The review integrates and systematizes literature data on the use of single-atom catalysts in methane chemistry, with the emphasis on the most recent results. The single-atom catalysts are heterogeneous catalysts of the latest generation in which single metal atoms supported on an inorganic material act as the active sites. The features of CH4 activation on the surface of these catalysts are considered and compared with the behaviour of other known heterogeneous catalysts containing metal nanoclusters or active metal nanoparticles in relation to the direct oxidative and non-oxidative conversion of methane into various chemicals. The efficiency of application of single-atom catalysts of various compositions and types (supported single metal atoms, mono- and polymetallic monoatomic contacts, complex disperse compositions, etc.) is considered for reactions involving methane, including dry, steam and oxidative reforming, partial oxidation to methanol, oxidative carbonylation and carboxylation to acetic acid, non-oxidative and oxidative methane coupling to ethane/ethylene, methane dehydroaromatization, and methylation of benzene with methane. The new prospects opened up in methane chemistry by using single-atom catalysts are discussed. The bibliography includes 307 references.

Recent achievements in the development of new methods for producing acetic acid (AA) from methane using heterogeneous catalysts are summarized and systematized. Modern heterogeneous-catalytic processes of methane conversion to AA via syngas and alternative one- and two-step AA production procedures via “low-temperature” oxidative methane conversion (via oxidative coupling, oxyhalogenation, oxidation into methanol, or oxidative transformations of СН 4 in the presence of carbon oxides) are considered. The major attention is paid to the one-step AA synthesis by methane oxydation with carbon dioxide (by carboxylation reaction). Specific features of heterogeneous catalysts recently developed for this reaction are discussed.

Oxidative conversion of methane to acetic acid at 150°С and a pressure of 6.5 MPa with the assistance of carbon monoxide on rhodium-modified ZSM-5 zeolites with different SiO2/Al2O3 molar ratios was studied. A decrease in SiO2/Al2O3 from 300 to 30 leads to a 2.7-fold increase in the acetic acid yield. Such behavior of the catalytic system correlates with an increase in the acidity, primarily with an increase in the density of Brønsted acid sites on the zeolite surface. Introduction of 0.1–0.5 wt % rhodium into the zeolite increases the acetic acid yield by a factor of more than 3. The highest acetic acid yield (0.53 mmol/gcat) is attained on the zeolite with SiO2/Al2O3 = 33 modified with 0.5 wt % Rh. The methane transformation to acetic acid occurs while involving both the acid sites of the zeolite and the sites formed by reactive rhodium particles.

Gas-phase oxidative carbonylation of methane was first performed on ZSM-5 zeolites. The addition of water vapor to a mixture of carbonylation gases leads to a multiple (by two orders of magnitude) increase in acetic acid yield. Zeolites with high acidity, primarily Brønsted acidity, favor the target product formation.

Изучены каталитические свойства магнийсодержащих цеолитных катализаторов в синтезе олефинов из диметилового эфира (ДМЭ). Установлены оптимальные концентрация магния в составе цеолитного катализатора и способ его введения. Исследовано влияние режимных параметров процесса превращения ДМЭ в низшие олефины на активность и селективность катализатора. Изучена стабильность каталитических свойств синтезированного катализатора после окислительной регенерации.

This review presents the recent achievements in the field of development of zeolite catalysts for the production of lower olefins from dimethyl ether. The characteristic features of the influence of the topology and acidity on the conversion of dimethyl ether are discussed. The data on various methods for increasing the selectivity of zeolite catalysts in the conversion of dimethyl ether to lower olefins are summarized. The possible methods of changing the acidic properties of zeolites, namely, modification by cations of various elements, hydrothermal treatment of zeolite catalysts, and variation of the SiO2/Al2O3 molar ratio are considered.

Modern methods for methane conversion to lower olefins having from 2 to 4 carbon atoms per molecule are generalized. Multistage processing of methane into ethylene and propylene via syngas or methyl chloride and methods for direct conversion of CH4 to ethylene are described. Direct conversion of syngas to olefins as well as indirect routes of the process via methanol or dimethyl ether are considered. Particular attention is paid to innovative methods of olefin synthesis. Recent achievements in the design of catalysts and development of new techniques for efficient implementation of oxidative coupling of methane and methanol conversion to olefins are analyzed and systematized. Advances in commercializing these processes are pointed out. Novel catalysts for Fischer – Tropsch synthesis of lower olefins from syngas and for innovative technique using oxide – zeolite hybrid catalytic systems are described. The promise of a new route to lower olefins by methane conversion via dimethyl ether is shown. Prospects for the synthesis of lower olefins via methyl chloride and using non-oxidative coupling of methane are discussed. The most efficient processes used for processing of methane to lower olefins are compared on the basis of degree of conversion of carbonaceous feed, possibility to integrate with available full-scale production, number of reaction stages and thermal load distribution. The bibliography includes 346 references.

Ash and slag waste (ASW) from coal-fired thermal power plants (TPPs), the amounts of which make several tens or even hundreds of millions of tons per annum, require allocation of large land areas for storing them. This waste is a source of pollution emitted into the atmosphere and it poisons the aqueous medium and soil. Ash and slag waste consists primarily of powderlike material containing a large quantity of unburned carbon (5–25%), magnetic materials (5–20%), and alumino-silicate components. All these components are a valuable raw material for industry, especially silicon and aluminum oxides, which can be used in the production of construction materials. For this purpose, ash must be preliminarily subjected to beneficiation using physical and physicochemical methods. The article presents an analysis of dry and wet ash beneficiation methods with a view to increase the volumes of using ASW produced from domestic power plants. For achieving higher strength of concretes, mechanical activation is carried out, which relates to dry ASW beneficiation methods. To obtain an alumino-silicate product containing 1.5–4.5% of carbon, such dry processing method as electrostatic separation is used. By subjecting dry ash to combined magnetic and electrostatic separation methods, it is possible to obtain an ash and a conducting product with a high concentration of carbon. For Russia, wet ASW beneficiation methods are of the greatest importance, because wet ash and slag removal is used at the majority of TPPs. Hydraulic classification of waste for obtaining products containing particles of different sizes is one of the wet beneficiation process stages. By using the froth flotation method, it is possible to obtain a concentrate containing 65–70% of carbon, a material that can serve as boiler fuel. The froth flotation is regarded as a necessary method for integrated utilization of ASW. Wet magnetic and electrostatic separation are the basic methods for producing magnetic concentrate containing 62–65% of iron. The article presents methods for separating hollow microspheres from AWS, which are a valuable product for aggregates used in the civil construction industry. The article also considers integrated ash beneficiation methods for obtaining four basic products (the figures in parentheses indicate the content of the relevant element): hollow microspheres, carbon product (64.5% of carbon), magnetic product (62% of iron), and alumino-silicate product (no more than 3% of carbon).

The synthesis of light C 2 –C 4 olefins from dimethyl ether (DME) in a three-phase system (slurry reactor) over nanosized MFI-type zeolites suspended in liquids with various chemical compositions (paraffins, hydrocarbon and silicone oils, and polyhydric alcohol esters) was studied. It was found that the target reaction can be accompanied by the catalytic decomposition of a dispersion liquid and its mechanical entrainment, which destabilizes the catalytic process. These negative factors can be minimized with the use of polydimethylsiloxane (Syltherm 800) as a dispersion liquid and MFI zeolite modified with magnesium as a catalyst. The rate of catalytic destruction of this oligomeric molecule in the presence of Mg–MFI was minimal at temperatures of 300°C or lower. The synthesis of olefins from DME at a temperature of 300°C over the Mg–MFI catalyst suspended in Syltherm 800 occurred in a stable way with high performance (70–90% conversion and 46–59% selectivity for the target products). The reaction carried out with the partial reflux of liquid reaction products after the dehydration of condensate excluded the loss of dispersion liquid in the course of the catalytic process due to its mechanical entrainment from the reactor.

The textural, acidic and catalytic properties of nanosized samples of commercial MFI zeolites with SiO2/Al2O3 molar ratios of 30, 50 and 80 supplied by Zeolyst Co. and some synthesized nanocrystallites of MFI zeolites with a SiO2/Al2O3 molar ratio of 55 and 80 were compared. It was shown that the SiO2/Al2O3 ratio had no impact on catalyst deactivation in the slurry reactor as in the conventional fixed-bed reactor. Irreversible deactivation was observed only for the samples with an extremely high external surface Brønsted acidity indicating that near-surface secondary processes are responsible in catalyst deactivation. It was shown that the reaction temperature influenced the product selectivity due to change in the contribution of both hydrogen transfer reaction and arene/alkene circles and can be considered to be an efficient tool of selectivity control for DME conversion in the slurry reactor.

Effect of mode parameters, such as the feed gas flow rate, its content of dimethyl ether, and content of a catalyst in the suspension, on the main parameters of the dimethyl ether conversion into light C 2 –C 4 olefins in a three-phase system (slurry reactor) in the presence of a catalytic suspension based on a nanosize zeolite Mg–MFI dispersed in silicone oil was examined. The values of the parameters, at which the conversion of dimethyl ether occurs in the steady state mode under favorable hydrodynamic conditions at a relative chemical stability of the dispersion medium and its minimum mechanical entrainment from the reactor, were found. Irrespective of the dimethyl ether concentration in the operating gas, the reaction was shown to occur with conversion of up to ~80% at selectivity of ~50%, and ethylene is the main reaction product (up to 30 wt %).

Nanodispersed suspensions that are effective in DME conversion and stable in the reaction zone in a three-phase system (slurry reactor) are obtained from MFI zeolite commercial samples (TsVM, IK-17-1, and CBV) in liquid media via ultrasonic treatment (UST). It is found that the dispersion medium, in which ultrasound affects zeolite commercial sample, has a large influence on particle size in the suspension. UST in the aqueous medium produces zeolite nanoparticles smaller than 50 nm, while larger particles of MFI zeolite samples form in silicone or hydrocarbon oils. Spectral and adsorption data show that when zeolites undergo UST in an aqueous medium, the acid sites are redistributed on the zeolite surface and the specific surface area of the mesopores increases. Preliminary UST in aqueous media of zeolite commercial samples (TsVM, IK-17-1, and CBV) affects the catalytic properties of MFI zeolite nanodispersed suspensions. The selectivity of samples when paraffins and olefins form is largely due to superacid sites consisting of OH groups of hydroxonium ion H 3 O + .