successive reactions: (I) 2CH 3 OH=CH 3 OOCH+2H 2 and (II) CH 3 OOCH=2CO+2H 2 . The methyl formate selectivity for the catalysts studied was close to 1.0 at low methanol conversion, X ≤0.1, where the dehydrogenation process is represented by reaction (I), occurring far from its equilibrium. At 0.2≤ X ≤0.55, the selectivity decreases with increasing conversion, and the ratio of the activities in successive reactions may serve as a comparative characteristic for the catalysts. At high conversions, when reaction (I) is close to its equilibrium, selectivity is independent of the properties of studied catalysts and depends on the methanol conversion. Reaction (I) shows low sensitivity to the state of metal copper of reduced catalysts and, hence, low sensitivity to the composition and structure of oxides-precursors. The catalysts’ activity in reaction (II) greatly depends on the state of metal copper in the catalysts. It was assumed that the catalyst activity in methyl formate conversion to CO and H 2 and, hence, the selectivity of methanol dehydrogenation with respect to methyl formate in the region of moderate methanol conversion depends on the strength of interaction between metal copper particles and catalyst oxide surface, which is determined by the composition and structure of oxide-precursor.

Magnetic nanoparticles: preparation, structure and properties

Abstract: The key methods for the preparation of magnetic nanoparticles are described systematically. The experimental data on their properties are analysed and generalised. The main theoretical views on the magnetism of nanoparticles are considered.

State of the art and perspectives in heterogeneous catalysis of CO2 hydrogenation to methanol.

Abstract: The ever-increasing amount of anthropogenic carbon dioxide (CO2) emissions has resulted in great environmental impacts. The selective hydrogenation of CO2 to methanol, the first target in the liquid sunshine vision, not only effectively mitigates the CO2 emissions, but also produces value-added chemicals and fuels. This critical review provides a comprehensive view of the significant advances in heterogeneous catalysis for methanol synthesis through direct hydrogenation of CO2. The challenges in thermodynamics are addressed first. Then the progress in conventional Cu-based catalysts is discussed in detail, with an emphasis on the structural, chemical, and electronic promotions of supports and promoters, the preparation methods and precursors of Cu-based catalysts, as well as the proposed models for active sites. We also provide an overview of the progress in noble metal-based catalysts, bimetallic catalysts including alloys and intermetallic compounds, as well as hybrid oxides and other novel catalytic systems. The developments in mechanistic aspects, reaction conditions and optimization, as well as reactor designs and innovations are also included. The advances in industrial applications for methanol synthesis are further highlighted. Finally, a summary and outlook are provided.

Ni-based sol–gel catalysts as promising systems for crude bio-oil upgrading: Guaiacol hydrodeoxygenation study

Abstract: Catalytic hydrotreatment or hydrodeoxygenation (HDO) has been researched extensively with the crude bio-oil and its model compounds over conventional sulfided Ni(Mo), Co(Mo) catalysts and supported noble metal catalysts. These types of catalysts showed themselves unsuitable for the target HDO process, which resulted in an urgent need to search for a new catalytic system meeting such requirements as low cost, stability against coke formation and leaching of active components due to adverse effect of the acidic medium (bio-oil). In the present work a series of Ni-based catalysts with different stabilizing components has been tested in the hydrodeoxygenation (HDO) of guaiacol (2-methoxyphenol), bio-oil model compound. The process has been carried out in an autoclave at 320 °C and 17 MPa H2. The main products were cyclohexane, 1-methylcyclohexane-1,2-diol, and cyclohexanone. The reaction scheme of guaiacol conversion explaining the formation of main products has been suggested. The catalyst activity was found to rise with an increase in the active component loading and depend on the catalyst preparation method. The most active catalysts in HDO of guaiacol were Ni-based catalysts prepared by a sol–gel method and stabilized with SiO2 and ZrO2. According to TPR, XRD, XPS, and HRTEM, the high activity of these catalysts correlates with the high nickel loading and the high specific area of active component provided by the formation of nickel oxide–silicate species. The effect of temperature on the product distribution and catalyst activity in the target process (HDO) has been investigated as well. The catalysts were shown to be very promising systems for the production of hydrocarbon fuels by the catalytic upgrading of bio-oil.