The paper compares the properties and activity of palladium clusters deposited on aluminum oxides of different phase compositions obtained by different methods. The numbers of palladium atoms available for the adsorption of hydrazine were determined for each catalyst. A correlation was found between the number of such atoms and the rate of hydrogen formation in the decomposition reaction of hydrazine monohydrate. It was concluded that an active palladium catalyst for the decomposition of hydrazine can be obtained using a modified support with a large specific surface area. The specific surface area and its modification determined the surface coverage with the active reagent. Obviously, the study of the role of various properties of supports in the formation of the active phase should be continued.

Pd-containing catalysts (1%Pd/Al2O3 and 5%Pd/Al2O3) deposited on aluminum oxide were studied in the decomposition reaction of hydrazine monohydrate. According to in situ IR spectroscopy, it was found that hydrazine monohydrate is adsorbed on the coordination unsaturated centers of the catalyst surface in a linear form. When the temperature rises, the adsorbed hydrazine monohydrate loses a water molecule, which is accompanied by a change in the geometry of the molecular complex. Adsorption of hydrazine on a support and its diffusion onto palladium clusters is a more advantageous process than direct adsorption on active centers. This circumstance shows that the hydrazine adsorbed on the support can be an intermediate of its decomposition process. The studied catalysts have a maximum activity in the temperature range of 100–120°C, while the ratio of hydrogen and nitrogen concentrations in the reaction products was equal to 2, which corresponds to 100% selectivity for hydrogen. As the reaction temperature increases, the selectivity decreases significantly. The explanation of the high selectivity for hydrogen at low temperatures is due to the fact that the adsorption of N2H4 is carried out through the formation of hydrogen–metal bonds. The hydrogen–metal bond strength in such a complex is higher than the nitrogen–metal bond strength, hence the barrier for breaking the N–H bond is lower than the barrier for breaking N–N bond, which leads to breaking N–H bond and preserving the N–N bond. At elevated temperatures, some of the hydrogen atoms formed recombine, the other reacts with the surface complexes of hydrazine to form the intermediate NH3–NH3, the breaking of the bond in which leads to the formation of ammonia molecules in the gas phase.

Pd-containing catalysts (1%Pd/Al2O3 and 5%Pd/Al2O3) deposited on aluminum oxide were studied in the decomposition reaction of hydrazine monohydrate. According to in situ IR spectroscopy, it was found that hydrazine monohydrate is adsorbed on the coordination unsaturated centers of the catalyst surface in a linear form. When the temperature rises, the adsorbed hydrazine monohydrate loses a water molecule, which is accompanied by a change in the geometry of the molecular complex. Adsorption of hydrazine on a support and its diffusion onto palladium clusters is a more advantageous process than direct adsorption on active centers. This circumstance shows that the hydrazine adsorbed on the support can be an intermediate of its decomposition process. The studied catalysts have a maximum activity in the temperature range of 100–120°C, while the ratio of hydrogen and nitrogen concentrations in the reaction products was equal to 2, which corresponds to 100% selectivity for hydrogen. As the reaction temperature increases, the selectivity decreases significantly. The explanation of the high selectivity for hydrogen at low temperatures is due to the fact that the adsorption of N2H4 is carried out through the formation of hydrogen–metal bonds. The hydrogen–metal bond strength in such a complex is higher than the nitrogen–metal bond strength, hence the barrier for breaking the N–H bond is lower than the barrier for breaking N–N bond, which leads to breaking N–H bond and preserving the N–N bond. At elevated temperatures, some of the hydrogen atoms formed recombine, the other reacts with the surface complexes of hydrazine to form the intermediate NH3–NH3, the breaking of the bond in which leads to the formation of ammonia molecules in the gas phase.

Pd-containing catalysts (1% Pd/Al 2 O 3 and 5% Pd/Al 2 O 3 ) supported on aluminum oxide were studied in the decomposition reaction of hydrazine monohydrate. According to in situ IR-spectroscopic data, hydrazine monohydrate was adsorbed in a linear form on the coordinatively unsaturated sites of the catalyst surface. As the temperature was increased, the adsorbed hydrazine monohydrate lost a water molecule with a change in the geometry of the molecular complex. The adsorption of hydrazine on a support and its diffusion onto palladium clusters is a more advantageous process than direct adsorption on active sites. This circumstance shows that the hydrazine adsorbed on the support can be an intermediate in the process of its decomposition. The test catalysts had a maximum activity at a temperature of about 100°C. At temperatures in a range of 100−120°C, the ratio between hydrogen and nitrogen concentrations in the reaction products was 2, which corresponds to 100% selectivity for hydrogen. The selectivity decreased significantly with the reaction temperature. The high selectivity for hydrogen at low temperatures was explained by the fact that N 2 H 4 was chemisorbed through the formation of hydrogen–metal bonds. The hydrogen–metal bond strength in such a complex is higher than the nitrogen–metal bond strength; hence, the N−H bond breaking barrier is lower than the N−N bond breaking barrier, and this fact led to the breaking of an N–H bond and the preservation of an N–N bond. At elevated temperatures, some of the formed hydrogen atoms recombined, and the other reacted with the surface complexes of hydrazine to form the intermediate NH 3 −NH 3 , in which N–N bond breaking led to the appearance of ammonia molecules in the gas phase.

Hydrazine and hydrazine monohydrate are commonly used in various fields of science and technology. Conventionally, these reagents are used as reducing agents for heavy metals. Recent interest in hydrazine and hydrazine monohydrate is attributed to the problem of producing impurity-free hydrogen via the catalytic decomposition of these reagents. A large number of various catalyst systems exhibiting fundamentally different activity and selectivity in the formation of hydrogen have been tested in the decomposition of hydrazine and hydrazine monohydrate. The review provides a detailed systematization of these data and analysis of the causes of the differences in the properties of the different catalyst systems. The available data suggest that the main role in determining the process direction is played by the form of activation of hydrazine. In addition, results of studying the hydrazine decomposition mechanism at low and high temperatures are discussed. The test results discussed in the review show that hydrazine and hydrazine monohydrate are fairly promising for both storing hydrogen and producing impurity-free hydrogen for the efficient operation of fuel cells.

Copper-containing catalysts based on CeO2–ZrO2 solid solutions were prepared by the Pecini method and studied using a set of physicochemical methods. It was found that the bond strength of oxygen on the catalyst surface, which depends on the properties of supported copper oxide clusters and a ratio between CeO2 and ZrO2 in the support, plays a main role in ethanol conversion. Ethoxy groups, acetate and formate complexes, and condensation products were detected as main surface intermediates formed in the course of ethanol conversion on the catalysts. The decomposition of the formate complexes was the key stage in the formation of hydrogen. Its appearance on the surface of the catalysts was due to the competition between the reactions of formate and acetate complex formation for oxygen with suitable properties.

The main features of the mechanism of selective reduction of nitrogen oxides by hydrocarbons (methane, propane, and propylene) in excess oxygen catalyzed by systems containing transition metal cations are considered. A combination of steady-state and non-steady-state kinetic studies, in situ Fourier-transform infrared (FTIR) spectroscopy, temperature-programmed desorption, and theoretical analysis of bond strengths and spectral data for adsorption complexes made it possible to determine reliably that surface nitrate complexes are key intermediates at real temperatures of catalysis. The rate-limiting step in these reactions includes the interaction of these complexes with hydrocarbons or their activated forms. Factors are considered that determine the structure, bond strength, and routes of nitrate complexes transformations under the action of hydrocarbons. Mechanistic schemes are proposed for the reaction of various types of hydrocarbons in which the determining role belongs to the formation of organic nitro compounds in a rate-limiting step. Their further fast transformation with the participation of surface acid sites resulting in the formation of ammonia, which is a highly efficient reducing agent, though not limiting the whole process, but determines nevertheless both the selectivity to the target product, molecular nitrogen, and the selectivity of hydrocarbon consumption for nitrogen oxide reduction.

In situ IR spectroscopic studies show that a formate, an aldehyde-like complex, and bridging and linear methoxy groups exist on the alumina surface involved in methanol conversion. In the absence of methanol in the gas phase, the interaction between two bridging methoxy groups yields dimethyl ether in the gas phase. When methanol is present in the gas phase, it interacts with methoxy groups on the surface. This reaction makes the main contribution to the formation of dimethyl ether. The linear methoxy group undergoes conversion via several routes. The main route is desorption with methanol formation in the gas phase, and no more than 10% of the linear methoxy groups are converted into formate and aldehyde, which are CO2 sources in the gas phase. In the absence of methanol in the gas phase, the conversion rate of the methoxy groups is independent of the presence of water and oxygen. A scheme of the surface reactions is suggested to explain the conversion of the methoxy groups.

Ethoxy groups, acetate complexes, and condensation products were detected on the surface of a 5% CuO/ZrO 2 catalyst using in situ IR spectroscopy under conditions of ethanol conversion. Formate complexes were not observed under the reaction conditions. Acetaldehyde, acetone, CO 2 , and ethylene were detected as the main reaction products of ethanol conversion; hydrogen, butane, and toluene were also formed in small amounts. Acetaldehyde was formed by the interaction of ethoxy groups and surface hydroxyl groups. Acetone, butane, and toluene resulted from the conversion of condensation products. The low rate of hydrogen formation on this catalyst was due to the absence of a high-temperature formate complex from the catalyst surface.

The article reports the synthesis of 5%CuO/Ce1– xZrxO2 catalysts based on CeO2, ZrO2 oxides and Ce1– xZrxO2 solid solutions with х = 0.2, 0.5, and 0.8. It is found that copper oxide is present in the catalysts in a highly dispersed form. In strong interaction with supports, it forms active oxygen, which participates in CO chemisorption and low-temperature oxidation of CO in the presence of hydrogen. In selective CO oxidation, the highest conversion (γmах = 100%) was obtained at temperatures of 120–160°С in the presence of 5%CuO/CeO2. In the modification of CeO2 by zirconium cations, the conversion on 5%Ce0.5Zr0.5O2 decreases to 92% at 160°С because oxygen binding strengthens on copper-containing sites. On the 5%CuO/ZrO2 sample, the maximum conversion is 67% at 180°С. The modification of ZrO2 by cerium cations leads to an increase in the conversion to 87% at 160°С on the 5%CuO/Ce0.2Zr0.8O2 sample as a result of increasing the amount of oxygen vacancies in the support. Taking into account the properties of CO complexes formed on copper-containing oxidation and adsorption sites, and the interaction of these complexes with adsorbed oxygen, their participation in the reaction of low-temperature CO oxidation by oxygen in excess of hydrogen on 5%CuO/CeO2 and 5%CuO/ZrO2 catalysts is considered.

To determine the mechanism of a heterogeneous catalytic reaction, a spectrokinetic method was used based on the comparison of simultaneously measured rates of transformation of surface complexes using in situ IR spectroscopy and the rate of formation of reaction products. Based on the of systemic studies of intermediates of heterogeneous catalytic reactions by this method, general patterns are found that shed light on the essence of the catalytic action. It is found that the main function of the catalyst is the preparation of a new reagent from the molecule in the gas phase (during adsorption). The transformation of this regent into the products on the surface occurs via a route that is fundamentally different from the route of transformation of the initial molecule in a gas-phase reaction. It was also found that, if the initial adsorption forms of the reactants in the reaction under study are the same for a certain group of catalysts, then the mechanism (as a sequence of steps) of this reaction on these catalysts is the same. The individual properties of different catalysts within such a group are manifested in the difference in the ratio of the rates of steps, i.e. in determining the limiting step.

In the conditions of ethanol conversion on the surface of a 5%Cu/CeO 2 catalyst, the method of in situ IR spectroscopy reveals ethoxy groups, acetate and formiate complexes, and consolidation products. Acetaldehyde, acetone, croton aldehyde, butadiene, hydrogen, CO, and CO 2 are observed in the reaction products. As the temperature of the experiment increases, the concentration of acetaldehyde passes through a maximum at T = 250°C. This product is formed due to the interaction of ethoxy and hydroxyl surface groups. The concentration of acetone, croton aldehyde, and butadiene also passes through a maximum in the 350–400°C range. These products are associated with the decomposition of the consolidation products. The concentration of hydrogen, CO and CO 2 steadily increases with temperature and only these reaction products are left at T > 400°C. A mechanism of hydrogen formation based on the conversion of the highest temperature formiate surface complex is discussed.

The dependence of the activity of СuO/ZrO2 catalysts in the CO oxidation reaction with oxygen in the presence of an excess of hydrogen and adsorption of СО over them on the CuO content (0.5 to 15%) and the structure of the support ZrO2, monoclinic (М), tetragonal (Т), or mixed (М + Т) has been studied. It has been found that the activity of CuO/ZrO2 is associated with the adsorption capacity of the samples for СО at 20°С. Thus, 5%CuO/ZrO2(Т + М) and 5% CuO/ZrO2(Т) samples, which exhibit the maximum activity (the СО conversion over them is 80–85% at 160°С), also possess a high chemisorption capacity towards CO (~2.2 × 1020 molecules/g). At the same time, CuO/ZrO2(М) samples with the CuO contents of 1 and 5% do not chemisorb СО and are inactive in the reaction at 160°С. The СО conversion over them does not exceed 32–36% at 250°С. On the basis of the data obtained by X-ray phase analysis, temperature-programmed reduction with Н2, temperature-programmed СО desorption, and electron paramagnetic resonance, a conclusion has been made that at low temperatures СО oxidation proceeds over CunOm clusters that are located on ZrO2(Т) crystallites. With the increase in the copper oxide content from 0.5 to 5%, the activity of the clusters increases, while the reaction temperature decreases. CuOm oxo complexes and particles of the СuO phase do not exhibit catalytic activity. The reasons for the low activity of the CuO/ZrO2(М) samples with the CuO contents of 1 and 5% in the СО oxidation and adsorption processes are discussed. The mechanism of the low-temperature СО oxidation with oxygen in an excess of hydrogen over a 5% CuO/ZrO2(Т + М) catalyst is considered.