Synthesis of vanadium-phosphorus oxide catalysts supported on pyrogenic silica and titanium dioxide

Various methods for the preparation of vanadium-phosphorus oxide (VPO) catalysts supported on aerosils A-300 and A-50 and TiO₂ were studied: a traditional method (in an organic solvent under varying the support addition time, the nature of the reducing agent, and the degree of reduction of vanadium oxide) and barothermal and mechanochemical syntheses. With the use of XRD analysis, it was found that the composition of the resulting VPO phase depends on the time of support addition to the synthesis and the temperature of thermal treatment. Conditions for the formation of a supported phase of VOHPO₄·0.5H₂O, the precursor of the active component (VO)₂P₂O₇, were determined. The presence of vanadium in an oxidation state of +4 was demonstrated using EPR and UV-VIS spectroscopy. The specific surface areas and pore structures of the synthesized catalysts were determined. The catalytic properties of samples in the reactions of n-butane oxidation in an excess of the hydrocarbon and oxidative ethane dehydrogenation were studied. It was found that, as compared with traditional bulk VPO catalysts, the use of the synthesized supported VPO catalysts made it possible to improve the process characteristics of n-butane oxidation and did not change these characteristics in the reaction of oxidative ethane dehydrogenation.     

Catalytic decomposition of hydrogen peroxide by Cu/M heterobimetallic complexes (M = Mn, Zn) with Schiff bases in the presence of electrolytes

A study was carried out on the effect of electrolytes KCl, CaCl₂, MnCl₂, ZnCl₂, CuCl₂, KNO₃, Ca(NO₃)₂, Mn(NO₃)₂, Zn(NO₃)₂, and Cu(NO₃)₂ on the kinetics of the decomposition of H₂O₂ catalyzed by [Cu(L¹/L²)][MCl₄] complexes (M = Zn, Mn; L¹ is 4,6,6-trimethyl-1,9-diamino-3,7-diaza-3-nonene, L² is 1,15-dihydroxy-7,9,9-trimethyl-3,6,10,13-tetraaza-6-pentadecene). The chloride ions were found to reversibly inhibit the catalyst. The major kinetic characteristics of this reaction were obtained using a mathematical model taking account of the reversible and irreversible inhibition of the catalyst. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 4, pp. 240–247, July–August, 2008.     

Barothermal modification of activated carbon with maleic anhydride

We have used the barothermal treatment method (heat and pressure) to modify the surface of activated charcoal with maleic anhydride. As a result of the modification, about 1 mmol/g of thermally stable carboxyl groups are formed on the surface with a decomposition temperature range of 330–470°C. We show that the proposed procedure makes it possible to obtain materials with a uniform coverage of functional groups.     

Kinetics of the gas-phase chlorination of activated carbon with carbon tetrachloride

The chlorination of activated charcoals KAU and SCN with CCl₄ vapor in the temperature range 300–600 °C and also the thermal stability of the added chlorine has been studied. It is shown that chlorination with CCl₄ vapor led to the addition of up to 22 mass % (6.2 mmol/g) of chlorine to the surface layer of the carbon. The added chlorine is desorbed from the surface with formation of HCl, while at temperatures above 500 °C desorption of chlorine goes practically to completion. The effective rate constants and the energies of activation of the processes of chlorination and desorption have been found.     

Quantum-chemical modelling of the reactivity of charcoal surface double bonds

LCAO MO SCF calculations using the 3-21G basis were used to study the electronic and three-dimensional structure of several polycyclic aromatic hydrocarbons as models for the surface of activated charcoal. Localized carbon-carbon double bonds capable of adding electrophilic reagents were found on the periphery of these molecules. The reactivity of the peripheral C=C bonds was evaluated relative to consecutive bromination reactions of the C₅₄H₁₈ molecule. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 1, pp. 30–34, January–February, 2008.     

New Prospective Ni-catalytic Materials

IR spectroscopy was applied to investigate the non-isothermal redox processes in Ni/NiO-gas phase system involving the elimination of CO₂. At the Curie temperature (T _c=633 K for Ni), a change in the mechanism of CO catalytic oxidation on NiO was observed. It was established by means of temperature-programmed desorption with mass-spectroscopic registration that fluctuations in the oxygen density on the NiO surface are generated at this temperature. Under the given chemical reaction conditions, these fluctuations bring about the formation of Ni microheterogeneity on the NiO surface. X-ray diffraction, electronic and magnetometric measurements were employed to determine the dimensions of the Ni particles. It was shown that an increase in the Ni dispersity in Ni/NiO may be responsible for an increased number of active surface sites. This was verified for the NiO/thermo-exfoliated graphite system. This revised version was published online in August 2006 with corrections to the Cover Date.     

The catalytic efficiency of Fe-containing nanocomposites based on highly dispersed silica in the reaction of CO2 hydrogenation

Research on Chemical Intermediates - Oxide Ni(80)Fe(20)/SiO2, Co(93)Fe(7)/SiO2, and Ni(19)Co(77)Fe(4)/SiO2 nanocomposites (NCs) were prepared using highly dispersed silica. It was modified by...     

Barothermal Diels-Alder functionalization of multi-walled carbon nanotubes

Abstract

Multi-walled carbon nanotubes (MWCNTs) have an ordered geometric structure, large specific surface area, prominent electrical conductivity, and unique mechanical properties. They are nontoxic and can be used in biomedicine. Physical and surface chemical characteristics of MWCNTs should be tuned to that required to improve certain properties and obtain a variety of functional materials. We modified the MWNTs by using the barothermal Diels-Alder reaction with dienophiles, p-benzoquinone, fumaronitrile, and maleimide, to address this issue. The prepared MWCNTs were studied by SEM-EDX, nitrogen adsorption porometry, ATR FTIR, and thermal analysis. Results showed that both separate and conjugated C?=?C bonds at the edge and outer/inner surface of walls could react with dienophiles. The grafted groups are separated by the temperature on weak (low-temperature) and strong (high-temperature) chemisorbed forms; they are detached at temperatures below and above 350?°C, correspondingly. Thermal analysis shows that up to 5% of the carbon atoms are involved in the [4?+?2] cycloaddition. The high-temperature forms of the grafted groups under extreme heating can be involved in the retro-Diels-Alder reaction that breaks six-membered rings, producing a dienophile.     

Kinetics of the dehydration of 2-propanol on modified activated charcoal containing acid sites

A study was carried out on the kinetics of the dehydration of 2-propanol on activated bone charcoal (ABC) with supported acid sites. The rate-limiting step is the loss of water from the alcohol molecule adsorbed on the acid site. The sites containing the minimum amount of water are the most active. The reaction on these sites presumably proceeds through a concerted mechanism, which is possible at sufficiently high temperatures (above 120 °C). Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 5, pp. 321–327, September–October, 2008.