Nadezhda M. Mikova

Chemical transformations of a SiO2-supported [Fe5RhC(CO)16]− cluster and catalysis of propylene hydroformylation

Chemical transformations of SiO2-supported [Fe5RhC(CO)16]− and [Fe4RhC(CO)14]− clusters in Ar, CO, and synthesis gas are studied by IR spectroscopy, Mössbauer spectroscopy, and transmission electron microscopy. It is shown that partial transformation of the [Fe5RhC(CO)16]− cluster to the [Fe4RhC(CO)14]− cluster occurs immediately after its deposition on the substrate surface with the simultaneous formation of Fe2+ ions. The complete conversion of the supported [Fe5RhC(CO)16]− cluster to [Fe4RhC(CO)14]− is observed at 323 K in the synthesis gas. At 373 to 423 K [Fe5RhC(CO)16]− transforms into a mixture of Fe4Rh2C(CO)16, [Fe4RhC(CO)14]−, and [Fe53Rh3C(CO)15]− clusters. In the 523 to 623 K range, the supported [Fe5RhC(CO)16]− cluster decarbonylates completely to form bimetallic species Å 5 Å in size. Silica-supported FeRh clusters are active in propylene hydroformylation at 423 to 473 K and form a mixture of butyl alcohols and butyraldehydes.

Effect of Lignin on the Properties of Organic and Carbon Gels from Polyphenols of the Larch Bark

The influence of lignin on the properties of organic and carbon gels synthesized by sol-gel polymerization of a mixture of formaldehyde and polyphenols isolated by various solvents from the larch bark was investigated. The porous structure and adsorption properties of polymer gels synthesized from mixtures of formaldehyde and ethanol extracts of bark by varying the pH value of initial solutions in the range of 4 to 12 were studied by BET and SEM methods. It was shown that an increase in pH value leads to the formation of organic gels with a more compacted texture and narrow pores. Carbonization of organic gels at 900 °C promotes the significant development of the specific surface area (up to 477 m2/g) of the obtained carbon gels. It was found that the addition of lignin in an amount of 10 % wt. to the polyphenols extracted by water from the larch bark improves the texture characteristics of the obtained organic and carbon gels and increases theirs elasticity and strength. But the increase of the lignin content to 20-30 % wt. reduces the total porosity and the total pore volume of the obtained gels. The effect of lignin on the properties of gels, obtained with the use of polyphenols extracted from larch bark by water–alkaline solution, is less pronounced.

Optimization of the Process of Synthesis of Lignin–Tannin-Formaldehyde Organic Aerogels

The method of experimental statistical analysis was applied to study the effect of mass ratio of phenol and lignin (factor X1) and the weight ratio of thereof mixture with formaldehyde (factor X2) on the values of specific parameters of the porous structure obtained organic lignin – phenolformaldehyde aerogels. Based on the evaluation of the mathematical model was established that under the observance terms of X1 = 0,65-0,78 and X2 = 1,7 the maximum predicted values of the specific surface area and mesopore volume of obtained organic aerogels are 485 m2 /g and 1,83 cm3/g, accordingly. Under optimal values of X1 = 0.25, and X2 = 1.25 calculated values reach a macropore volume of 4.05 cm3 /g and total pore volume – 4.67 cm 3 /g.

The Carbon Materials Obtaining by Thermochemical KOH Activation of Bark Birch

By elemental and thermogravimetric analysis, scanning electron microscopy and BET studies have examined the possibility of obtaining microporous carbon materials (CM) with specific surface area about 1350 m 2 /g by chemical activation at 800 °C of birch bark with potassium hydroxide used in solid and in solution form . The porous structure obtained from birch bark and betulin CM s was studied based on the N 2 adsorption isotherms taken at 77K. .

Modifying Effect of Betulinol on Carbon Sorbents Produced from Betula birch Wood

A lack of high-quality carbon adsorbents (CA) with a uniform microporous structure is the main impediment to the development of new and the improvement of existing adsorption methods for purifying and separating gases. The sorbent structure, i.e., the size, volume, and ratio of principal pore types, is determined by the nature of the precursor and its processing into activated carbon. As a rule, the porosity of carbonized carbons from wood and plant material is known to be disorganized. Structure formation in a particular direction is difficult to regulate accurately. The sizes and distribution of pores in CA could possibly be controlled by modifying the porosity of finished activated carbon with an organic binder and/or a pore-former or by applying a layer of organic polymer or hydrocarbon thermal decomposition products to the carbon substrate [1]. The goal of the present work was to study the effect of modifying the porous structure of previously carbonized Betula birch wood with betulinol and subsequent activation with KOH on the properties of the produced CA. It was found that thermochemical activation (800°C, 1 h) of previously carbonized (300–800°C) B. birch wood in the presence of KOH promoted the formation and development of micropores. The resulting carbon materials were distinctly porous and absorbed a broad spectrum of chemicals (benzene, hexane, CCl4, H2O, etc.). The carbonized (400°C) B. birch wood sample that was activated by KOH (3:1) (CBW-400/KOH) had the highest specific surface area (SBET 1980 m 2/g) and total pore volume (0.83 cm3/g) [2]. As the carbonization temperature was raised from 600 to 800°C, the KOH-activated CA were highly selective for the separation of a model mixture of H2(He) and CH4. Their separation coefficients (Ks) were 3.0–3.8, were used as criteria of the separating capability, and were estimated by chromatography. This represented a high degree of separation for He–CH4 [3]. The possibility of improving the Ks values by regulating the reactivity of the B. birch precursors that were carbonized at 500–800°C was studied. Existing pores were modified by the natural product betulinol (25 mass%) and then activated by KOH. Betulinol (betulin) is the pentacyclic lupane triterpene alcohol C30H50O2 with MW 442.7. It was isolated by extraction from B. birch bark. A coating of pyrolyzed carbon will form on the external surface of the carbon if the organic modifier is used under conditions where it is selectively decomposed (450°C). The carbon composite formed at this point is activated by KOH, which is effective on both components. As a result, modified CA with a controlled capability for selective adsorption and separation of H2(He)–CH4 mixtures were produced at 800°C. The effect of the organic modifier on the CA porous structure was studied using CBW (700°C) activated by KOH (CBW-700/KOH) as an example. Figure 1 shows the N2 adsorption isotherms at 77 K under standardized conditions (Fig. 1). The N2 adsorption isotherms for unmodified CBW-700/KOH (Fig. 1, 3) and for CA from pure betulinol (Fig. 1, 2), which was prepared for comparison under analogous KOH activation conditions, were characteristic of microporous materials. The shape of isotherm 1 was indicative of further pore development throughout the whole volume of CBW-700 because of modification with betulinol and subsequent activation by KOH. The fraction of micropores increased because pieces of pyrolyzed material were located near the entrances to larger pores. This shifted the pore-size distribution to a predominant size up to 1.8 nm (~90%) and gave a more uniform microtexture that was more favorable for He-CH4 separation. The Ks values of the modified CA from B. birch wood (Ks = 3.87–4.11) exceeded those of CA that were prepared analogously but were unmodified (Ks = 3.0–3.8) [3]. Table 1 shows that the modifying action of betulinol and subsequent activation by KOH were manifested best at carbonization temperatures of 600–800°C. Modified sample CBW-700 had the highest Ks value (4.11) for H2(He)–CH4 under controlled KOH activation conditions.

Effect of methods for thermal and alkaline modification of birch wood on properties of porous carbon materials obtained

Study of the carbonization of birch wood demonstrated that, under conditions of a preliminary carbonization at a temperature of 400°C, KOH favors better, compared with NaOH, development of the specific surface area (SBET ≈ 2000 m2 g−1) and microporous volume (0.6 cm3 g−1). The resulting porous carbon materials possess improved adsorption properties and are effective in separation of He(H2)-CH4 mixtures.

Synthesis of hydrocarbons from CO and H2 on SiO2 supported iron-cobalt clusters

Bimetallic catalysts (Fe+Co)/SiO2 were prepared by impregnation of SiO2 with solutions of carbonyl clusters [FeCo3(CO)12][(C2H5)4N], [Fe3Co(CO)13][(C2H5)4N], HFeCo3(CO)12, [Fe5CoC(CO)16][(C2H5)4N], and Co2(CO)8, Fe(CO)5. At 20 °C, no reaction occurs between the compounds supported and the surface of the support. The stability of the supported clusters to thermodecarboxylation in a hydrogen atmosphere depends on their composition and is the highest for the catalyst [FeCo3(CO)12]−/SiO2. The catalytic properties of supported clusters in CO hydrogenation are mostly determined by the preactivation technique. The properties of Fe-Co catalysts which were pretreated at high temperatures, are in general similar to those of standard metal catalysts. Product distribution for the same samples prepared without preactivation does not fit the Schulz-Flory equation. The catalyst HFeCo3(CO)12/SiO2 favors the formation ofC1–C11 hydrocarbons in the temperature range of 468–473 K; the catalyst [Fe3Co(CO)13]−/SiO2 gives ethylene in the temperature range of 453–473 K.