N. V. Nekrasov

The mechanism of carbon dioxide hydrogenation on copper and nickel catalysts

The mechanism of the reaction of CO2 with H2 on copper and nickel catalysts was studied by means of isotope, non-steady-state, and steady-state methods. Staged schemes of the process were proposed. The slow step of CO formation on the test catalysts is the reaction of the adsorbed carboxylate complex with a hydrogen atom. It was shown that hydrogen adsorption on the copper catalyst is dissociative in character. A formyl complex and hydrogen are involved in the slow step of methane formation on the nickel catalyst. It was found that the methane formation proceeds via a consecutive scheme through CO.

Kinetics and mechanism of the oxidative dehydrogenation of isobutane on cobalt, nickel, and manganese molybdates

The kinetics of oxidative dehydrogenation of isobutane in the presence of atmospheric oxygen on manganese molybdate has been studied. The experiments have been carried out in a circulation flow reactor at 470–530°C. The form of kinetic equations and the mechanism of the formation of isobutene, carbon oxides, and cracking products on manganese molybdate are similar to those found previously for the same reaction on cobalt and nickel molybdates. The highest yields of isobutene and propene (isobutane cracking products) are achieved on Co0.95MoO4. The mechanism of the process has been investigated by the unsteady-state response method. Manganese molybdate contains the largest amount of reactive oxygen, whereas nickel molybdate contains the smallest amount of reactive oxygen. The earlier conclusion that molybdate lattice oxygen and chemisorbed oxygen play the main role in the formation of iso-C4H8 and in deep oxidation processes, respectively, is confirmed.

Kinetics of benzene and toluene hydrogenation on a Pt/TiO2 catalyst

The kinetics and mechanism of benzene and toluene hydrogenation on a Pt/TiO2 catalyst were studied in steady-state and non-steady-state regimes in the presence or absence of strong metal–support interactions (SMSI). It was found that the kinetics and mechanism of the test reactions were independent of SMSI. The observed effect of a decrease in the catalytic activity in the SMSI state was due to structural changes in the active centers of the catalyst and to the presence of strongly bound hydrogen species on the surface; this was also supported by thermal-desorption data.

Kinetics of carbon monoxide methanation on nickel catalysts

The kinetics of CO methanation in excess H2 on CaO- and CeO2-doped nickel catalysts supported on Al2O3 and TiO2 was studied at atmospheric pressure in a temperature range of 180–240°C. It was found that the same rational fractional rate equation corresponding to the reaction taking place at high surface coverages, is valid for all of the catalysts. The activity of nickel catalysts in the methanation reaction and their adsorption capacity with respect to reaction mixture components depend on the nature of the support and dopants.

Reaction mechanism of CO methanation on nickel catalysts, as studied by isotopic and nonstationary methods

Kinetic isotope effects were measured upon the replacement of hydrogen by deuterium in the reaction of carbon monoxide methanation on nickel catalysts supported on TiO2 and γ-Al2O3. Data on the mechanism of the process were obtained with the use of a nonstationary method. A step-scheme was proposed, in which the interaction of oxygen-containing compounds with hydrogen is a slow step of the process.

Kinetic and Mechanistic Study of the Oxidative Dehydrogenation of Isobutane over Cobalt and Nickel Molybdates

The kinetics and mechanism of the oxidative dehydrogenation of isobutane on nickel and cobalt molybdates are studied. Cobalt molybdate is found to be more active than nickel molybdate. The rate laws and mechanisms for the formation of isobutene, carbon oxides, and cracking products are the same for both catalysts. Isobutene is formed via the redox mechanism with the participation of lattice oxygen. The formation of carbon oxide occurs with the participation of chemisorbed oxygen. The steps of the mechanism are proposed.

Ethane aromatization on Ga-Pt/HZSM-5 zeolites prepared by solid-state modification

The results of a comparative study of the catalytic properties of gallium and platinum pentasil (ZSM-5) zeolites, prepared according to the solid-state modification and impregnation techniques, in the ethane aromatization reaction are reported. It has been found that the procedure for the preparation of bimetallic catalysts has no substantial effect on their activity and selectivity for aromatic hydrocarbons. The formation of the active sites of the catalysts obtained by solid-state modification was investigated with the use of X-ray diffraction and X-ray photoelectron spectroscopy, and it has been supposed that Ga-Pt clusters similar to the species revealed earlier in bimetallic pentasil catalysts prepared by impregnation are produced as a result of topochemical reactions involving hydrogen. Based on the catalytic and physicochemical data, a reaction scheme for the ethane aromatization on Ga-Pt/HZSM-5 is proposed, which suggests the involvement of bimetallic clusters in a key step, the dehydrogenation of ethane followed by the formation of ethylene oligomers and their dehydrocyclization.

Transient response studies of isobutane oxidative dehydrogenation over molybdenum catalysts

Kinetics and mechanism of isobutane oxidative dehydrogenation were studied over cobalt and nickel molybdate catalysts. The data obtained in nonstationary and stationary regimes showed that kinetics and mechanism are the same over both catalysts. Isobutene and carbon oxides are primary reaction products. Lattice oxygen takes part in dehydrogenation reactions. Carbon oxides formation proceed by the interaction with adsorbed oxygen. Cobalt molybdate is more active and selective catalyst for isobutane oxidative dehydrogenation. It was shown that nickel molybdate catalyst is stable only at high oxygen concentration while cobalt molybdate catalyst can work at lower oxygen concentrations.

Physicochemical study of catalysts for the oxidative dehydrogenation of isobutane: Cobalt, nickel, and manganese molybdates

Temperature-programmed desorption and IR spectroscopic studies of the physicochemical properties of cobalt, nickel, and manganese molybdates are reported. These properties are correlated with the catalytic properties of the molybdates in the oxidative dehydrogenation of isobutane with atmospheric oxygen. It is demonstrated by an analysis of the IR spectra of the molybdates that the isobutene yield grows as the proportion of tetrahedrally coordinated molybdenum in the catalyst structure increases in isobutane dehydrogenation. NiMoO4 has the highest surface concentration of strong acid sites, and it binds adsorbed isobutene more strongly than the other catalysts

Kinetics of the total oxidation of para-xylene and its mixtures with carbon monoxide over supported copper catalysts

The kinetics of the total oxidation of para-xylene and its mixtures with CO over alumina-supported copper catalysts has been investigated at atmospheric pressure in the temperature range from 200 to 270°C. The reactions over the catalysts 10%CuO/γ-Al2O3 and (10%CuO + 20%CeO2)/γ-Al2O3 obey the same kinetic equations in fractional rational form. These equations imply that the reactions occur at medium surface coverages of adsorbed substances and differ only in numerical values of constants. The simultaneous oxidation of para-xylene and CO reveals a complicated mutual influence associated with the formation of new intermediates inducing a change in the kinetics of the process.