The catalytic oxidation of CO is of great technological importance for the treatment of vehicle and industrial exhaust gases. PtCe-catalysts of low-temperature CO oxidation were prepared by the impregnation of ZSM-5 zeolite (Z) with aqueous solutions of H2PtCl6 and Ce(NO3)3, varying the order of metal deposition and thermal treatment conditions. The relationships between structure transformations and catalyst performance were established based on the SEM, TEM, EDX, DRIFT, and X-ray photoelectron spectroscopies data. For the Ce/Pt/Z sample, in which cerium was deposited after platinum, the 100% CO conversion temperature was only 120 °C. The inverse deposition sequence of metals (Pt/Ce/Z catalyst) resulted in CO oxidation at a higher temperature that can be decreased to 110 °C by redox treatment. The prepared catalysts were also active in the CO oxidation in excess hydrogen (PROX) but were not selective enough. However, the activity of PtCe-modified ZSM-5 enhanced greatly in the repeated cycles of CO oxidation (TOX) after testing in PROX. It is suggested that enhancing the interaction between Pt and Ce is a key factor in tuning the catalyst performance. The 0.2 wt.% Pt catalysts showed the best performance and provided complete CO conversion at 95 °C, which is a pronounced result for low-loaded Pt catalysts.

Diffuse reflectance infrared Fourier transform spectroscopy of adsorbed carbon monoxide is used along with X-ray absorption spectroscopy to study the effect a second alloying metal (Zn, Cu) has on the electronic state and local structure of rhodium on the surfaces of Rh/HZSM-5 zeolite catalyst. It is established that introducing copper and zinc helps improve the stability of rhodium toward aggregation (the formation of clusters) under conditions of the oxidative carbonylation of methane into acetic acid. Compared to monometallic catalyst Rh/HZSM-5, where single atom rodium sites are partially aggregated into clusters, the proportion of Rh° is halved in the case of Rh–Zn/HZSM-5, and Rh clustering does not occur in the case of Rh‒Cu/HZSM-5. The stabilizing effect of Cu is due to the interaction between copper and rhodium cations on the surface of zeolite.

Cu-Ce-modified zeolites are shown to be effective in preferential CO oxidation (CO-PROX) in H-2-rich stream. Catalysts containing copper and cerium based on zeolites ZSM-5 (Si/Al = 15, 28 and 40) and Beta (Si/Al = 19) are synthesized by sequential incipient wetness impregnation and tested in total (CO-TOX) and preferential oxidation of CO. The influence of zeolite framework type, Si/Al ratio, metal loading and order of metal introduction on the formation of active sites and their activity and selectivity are studied. Based on XRD, TEM, XPS, adsorbed CO DRIFTS and H-2-TPR studies it is shown that of the key importance is synergistic interaction of copper and cerium not only on the surface, but in the zeolite channels. Cu+ incorporated in CeO2 and mixed copper-cerium oxo/hydroxocations can both be active sites in CO oxidation. Wider channels of Beta framework favor the penetration of metal cations, but not formation of necessary active sites. The presence of CuO phase in the catalysts negatively affects the stability and selectivity in CO-PROX. ZSM-5-based catalyst containing largest amount of oxocations (2.6 wt% Cu, 10 wt% Ce, Si/Al = 15) makes it possible to completely remove CO from H(2 )rich mixture in CO-PROX at 150-190 C.

Two types of nanosilicas with different pore structures are synthesized and decorated via impregnation with cobalt and cerium oxides. Meso–microporous spherical silica particles with thin walls of SiO 2 nanochannels having specific surface area and pore volume of up to 1400 m 2 /g and 0.8 cm 3 /g, respectively, are used. Macroporous three-dimensionally ordered structures based on SiO 2 (so-called synthetic opals) consisting of close-packed submicron spherical silica particles with respective porosity characteristics of 11 m 2 /g and 0.2 cm 3 /g are also used. The synthesized materials are characterized via low-temperature nitrogen adsorption, X-ray diffraction, SEM, XPS, and Fourier transform IR spectroscopy, and tested as catalysts for the selective oxidation of CO in excess H 2 (CO-PROX). The effect of silica, the ratio of introduced oxides, and the order of their introduction on the structure and catalytic properties of Co–Ce/SiO 2 are revealed. The catalytic behavior of the synthesized materials is determined from the specificity of interactions among the metal oxides and with the silica surface.

Zeolite catalysts for the conversion of dimethyl ether to light olefins with a monoatomic distribution of rhodium are studied via infrared spectroscopy of the diffuse reflection of adsorbed carbon monoxide and X-ray absorption spectroscopy. The zeolite is preliminarily treated with ultrasound to obtain a monatomic distribution of the active component on the support’s surface, and a polymer (chitosan hydrochloride) is used as the medium for dispersing rhodium at the stage of impregnation. A sample prepared via the traditional impregnation of zeolite with an aqueous solution of rhodium chloride is studied for purposes of comparison. It is shown that rhodium in the structure of zeolite treated with ultrasound is in the form of isolated metal centers whether it is deposited with or without a polymer. Synthesis with chitosan results in a more disperse distribution of rhodium on the outer surface of the zeolite and greater oxidizing ability of the catalyst.

A series of mono- and bimetallic copper–cerium catalysts based on ZSM-5 zeolite with different aluminum content (SiO2/Al2O3 = 30 and 55) was synthesized by incipient wetness impregnation. The copper content was 0–4.3 wt

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.

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

A series of mono- and bimetallic cobalt–cerium catalysts based on ZSM-5 zeolite with different silicate moduli (SiO2/Al2O3 = 30, 55, and 80) was synthesized by incipient wetness impregnation. The atomic ratio of metals (Co + Ce)/Al in bimetallic samples ranged from 0.5 to 1.5. A synergistic catalytic effect of cobalt and cerium in the prepared composites manifested itself in the reactions of total and preferential oxidation of CO (CO-PROX) in an excess of hydrogen. The catalysts in which an atomic ratio between Co and Ce was close to 3 were the most active. In these cases, the conversion of CO in the CO-PROX reaction reached 95% at 190–200°C. With the use of TEM, SEM, and DRIFT spectroscopy of adsorbed CO, including in situ studies of reduction processes under the action of CO, it was found that cobalt oxo cations and mixed cobalt and cerium oxo cations located in exchange positions of the zeolite play a key role in the oxidation reactions. The use of zeolite with SiO2/Al2O3 = 55 provided an optimal balance between the high activity of Co/Ce catalysts in CO oxidation and the selectivity of CO2 formation in the presence of hydrogen.

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.

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.

— Silica particles containing large mesopores (5–25 nm in size) and micropores (0.6–2 nm in size) have been prepared by chemical etching of spherical micro- and mesoporous silica particles in an ammonia + water + hydrogen peroxide mixture. The specific surface area and pore volume of the particles are 510 m 2 /g and 0.8 cm 3 /g, respectively. Using capillary impregnation, we have synthesized Co 3 O 4 (2–4 wt %) in pores of the particles. The composition and structure of the resultant materials have been studied. The Co 3 O 4 /SiO 2 composite particles have been shown to be stable and exhibit catalytic activity for the CO oxidation process.

This work elucidates the role of surface coverage of alumina with Pt nanoparticles on the catalyst efficiency in CO oxidation. Size-selected Pt nanoparticles were deposited on the outer surface of alumina pellets by the laser electrodispersion technique. The alumina surface coverage with Pt varied from 0.04 to 3.5 nanoparticle layers and affected the Pt electronic state and catalyst efficiency. Even in the multilayer coatings nanoplatinum particles remained isolated. The catalysts were tested in CO oxidation at CO/O-2 ratios of 0.2, 1 and 2 in the temperature-programmed and pulse reaction modes. At CO/O-2 = 0.2 the temperature of 50% CO conversion increased with decreasing the surface coverage with Pt particles. At CO/O-2 = 2 the decrease in the surface coverage enhanced the catalyst activity. Pt-0 dominates only in multilayer catalysts, however, approximately half of platinum remained non-oxidized even at such a low metal loading as 0.01 wt%. The change in the electronic state of platinum under the thermal treatment in the reaction mixture affected the catalyst efficiency. The oxidation state of Pt depended on the metal loading, reaction temperature, CO/O-2 ratio in the reaction mixture, mode of its feeding and surface coverage with Pt nanoparticles that influenced the interparticle and particle support interactions.

PdCu/Al2O3 (Pd = 0.1 wt.%, Cu = 0.1 wt.%) catalyst and its monometallic analogues (Pd/Al2O3 and Cu/Al2O3) were prepared by combination of deposition-precipitation and impregnation methods. The structure of the catalysts was studied by means of XRD, TEM, EDS, TPD-NH3, and DRIFTS. In a standard run (275 White circleC, 5 h), Cu/ Al2O3 converts 11 % of ethanol to alpha-alcohols with 0.6 % selectivity, whereas Pd/Al2O3 converts 24 % of ethanol to alpha-alcohols with 70 % selectivity. The high performance of Pd/Al2O3 was attributed to the catalysis on the Pd degrees Al2O3 interfaces. After 3 sequential runs, the activity of Pd/Al2O3 decreases by 98 %. It was explained by blocking of Pd degrees sites in Pd/Al2O3 by CO molecules produced in side reactions. Modification of Pd/Al2O3 with Cu species results in the formation of PdCu/Al2O3 catalyst containing PdCu alloy particles with the size of 4 nm. This leads to an increased durability of bimetallic sample, because of suppressing CO sorption on Pd degrees sites in alloy particles. As a result, for the PdCu/Al2O3 catalyst, sustained and high conversion (41 %) accompanied by high selectivity to alpha-alcohols (91 %) was observed in 20 sequential runs.