Significant differences in hydrogen adsorption on amorphous and crystalline gold nanoparticles deposited on highly oriented pyrolytic graphite (HOPG) were revealed. Crystalline nanoparticles were synthesized via the impregnation-precipitation method followed by annealing at 700 K, whereas amorphous ones were obtained using the laser electrodispersion method. The morphology and electronic structure of single nanoparticles were investigated with high spatial resolution using scanning tunneling microscopy and spectroscopy (STM/STS) in ultra-high vacuum both before and after exposure to molecular hydrogen at doses of 400-6000 L. Experiments performed at room temperature showed that the surface coverage by the adsorbate in both cases begins at the Au-HOPG interface, spreads towards the center of the particle, and corresponds to the island growth model. However, amorphous nanoparticles have fewer growth sites at the periphery compared to crystalline ones. The local electronic structure of amorphous nanoparticles is more inhomogeneous compared to crystalline ones, demonstrating variation across different points on the nanoparticle surface. It was shown that dissociative chemisorption of hydrogen takes place on amorphous gold nanoparticles with a size of 4-6 nm. Chemisorption is completely inhibited when the nanoparticle size is reduced to 2 nm or less.

A series of alumina-based catalysts containing from 0.004 to 0.01 wt% of palladium were prepared via laser electrodispersion and impregnation methods. Three alumina modifications, gamma-Al2O3, theta-Al2O3, and alpha-Al2O3, were used as supports. In the case of the laser electrodispersion method, Pd particles of 2.5 nm in size were evenly distributed on the outer surface of the alumina grains. Contrarily, the impregnation procedure provided the distribution of Pd throughout the whole volume of the support. The catalytic properties of the prepared samples were studied in an acetylene hydrogenation reaction. As found, the catalysts prepared by laser electrodispersion possess a slightly lower activity along with a higher selectivity compared to the impregnated ones. The phase modification of alumina was found to affect the catalytic behavior noticeably. Thus, a decrease in acetylene conversion and an increase in ethylene selectivity were observed for the following order: theta-Al2O3 > gamma-Al2O3 > alpha-Al2O3. The main factors defining the efficiency of the catalysts are metal-support interactions, electronic state, and dispersion and distribution of Pd on the alumina surface. The strongest metal-support interaction was observed for the Pd/theta-Al2O3 sample prepared by laser electrodispersion. This sample has the highest content of Pd2+ species and exhibits high activity but low selectivity to ethylene. In the case of the alpha-Al2O3 support, Pd particles are located close to each other on the outer surface and, therefore, undergo fast deactivation. The X-ray photoelectron spectroscopy data revealed the carbon accumulation during the reaction for all the studied samples.

Zeolites and metal-doped zeolites are now widely considered as low-temperature hydrocarbon traps to be a part of emission control systems in automobiles. However, due to the high temperature of exhaust gases, the thermal stability of such sorbent materials is of great concern. To avoid the thermal instability problem, in the present work, laser electrodispersion was used to deposit Pd particles on the surface of ZSM-5 zeolite grains (SiO2/Al2O3 = 55 and SiO2/Al2O3 = 30) to obtain Pd/ZSM-5 materials with a Pd loading as low as 0.03 wt.%. The thermal stability was evaluated in a prompt thermal aging regime involving thermal treatment at temperatures up to 1000 °C in a real reaction mixture (CO, hydrocarbons, NO, an excess of O2, and balance N2) and a model mixture of the same composition with the exception of hydrocarbons. Low-temperature nitrogen adsorption and X-ray diffraction analysis were used to examine the stability of the zeolite framework. Special attention was paid to the state of Pd after thermal aging at varied temperatures. By means of transmission electron microscopy, X-ray photoelectron spectroscopy, and diffuse reflectance UV–Vis spectroscopy, it was shown that palladium, having been initially located on the surface of zeolite, undergoes oxidation and migrates into the zeolite’s channels. This enhances the trapping of hydrocarbons and their subsequent oxidation at lower temperatures.

New Pt-Co catalysts of hydrogen purification from CO impurities for fuel cells were fabricated via the deposition of monodispersed 1.7 nm Pt nanoparticles using laser electrodispersion on Co-modified ZSM-5 prepared by the Co(CH3COO)2 impregnation. The structure of prepared Pt-Co zeolites was studied by low-temperature N2 sorption, TEM, EDX, and XPS methods. The comparative analysis of samples with different Pt (0.01–0.05 wt.%) and Co (2.5–4.5 wt.%) contents on zeolites with the ratio of Si/Al = 15, 28, and 40 was performed in the CO-PROX reaction in H2-rich mixture (1%CO + 1%O2 + 49%H2 + 49%He). The synergistic catalytic action of Pt and Co on zeolite surface makes it possible to completely remove CO from a mixture with hydrogen in a wide temperature range from 50 to 150 °C; the high efficiency of designed composites with low Pt loading is maintained for a long time. The enhancement of PROX performance originates from the formation of new active sites for the CO oxidation at the Pt-Co interfaces within zeolite channels and at the surface. In terms of their activity, stability, and selectivity, such composites are significantly superior to known supported Pt-Co catalysts.

The paper presents the results of a comparative analysis of the differential selectivity of the Suzuki–Miyaura reaction with aryl bromides using various heterogeneous Pd precursors ( PdCl_4^2 - and Pd0) obtained by chemical modification and laser electrodispersion of palladium on heterogeneous supports of two types: SiO2 modified with an ionic liquid and γ-Al2O3. The catalytic experiments were carried out under “ligand-free” conditions implying no additives of phosphines, amines, carbenes, or any other organic ligands for Pd stabilization. Changes in the differential selectivity of competing aryl bromides were observed while varying the nature and concentration of the Pd precursor, indicating a substantial contribution of true heterogeneous catalysis to the total conversion of substrates.

Platinum particles of 1.7 nm size were deposited on the external surface of HZSM-5 zeolites with Si/Al = 15, 28, and 40 using laser electrodispersion (LED) method. The obtained materials with low Pt loading (0.01–0.05 wt.

Pd/Al2O3 catalyst of the “crust” type with Pd loading of 0.03 wt.% was prepared by the deposition of 2 nm Pd particles on the outer surface of the alumina support using laser electrodispersion (LED). This technique differs from a standard laser ablation into a liquid in that the formation of monodisperse nanoparticles occurs in the laser torch plasma in a vacuum. As is found, the LED-prepared catalyst surpasses Pd-containing three-way catalysts, obtained by conventional chemical synthesis, in activity and stability in CO oxidation under prompt thermal aging conditions. Thus, the LED-prepared Pd/Al2O3 catalyst showed the best thermal stability up to 1000 °C. The present research is focused on the study of the high-temperature evolution of the Pd/Al2O3 catalyst in two reaction mixtures by a set of physicochemical methods (transmission electron microscopy, X-ray photoelectron spectroscopy, and diffuse reflectance UV-vis spectroscopy). In order to follow the dispersion of the Pd nanoparticles during the thermal aging procedure, the testing reaction of ethane hydrogenolysis was also applied. The possible reasons for the high stability of LED-prepared catalysts are suggested.

Laser electrodispersion has been used as an alternative to the chemical synthesis of palladium-containing catalysts. The thus produced catalysts supported on alumina and HZSM-5 zeolite have high catalytic activity and stability at ultralow palladium content (0.03 wt

Advantages of Laser Electrodispersion for the Synthesis of CO Oxidation Catalysts with Low Loading of Precious MetalsMetal target Laser beam 1 GW/cm 2 Piezoelectric plate Support Maternal drops* Nanoparticles -Deposition of one-size single particles; -"Crustlike" distribution; -High resistance to aggregation; -Particle size independence from the support and metal loading; -Linear dependence of metal loading on the deposition time LED Technique Advantages Pd and Pt catalysts

The set of heterogeneous Pd catalysts containing different forms of Pd (PdCl42– or Pd0) was prepared by chemical modification and laser electrodispersion using two types of + supports, namely, SiO2 modified by ionic liquid and γ-Al2O3. Testing of the synthesized catalysts in the Suzuki–Miyaura reaction with aryl bromides pointed out the possibility to achieve the prominent TOF and TON values. The dependencies of TOF on the catalyst loading indicate that only a fraction of loaded Pd was involved in the catalysis.

Small amounts of nearly 2-nm Pd nanoparticles (0.01–0.03 wt.%) were deposited onto the surface of the ZSM-5 and BEA zeolites by laser electrodispersion. Materials thus prepared were studied by low-temperature nitrogen adsorption, thermo-programmed desorption of ammonia, transmission electron microscopy, and X-ray photoelectron spectroscopy. They were also tested in total catalytic oxidation of CO and CH4. It was demonstrated that the oxidation state of Pd and the character of distribution of isolated metal particles or their aggregates over the external surface or in the bulk of the zeolite is affected by the palladium content and by the zeolite nature. The activity of the Pd/ZSM-5 catalysts decreases with increasing Si/Al ratio of the zeolite and depends on the oxidation state of the metal. In the most active catalysts 65–75% of Pd occur as metal, whereas 35–25% make up oxidized palladium. The oxidation of carbon monoxide on the ZSM-5 catalyst (Si/Al = 15, 0.01 wt.% Pd) whose surface is uniformly covered with isolated Pd nanoparticles begins at 90 °C, which is 70–80 °C lower compared to CO oxidation on other Pd-modified ZSM-5 and BEA zeolites containing aggregates of palladium nanoparticles.

BACKGROUND Palladium particles with a size of 2 nm were obtained by laser electrodispersion (LED) and used to prepare the Pd-ZnHZSM-5(LED) catalyst (Pd = 0.0005 wt%). The deposition of the LED palladium particles on the surface of ZnHZSM-5 provided a high dimethyl ether (DME) conversion into liquid hydrocarbons; the percentage of the unreacted intermediate (methanol) decreased by an order of magnitude and the selectivity for i-alkanes increased (more than 80 wt%). The Pd-ZnHZSM-5(LED) catalyst showed higher activity and selectivity than the traditional Pd-ZnHZSM-5 catalyst (impregnation). RESULTS The features of the catalytic action of Pd-ZnHZSM-5(LED) are associated with the high density of nanosized Pd-0 and Pd2+ phases on the ZnHZSM-5 surface. The LED particles are immersed in the surface of the zeolite to a maximum depth of 0.5 nm and do not penetrate deep into the pores of the zeolite. In Pd-ZnHZSM-5(LED), the zinc sites and palladium sites are separate. On Bronsted acid sites and zinc sites in the micropores of the zeolite occure target reactions. Part of arenes and unreacted alkenes exit the pores of zeolite are hydrogenated on the palladium. The product obtained on Pd-ZnHZSM-5(LED) is characterized by a high content of i-alkanes (more than 80 wt%) and a low content of arenes (no more than 5 wt%). CONCLUSION The results demonstrate the high promise of the LED method for the preparation of high-performance catalysts with ultra-low content of noble metal for conversion of oxygenates to synthetic liquid hydrocarbons with a high yield of i-alkanes and low yield of arenes. (c) 2022 Society of Chemical Industry (SCI).

In recent years, the interest in using the structures consisting of amorphous nanoparticles has increased significantly due to their peculiar electric, magnetic, and catalytic properties. One important problem in the practical application of such particles is the development of new technologies for their formation. The studies aimed at the solution of this problem reveal that fragmentation of microdroplets of metals charged in a laser jet plasma is the most effective method for obtaining of amorphous metallic nanoparticles. However, in spite of the fact that the application of this method has made it possible to obtain such structures from various types of metals, the theoretical analysis of microdroplet fragmentation effect has been performed without detailed investigation of nanodroplet charging, which limits to a considerable extent the use of available theoretical models for developing new technologies. We propose a model that makes it possible to formulate more exactly the requirements for the parameters of laser jet plasma, for which effective fragmentation of microdroplets of metals to a nanometer size is realized.

The structural properties of amorphous nanocarbon films fabricated by laser sputtering of a graphite target are investigated by means of Raman spectroscopy. Analysis of the spectral features in the region of 100–3600 cm -1 allowed us to determine the allotrope composition of the films and the degree of disorder in terms of average crystallite size. The results obtained are important for application of such films in the field of electrode coatings.

Laser electrodispersion (LED) uniformly distributes metal over the external surface of a support as particles of strictly controlled size, composition, and shape. LED is used to synthesize model catalysts and determine the role of interaction between particles of an active metal in catalysis using nanostructured materials. In Moscow State University’s Development Program the experimental possibilities of physicochemical analysis of LED-produced systems with very low content of metals have been extended considerably, allowing the acquisition of new data on the relationship between the structure and properties of mono- and bimetallic catalysts. The resulting data are used to develop crusted catalysts with a reduced content of active metal/metals. Such catalysts have the optimum surface particle density and extremely high activity in a number of environmentally important processes that is orders of magnitude higher than in analogs produced via wet chemistry. Studies of the processing of toxic organochlorine compounds by hydrodechlorination, performed under the supervision of Academician V.V. Lunin with the participation of Profs. V.V. Smirnov, E.S. Lokteva, and others, were awarded Moscow State University’s Lomonosov Prize. The prospects for using LED are demonstrated by the examples of synthesizing catalysts of oxidation of carbon monoxide, methane, and sulfur-containing compounds.

В последние годы значительно усилился интерес к использованию структур, состоящих из аморфных наночастиц, который обусловлен их необычными электрическими, магнитными и каталитическими свойствами. Одной из важных задач, стоящих на пути к практическому применению таких структур, является разработка новых технологий их формирования. Исследования, проведенные в рамках решения этой задачи, показали, что наиболее эффективным способом получения аморфных металлических наночастиц является дробление микрокапель металлов, заряжаемых в плазме лазерного факела. Однако, несмотря на то, что использование этого метода позволило создать такие структуры из различных типов металлов, теоретический анализ эффекта дробления микрокапель проведен без детального рассмотрения процесса зарядки нанометровых капель, что в значительной мере ограничивает возможность использования имеющихся теоретических моделей для разработки новых технологий. Представлена модель, позволяющая более точно определить требования к параметрам плазмы лазерного факела, при которых реализуется эффективное дробление микрокапель металлов до нанометровых размеров. Ключевые слова: термополевая эмиссия, плазма лазерного факела, аморфные наноструктуры, предел Рэлея, каскадное электродиспергирование.