A study is performed of bimetallic catalysts NiZn/ND with ratios Ni : Zn = 1 : 1 and 1 : 3 prepared by impregnation using detonation nanodiamond (ND) as a support. They were compared with monometallic Ni/ND and Zn/ND. It is shown by nitrogen adsorption/desorption, scanning and transmission electron microscopy that metal deposition does not affect the porous structure or morphology of a support. Coordination of metal precursors on a nanodiamond surface proceeds with the participation of functional groups, as is confirmed by a change in the electrokinetic charge of the surface. The reduction of metal precursors is studied by temperature-programmed reduction and in situ XAFS spectroscopy. In Ni-containing samples, two forms of Ni 2+ are found that are bonded differently with the support. ZnO is not reduced in the samples upon treatment with hydrogen at temperatures up to 400°C. The fraction of reduced nickel is determined by analyzing XANES spectra. Virtually full reduction of nickel is observed in a catalyst with a Ni : Zn ratio of 1 : 1 after 4 h of in situ treatment with hydrogen inside a spectrometer cell at 400°C, but not at a Ni : Zn ratio of 1 : 3 under the same conditions. The highest selectivity of styrene formation in the reaction of phenylacetylene hydrogenation throughout the investigated range of temperatures (100–350°С) is ensured by NiZn/ND; NiZn 3 /ND is less active and selective, since ZnO closes the active nickel centers and prevents the adsorption of phenylacetylene.

Metal precursor coordination and its reduction mechanism in Ni catalysts supported on detonation nandiamonds (ND) have been studied. TPR demonstrated multistage reduction of NiO supported on ND, which was explained by the presence of two types of Ni species on the ND surface. Weakly bonded Ni species are held on the ND surface by van der Waals forces, whereas strongly bonded ones are chemically bonded to the functional groups on the ND surface. Both Ni-Ni and Ni-O-C scattering paths were found in Ni/ND catalysts using Morlet wavelet analysis of EXAFS data. The ratio of weakly and strongly bonded Ni species in the catalyst was tailored either by removal of functional groups by annealing of ND support in Ar at 900 degrees C or by calcination of NiO/ND precursor in air at 300 degrees C. The former resulted primarily in weakly bonded Ni species in the catalyst, while the latter led to strongly bonded ones. These two catalysts demonstrated drastic differences in selective styrene formation upon phenylacetylene hydrogenation: weakly bonded Ni species gave rise mainly to ethylbenzene, while Ni species strongly bonded to the surface through the Ni-O-C bond afforded mainly styrene. (C) 2016 Elsevier Inc. All rights reserved.

Никельсодержащие металл-углеродные нанокомпозиты (Ni@C), синтезированные методом бесконтактной левитационной плавки в токе смеси инертного газа и углеводорода, использованы в качестве катализаторов реакции гидрирования фенилацетилена. Нанокомпозиты охарактеризованы методами рентгеновской фотоэлектронной спектроскопии, синхронного термического анализа и температурно-программированного восстановления. Установлено, что никель-углеродные нанокомпозиты устойчивы при хранении на воздухе: после 3.5 лет хранения происходит окисление малой части металла (до 13% от общего количества никеля). Показано, что кроме полностью покрытых наночастиц, в композитах присутствуют частично покрытые углеродом металлические частицы, легко окисляющиеся на воздухе, причем оба типа частиц проявляют каталитическую активность в гидрировании фенилацетилена; увеличение содержания частично покрытого углеродом никеля способствует увеличению активности в гидрировании фенилацетилена и снижению селективности образования стирола. Определена минимальная температура полупревращения (75°С) наблюдается для специально приготовленного образца Ni@C с увеличенным содержанием окисленного никеля (28%). Максимальная селективность по стиролу, ( 75 при 150°С), зафиксирована в присутствии образца, содержащего наименьшее количество окисленной формы никеля (менее 4%).

Me@C nanocomposites were prepared by evaporation of overheated liquid drop of Me in the flow of inert gas containing a hydrocarbon. The resulting carbon-coated nickel and iron nanoparticles contain metal cores of about 5 nm in size that are wrapped in a few layers of graphene-like carbon. Experimental data and theoretical results give evidence of the ability of carbon coating in nanocomposites Fe@C and Ni@C to H-2 activation by dissociative adsorption due to the presence of space and structure defects and/or the presence of transition metal in subsurface layer. Since molecular hydrogen dissociation is the key step of hydrogenation reactions, both Ni@C and Fe@C provide high conversion of phenylacetylene (PA) (about 100%) during hydrogenation at the temperatures above 150 and 300 degrees C, respectively. Fe@C provides excellent styrene (ST) selectivity: 86% at 99% PA conversion at 300 degrees C. ST selectivity is moderate on Ni@C (about 60%) in the temperature range of 100-150 degrees C end low at higher temperatures. (C) 2014 Elsevier Ltd. All rights reserved.

Nickel-containing metal-carbon nanocomposites (Ni@C) synthesized by levitation melting in a flow of an inert gas-hydrocarbon mixture were used as catalysts of the hydrogenation of phenylacetylene (PA). The nanocomposites were characterized by X-ray photoelectron spectroscopy, simultaneous thermal analysis, and temperature-programmed reduction. The nickel-carbon nanocomposites were stable on storage in air, with only 13% of the total amount of nickel oxidized after 3.5 years of storage. In addition to nanoparticles completely covered with carbon, the composites contained partially coated metal particles, which are readily oxidized in air. Both types of particles exhibited the catalytic activity in phenylacetylene hydrogenation. At higher contents of nickel partially coated with carbon, the activity increased and the selectivity of styrene formation decreased. The minimum half-conversion temperature (75°C) was determined for a specially prepared Ni@C sample with an increased content of oxidized nickel (28%). The maximum selectivity of styrene formation (∼75% at 150°C) was recorded in the presence of the sample with the smallest amount of oxidized nickel (less than 4%).

The properties of palladium and nickel catalysts supported on ultradispersed diamond (UDD) were studied in the vapor-phase hydrodechlorination (HDC) reaction of chlorobenzene and the multiphase HDC of polychlorobenzenes. The catalysts on UDD exhibited a number of advantages: the vapor-phase HDC of chlorobenzene on Ni/UDD occurred at lower temperatures, and the multiphase HDC of chlorobenzene, 1,3,5-trichlorobenzene, and 2,4,8-trichlorodibenzofuran on Pd/UDD occurred more rapidly than that on catalysts supported on activated carbon. The structure of the catalysts and the electronic states of the active components were studied using IR spectroscopy, temperature-programmed reduction, and adsorption techniques. It was found that the properties of the catalysts depend on the electronic state of palladium, which depends on its concentration in the sample; the structural properties, which are responsible for the accessibility of the active surface to adsorption; and the presence of other metal impurities.