Jerzy Słoczyński

The role of different MoO3 crystal faces in elementary steps of propene oxidation

Abstract Activity and selectivity of MoO 3 crystallites of different properties in the oxidation of allyl compounds were compared with those observed in the oxidation of propene in order to elucidate the role of different crystal faces in the elementary steps of oxidation. The yield of acrolein from allyl compounds was linearly dependent on the surface area of the basal (010) face, indicating that this face is responsible for insertion of oxygen into the activated hydrocarbon molecule. Product distribution from propene may be explained by assuming that its activation takes place at the side (100) and (101) faces, and the total oxidation at all faces.

Catalytic activity of V2O5−TiO2 systems in the oxidation of o-xylene

The catalytic activity of V−Ti−O catalysts in the oxidation of o-xylene was studied with the pulse method for samples of different V/Ti ratios. The selectivity to C8 products of oxidation changes with the V2O5 content, the maximum selectivity being observed at low V2O5 contents (2–10 mol%).AbstractКаталитическая активность катализаторов V−Ti−O при окислении o-ксилола была изучена импульсньм методом в случае различных отношений V/Ti. Селективность по отношению к продуктам окисления C8 изменяется с изменением содержания V2O5; максимальная селективность наблюдалась при низком содержании V2O5 (2–10 мол. %).

Kinetics of oxidative dehydrogenation of propane over V2O5/TiO2 catalyst

Application of the pseudo-homogenous and steady-state adsorption model (SSAM) was analyzed for the description of the oxidative dehydrogenation (ODH) of propane over vanadia-titania catalyst, using an extensive set of the experimental data. It has been shown that the SSAM model adequately describes the kinetics of the studied reaction for a broad range of feed mixture, propane conversion and temperature. The pseudo-homogenous models must be consider as a rough approximation of the experimental results. It is possible to solve analytically the set of differential equations describing the SSAM model and to present the selectivities to propene and to the products of total oxidation (CO, CO2) as a function of the propane conversion and the temperature. Numerical methods (the Runge–Kutta method combined with the Levenberg–Marquardt method) were applied to solve the systems of differential equations which describe the kinetic of the ODH of propane as a function of contact time and to fit the solutions to the experimental data. The calculations allowed us to determine the rate constants (activation energies and pre-exponential factors) for all reaction steps considered.

The Co-Mo-Te-O Oxide System for Oxidation of Hydrocarbons - A Review

Abstract The following article is a review of work published in recent years on the Co-Mo-Te-O oxide system for oxidation of olefins. The catalytic activity in hydrocarbon oxidation reactions and some physicochemical properties of various compounds present in this system are reviewed, with particular attention being paid to cobalt molybdate and newly discovered cobalt telluromolybdates. The mechanism of propene oxidation on the system is discussed in terms of current views on selective oxidation processes. The role of cobalt molybdate in multicomponent molybdate catalysts(MCM) is also considered.

Oxygen adsorption and catalytic performance in oxidative dehydrogenation of isobutane on chromium oxide-based catalysts

Oxygen adsorption on γ-Al2O3-, TiO2 (anatase)-supported chromium oxide and on unsupported chromia in amorphic and crystalline form, has been studied with a gravimetric method in the temperature range 523–623 K. The equilibrium oxygen uptake at p→∞ was the same for all the studied catalysts, the rate of the adsorption was, however, different, increasing in the order: CrOx/Al2O3<CrOx/TiO2<Cr2O3 amorph.<Cr2O3 cryst. Measurements of oxidative dehyrogenation of isobutane on the catalysts given above have shown that the selectivity to isobutene decreases in the same sequence. The higher selectivity values and the change in the rate constant of the isobutane oxidative dehydrogenation with conversion, observed for the Al2O3- and TiO2-supported chromium oxide catalysts, have been ascribed to the lower coverage of the surface of the catalyst with oxygen in the stationary state of the isobutane oxidative dehydrogenation, as compared with unsupported chromia.

CoTeMoO6, Co4TeMo3O16: Two new cobalt molybdotellurates

Abstract It has been found that a solid-state reaction of CoMoO 4 with TeO 2 at 500°C yields a new compound of the formula CoTeMoO 6 . This compound is also formed in the course of annealing of CoMoO 4 H 6 TeO 6 mixtures. Another new compound, the cobalt molybdotellurate containing Te 6+ , was prepared by a solid-state reaction of Co 5 TeO 8 with MoO 3 . It has the formula Co 4 TeMo 3 O 16 . Both CoTeMoO 6 and Co 4 TeMo 3 O 16 have been characterized by X-ray method. The latter has the structure of a wolframite type with the unit cell dimensions a = 4.66, b = 5.67, c = 4.96 A, β ⋍ 90°.

Oxidation of propene over silica supported MoO3-CoO, MoO3-NiOand MoO3-MnO catalysts

Abstract The Raman spectra of MoO 3 -MeO/SiO 2 catalysts (Me = Co, Ni, Mn) revealed the presence of molybdate phases and the EPR spectra indicated changes in the oxidation state of molybdenum occurring on interaction with reaction mixtures containing various C 3 H 6 /O 2 ratios. Co and Ni enhanced the reducibility of the catalysts while Mn had practically no influence on the rate of catalyst reduction. It has been found that the concentration of Mo(V) influences the propene conversion and selectivity to acetaldehyde, as well as the total oxidation and coke deposition or ethene formation on the catalyst surface. On the other hand, selectivity to acrolein depends on the Mo(VI) concentration. The catalytic results were discussed in terms of the nucleophilic and electrophilic character of the oxygen species and the stability of the surface intermediates.

IR-spectroscopic studies of the interaction of propylene and acrolein with a CoMoO4 catalyst

IR spectra of propylene and acrolein adsorbed at different temperatures on CoMoO4 supported on MgO were recorded. Four different surface species were found: a π-complex, an oxygen bonded carbonyl complex, acrylic acid and a carboxylate type complex. The mechanism of their transoformation is discussed.AbstractБыли регистрированны ИК-спектры пропилена и акролеина адсорбированных при различных температурах на CoMoO4 нанесенном на MgO. Спектры указывают, что на поверхности катализатора образуются 4 различные комплексы: π-комплекс, карбонильный комплекс, связанный с поверхностью через атом кислорода, акриловая ислота и карбоксилатный комплекс. Рассмативается механизм взаимых превращений этих комплексов.

Influence of gas phase on the polymorphic transformations in CoMoO4

Abstract Polymorphic transformation b-CoMoO4 → a-CoMoO4 at 400°C was studied in the high-temperature X-ray camera in nitrogen, propylene, and hydrogen. It was found that the transformation is inhibited in the reducing atmosphere due to the interaction of the reducing agent from the gas phase with crystal nuclei of the new phase. Being very reactive, they are rapidly reduced, their elimination from the surface of crystallites inhibiting the transformation.

Kinetics and mechanism of synthesis of cobalt telluromolybdate Co4TeMo3O16

Abstract The kinetics of synthesis of cobalt telluromolybdate, proceeding according to the equation, Co 5 TeO 8 + 4MoO 3 = Co 4 TeMo 3 O 16 + CoMoO 4 , have been studied in the temperature range from 500 to 650°C. Reaction products were identified by X-ray diffraction, optical microscopy, and X-ray microanalysis. It has been observed that the reaction products form compact, distinctly separated layers on the surface of cobalt tellurate grains. Transport of MoO 3 takes place by sublimation of this oxide, which is the rate-determining step of the reaction.