P. G. Tsyrul’nikov

State of palladium in palladium-aluminosilicate catalysts as studied by XPS and the catalytic activity of the catalysts in the deep oxidation of methane

Palladium catalysts based on Siralox and AS aluminosilicate supports for the deep oxidation of methane were studied. With the use of XRD analysis, it was found that they were heterophase systems consisting of an amorphous aluminosilicate and γ-Al2O3 stabilized against agglomeration. It was found that the catalytic activity of palladium-aluminosilicate catalysts in the deep oxidation of methane at 500°C depended on the support precalcination temperature. X-ray photoelectron spectroscopy (XPS) was used to study the states of the AS-30 aluminosilicate support calcined at 600, 800, or 1000°C and palladium supported on it. It was found that the action of an acid impregnation solution of palladium nitrate on the aluminosilicate calcined at 800°C resulted in a structural rearrangement of the aluminosilicate surface. This rearrangement resulted in the stabilization of both palladium oxide and palladium metal particles at surface defects and the incorporation of these particles into the aluminosilicate after catalyst calcination. As a result, an anomalous decrease in catalytic activity was observed in aluminosilicate samples calcined at 800°C. According to XPS data, palladium in the catalyst was stabilized in the following three phases: metal (Eb(Pd 3d5/2) = 334.8 eV), oxide (Eb(Pd 3d5/2) = 336.8 eV), and “interaction” (Eb(Pd 3d5/2) = 335.8 eV) phases. The ratio between these phases depended on support and catalyst calcination temperatures. The interaction phase, which consisted of PdOx clusters stabilized in the aluminosilicate structure, was responsible for the retention of activity after calcination at high temperatures (800°C). Based on an analysis of XPS data, it was hypothesized that palladium in the interaction phase occurred in a charged state with the formal charge on the Pd atom close to 1 + (δ+ phase).

Liquid-phase hydrogenation of acetylene on the Pd/sibunit catalyst in the presence of carbon monoxide

The liquid-phase catalytic hydrogenation of acetylene into ethylene in the presence of CO over palladium supported on the graphite-like material Sibunit has been investigated. Carbon monoxide is an effective modifier of the selective hydrogenation process, exerting its effect by competing with acetylene and ethylene for chemisorption sites on the palladium surface. Under the optimum conditions (T = 90°C; N-methylpyrrolidone solvent; feed consisting of 2 vol % C2H2, 90 vol % H2, and He balance), the introduction of 2 vol % CO ensures a high ethylene selectivity of 89.6 ± 1.5% at an acetylene conversion of 95.8 ± 1.3%, with the acetylene converted into hydrooligomers taken into account.

Pyrolysis of methane on a heat-treated FeCrAl coil heated with electric current

We studied methane pyrolysis of at 750 to 1100°C on a heat-treated FeCrAl wire heated by electric current both in the absence of oxygen and at CH4 : O2 = 15 : 1 and 9 : 1. The process proceeds in two temperature ranges differing in pyrolysis product selectivity. In the transition region, intensive carbon deposition occurs on the wire surface. The presence of oxygen shifts the methane conversion versus temperature and product selectivity versus temperature curves to higher temperatures. We believe that the existence of two process regions is due to the coking of the catalyst surface.

Preparation of CuO-CeO2 catalysts deposited on glass cloth by surface self-propagating thermal synthesis

Abstract(CuO-CeO2)/glass cloth acting as CO oxidation catalyst was prepared by surface selfpropagating thermal synthesis. In the process of synthesis of (CuO-CeO2)/glass cloth samples, the content of active components (CuO-CeO2) and fuel additives and the conditions of thermal synthesis were varied. Impact of the nature of fuel additives and salts that are precursors of active components, and their ratio on the reaction of solid-phase combustion were studied. The resulting catalysts were studied with the use of scanning electron microscopy and in situ time-resolved synchrotron radiation powder x-ray diffraction.

Methanation of the carbon supports of ruthenium ammonia synthesis catalysts: A review

The propensity of carbon support for methanation in a hydrogen-containing medium is a problem for active ruthenium ammonia synthesis catalysts, since this leads to the degradation of the support and the sintering of the active component. This review analyses some key works on approaches to methanation inhibition and their results to show that, on the whole, an algorithm for solving the methanation problem has been found, i.e., the graphitization of carbon supports at high temperatures (up to 2000°C) and the introduction of ruthenium promoters, specifically alkali (Cs, K) and alkali-earth (Ba) oxides, whose role is to modify the electron state of ruthenium and block the surface of a carbon support to prevent it from interacting with active hydrogen. The most efficient catalyst not liable to methanation up to 700°C and a hydrogen pressure of 100 atm has been found. The resulting analysis can be useful in selecting and preparing Me/C catalysts in which Me represents metals of the VIII Group and others.

Vanadium oxide catalysts on structured microfiber supports for the selective oxidation of hydrogen sulfide

Vanadium(V) oxide catalysts for the selective oxidation of hydrogen sulfide to sulfur on a nonporous glass-fiber support with a surface layer of a porous secondary support (SiO2) are studied. The catalysts are obtained by means of pulsed surface thermosynthesis. Such catalysts are shown to have high activity and acceptable selectivity in the industrially important region of temperatures below 200°C. A glass-fiber catalyst containing vanadium oxide (10.3 wt % of vanadium) in particular ensures the complete conversion of H2S at a temperature of 175°C and a reaction mixture hourly space velocity (RMHSV) of 1 cm3/(gcat s) with a sulfur yield of 67%; this is at least 1.35 times higher than for the traditional iron oxide catalyst. Using a structured glass-fiber woven support effectively minimizes diffusion resistance and greatly simplifies the scaleup of processes based on such catalysts. Such catalysts can be used for the cleansing of tail gases from Claus units and in other processes based on the selective oxidation of H2S.

Structured woven glass-fiber IC-12-S111 catalyst for the deep oxidation of organic compounds

A platinum woven fiberglass supported IC-12-S111 catalyst whose preparation is based on pulsed surface thermosynthesis is developed. The IC-12-S111 catalyst contains small amounts of platinum (0.05–0.10 wt %), and cheap and commercially available types of fiberglass cloths are used in its production. The production technology is characterized by a small number of process stages and no wastes or platinum losses. The developed catalyst is superior to known platinum and oxide catalysts in its activity in the deep oxidation reactions of hydrocarbons, and exhibits high thermal and operational stability. IC-12-S111 based catalytic cartridges with regularly structured channels are characterized by low hydraulic resistance and minimize deposits of solid particles in a catalyst bed during operation in contaminated flows. The cartridges can be used to create beds of any size and configuration. The developed catalyst can be used for the afterburning of hydrocarbons and organic compounds in flue gases, the flameless oxidation of flare gases, and the catalytic combustion of hydrocarbon fuels in local power supply systems.

Carbon deposits on a resistive FeCrAl catalyst for the suboxidative pyrolysis of methane

The carbon deposits forming upon the suboxidative pyrolysis of methane on resistive FeCrAl catalysts heated with electric current were studied. The suboxidative pyrolysis of methane was carried out in a flow reactor at the ratio CH4: O2 = 15: 1 in a catalyst-coil temperature range of 600–1200°C; a cold reaction mixture (∼20°C) was supplied. The morphology and structure of the carbon deposits and changes in the composition and structure of the catalyst were characterized by scanning electron microscopy, transmission electron microscopy with EDX analysis, Raman spectroscopy, and X-ray diffraction analysis. Various forms of carbon deposits, including branched nanotubes, and metal carbides formed by catalyst constituents were detected. It was found that the carbon deposits on the catalyst surface were morphologically different from the deposits on quartz reactor walls. The reasons for these differences were considered.

(CuO-CeO2)/glass cloth catalysts for selective CO oxidation in the presence of H2: The effect of the nature of the fuel component used in their surface self-propagating high-temperature synthesis on their properties

The potential of surface self-propagating high-temperature synthesis (SSHS) for obtaining (CuO-CeO2)/glass cloth catalysts is demonstrated. The dependence of the structural and catalytic properties of the catalysts on their preparation conditions (nature of the fuel component) is considered. X-ray diffraction, electron microscopy, and EXAFS data suggest that the short-term action of high temperature in the SSHS leads to the complete decomposition of the precursors and has an effect on the distribution of the resulting phases. According to H2 TPR and XPS data, the degree of dispersion of CuO and the electronic state of the reacting CuO and CeO2 phases depend on the choice of fuel. This is likely due to fuels varying in the amount of heat released in their combustion. The degree of dispersion of CuO and the total contribution from Cu1+ and Ce4+ to the electronic state of the active component increase as the standard enthalpy of combustion increases in the urea < glycerol < citric acid order. This leads to an increase in the catalytic activity of the (CuO-CeO2)/glass cloth system in selective CO oxidation.

Pd/Fiber glass and Pd/5% γ-Al2O3/Fiber glass catalysts by surface self-propagating thermal synthesis

The technique of Surface Self-propagating Thermal Synthesis (SSTS) was used to prepare Pd/γ-Al2O3/fiber glass (FG) catalysts for selective liquid-phase hydrogenation of acetylene in the presence of CO. The results of XRD SR analysis (in synchrotron radiation) in combination with the technique of arrested combustion shed new light on the dynamic of phase transformations in the systems under study and variation in the size of diffraction-active crystallites. The catalytic performance of synthesized catalysts was found to be close to that of similar conventionally prepared catalysts. The EXAFS and TEM data afforded to estimate the variation in relative amounts of Pd0 and PdO in synthesized catalysts. In the course of selective hydrogenation, PdO rapidly (<15 min) reduced to Pd0.