M. Georgieva

Investigation of a nickel oxide system for heterogeneous oxidation of organic compounds

The structure of a nickel oxide system, which is an efficient oxidant for organic compounds, has been studied by spectroscopic methods such as IR, X-ray photoelectron spectroscopy, electron spin resonance, X-ray spectroscopy as well as by thermal and chemical analyses. It has been clearly shown that the reagent is not a peroxide, but a higher nickel oxide. An oxidation reaction mechanism of organic compounds has been proposed.

Low-temperature iron-modified cobalt oxide system. Part 2. Catalytic oxidation of phenol in aqueous phase

Abstract Liquid-phase oxidation using a solid catalyst provides a potential method for removal of dissolved toxic organic pollutants from waste waters. Low-temperature heterogeneous oxidation of phenol on a cobalt oxide system modified with Fe has been studied. The conversion of phenol into nontoxic compounds occurs in air-equilibrated aqueous media. The major hydroxylated aromatic intermediates have been identified by UV–VIS spectroscopy and HPLC: catechol, hydroquinone and hydroxyhydroquinone. An oxidation mechanism has been proposed based on the results of the kinetic investigations and on the data obtained by IR and UV spectroscopic studies of the sample. The results obtained show that the Co–Fe-oxide system is a promising catalyst for practical application.

Low-temperature iron-modified cobalt oxide system: Part I. Preparation and characterisation

Abstract The cobalt oxide system, modified with Fe was prepared by a solution technique at a room temperature. The periodic method of precipitation with inverse order of feeding the precipitator to the system (Me 2+ →OH − +OCl − ) is used, which favors the formation of amorphous and highly disperse oxide system with non-stationary surface properties. The fresh sample as well as the samples obtained by its thermal treatment at different temperatures were characterized by Mossbauer and Infrared spectral analysis, X-ray diffraction and chemical analyses. A comparative consideration of the composition and structure of individual and modified with Fe cobalt oxide system has been carried out in order to clarify the influence of Fe as a modifying additive on the activity and selectivity of the sample. The results obtained show that the inclusion of Fe leads to the appearance of new active sites in the fresh samples — Fe(III) ions in octahedral coordination and to increasing the mobility of the reactive oxygen. The synthesized oxide system shows suitable properties for catalytic oxidation of toxic organic and inorganic compounds in an aqueous medium.

Low-temperature catalytic oxidation of water containing 4-chlorophenol over Ni-oxide catalyst

Abstract The catalytic oxidation of 4-chlorophenol (4-CP; chosen as an aromatic model pollutant) over Ni-oxide system in an aqueous medium has been studied. Experiments were carried out to investigate the effect of such parameters as pH, temperature, and catalyst dosage both on the reaction efficiency and on the reaction mechanism. The current concentrations of 4-CP as well as those of reaction intermediates—hydroquinone, benzoquinone, and 4-chlorocatechol—during the kinetic investigations were monitored by UV-Vis spectral analysis. Pseudo first-order kinetics with respect to the parent compound was observed. Experimental results demonstrated that 4-CP could be completely converted into the environmentally harmless CO 2 , H 2 O, and mineral acid under certain conditions. A probable kinetic model for the degradation pathway is proposed.

Study on the thermal stability of a high Co-oxide used as low-temperature catalyst and oxidant for complete oxidation

Abstract A new higher Co-oxide has been synthesized. Its features are presented by means of IR-spectroscopy, X-ray analysis, XPS-spectroscopy, EPR, magnetic measurements and chemical analysis in a separate paper by the present authors. On the grounds of the obtained results the following formula, determining the content of the higher Co-oxide, has been put forward: Co +2 1− x Co +4 x O y ·(OH) y · m H 2 O, with the Co-ions being in their highest oxidation degrees (i.e. +4) and in an octahedral position. The synthesized Co-oxide system can be utilized as an active phase of a low-temperature catalyst as well as a strong oxidant for a complete oxidation in liquid and gas mediums. The present paper also studies the thermal stability of the synthesized Co-oxide system by means of thermal analysis, IR-spectroscopy, X-ray and chemical analysis. The results show that both the freshly obtained higher Co-oxide and the thermally treated (up to 250°C) samples maintain their composition, structure and activity in the oxidation processes. Heated at temperature above 250°C, the Co-oxide system undergoes changes in its composition and structure, turning it into a cobaltite with a spinel structure. This is the reason for the sharp decrease of the activity of the studied system in the oxidation processes.

Low-temperature methanol oxidation on a higher nickel oxide in gaseous and aqueous phase. Part II

Abstract The IR-spectroscopy analysis brought about the conclusion that methoxyl groups are formed on the surface of Ni-oxide during adsorption of methanol at 25°C. Further on, they are oxidized partially to CO 2 by surface active oxygen at temperatures 25–35°C. O − forms (taking part in the oxidation process) are observed on the surface of the oxide. The methoxyl groups undergo a complete oxidation to form formiate complexes in the presence of oxygen in gaseous phase at temperatures higher than 35°C. The latter give the products of complete oxidation – CO 2 and H 2 O.

Mixed Ni-Mn-oxide systems as catalysts for complete oxidation. Part I. Preparation and characterization

A method for synthesis of new Ni-Mn-oxide systems is proposed. The synthesized systems have been characterised by a variety of methods including chemical analysis, infrared (IR) spectroscopy, X-ray diffraction (XRD) analysis, thermal analysis, and X-ray photoelectron spectroscopy (XPS). The results obtained reveal that the synthesized catalytic system can be successfully applied as an active phase in low temperature catalysts for complete oxidation carried out both in aqueous medium and in gas phase. The synthesis operating conditions yield hydrophilic and amorphous catalytic systems with high active oxygen (∼8%), taking part in oxidation processes. The Ni-Mn-oxide system is characterized by high thermal stability and its composition is kept constant up to 550 °C. Experimental data indicate that modifying a separate Ni-oxide system with Mn one can prepare new catalytic systems with high active oxygen content, larger specific area and higher thermal stability.

LOW-TEMPERATURE AQUEOUS PHASE OXIDATION OF CYANIDE IONS WITH THE PARTICIPATION OF NICKEL OXIDE SYSTEM

The low-temperature oxidation of cyanide ions to CO2 and N2 in an aqueous phase in the presence of Ni-oxide system has been studied. The effect of pH, temperature and catalyst amount on the rate and selectivity of the oxidation process have been investigated. A kinetic model of the reaction studied is proposed based on the experimental results. It can be used to develop a catalytic method for purification of CN containing wastewaters.

Low-Temperature Catalytic Oxidation of Sulfide Ions in Aqueous Solutions on a Ni-Oxide System

Catalytic oxidation of sulfide ions in aqueous solutions by air oxygen has been investigated using a Ni-oxide system as a catalyst. The kinetics and the selectivity of the oxidation process were studied by varying the pH, catalyst amount and reaction temperature. A reduction/oxidation mechanism of the reaction has been supposed comprising interaction between the surface active oxygen of the catalyst and HS− and reoxidizing of the reduced catalyst by the dissolved oxygen. The results obtained show that the Ni-oxide system is a promising catalyst for practical application.

Low-temperature heterogeneous oxidation of sulfide ions on a higher Co oxide system in aqueous medium

Low-temperature heterogenous oxidation of sulfide ions on a higher Co oxide system in aqueous medium has been studied. The effects of pH, temperature and catalyst amount on the kinetic parameters as well as on the selectivity of the oxidation process were investigated. An oxidation mechanism has been proposed based on the results of kinetic investigations and on the data obtained by IR and XPS spectroscopic studies of Co oxide before and after sulfide ion oxidation.