Selective Oxidation Of Propane Research Articles

Multifunctionality of Crystalline MoV(TeNb) M1 Oxide Catalysts in Selective Oxidation of Propane and Benzyl Alcohol

Propane oxidation at 653–673 K and benzyl alcohol oxidation at 393 K over phase-pure MoV(TeNb) M1 oxide catalysts were studied to gain insight into the multiple catalytic functions of the surface of the M1 structure. Electron microscopy and X-ray diffraction confirmed the phase purity of the M1 catalysts. Propane oxidation yields acrylic acid via propene as intermediate, while benzyl alcohol oxidation gives benzaldehyde, benzoic acid, benzyl benzoate, and toluene. The consumption rates of benzyl alcohol and propane level in the same range despite huge difference in reaction temperature, suggesting high activity of M1 for alcohol oxidation. Metal–oxygen sites on the M1 surface are responsible for the conversion of the two reactants. However, different types of active sites and reaction mechanisms may be involved. Omitting Te and Nb from the M1 framework eliminates acrylic acid selectivity in propane oxidation, while the product distribution in benzyl alcohol oxidation remains unchanged. The results suggest...

Catalytic Effect of Configuration Structures of Transition Metal Ions in Catalysts with Highly Dispersed and Isolated Active Sites on the Selective Oxidation of Propane

The catalytic performances of the potassium-modified silica-supported catalysts with highly dispersed and isolated active sites containing a tiny amount of transition metal oxide(i.e.,K-M/SiO2(n(K)∶ n(M)∶n(Si)=10∶ 1∶ 1000);M=V,Cr,Mn,Fe,Co,Ni,Cu,Zn) for the selective oxidation of propane were evaluated.The structures and physico-chemical properties of these catalysts were characterized by means of UV-Raman,CO2-TPD.The relationships among the catalytic performances of this series of catalysts for the selective oxidation of propane and their configuration structures of the transition metal cations were studied.The results indicate that the configuration structures of transition metal cations have large effect on the catalytic performances of the catalysts for the selective oxidation of propane.The stable cation structures with d-orbitals,which are fully occupied or empty,are good for the selective oxygenation of propane.But the cations,which have the relatively unstable d-electron structures with mixed valences,are good for the deep oxidation of propane.This relation between the cation structures of highly dispersed and isolated active sites of the catalysts and their catalytic performances is very similar to that found in the selective oxidation of ethane,which further demonstrates that the configuration structures of transition metal cations in the catalysts with highly dispersed and isolated active sites is the most important controlling factor to affect the catalytic performances of this kind of catalysts for the selective oxidation of low alkanes.

Au–metal oxide support interface as catalytic active sites

The importance of the exposed interface between Au and the support metal oxide has been suggested in the literature. Here we summarize evidence that provide strong support as well as conflicting evidence for this type of active sites and the potential reaction mechanism that takes place. Evidence from three reactions are summarized: CO oxidation, water gas shift (WGS) reaction, and selective oxidation of propane. Implications for potential future research and ability to truly design selective catalysts are discussed.

CuAu/SiO2 catalysts for the selective oxidation of propene to acrolein: the impact of catalyst preparation variables on material structure and catalytic performance

CuAu/SiO2 catalysts are active and selective for the synthesis of acrolein from propene by selective oxidation using a mixture of H2 and O2 as oxidant. The catalyst synthesis method (impregnation or deposition) and the activation procedure (reduction, calcination or reduction followed by calcination and the choice of reducing agent) all affect the structure of the catalyst and therefore the performance in catalysis. For a material prepared by coimpregnation of HAuCl4 and Cu(NO3)2, reduction with hydrogen leads to a catalyst with a significant level of CuAu alloy, whilst reduction with NaBH4 solution leads to small particles but with negligible interaction between copper and gold. Subsequent high temperature calcination of these materials destroys any CuAu phase but retains a Cu–Au interaction as observed by Transmission Electron Microscopy. Preparation of the catalyst by a two-step deposition method gives smaller particles than coimpregnation when reduced by H2 but a different alloy phase is observed by EXAFS. Calcination of this material gives a catalyst which combines high activity with excellent selectivity to acrolein. Characterisation of the materials using various techniques allows the nature of the active sites to be understood.

Monitoring Silica Supported Molybdenum Oxide Catalysts at Work: A Raman Spectroscopic Study

The structure of silica SBA-15-supported molybdenum oxide catalysts is investigated during selective oxidation of propylene at 500 °C using operando Raman spectroscopy. The active catalysts contain mixtures of dispersed molybdenum oxide species exhibiting monooxo and dioxo structure. An increase in molybdenum oxide loading results in a decrease of the ratio of dioxo and monooxo species from 3.8 to 1.9, as determined by quantitative analysis of Raman spectra. Additional in situ Raman studies at 500 °C reveal that the dioxo/monooxo ratio increases in the presence of steam at higher molybdenum oxide loadings. The observed structural changes are assigned to shifts in the equilibrium between dioxo and monooxo species resulting from hydration/dehydration of the catalyst. This study demonstrates that the detailed structure of nanostructured molybdenum oxide catalysts depends on temperature, gas-phase composition, and molybdenum oxide loading.

Reaction path analysis of propene selective oxidation over V2O5 and V2O5/TiO2

The selective oxidation of propene on the vanadyl and bridging oxygen sites of the fully oxidized (001) V2O5 surface and of an epitaxial vanadia monolayer supported on (001) TiO2 anatase is analyzed using periodic density functional theory (DFT). The formation of several oxygenated products, that is, allyl alcohol, propene oxide, acrolein, formaldehyde and acetaldehyde, is investigated. Selective oxidation proceeds via a Mars–van Krevelen redox mechanism and its elementary steps on the vanadia surface are identified. Propene activation occurs preferentially on the vanadyl oxygen sites, with allyl CH and CC bond activation being equally favorable. Supporting a vanadia monolayer on titania strongly enhances both bond activations as compared to unsupported V2O5, yielding a lower activation energy. No dominant pathway is found on V2O5, with allyl alcohol, propene oxide, and acrolein formation being almost equally favorable, while acrolein formation is expected on V2O5/TiO2. However, propene oxidation to acrolein is overall less preferable on V2O5/TiO2 than V2O5, due to the reduced activity of the supported catalyst in oxygenation reactions. The latter is linked to the creation of V3+ sites during propene oxidation over V2O5/TiO2. On the other hand, the electrons injected in the empty V 3d states during propene oxidation over V2O5 lead to the creation of V4+ sites.

Preparation of (Mo, V) Oxide Nitrides with Mo5O14 Structure as Model Catalysts for Selective Propene Oxidation

Preparation of (Mo, V) Oxide Nitrides with Mo₅O₁₄ Structure as Model Catalysts for Selective Propene Oxidation

KINETIC INVESTIGATION OF CARBON DIOXIDE, ACETIC ACID, ACRYLIC ACID FORMATION ON DILUTED AND LEACHED MoVTeNb CATALYST

Reaction kinetics for the oxidation of propane over diluted-leached MoVTeNb is described. This paper is focused on the study of determination of the orders of carbon dioxide, acetic acid and acrylic acid formation. Deep oxidation of propane to carbon dioxide is first order with respect to hydrocarbon, and partial order (0.31) with respect to oxygen. The selective oxidation of propane to acrylic acid is partial order (0.49) with respect to hydrocarbon and partial order (0.09) with respect to oxygen.

KINETIC INVESTIGATION OF CARBON DIOXIDE, ACETIC ACID, ACRYLIC ACID FORMATION ON DILUTED AND LEACHED MoVTeNb CATALYST

Reaction kinetics for the oxidation of propane over diluted-leached MoVTeNb is described. This paper is focused on the study of determination of the orders of carbon dioxide, acetic acid and acrylic acid formation. Deep oxidation of propane to carbon dioxide is first order with respect to hydrocarbon, and partial order (0.31) with respect to oxygen. The selective oxidation of propane to acrylic acid is partial order (0.49) with respect to hydrocarbon and partial order (0.09) with respect to oxygen.

The influence of over-stoichiometry in La2Ni0.9V0.1O4.15+δ on selective oxidative dehydrogenation of propane

In this study, the non-stoichiometric redox compound La2Ni0.9V0.1O4.15+δ has been tested as an oxidant in selective oxidation of propane. The extent of over-stoichiometry (δ) was varied via both removing oxygen with propane in pulse experiments, as well as partial re-oxidation with oxygen. The optimal degree of over-stoichiometry (δ) has been quantified; olefins are formed whereas formation of CO2 is prevented provided that δ is below 0.03. Additionally, the structural stability of the material was tested with in situ X-ray diffraction in H2 (H2-XRD), temperature programmed reduction (TPR), thermo-gravimetric analysis (TGA), propane-pulse-experiments and re-oxidation cycles. La2Ni0.9V0.1O4.15+δ has demonstrated structure stability at 550°C and reversibility during oxidation–reduction cycles at 800°C. Therefore, La2Ni0.9V0.1O4.15+δ is considered suitable for selective oxidative dehydrogenation of propane, provided that the degree of over-stoichiometry is limited to 0.03.

Elaboration, characterization and properties of silica-based single-site heterogeneous photocatalysts

This study concerns single-site heterogeneous photocatalysts, composed of isolated transition metals ions (single-sites) dispersed on silica-based supports, which can be used as photocatalysts. The first part gives the definition of single-site heterogeneous catalysts. The main difficulty to prepare the latter resides in the speciation of the key elements (metal of the catalytically active phase and oxygen of the solid support) and other species (notably counter ions and ligands) the presence of which depends on the synthesis method adopted. The best preparation methods as well as the ideal features of single-site heterogeneous photocatalysts are discussed before the study focuses on single-site heterogeneous photocatalysts. Case studies are presented with photocatalysts involving titanium and chromium, and their photocatalytic reactions such as CO 2 reduction with H 2 O, degradation of organic pollutants diluted in water, NO decomposition and selective oxidation of propane are also described.

Reaction path analysis of propane selective oxidation over V2O5 and V2O5/TiO2

The selective oxidation of propane on the vanadyl and bridging oxygen sites of the fully oxidized (001) V2O5 surface and of an epitaxial vanadia monolayer supported on (001) TiO2 anatase is analysed using periodic density functional theory (DFT). Both the oxidative dehydrogenation leading to propene and the formation of oxygenated products, namely n-propanol, i-propanol, propanal and acetone, are investigated. Selective oxidation proceeds via a Mars–van Krevelen redox mechanism, and its elementary steps on the vanadia surface are identified. Propane chemisorption preferentially occurs through a secondary CH bond activation via a direct hydrogen abstraction by a lattice oxygen. Supporting a vanadia monolayer on titania strongly enhances the CH bond activation as compared to unsupported V2O5, yielding a lower activation energy and a more exothermic propane chemisorption. In accordance with experimental observations, the calculations show that the titania support not only modifies the activity of the vanadia monolayer but it also affects the selectivity of the catalyst, favouring the formation of propene compared to the formation of i-propanol and acetone. The vanadyl oxygen is overall the most active site on V2O5 and V2O5/TiO2, while the bridging oxygen is more selective towards propane dehydrogenation.

Metal nanoparticle catalysts decorated with metal oxide clusters

Au nanoparticles decorated with mononuclear Ti-oxo units dispersed in silica clusters were formed by activating Au nanoparticles (~2 nm) stabilized with Ti- and amine-functionalized siloxane oligomers. These Au nanoparticles were active catalysts for selective oxidation of propane to acetone, and the activity increased with increasing Ti density.

In-situ X-ray diffraction study of phase crystallization from an amorphous MoVTeNb oxide catalyst precursor

Abstract The formation of the crystalline phases M2, M1, orthorhombic MoO 3 , and a tetragonal M 5 O 14 (M = Mo,V,Nb) type phase during heat treatment of an amorphous Mo-V-Te-Nb oxide precursor in helium is investigated applying in - situ X-ray diffraction. The precursor was synthesized by precipitation, spray-drying and subsequent calcination of the dried orange powder in air at 275 °C. Crystallization of M2 starts at 450 °C, and it occurs simultaneously with the initial liberation of tellurium. Concurrent formation of M1, M 5 O 14 , and MoO 3 at temperatures higher than 550 °C suggests that structural building blocks consumed during crystallization are competitively supplied from a common amorphous precursor. The results indicate that the availability of tellurium could play a decisive role with respect to phase distribution in the final catalyst providing one possible explanation for the susceptible response of the phase composition of Mo-V-Te-Nb oxide catalysts for selective oxidation of propane to acrylic acid on the experimental conditions of thermal activation.

Synergy effects in mixed Bi2O3, MoO3 and V2O5 catalysts for selective oxidation of propylene

In this work, the possible synergy effects between Bi2O3, MoO3 and V2O5, and between Bi2Mo3O12 and BiVO4, were investigated. The catalytic activity of the “mechanical mixture” of these compounds was measured. The mixture containing 36.96 mol% Bi2O3, 39.13 mol% MoO3 and 23.91 mol% V2O5 (21.43 mol% Bi2Mo3O12 and 78.57 mol% BiVO4), corresponding to the compound Bi1−x/3V1−xMoxO4 with x = 0.45 (Bi0.85V0.55Mo0.45O4), exhibited the highest activity for the selective oxidation of propylene to acrolein. The mixed sample prepared chemically by a sol–gel method possessed higher activity than that of mechanical mixtures.

Surface chemistry of phase-pure M1 MoVTeNb oxide during operation in selective oxidation of propane to acrylic acid

The surface of a highly crystalline MoVTeNb oxide catalyst for selective oxidation of propane to acrylic acid composed of the M1 phase has been studied by infrared spectroscopy, microcalorimetry, and in situ photoelectron spectroscopy. The acid–base properties of the catalyst have been probed by NH3 adsorption showing mainly Brønsted acidity that is weak with respect to concentration and strength of sites. Adsorption of propane on the activated catalyst reveals the presence of a high number of energetically homogeneous propane adsorption sites, which is evidenced by constant differential heat of propane adsorption qdiff,initial=57kJmol−1 until the monolayer coverage is reached that corresponds to a surface density of approximately 3 propane molecules per nm2 at 313K. The decrease of the heat to qdiff,initial=40kJmol−1 after catalysis implies that the surface is restructured under reaction conditions. The changes have been analyzed with high-pressure in situ XPS while the catalyst was working applying reaction temperatures between 323 and 693K, different feed compositions containing 0mol.% and 40mol.% steam and prolonged reaction times. The catalytic performance during the XPS experiments measured by mass spectrometry is in good agreement with studies in fixed-bed reactors at atmospheric pressure demonstrating that the XPS results taken under operation show the relevant active surface state. The experiments confirm that the surface composition of the M1 phase differs significantly from the bulk implying that the catalytically active sites are no part of the M1 crystal structure and occur on all terminating planes. Acrylic acid formation correlates with surface depletion in Mo6+ and enrichment in V5+ sites. In the presence of steam in the feed, the active ensemble for acrylic acid formation appears to consist of V5+ oxo-species in close vicinity to Te4+ sites in a Te/V ratio of 1.4. The active sites are formed under propane oxidation conditions and are embedded in a thin layer enriched in V, Te, and Nb on the surface of the structural stable self-supporting M1 phase.

Synthesis of MoVTeNb Oxide Catalysts with Tunable Particle Dimensions

AbstractReliable procedures for the controlled synthesis of phase‐pure MoVTeNb mixed oxides with M1 structure (ICSD 55097) and tunable crystal dimensions were developed to study the structure sensitivity of the selective oxidation of propane to acrylic acid. A series of powdered M1 catalysts was successfully prepared on a gram scale by using a hydrothermal‐based route, purification of biphasic M1‐M2 (M2 phase – ICSD 55098) oxide systems, and an innovative approach utilizing a superheated water vapor treatment of calcined precursors. The influence of the preparation technique on the particle morphology and the size is discussed. Detailed experimental studies highlight that the as‐derived catalytic materials were indeed phase‐pure and compositionally uniform MoVTeNb oxide M1 powders, composed of single‐crystalline and structural defect‐free crystals grown along the c axis. The morphologically different catalysts were studied in the selective oxidation of propane to acrylic acid, revealing that active sites appear on the entire M1 surface and illustrating the high sensitivity of catalyst performance on the catalyst synthesis method.

Model Catalysts for the Selective Oxidation of Propene Probed by Fast Redox Cycling

AbstractZyklische temperaturprogrammierte Reduktions‐ und Reoxidationsexperimente können dem Mars‐van‐Krevelen‐Oxidationsmechanismus entsprechen, sofern als Reduktionsmittel ein Kohlenwasserstoff eingesetzt wird. Damit ermöglichen diese Redoxzyklen die schnelle Analyse der Aktivität und Selektivität von Multikomponenten‐Mischoxid‐Katalysatoren für die selektive Oxidation von Kohlenwasserstoffen wie Propen oder Buten. Mittels dieser Technik wurde quantitativ zwischen redoxaktiven Bismutmolybdaten und inaktiven Bismutwolframaten (Bi2MxO3x+3, M = Mo, W) unterschieden, die als Komponenten von technischen Katalysatoren für die Selektivoxidation von Propen zu Acrolein fungieren. Die Trägerphase Fe3Co7Mo12O46 wies aufgrund ihrer relativ hohen Oberfläche nur eine geringe spezifische Reduzierbarkeit auf.

Structural changes occurring at the surface of alumina-supported nanoscaled Mo–V–Nb–(Te)–O catalytic system during the selective oxidation of propane to acrylic acid

The effect of total coverage on alumina is evaluated for Mo 5V 4Nb 1/Al 2O 3 catalysts by operando Raman-GC spectroscopy during reaction, demonstrating structural changes during reaction that do not occur during catalyst calcination. XRD detects show no appreciable change but Operando Raman-GC studies are sensitive to changes occurring in the nanometer scale, which modulate the performance during propane oxidation, delivering the structure–activity relationship for deactivation. Raman spectra confirm the formation of nanocrystalline MoO 3-type structures during reaction up to 375 °C, accompanied by coke deposits, able to block the active sites, being detrimental for the acrylic acid formation. Three new catalysts were preparing by the addition of tellurium as dopant, in this case, the presence of MoO 3 is not detected under reaction conditions, since the formation of a distorted rutile structure under reaction conditions is observed, and in this case acrylic acid is obtained as the main reaction product with a yield of ca. 25% at 400 °C.

Crystalline structure of mixed metal oxide catalysts for propane selective oxidation to acrylic acid

The effects of the preparation procedure on the formation of crystal phases and catalytic performance of the MoVTeNbO mixed metal oxide catalysts in selective oxidation of propane to acrylic acid were investigated. The results show that the preferred drying method is the rotavapor method, which favors the formation of an effective crystal phase and suppresses the formation of impurity phases. The preferred calcination atmosphere is an Ar atmosphere. The MoVTeNb mixed metal oxide catalysts can be obtained by solution method after heat-treatment at 600°C in an Ar atmosphere, via a rotavapor with a warm water bath at 60°C, and a pH value of 4.0. The catalyst with a MoVTeNb molar ratio of 1.0:0.3:0.23:0.12 is the most effective and extremely active.