N. B. Shitova

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.

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.

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.

Supported palladium catalysts prepared by surface self-propagating thermal synthesis

Supported Pd/fiber glass, Pd/γ-Al2O3/fiber glass, Pd/γ-Al2O3 catalysts were prepared by Surface Self-propagating Thermal Synthesis (SSTS) and tested in selective hydrogenation of acetylene to ethylene in the presence of CO. Temperature change in local liquid-phase surrounding of Pd atoms was monitored by XAFS in situ by modeling the catalysts synthesis. The phase composition of samples at various synthesis stages was determined by XAFS spectroscopy and synchrotron X-ray diffraction (SR XRD). The type of support material and SSTS conditions were found to affect the catalytic activity of supported Pd catalysts. Thermal synthesis of Pd catalysts on the surface of supports was found to proceed via formation of the metallic phase followed by its transformation to oxide. The catalytic activity of thus prepared catalysts on fiber glass supports can expectedly be improved upon deposition of additional support (alumina) onto a fiber glass.

Self-propagating synthesis of Pd-CeO2/Al2O3 automotive monolith catalysts

Pd-CeO2 catalysts on a monolith support with a honeycomb structure have for the first time been prepared by surface self-propagating thermal synthesis (SSTS). Decomposition routes for the cerium precursors are deduced from TG-DTA data and from the mass spectra of decomposition intermediates. The Pd-CeO2/Al2O3 monoliths prepared by SSTS are more active in CO oxidation, total hydrocarbon oxidation, and nitrogen oxide reduction than the catalysts obtained by conventional impregnation. This is explained by the fact that the SSTS products have a larger specific surface area and their active component has a smaller particle size.

Structure of a Platinum–Alumina Catalyst Prepared from the Carbonyl Cluster H2[Pt3(CO)6]5

The state of a platinum carbonyl cluster in an initial aqueous acetone solution and its transformations on the surface of aluminum oxide in the course of catalyst preparation were studied by EXAFS spectroscopy. It was found that water enters the polynuclear framework of the dissolved cluster (the Pt–O distance is 2.55 Å, where O is the oxygen atom of water). Structural changes in the supported cluster in the course of catalyst preparation exhibited a strong interaction of platinum with alumina (the Pt–O distance is 1.92–1.95 Å), beginning at the step of H2[Pt3(CO)6]5 adsorption. This interaction was retained upon the subsequent high-temperature treatments of the catalyst. The structures of samples prepared from platinum carbonyl and chloroplatinic acid were significantly different. In the former case, a surface prototype was formed from the initial cluster; in the latter case, the sample consisted of platinum metal clusters of a considerable size.

Comparative EXAFS and TEM study of Pd/Sibunit and Pd-Ga/Sibunit catalysts for liquid-phase acetylene hydrogenation

The structural characteristics and catalytic properties of Pd/Sibunit and Pd-Ga/Sibunit catalysts for the liquid-phase hydrogenation of acetylene prepared via impregnation of joint alcoholic precursor solutions are studied. A surface film of gallium oxide covering the surfaces of bimetallic particles forms on a sample modified with gallium, leading to partial blocking of its active centers. This explains the lower activity and selectivity to ethylene of Pd-Ga/Sibunit catalyst, relative to Pd/Sibunit.

The influence of a carbon support on the catalytic properties of Pd/Sibunit and Pd-Ga/Sibunit catalysts for liquid-phase acetylene hydrogenation

The Pd/Sibunit and Pd-Ga/Sibunit catalysts, which were supported on Sibunit with different textural characteristics, for liquid-phase acetylene hydrogenation were investigated. It was shown that the use of the support with a large surface area leads to an increase in catalytic activity and selectivity due to the increased dispersion of the active component. The promoting effect of gallium correlates with the probability of contact between the supported Pd and Ga components.