A. V. Vosmerikov

Properties and deactivation of the active sites of an MoZSM-5 catalyst for methane dehydroaromatization : Electron microscopic and EPR studies

The MoZSM-5 (4.0 wt % Mo) catalyst has been characterized by high-resolution transmission electron microscopy, EDXA, and EPR. Two types of molybdenum-containing particles are stabilized in the catalyst in the course of nonoxidative methane conversion at 750°C. These are 2-to 10-nm molybdenum carbide particles on the zeolite surface and clusters smaller than 1 nm in zeolite channels. According to EPR data, these clusters contain the oxidized molybdenum form Mo5+. The surface Mo2C particles are deactivated at the early stages of the reaction because of graphite condensation on their surface. Methane is mainly activated on oxidized molybdenum clusters located in the open molecular pores of the zeolite. The catalyst is deactivated after the 420-min-long operation because of coke buildup on the zeolite surface and in the zeolite pores.

Nonoxidative conversion of methane into aromatic hydrocarbons on Ni-Mo/ZSM-5 catalysts

The nonoxidative conversion of methane into aromatic hydrocarbons on high-silica zeolites ZSM-5 containing nanosized powders of molybdenum (4.0 wt %) and nickel (0.1–2.0 wt %) was studied. Data on the acid characteristics of the catalysts and the nature and amount of coke deposits formed on the surface of the catalysts were obtained using the thermal desorption of ammonia and thermal analysis. The microstructure and composition of Ni-Mo/ZSM-5 catalysts were studied by high-resolution transmission electron microscopy and energy-dispersive X-ray analysis. The formation of various chemical species in the samples was detected: oxide-like clusters of Mo within zeolite channels (∼1 nm), molybdenum carbide particles (5–30 nm) on the outer surface of the zeolite, and Ni-Mo alloy particles with different compositions (under reaction conditions, carbon filaments grew on these particles). It was found that, as the Ni content was increased from 0.1 to 2.0 wt %, the rate of deactivation of the catalytic system increased because of blocking pores in the zeolite structure by filamentous carbon up to the formation of condensed coke deposits.

Physicochemical properties and activity of Mo-containing zeolite catalysts of nonoxidative conversion of methane

High-silica zeolites of ZSM-5 structural type were synthesized using various structure-forming additives and without them. Mo-containing catalytic systems were prepared on the basis of these zeolites. Their physicochemical properties and activity in the course of the nonoxidative conversion of methane were studied. The Mo/ZSM-5 catalyst obtained on the basis of zeolite synthesized with hexamethylenediamine showed high aromatizing activity and stability.

Ethane aromatization on galloaluminosilicate modified with platinum and palladium

Ethane conversion into aromatic hydrocarbons on galloaluminosilicate of the ZSM-5 structural type modified with platinum and palladium was studied. The acid properties of the catalyst were investigated by ammonia temperature-programmed desorption. The microstructure and composition of the Pt- and Pd-containing zeolites was determined by transmission electron microscopy and energy-dispersive X-ray analysis. It was shown that modifying the galloaluminosilicate enhances its activity and selectivity in the formation of aromatic hydrocarbons.

Ultra-high-Silica ZSM-5 Zeolites: Synthesis and Properties

ZSM zeolites with silica ratios of 100–260 were synthesized with hexamethylenediamine (HMDA) as the structure former. IR spectroscopy and X-ray powder diffraction identified the products with ZSM-5 zeolites with more than 90% crystallinity. The unit cell parameters, specific surface area, and morphology were determined for zeolite samples. The composition of precursor alumina—silica gel was shown to influence the physicochemical characteristics of zeolites.

Conversion of Lower Alkanes in the Presence of Metal Nanoparticles Supported on a Zeolite Matrix

It is shown that pentasil-type zeolites involving Zn and Pt nanoparticles display a high aromatizing activity in the conversion of lower alkanes. The effects of the zeolite matrix composition and the concentration and nature of a modifying additive on the activity, selectivity, and stability of the obtained catalysts are studied. It is found that upon the addition of Pt nanopowder, the duration of the stable operation of gallium-containing zeolite increases.

Catalytic aromatization of ethane on zinc-modified zeolites of various framework types

Zeolites of the ZSM-5, ZSM-8, ZSM-11, and ZSM-12 framework types have been prepared by hydrothermal synthesis from alkaline alumina-silica gels, and modified with zinc by the impregnation method. The acid properties of the zeolites have been examined, and it has been found that the catalysts differ from one another in distribution and relative amount of acid centers of various types. The feasibility of the direct chemical conversion of ethane to aromatic hydrocarbons on the zinc-containing zeolites of various framework types has been shown. It has been found that the structure of high-silica zeolites affects the activity and selectivity of the zinc-containing catalysts prepared from them. It has been shown that the most effective catalyst for the ethane-to-aromatics conversion process is the zinc-modified ZSM-5 type zeolite.

Physicochemical properties and activity of nanopowder catalysts in the hydrodesulfurization of diesel fraction

New hydrofining catalysts based on molybdenum, nickel, and aluminum nitride nanopowders produced by electrical explosion are obtained. Their physicochemical properties are studied. The direct sulfurizing of molybdenum nanopowders with sulfides from straight-run diesel oil fraction is shown to be possible. The high hydrodesulfurization capability of nanopowder catalysts is established.

Methane conversion into aromatic hydrocarbons over Ag-Mo/ZSM-5 catalysts

Nonoxidative methane conversion into aromatic hydrocarbons over ZSM-5-type high-silica zeolites modified with nanosized powders of molybdenum (4.0 wt %) and silver (0.1–0.5 wt %) is reported. The acidic properties of the catalysts have been investigated by temperature-programmed ammonia desorption. The microstructure and composition of the Ag-Mo/ZSM-5 catalytic systems have been studied by high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. The doping of the Mocontaining zeolite with silver enhances its activity and stability in nonoxidative methane conversion into aromatic hydrocarbons.

Nonoxidative methane conversion into aromatic hydrocarbons on tungsten-containing pentasils

The effects of the tungsten concentration and of the method of tungsten introduction into ZSM-5 pentails with different SiO2/Al2O3 molar ratios on the acidity and the activity of the resulting catalysis in nonoxidative methane conversion into aromatic hydrocarbons are considered. The catalysts obtained from the SiO2/Al2O3 = 40 pentasil and a nanosized tungsten powder are the most active and the most stable. The maximum methane conversion and the highest yield of aromatic hydrocarbons are achieved on the zeolite containing 8.0 wt % tungsten nanopowder.