Luis E. Cadús

Selective oxidation of propane on MgO/γ‐Al2O3‐supported molybdenum catalyst: influence of promoters

The influence of promoters, potassium and samarium, on molybdenum supported over MgO–γ‐Al2O3 catalyst has been investigated in the oxidative dehydrogenation of propane. The acidities of catalysts were determined by temperature‐programmed desorption of NH3 and by decomposition of 2‐propanol. The K‐promoted catalyst showed the lower acidity followed by the Sm, whereas the unpromoted sample showed the highest acidity. The higher the acid character of the catalyst, the lower the selectivity to propene. Redox properties determined from EPR spectra change with the addition of the promoter. A parallelism between Mo6+ reducibility and catalytic activity was found.

Synergy effects in the oxidative dehydrogenation of propane over MgMoO4-MoO3 catalysts

Oxidative dehydrogenation of propane was studied over MgMoO4-MoO3 catalysts with a wt% of MoO3 varying from 0 to 100. The samples were characterized by XRD, EPR, DTA, laser Raman, and BET. The catalytic behavior of the mechanical mixtures was quite different from that of pure phases. These differences were discussed in terms of possible synergy effects between the phases. Propane conversion and selectivity to propene were closely related to the change in redox properties of the catalysts due to the appearance of Mo5+ ions.

XPS studies for vanadium pentoxide along the catalytic bed: oxidative dehydrogenation of propane

Abstract In this work, the effect of reaction conditions of oxidative dehydrogenation of propane on V 2 O 5 reducibility along the catalytic bed was studied. Extreme conditions of catalytic test (high temperature, P O 2 / P C 3 H 8 ratio =1) have been used. After the catalytic test, V 2 O 5 original orange color changed along the catalytic bed. Thus, three portions differentiated by their color were picked up separately and analyzed by XRD and XPS. The reduction of V 2 O 5 –V 2 O 3 along the catalytic bed was observed by XRD; while surface reduction from V 5+ to V 3+ was also detected by XPS. Assuming that V 5+ –V 4+ redox couple plays a key role in oxidative dehydrogenation reactions, it is concluded that the choice of reaction conditions is very important in order to avoid an excessive reduction of vanadium ions and obviously, to analyze the results properly.

Structure and activity of Sn-Mo-O catalysts: partial oxidation of methanol

This work deals with the catalytic behavior of a series of Sn-Mo-O catalysts in the partial oxidation of methanol. The catalysts of different Sn:Mo ratios, were prepared by co-precipitation and they were investigated by means of dynamic experiments, test reactions (methanol–formaldehyde partial oxidation, isopropyl alcohol decomposition) and physico-chemical characterization (XRD, BET, TPD of NH3, TPR, XPS and EPR). It was observed that interdispersion between MoO3 and SnO2 favors a superficial architecture in which the Sn-Mo interaction plays a major role modifying the reactivity of the lattice oxygens and the reducibility of Mo ions and, therefore, the catalytic behavior. The partial oxidation of methanol induces a reordering of the catalyst structural organization leading to a Mo surface enrichment. The absence of chemical shifts for Sn (XPS) suggests that the O–Mo bond is mainly responsible for the methanol reaction.

Vanadium species: Sm-V-O catalytic system for oxidative dehydrogenation of propane

Abstract This work deals with the catalytic behavior of SmVO 4 impregnated with vanadium in the oxidative dehydrogenation of propane. SmVO 4 prepared by the citrate method was impregnated using NH 4 VO 3 as precursor of vanadium species. The vanadium contents have been selected to obtain surface coverages as follows: (a) below the theoretical monolayer; (b) slightly above the theoretical monolayer; and (c) equivalent to the double of the theoretical monolayer. Catalysts were investigated by several physicochemical characterization techniques, i.e. BET specific surface area (SSA), X-ray diffraction (XRD), temperature programmed reduction (TPR), Fourier transform infrared spectroscopy (FT-IR), laser Raman spectroscopy (LRS), and electron paramagnetic resonance (EPR). A slight excess of samarium on SmVO 4 was found and it was responsible for the direct combustion of propane. Part of the vanadium added by impregnation reacted with the excess of samarium towards to the formation of SmVO 4 . Then on the impregnated catalysts, the direct combustion of propane was controlled and higher selectivity to propene at low conversion levels was obtained. At vanadium loading below the theoretical monolayer, surface VO x species were formed. They were easily reducible and the bridging oxygen atoms (VOV) would increase the catalytic activity at low reaction temperature. At vanadium loading above the theoretical monolayer, the appearance of V 2 O 5 crystals was favored. The terminal oxygen atoms (VO) existing in V 2 O 5 cause the consecutive combustion of propene. From the Raman and EPR results on the catalysts before and after the catalytic test, the effect of the reaction on the surface definition of the catalysts can be inferred.

Catalytic Combustion of n-Hexane Over Alumina Supported Mn–Cu–Ce Catalysts

Supported MnCuCe and MnCe mixed oxides catalysts were prepared and evaluated in n-hexane combustion reaction. They presented an excellent catalytic activity in total combustion of n-hexane. Catalysts were characterized by means of XRD, XPS, SBET and TPR techniques. The addition of Cu did not enhance the catalytic activity of MnOx/Al2O3 due to the formation of the complete Mn2CuO4 spinel. The presence of cerium favored the formation of manganese oxide species with low crystallinity, with high oxygen mobility and high oxygen vacancies. A higher content of Ce was necessary to obtain catalysts with higher oxidation state of Mn and Ce species.Graphical Abstract

Evaluation and characterization of Sm-V-O catalytic system for propane oxydehydrogenation: Sm2O3-impregnated V2O5 catalysts

Abstract Sm-V-O based catalysts were prepared by impregnating V2O5 with different amounts of Sm2O3. These catalysts and the pure phases of reference (V2O5, Sm2O3, and SmVO4) were characterized by specific surface area measurements by the BET method, X-ray diffraction (XRD), temperature programmed reduction (TPR), laser Raman spectroscopy (LRS), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), and adsorption–desorption of CO2. Its catalytic performance was compared by using propane oxidative dehydrogenation reaction. The results of physico-chemical characterization indicated that the system evolves to SmVO4 formation by a reaction in the solid state, producing segregation of this new phase. However, due to the fact that the surface tends to become rich in vanadium, mainly in the V2O5 form, the catalytic behavior of V2O5 impregnated with Sm2O3 is not significantly different from that presented by the pure phase. This surface architecture would be achieved because V2O5 can easily migrate on the surface of other oxides when heated at high temperature. But, in the presence of the reaction atmosphere (propane/oxygen mixture), its migration would occur at lower temperatures.

Preparation and characterization of MgO-γ Al2O3 composite oxides

Abstract Studies of the chemical preparation, surface area, pore distribution, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectra (XPS) and acid-base properties of magnesia–alumina composite oxides were carried out. The preparation method led to supports with high surface areas where Mg was homogeneously distributed upon the surface. The base properties of the composite oxides can be controlled by the Mg loading for an optimum catalyst performance.

Synergy in the SnMoO catalysts: The selective oxidation of methanol

Abstract This work deals with the performance of mechanical mixtures of SnO 2 and MoO 3 (prepared separately) in the selective oxidation of methanol. Synergetic cooperations occur between these phases in the oxidation of methanol. The catalysts are investigated by different techniques (XRD, XPS, SSA, DTA, Redox cycles and EPR) in order to explain the catalytic behavior. Catalytic activities of artificially contaminated phases by impregnation are also measured. Methanol conversion and selectivity to methyl formiate are closely related to the increase in the redox capacity of the catalyst and to the appearance of Mo 5+ ions. The synergy in the catalytic activity might be accounted by the creation of new active sites.

Highly effective molybdena–manganese catalyst for propane oxidative dehydrogenation

A manganese oxide catalyst impregnated with molybdenum exhibits high yield, productivity and stability in the oxidative dehydrogenation of propane to propene. This catalyst exhibits catalytic activity and yield to propene at temperatures as low as 623 K.