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Metallic Co–MoO 3 catalysts supported on ordered mesoporous SBA-15 were first prepared through in situ reaction of SBA-15-supported Co–Mo oxides with 1,10-phenanthroline. The resulting Co–MoO 3 /NC@SBA-15 catalysts with N-doped carbon (NC) exhibited high catalytic activity and chemoselectivity for selective reduction of various functionalized nitroarenes to the corresponding arylamines in ethanol with hydrazine hydrate at near room temperature (30 °C). For reduction of all tested substrates (28 examples), the catalyst could afford a conversion of >99% and arylamine selectivity of >99%. The excellent catalytic performance of the Co–MoO 3 /NC@SBA-15 was attributed to the Co–N χ (C)–Mo active sites generated through the interaction between the surface Co–N χ (C) and MoO 3 species, promoting the dissociation of hydrazine molecule into the active H* species for the reduction of nitro groups. After the seventh cycle for reduction of 4-methoxylnitrobenzene, the 2%Co–MoO 3 /NC@SBA-15 showed little change in catalytic performance, textural properties, size and dispersion of metal species and valence states of elements, indicating high stability and recyclability. [ABSTRACT FROM AUTHOR]

This paper presents an in situ study of the crystallographic phases formed during the thermal treatment of precursors of vanadium and molybdenum oxides, measured under synchrotron X-ray diffraction. The interest in the speciation of Mo x V y O z mixed oxides lies in the excellent catalytic performance of these materials for the selective conversion of glycerol to acrylic acid employing the oxydehydration reaction. The crystallographic structure of the active phases of Mo x V y O z directly influences on the nearby metal valence and, therefore, on the dynamic changes in metal oxidation states during the catalytic reaction. In the present study, the thermal treatment of a mixture of the precursors of Mo and V under oxidizing or inert atmospheres revealed the major formation of 61% of MoV 2 O 8 or 29% of Mo 4 V 6 O 25 , respectively, at a final temperature of 500 °C. The most active phase for acrylic acid formation was MoV 2 O 8 (3.5 times more active than the separate metal oxides), due to the instability of the phase with respect to framework oxygen at the reaction temperature. The cycle of reduction and oxidation of the vanadium in MoV 2 O 8 during the reaction caused pronounced dynamic formation of oxygen vacancies, resulting in 97% conversion of glycerol and 32% selectivity towards acrylic acid. [ABSTRACT FROM AUTHOR]

We use Density-Functional Theory calculations to investigate the mechanism of the retro-aldol fragmentation of fructose to glyceraldehyde (GLA) and dihydroxyacetone (DHA) on MoO 3 . We find that the reaction follows the classic mechanism of C C bond activation by proton abstraction from the β OH group of the sugar and stabilization of the transition state and resulting enolate intermediate by charge delocalization through coordination of the sugar’s carbonyl group to a Lewis acidic Mo atom. The deprotonation of fructose and the C C bond scission take place in a concerted fashion. On MoO 3 , fructose can also undergo epimerization to d -hamamelose through a 1,2-carbon shift along a pathway that is as probable kinetically as the one that leads to retro-aldol fragmentation but is somewhat more favourable thermodynamically. We see that hamamelose formation does not have an adverse effect on the overall yield of alkyl lactates, because hamamelose can itself undergo retro-aldol fragmentation to GLA, which can further be converted to alkyl lactates through a cascade of thermodynamically favorable reactions involving isomerization via 1,2-hydrogen shift, dehydration and ketalization, all catalyzed by the Lewis acidic zeolite Sn-MFI. [ABSTRACT FROM AUTHOR]

A redox catalyst with MoO 3 loaded on CaMnO 3 perovskite was evaluated for chemical-looping oxidative dehydrogenation (ODH) of propane to produce propylene. This approach requires less energy for the production per unit of propylene with minimum CO 2 emission, which is highly desirable from an environmental perspective. H 2 -TPR indicates that the incorporation of MoO 3 minimizes the release of surface oxygen, which is favorable for high propylene selectivity. XRD reveals the presence of active sites, while scanning SEM-EDX show uniform dispersion of deposited MoO 3 on CaMnO 3. XPS analysis demonstrates that MoO 3 addition promotes the formation of lattice oxygen which improves the propylene selectivity. The highest propylene yield of 30.6% with a propylene selectivity of 59% was achieved at 550 ℃ with 10% MoO 3 /CaMnO 3. The catalysts also show stable activity in successive redox cycles. The addition of MoO 3 enhances propylene yield and selectivity, due to free lattice oxygen, as revealed by XPS and H 2 -TPR. [Display omitted] [ABSTRACT FROM AUTHOR]

The catalytic properties of molybdenum-alumina systems depend on the synthesis conditions. Herein, we considered the effect of MoO 3 /Al 2 O 3 catalyst pretreatment conditions on their activity in propylene and propane conversion. MoO 3 /Al 2 O 3 catalysts were synthesized by wetness impregnation of the support with a solution of molybdenum citrate complex and activated in different atmospheres at 550–590 °С. The maximum conversion of propylene and yields of metathesis products were observed for the sample activated in an inert gas flow. This is caused by the formation of precursors of the metathesis active sites in this sample, i.e. isolated surface monomolybdate species. Activation of the catalyst in hydrogen leads to the reduction of Mo6+ to Mo5+/Mo4+, which ensure the increased activity and selectivity in propane dehydrogenation. Therefore, it was shown that make it possible to purposefully change the properties of the same molybdenum-alumina catalyst to suit the problems of the specific reaction (metathesis, oligomerization, dehydrogenation, aromatization, cracking). [Display omitted] • Pretreatment conditions affect the formation of MoO 3 /Al 2 O 3 active sites. • UV-Vis, Raman Spectroscopy and XPS were used to characterize the catalyst. • Isolated Мо6+ species are precursors of active sites for alkene metathesis. • Reduced Mo4+ and/or Mo5+ species are associated with dehydrogenation/aromatization. • Catalyst pretreatment conditions have an effect on surface acidity. [ABSTRACT FROM AUTHOR]

The catalytic properties of well-defined hierarchically assembled Bi2WO6 nanoflakes with surface dispersed molybdena have been studied with selective oxidation of propene as probe reaction. The adsorption of oxygen causes the decrease in the conductivity of Bi2WO6, demonstrating its nation of n-type semiconductor. The adsorption of oxygen gains electrons from the conduction band of Bi2WO6 to produce oxygen species active for propene reaction at low temperatures, which, however, gives mainly COx as products. The modification by surface molybdena significantly inhibited the total oxidation reaction of propene over the Bi2WO6, while dramatically increased the conversion of propene and selectivity to acrolein simultaneously, without the formation of acrylic acid. The characterization of conductivity measurements, H2-TPR, O2-TPD, XPS and TPSR indicated that the thermally excited electrons from the Bi2WO6 were combined with surface dispersed molybdena and resulted in an extraordinary increase of selective oxidation performance. The unique effects of the hierarchically assembled Bi2WO6 nanoflakes on the catalytic property of molybdena were discussed and the mechanism of the catalyst for the selectively catalytic oxidation was proposed. The results are useful to design novel catalysts for important reactions with nano concepts. [ABSTRACT FROM AUTHOR]

Highlights: [•] Several typical catalysts changes often occurring during catalytic processes are surveyed. [•] Textural change, decomposition, volatilization, sulphation, etc. of active phases are addressed. [•] Modifications of the catalysts may become beneficial when induced in suitable conditions. [•] Taming a priori unwanted changes may lead to improve the performance. [•] Partial and total oxidations on Mo, Re and Mn based catalysts are evoked. [ABSTRACT FROM AUTHOR]

Highlights: [•] Alumina supported Mo- and Mo–V-oxide catalysts prepared in one step. [•] FSP leads to high surface area and good dispersion as confirmed by Raman, XRD and UV–vis. [•] Highest propene selectivity observed at low loadings for mixed molybdenum–vanadium oxide. [•] Interaction between molybdenum and vanadium oxide surface species increases TOF. [•] Simple kinetic model used for optimizing reaction conditions for high propene yield. [ABSTRACT FROM AUTHOR]

Highlights: [•] Textural/catalytic properties of Mo/mesoporous lamellar zeolites were investigated. [•] Mesopore facilitates dispersion of Mo species in zeolite catalysts. [•] Higher aromatic and coke formation was observed in the initial reaction stage. [•] Mo-acid species in mesopores account for fast reaction and deactivation rates. [•] Mo-acid species in micropores are responsible for the long term catalyst activity. [Copyright &y& Elsevier]

Highlights: [•] H2 reduction of Pt/MoO3 at 773K yielded porous MoO x . [•] MoO x obtained by reduction with a slow rate had the largest surface area of 340m2/g and the highest isomerization activity. [•] The reduction rate depended on the flow rate of H2. [Copyright &y& Elsevier]

Abstract: The structure of molybdenum oxide supported by silica SBA-15 has been studied by visible Raman spectroscopy, diffuse reflectance UV–Vis spectroscopy and X-ray absorption spectroscopy in the dehydrated state obtained after thermal treatment at elevated temperatures (≥350°C). No dependence of the molybdenum oxide structure on preparation procedure or loading has been observed within the range of loadings studied in detail (0.2–0.8Mo/nm2). X-ray absorption spectroscopy (XAS) reveals that the dehydrated state consists of a mixture of monomeric and connected molybdenum oxide centres. While the presence of crystalline MoO3 can be excluded by Raman spectroscopy, tetrahedrally and octahedrally coordinated MoO4 and MoO6 units are identified by XAS. The MoO6 units possess connectivity similar to that of MoO3 building blocks, whereas the MoO4 units are isolated or connected to other Mo x O y units. These results are supported by UV–Vis spectra showing intensity at wavelengths (>300nm) typical for dimeric and/or oligomeric species. [Copyright &y& Elsevier]

Abstract: The heptane isomerization activity of Pt/MoO3–SiO2 reduced by H2 at 773K for 6h was investigated, in particular its relation to the physicochemical properties. H2-reduced Pt/MoO3–SiO2 with a larger amount of MoO3 had a higher isomerization activity. The same tendency was observed in the activity for 2-propanol dehydration. The isomerization activity was related to the number of acid sites, which was determined from NH3-TPD. XRD studies of H2-reduced Pt/MoO3–SiO2 showed that the formation of MoO x H y was promoted as the MoO3 loading was increased. The conversion of MoO3 to H1.68MoO3 in the initial stage of reduction varied with the amount of MoO3; only a part of MoO3 was converted to H1.68MoO3 in Pt/MoO3–SiO2 with a small amount of MoO3, while the complete conversion to H1.68MoO3 was observed in Pt/MoO3. Based on these findings, we conclude that the isomerization activity of H2-reduced Pt/MoO3–SiO2 can be governed by the formation of MoO x H y , which is yielded from the reduction of MoO3 through H1.68MoO3. [Copyright &y& Elsevier]

Abstract: This study reports improved catalytic activities and stabilities for the oxidation of dimethyl sulfide (DMS), a major pollutant of pulp and paper mills. Ozone was used as an oxidant and activities of Cu, Mo, Cr and Mn oxides, and mixed metal oxides supported on γ-alumina, were tested over the temperature ranging from 100 to 200°C. The best catalytic activity was obtained over 10wt.% CuO-10wt.% MoO3 supported on γ-Al2O3 with 100% DMS conversion and high selectivity (≈96%) towards complete oxidation products such as CO2 and SO2. The addition of molybdenum to the CuO/γ-Al2O3 significantly enhanced the selectivity of the reaction towards complete oxidization products indicating that MoO3 acts as a good promoter when used with CuO. Catalyst characterization by XRD, TPR and NH3-TPD analyses suggested that these promoting effects are due to the formation of Cu3Mo2O9 and CuMoO4 species on CuO-MoO3/γ-Al2O3, and also a substantially higher quantity of acid sites and a stronger acid strength in CuO-MoO3/γ-Al2O3 than CuO/γ-Al2O3 catalyst. This study also reports the optimization of reaction parameters and effects the catalyst physico-chemical properties have on the catalytic activity. [Copyright &y& Elsevier]

Abstract: The phase composition and the physico-chemical nature of the “carbon-modified molybdenum sub-oxide” catalyst during the isomerization of n-heptane were studied. It was found that different phases of molybdenum sub-oxides coexist, MoO2, MoO, besides MoO3−x . Our results indicate that MoO is present as dispersed nano-structures inside the bulk catalysts. The thermal oxidation study revealed that the O2 is consumed to oxidize part of the reduced oxide as well as carbonaceous deposits simultaneously, giving an additional evidence of the mixture of oxide phases during reaction. A thermo-kinetic study of the different oxidation process is included and the results are discussed in terms of the activation energy for the oxidation of each phase. The structural and thermal characterization has revealed the complexity of the system, but has also opened a window to a new insight into the understanding of MoO3 catalyst. [Copyright &y& Elsevier]

The catalytic properties of H2-reduced Pt/MoO3 for the isomerization of pentane and heptane were compared to those of Pt/zeolites. H2-reduced Pt/MoO3 was more active for pentane isomerization than Pt/Hβ and Pt/USY. In contrast, the heptane isomerization activity decreased in the following order: Pt/Hβ>H2-reduced Pt/MoO3>Pt/USY. All of the catalysts gave negative kinetic orders toward hydrogen in both pentane and heptane isomerization. The reaction order toward pentane was positive in all cases. The reaction order toward heptane on H2-reduced Pt/MoO3 was found to be −0.3, whereas those on Pt/Hβ and Pt/USY were zero and positive, respectively. These results indicate that heptane was more strongly adsorbed on H2-reduced Pt/MoO3, resulting in the low heptane isomerization activity. Adsorption studies showed that interaction of heptane with the surface of H2-reduced Pt/MoO3 was hindered, probably by its porous structure. We suggest from these results that the low catalytic activity of H2-reduced Pt/MoO3 for heptane isomerization can be caused by steric effects as well as by the strong adsorption of heptane. [Copyright &y& Elsevier]

The catalytic properties of H2-reduced MoO3 for the isomerization of C5–C7 alkanes were compared to those of Pt/HY and Pt/Hβ zeolites. The pentane isomerization activity decreased in the following order: Pt/Hβ>H2-reduced MoO3>Pt/HY. In contrast, H2-reduced MoO3 exhibited the lowest activity for heptane isomerization among the catalysts tested. H2-reduced MoO3 catalyzed the isomerization of heptane more selectively than other catalysts, although no appreciable difference appeared in the selectivity for pentane isomerization. Kinetic parameters on H2-reduced MoO3 were identical with those on Pt/zeolites, suggesting that isomerization reactions on H2-reduced MoO3 proceeded via the bifunctional mechanism. We suggested from the results of 2-propanol conversion that the low dehydrogenation–hydrogenation activity of H2-reduced MoO3 was a reason for its low isomerization activity. Adsorption of heptane was found to be restricted on H2-reduced MoO3, leading to the low activity for heptane isomerization. [Copyright &y& Elsevier]

Mo–Sn–O systems were characterized by Raman spectroscopy and electrical conductivity measurements. The catalysts were obtained from precipitation of SnCl4 by ammonia in the presence of (NH4)2Mo7O24 using four different levels of Mo concentration. The electrical conductivity measurements showed that particles are formed by agglomeration of SnO2 crystals aggregated by polymolybdate. Raman spectroscopy suggested that four-coordinated species are dispersed at the external surface while six-coordinated species are inside the particles. For high Mo concentration (Mo >10%), octahedral coordinated species are also on the surface. Bulk MoO3 oxide was not observed. These results confirm the model previously proposed. [Copyright &y& Elsevier]

• Bimetallic molybdenum-cobalt carbon spheres were prepared via in situ hydrothermal reduction using glucose. • The synergistic interaction between MoO 2 and Co active sites mediated C 2+ alcohols formation. • The in situ potassium incorporation during hydrothermal synthesis stabilised the high-valence molybdenum oxide (MoO 2). • KMoCo carbon spheres enhanced C 2+ alcohols yield under mild operating conditions. Catalytic conversion of syngas to higher carbon number alcohols remains challenging till date owing to poor alcohols selectivity and limited understanding of catalytic active sites. In this study, we report bimetallic molybdenum-cobalt carbon spheres produced via in-situ hydrothermal reduction mediated by monosaccharides (glucose). The addition of potassium promoter (K/Mo = 0.14) during hydrothermal synthesis increased the concentration of high-valence molybdenum (MoO 2) and selectivity towards higher alcohols (28 %). The field emission-SEM and HR-TEM images revealed a spherical morphology, embedding nanocrystalline MoCo oxides. The resulting carbon spheres enabled C 2+ alcohols synthesis under mild operating conditions (270 ⁰C, 30 bar, and 3000 h−1). [ABSTRACT FROM AUTHOR]

• The use of TiO 2 support results in faster nitrobenzene adsorption. • Surface adsorbed hydrogen provides hydrogen sources to form aniline without the need for ethylbenzene. • Oxygen vacancies remove oxygen of nitrobenzene, reducing the amount of ethylbenzene needed. • Traditional stoichiometry is only valid when surface adsorbed hydrogen and oxygen vacancies are no longer in abundance. Catalytic coupling of ethylbenzene (EB) dehydrogenation with nitrobenzene (NB) hydrogenation offers potential economical and energetic benefits. However, several studies in the literature have shown that NB conversion could be higher than that of EB, violating the law of mass conversion. This work provides a new understanding of this reaction coupling scheme over MoO 3 /TiO 2 catalysts to elucidate this scientific mystery. Our results suggest that EB and NB have different adsorption rates on the TiO 2 surfaces, resulting in higher NB conversion. In addition, three distinct reaction schemes, each follows a different EB to NB stoichiometric ratio, were identified on the MoO 3 surfaces. The occurrence of the reactions is dependent on catalyst pretreatment by hydrogen reduction and the amount of oxygen vacancies on the surfaces. Our work explains why mass conservation was not satisfied in some previous studies due to the incorrect reaction stoichiometry used for analyzing the reactant conversions. [ABSTRACT FROM AUTHOR]