Selective Oxidation of n-Butane and Butenes over Vanadium-Containing Catalysts

Abstract The oxidative dehydrogenation (OXDH) of n-butane, 1-butene, and trans-2-butene on different vanadia catalysts has been compared. MgO, alumina, and Mg–Al mixed oxides with Mg/(Al+Mg) ratios of 0.25 and 0.75 were used as supports. The catalytic data indicate that the higher the acid character of catalysts the lower is both the selectivity to C4-olefins from n-butane and the selectivity to butadiene from both 1-butene or trans-2-butene. Thus, OXDH reactions are mainly observed from n-butane and butenes on basic catalysts. The different catalytic performance of both types of catalysts is a consequence of the isomerization of olefins on acid sites, which appears to be a competitive reac…

Insights into the catalytic production of hydrogen from propane in the presence of oxygen: Cooperative presence of vanadium and gold catalysts

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Selective oxidation of ethane: Developing an orthorhombic phase in Mo–V–X (X=Nb, Sb, Te) mixed oxides

Abstract Mo–V–X (X = Nb, Sb and/or Te) mixed oxides have been prepared by hydrothermal synthesis and heat-treated in N2 at 450 °C or 600 °C for 2 h. The calcination temperature and the presence or absence of Nb determines the nature of crystalline phases in the catalyst. Nb-containing catalysts heat-treated at 450 °C are mostly amorphous solids, while Nb-free catalysts heat-treated at 450 °C and samples treated at 600 °C clearly contain crystalline phases. TPR-H2 experiments show higher H2-consumption on catalysts with amorphous phases. Catalytic results in the oxidative dehydrogenation of ethane indicate that the selective production of the olefin is strongly related to the development of …

On the influence of the acid-base character of catalysts on the oxidative dehydrogenation of alkanes

Vanadium oxides supported on metal oxide, i.e. Al2O3, MgO and Mg-Al mixed oxide, and V-containing microporous materials (VAPO-5 and MgVAPO-5) have been tested in the oxidative dehydrogenation of C2-C4 alkanes. In all cases, tetrahedral vanadium species (isolated and/or associated) were mainly observed from51V-NMR and diffuse reflectance spectroscopies. The reducibility of V5+-species, determined from the onset-reduction temperature, decreases as follows: VOx/AL > VAPO-5 > MgVAPO-5 =VOx/MG > VOx/MG + AL. The acid character of catalysts, determined from the FTIR spectra of pyridine adsorbed, decreases as: MgVAPO-5 > VOx/AL > VAPO-5 > VOx/MG + AL > VOx/MG. A similar trend between V-reducibilit…

The effect of potassium on the selective oxidation ofn-butane and ethane over Al2O3-supported vanadia catalysts

The catalytic properties of undoped and K-doped (K/V atomic ratio of 0.5) Al2O3-supported vanadia catalysts (∼4.5 wt% of V2O5) for the oxidation ofn-butane and ethane were studied. Isolated tetrahedral V5+ species are mainly observed in both undoped and K-doped samples. The incorporation of potassium decreases both the reducibility of surface vanadium species and the number of surface acid sites. Potassium-free vanadium catalysts show a high selectivity during the oxidative dehydrogenation (ODH) of ethane but a low selectivity during the ODH ofn-butane. However, the presence of potassium on the vanadium catalysts strongly influences their catalytic properties, increasing the selectivity to …

SiO2-supported vanadium magnesium mixed oxides as selective catalysts for the oxydehydrogenation of short chain alkanes

Abstract Unsupported and SiO 2 -supported VMgO mixed oxides catalysts have been prepared, characterized and tested in the oxidation of propane, n -butane and propylene. Mg-vanadates are observed by XRD, IR and Raman spectroscopy in both pure and supported VMgO catalysts, although the effective Mg/V ratio, in the VMgO phases formed, depends on the silica content. Since SiO 2 reacts partially with MgO during the calcination step, forming Mg 2 SiO 4 , the effective Mg/V ratio depends on the silica content. In this sense, pyro -Mg 2 V 2 O 7 is mainly formed on supported catalysts with Mg/V atomic ratios lower than 4, while ortho -Mg 3 V 2 O 8 is observed on supported catalysts with Mg/V atomic …

Reaction products and pathways in the selective oxidation of C-2-C-4 alkanes on MoVTeNb mixed oxide catalysts

[EN] The catalytic properties of MoVTeNbO catalysts during the selective oxidation of short chain alkanes and olefins (C-2-C-4) have been comparatively studied The main reaction products have been ethylene from ethane acrylic acid from propane maim anhydride from n-butane and methacrolein from isobutane FTIR studies of the adsorption of the main reaction products i e olefins and aldehydes over MoVTeNbO catalyst has been carried out Accordingly the reaction pathway is explained on the basis of the characteristics of the alkane fed the stability and reactivity of both the intermediates and the reaction products and the nature of the catalytic sites involved in each reaction (C) 2010 Elsevier …

Selective oxidation of propane and ethane on diluted Mo–V–Nb–Te mixed-oxide catalysts

Abstract Te-free and Te-containing Mo–V–Nb mixed oxide catalysts were diluted with several metal oxides (SiO 2 , γ -Al 2 O 3 , α -Al 2 O 3 , Nb 2 O 5 , or ZrO 2 ), characterized, and tested in the oxidation of ethane and propane. Bulk and diluted Mo–V–Nb–Te catalysts exhibited high selectivity to ethylene (up to 96%) at ethane conversions 10 % , whereas the corresponding Te-free catalysts exhibited lower selectivity to ethylene. The selectivity to ethylene decreased with the ethane conversion, with this effect depending strongly on the diluter and the catalyst composition. For propane oxidation, the presence of diluter exerted a negative effect on catalytic performance (decreasing the forma…

Oxidative dehydrogenation of ethane on Te-containing MoVNbO catalysts

Abstract Ethylene has selectively been obtained during the oxidative dehydrogenation of ethane on a Mo–V–Te–Nb–O mixed oxide catalyst. The catalyst was prepared hydrothermally and heat-treated at 600 °C for 2 h in a N2-stream. For comparison, undoped and Te-doped Mo–V–Nb–O catalysts and Mo–V–Te–O and Mo–Te–Nb–O mixed oxides have also been prepared. The catalytic performance of the Mo–V–Nb–Te–O mixed oxide catalyst cannot be explained by the incorporation of Te on the surface of a Mo–V–Nb–O mixed oxide but by the presence of an orthorhombic Te2M20O57 (M=Mo, V, Nb) crystalline phase. The role of tellurium in these catalysts is also discussed.

Selective oxidative dehydrogenation of ethane over MoVSbO mixed oxide catalysts

Abstract Mo–V–Sb–O mixed metal oxides were prepared, characterized and tested for the oxidative dehydrogenation of ethane (ODH). These catalysts are active and selective in the oxidative dehydrogenation of ethane to ethylene, although their catalytic performance depends strongly on the calcination temperature. The best catalytic results were obtained on samples heat-treated at 600 °C in N 2 (with selectivities to ethylene higher than 80% at ethane conversions about 65%). Moreover, a loss in the catalyst activity is initially observed on these catalysts as a consequence of modifications in the nature of the crystalline phases. Changes on the oxidation state of antimony ions on the surface of…

Oxidative dehydrogenation of n-butane on MgO-supported vanadium oxide catalysts

Abstract Vanadium–magnesium oxide (VMgO) catalysts have been prepared, characterized and tested in the ODH of n-butane. The catalysts were prepared by two variations of the wet-impregnation method using aqueous ammonium metavanadate or organically-based methanolic vanadyl acetylacetonate solutions. The catalyst surface area depends on the vanadium content and the preparation method. Catalyst characterization (i.e. XRD, 51V NMR, FTIR, LRS) results indicate the presence of poor crystalline Mg-orthovanadate (Mg3V2O8), while the presence of other Mg-vanadates is not clear. Oxygen isotopic-exchange experiments on VMgO catalysts indicate an R2 process: [ 18 O 2 +2 16 O 2− (s) → ( 18 O 18 O 16 O 1…

Selective oxidative dehydrogenation of ethane on MoVTeNbO mixed metal oxide catalysts

Abstract MoVTeNbO catalysts, prepared by hydrothermal synthesis, are active and highly selective in the ODH of ethane, especially those with a MoVTeNb molar ratio of 1–0.15–0.16–0.17 and heat-treated at 600–650 °C. On the best catalyst, selectivities higher than 80% at ethane conversion levels higher than 80% have been obtained operating at relatively low reaction temperatures (340–400 °C). Thus, yields of ethylene of ca. 75% have been obtained, which exceeds the best yield reported in the literature. Te 2 M 20 O 57 ( M =Mo, V, Nb) and (V,Nb)-substituted θ -Mo 5 O 14 , in addition to small amounts of the Te 0.33 M O 3.33 ( M =Mo, V, Nb) phase, can be proposed in the most selective cataly…

Porous clays heterostructures as supports of iron oxide for environmental catalysis

[EN] Porous Clays Heterostructures (PCH) from natural pillared clays (bentonite with a high proportion of montmorillonite) have been used as supports of iron oxide for two reactions of environmental interest: i) the elimination of toluene (a representative compound of one of the most toxic subsets of volatile organic compounds, aromatics) by total oxidation and ii) the selective oxidation of H2S to elemental sulfur. For both reactions these catalysts have resulted to be remarkably more efficient than similar catalysts prepared using conventional silica as a support. Thus, in the total oxidation of toluene it has been observed that the catalytic activity obtained using siliceous PCH is two o…

Preparation, characterization and catalytic properties of vanadium oxides supported on calcined Mg/Al-hydrotalcite

Abstract Vanadium oxide supported on calcined hydrotalcite has been investigated for the oxidehydrogenation of n-butane in the 500–550°C temperature interval. Hydrotalcite (Mg/Al atomic ratio of 2.77), consisting of a single phase only, has been employed as a support precursor. The vanadium catalysts (0–50, referred as wt.-% V 2 O 5 ) were prepared by impregnation of calcined hydrotalcite (450°C) with ammonium metavanadate (in an aqueous solution) or vanadyl acetylacetonate (in a methanolic solution), and then calcined at 600°C for 4 h. During the impregnation step, the support is transformed into hydrotalcite if aqueous solutions are used. However, it is not modified if methanolic solution…

The selective oxidative dehydrogenation of ethane over hydrothermally synthesised MoVTeNb catalysts

Mo–V–Te–Nb metal oxide catalysts prepared by hydrothermal synthesis and heat-treated in N2 at high temperatures (600–700 °C) show high activity and selectivity for the oxidative dehydrogenation of ethane to ethene. Yields of ethene of 75% have been obtained at 400 °C on the best catalysts. Dejoz Garcia, Ana Maria, Ana.M.Dejoz@uv.es

V-containing MCM-41 and MCM-48 catalysts for the selective oxidation of propane in gas phase

Well-organised V-containing MCM-41 and -48 (0.3‐1 wt.% of V content) have been synthesised by one-pot synthesis or by grafting using VOSO4 or VOCl3 as V sources, respectively. The samples before and after the calcination step have been characterised by several physicochemical techniques (Ar and N2 adsorption, XRD, diffuse reflectance-UV‐VIS (DR-UV‐VIS) spectroscopy, temperature-programmed reduction). It was found that V species in the as-prepared catalysts were mainly as vanadyl ions (VO 2C ), while highly dispersed V 5C species with tetrahedral coordination were observed in the calcined materials. The catalytic behaviour of the calcined materials for the gas phase oxidation of propane has …

Mo–V–Nb mixed oxides as catalysts in the selective oxidation of ethane

Abstract Mo–V–Nb–O mixed metal oxides, obtained by heat-treatment in N 2 at 425 °C, have been studied as catalysts in the oxidative dehydrogenation of ethane. They present higher catalytic activity, while maintaining the same selectivity to ethylene, than the corresponding metal oxides calcined under air. Both amorphous and crystalline phases are present on active and selective catalysts. The implications of the presence of these phases as well as their physicochemical characteristics on the nature of active and selective sites are discussed.

Corrigendum to “Selective oxidative dehydrogenation of ethane on MoVTeNbO mixed metal oxides catalysts” [J. Catal. 225 (2) (2004) 428–438]

The role of metal oxides as promoters of V2O5/γ-Al2O3 catalysts in the oxidative dehydrogenation of propane

Summary The physicochemical properties of potassium-, bismuth-, phosphorous- and molybdenum-doped (Me/V atomic ratios of 0 to 1) V 2 O 5 /γ-Al 2 O 3 catalysts and their catalytic behavior in the oxidative dehydrogenation of propane have been compared. The incorporation of metal oxides modifies the catalytic behavior of alumina-supported vanadia catalysts by changing both their redox and their acid-base properties. In this way, the addition of potassium leads to the best increase in the selectivity to propylene. This performance can be related to the modification of the acid character of the surface of the catalysts. The possible role of both redox and acid-base properties of catalysts on th…

The role of molybdenum in Mo-doped V–Mg–O catalysts during the oxidative dehydrogenation of n-butane

Abstract A detailed study on the influence of the addition of molybdenum ions on the catalytic behaviour of a selective vanadium–magnesium mixed oxide catalyst in the oxidation of n-butane has been performed. The catalysts have been prepared by impregnation of a calcined V–Mg–O mixed oxides (23.8 wt% of V2O5) with an aqueous solution of ammonium heptamolybdate, and then calcined, and further characterised by several physico-chemical techniques, i.e. SBET, XRD, FTIR, FT-Raman, XPS, H2-TPR. MgMoO4, in addition to Mg3V2O8 and MgO, have been detected in all the Mo-doped samples. The incorporation of molybdenum modifies not only the number of V5+-species on the catalyst surface and the reducibil…

Molybdenum–vanadium supported on mesoporous alumina catalysts for the oxidative dehydrogenation of ethane

Abstract Vanadium and/or molybdenum oxides supported on mesoporous alumina have been prepared by a “wet” impregnation method, characterized (by using several physico-chemical techniques TPR, DR-UV–vis, Raman spectroscopies) and tested in the oxidative dehydrogenation (ODH) of ethane. For comparison Mo–V-mixed oxides supported on γ-Al2O3 have also been studied. The characterization results indicate that the main vanadium species in both Mo-free and Mo-containing V-based samples present low aggregation and coordination, whereas molybdenum is present as monomeric or polymeric tetrahedral molybdenum species. Interestingly, no apparent interaction between molybdenum and vanadia takes place. The …

NiO diluted in high surface area TiO2 as efficient catalysts for the oxidative dehydrogenation of ethane

[EN] Catalysts consisting of NiO diluted in high surface area TiO2 can be as efficient in the oxidative dehydrogenation of ethane as the most selective NiO-promoted catalysts reported previously in the literature. By selecting the titania matrix and the NiO loading, yields to ethylene over 40% have been obtained. In the present article, three different titanium oxides (TiO2) have been employed as supports or diluters of nickel oxide and have been tested in the oxidative dehydrogenation of ethane to ethylene. All TiO2 used present anatase as the main crystalline phase and different surface areas of 11,55 and 85 m(2) g(-1). It has been observed that by selecting an appropriate nickel loading …