MoO3 Species Research Articles

Enhanced sulfur‐resistant methanation performance over MoO3–ZrO2 catalyst prepared by solution combustion method

Sulfur‐resistant methanation of syngas was studied over MoO3–ZrO2 catalysts at 400°C. The MoO3–ZrO2 solid‐solution catalysts were prepared using the solution combustion method by varying MoO3 content and temperature. The 15MoO3–ZrO2 catalyst achieved the highest methanation performance with CO conversion up to 80% at 400°C. The structure of ZrO2 and dispersed MoO3 species was characterized using X‐ray diffraction and transmission electron microscopy. The energy‐dispersive spectrum of the 15MoO3–ZrO2 catalyst showed that the solution combustion method gave well‐dispersed MoO3 particles on the surface of ZrO2. The structure of the catalysts depends on the Mo surface density. It was observed that in the 15MoO3–ZrO2 catalyst the Mo surface density of 4.2 Mo atoms nm−2 approaches the theoretical monolayer capacity of 5 Mo atoms nm−2. The addition of a small amount of MoO3 to ZrO2 led to higher tetragonal content of ZrO2 along with a reduction of particle size. This leads to an efficient catalyst for the low‐temperature CO methanation process.

Protection of GaInP2 Photocathodes by Direct Photoelectrodeposition of MoSx Thin Films.

Catalytic MoSx thin films have been directly photoelectrodeposited on GaInP2 photocathodes for stable photoelectrochemical hydrogen generation. Specifically, the MoSx deposition conditions were controlled to obtain 8-10 nm films directly on p-GaInP2 substrates without ancillary protective layers. The films were nominally composed of MoS2, with additional MoOxSy and MoO3 species detected and showed no long-range crystalline order. The as-deposited material showed excellent catalytic activity toward the hydrogen evolution reaction relative to bare p-GaInP2. Notably, no appreciable photocurrent reduction was incurred by the addition of the photoelectrodeposited MoSx catalyst to the GaInP2 photocathode under light-limited operating conditions, highlighting the advantageous optical properties of the film. The MoSx catalyst also imparted enhanced durability toward photoelectrochemical hydrogen evolution in acidic conditions, maintaining nearly 85% of the initial photocurrent after 50 h of electrolysis. In total, this work demonstrates a simple method for producing dual-function catalyst/protective layers directly on high-performance, planar III-V photoelectrodes for photoelectrochemical energy conversion.

Characterization and Application of Catalysts Hard Green Clay and MoO<sub>3</sub>/ Hard Green Clay in Transesterification Reaction of Soybean Oil

The present study describes the preparation of catalyst MoO3 supported on smectite clay by the solution impregnation method and its evaluation as a heterogeneous catalyst in the production of biodiesel from soybean oil. The individual effects of catalyst (hard green clay and MoO3/hard green clay) on kinematic viscosity of produced biodiesel and conversion were investigated. The samples were characterized by X-ray diffraction, X-ray fluorescence spectroscopy and N2 adsorption-desorption. Conditions of soybean oil transesterification were: 5% catalyst by weight, 1:12 oil to methanol molar ratio, at 200 oC for 60 minutes. Patterns of X-ray diffraction showed the characteristic peaks of the structure of smectite. The results of X-ray diffraction suggests that MoO3 species exist as highly dispersed surface species. Molybdenum metal identified as effective catalysts for the transesterification reaction of soybean oil with methanol. A preliminary design assessment show that this catalysts (MoO3/HGC) is sufficiently active achieving conversion in excess of 62,07% at temperature below 200 oC.

Highly dispersed molybdenum containing mesoporous silicate (Mo-TUD-1) for olefin metathesis

Abstract Employing a one-pot sol-gel synthesis technique, molybdenum with variable loadings (2–14 wt%), was successfully incorporated into a mesoporous TUD-1 silicate framework. Diffuse reflectance UV–vis and Raman spectra of samples dehydrated at reaction temperatures (450 °C) revealed the dominant presence of highly dispersed tetrahedral di-oxo (Si-O)2Mo(=O)2 species. Neither bulk nor crystalline MoO3 was evident at Mo loadings from 2 to 7 wt.% from complementary analytical techniques suggesting that a high dispersion of MoOx species is achieved by this synthesis method. Mo L-edge XANES of catalyst samples at ambient conditions and Mo K-edge XAS of catalyst samples dehydrated at the reaction temperature (450 °C) further confirm the existence of mixed tetrahedral and octahedral Mo sites. The relative population of dioxo Mo species observed in Mo-TUD-1 catalysts at various Mo loadings correlate well with the Lewis acidity and apparent TOFs (mmol propene/mol Mo/s) observed with these samples. These observations confirm that the dioxo Mo species are the active site precursors, as also reported previously with other Mo-based catalyst formulations. Compared to Mo-impregnated SiO2 (Mo/SiO2) catalyst, the Mo-TUD-1 catalysts (2–7 wt% Mo loadings) provide higher apparent TOFs. At higher Mo loadings, the fraction of MoO3 species that are Bronsted acidic in nature increases, resulting in decreased TOFs and increased catalyst deactivation due to the formation of heavier hydrocarbons that deposit on the catalyst surface. However, the metathesis activity is fully restored after simple air regeneration of the catalyst.

Iron-depleted pelagic water at the end-Permian mass extinction inferred from chemical species of iron and molybdenum in deep-sea sedimentary rocks

This study determined chemical species of iron (Fe) and molybdenum (Mo) in a pelagic deep-sea Permian–Triassic boundary section, that records redox variations across the severe mass extinction event. We applied X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) at the Fe K-edge and X-ray absorption near-edge structure (XANES) at the Mo K-edge to silicic sedimentary rock samples for analysis of the studied section. According to the EXAFS and XRD analyses, pyrite was the dominant Fe-bearing mineral in most samples, whereas ferric minerals such as hematite were absent throughout the Permian–Triassic transition. This result supports those of previous studies of other deep-sea Japanese Permian-Triassic boundary (PTB) sections. The Fe in pyrite mineral quantified by EXAFS spectra displayed synchronous variation with sulphide-sulphur (Ssulphide) but with total organic carbon content, which revealed the Fe-limited conditions for pyrite formation in the pelagic Panthalassa region. The XANES analysis indicated the presence of tetrahedral and octahedral configurations of Mo bonded to oxygen (O) and sulphur (S), which were referred to as MoO42−, MoO3 (as a possible alternative reference material of Mo in organic ligands), MoO2 and MoS2. The MoS2 species dominated in the end-Permian horizons, coinciding with high abundances of total Mo, which suggests a sulphidic depositional environment. The MoS2 and MoO3 species were the main contributors to these high Mo abundances in the end-Permian strata. The presence of the molybdenite (MoS2) species in the studied section indicates that the samples were subjected to alteration under high temperatures, with sufficiently sulphidic and limited reactive Fe availability conditions for MoS2 formation during late diagenesis. The Fe in pyrite decreased across the mass extinction boundary, which coincided with the highest total Mo amount with the MoS2 and MoO3 species. These trends reflected a decrease in reactive Fe in the sediments and contemporaneous seawaters under sulphidic conditions. The low reactive Fe condition could be due to massive pyrite formation under prolonged sulphidic water conditions in the pelagic and ambient continental margin regions in the end-Permian.

Structuring-agent role in physical and chemical properties of Mo/SiO2 catalysts by sol-gel method

Molybdenum supported on silica was prepared by the sol-gel method modifying the type of template. Amorphous silica structures were obtained and MoO3 species were observed when the molybdenum load was 6 wt%. The increase of molybdenum loading produces a decrease in the surface area by the formation of Mo–O–Si or Mo=O–Si bonds. Oxalic acid allows obtaining materials with higher surface area relative to citric acid. The larger size of the molecule of citric acid plays an important role as a chelating agent of molybdenum.

Methane dehydroaromatization – A study on hydrogen use for catalyst reduction, role of molybdenum, the nature of catalyst support and significance of Bronsted acid sites

Abstract Methane dehydroaromatization was studied over Mo/SiO2 and Mo/HZSM-5 with different Mo loadings (2, 5, 10 wt%) at 973 K and 1023 K in a recirculating batch reactor. H2 pretreatment at 1023 K prior to methane activation has significantly improved the catalyst activity with increase in Mo loading and reduced the induction time on benzene formation in both Mo/SiO2 and Mo/HZSM-5. 10 wt% Mo/HZSM-5 gave a maximum methane conversion of 19% and ∼67% benzene selectivity at 1023 K. The XRD analysis of used catalysts revealed that the MoO3 species were converted to β-Mo2C phase. Studies on Mo/SiO2 catalysts showed that benzene was formed even in the absence of acidic zeolite sites. Reactions of ethylene in the presence of pure silica, HZSM-5 and in a blank reactor revealed that conversion of ethylene to aromatics was similar in case of the blank reactor and silica. Thus, it is believed that molybdenum carbide sites act as active sites only for C–H bond activation of methane and ethylene formation. Even though, ethylene can undergo subsequent oligomerization without any catalytic aid to form benzene at 973 K and above addition of acidic zeolites improved the selectivity of benzene.

Structure and Evolution of Confined Carbon Species during Methane Dehydroaromatization over Mo/ZSM-5

Surface carbon (coke, carbonaceous deposits) is an integral aspect of methane dehydroaromatization catalyzed by Mo/zeolites. We investigated the evolution of surface carbon species from the beginning of the induction period until the complete catalyst deactivation by the pulse reaction technique, TGA, 13C NMR, TEM, and XPS. Isotope labeling was performed to confirm the catalytic role of confined carbon species during MDA. It was found that “hard” and “soft” coke distinction is mainly related to the location of coke species inside the pores and on the external surface, respectively. In addition, MoO3 species act as an active oxidation catalyst, reducing the combustion temperature of a certain fraction of coke. Furthermore, after dissolving the zeolite framework by HF, we found that coke formed during the MDA reaction inside the zeolite pores is essentially a zeolite-templated carbon material. The possibility of preparing zeolite-templated carbons from the most available hydrocarbon feedstock is important for the development of these interesting materials.

N-doped graphitic carbon-improved Co–MoO3 catalysts on ordered mesoporous SBA-15 for chemoselective reduction of nitroarenes

Metallic Co–MoO3 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–MoO3/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–MoO3/NC@SBA-15 was attributed to the Co–Nχ(C)–Mo active sites generated through the interaction between the surface Co–Nχ(C) and MoO3 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–MoO3/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.

Effect of Co-Generated MoO3 on the Electrocatalytic Hydrogen Evolution Performance of O2 Plasma Modified MoS2

Extensive efforts have been devoted to developing MoS2 nanostructures to maximize the number of active edge sites [1], but little attention has been paid to simultaneously tailoring of both the edge and planar structure itself for enhancing the HER kinetics. In this work, we used the one-step O2 plasma modification to simultaneously engineer the edge and planar structure of MoS2 to fabricate the high-performance MoS2 electrocatalyst with defect-rich edge and oxygen-doped planar structure. We further notice that the influence of the inevitably generated MoO3 species on the HER activity and stability of MoS2 and its structure changes after long-term electrocatalytic reaction, which are significant to understand the HER electrocatalysis on the O-incorporated MoS2 catalysts, however, are still unknown [2]. Herein, controlled plasma exposure time has been designed to explore the influence of MoO3 species on the HER performance of O2 plasma modified MoS2 catalysts. We find that the MoO3 species in MoS2 are not conductive to the HER electrocatalysis. More importantly, these co-generated MoO3 species are reduced and resolved from the MoS2 lattice during the electrocatalytic hydrogen evolution, leading to a holey structure in the MoS2 nanosheets and thus a significant improvement of its hydrogen evolution stability (Figure 1a). This work is the first to explore the Janus effect of O2 plasma modification on MoS2 for acceleration the hydrogen evolution reaction, and opens a new way to developing layered materials for electrochemical energy applications. Aside from the fundamental insight attained from the rational materials design, the MoS2 O2-plasma 60s catalyst exhibits a boosted HER activity with the overpotential as low as 131 mV at the current density of 10 mA/cm2 and striking long-term durability, better than most reported MoS2-based catalysts (Figure 1b). Figure captions Figure 1. (a) Polarization curves recorded from the MoS2 O2-plasma 60s catalyst at a scan rate of 5 mV/s before and after the chronopotentiometry test. Inset: chronopotentiometry responses (η ~ t) recorded at a constant current density of -10 mA/cm2. (b) TEM image of the MoS2 O2-plasma 60s sample after the chronopotentiometry test at -10 mA/cm2 for 20 hours.

Janus effect of O2 plasma modification on the electrocatalytic hydrogen evolution reaction of MoS2

Oxygen incorporation is a promising and effective way for simultaneously engineering the edge and planar sites of MoS2 to fabricate high-performance HER electrocatalysts. However, the insulating MoO3 species are inevitably generated during the oxygen incorporation process. Here, controlled plasma exposure time has been designed to explore the influence of MoO3 species on the HER performance for the O2 plasma modified MoS2 catalysts. We find that the MoO3 species in MoS2 are not conductive to the HER electrocatalysis. More importantly, the Raman spectrum, X-ray photoelectron spectroscopy, energy-disperse X-ray spectrum and transmission electron microscope analyses demonstrate that these co-generated MoO3 species are reduced and resolved from the MoS2 lattice during the electrocatalytic hydrogen evolution, leading to a holey structure in the MoS2 nanosheets and thus a significant improvement of its hydrogen evolution stability. This work not only helps to understand the electrocatalytic influence of the co-generated MoO3 species in MoS2, but also presents a methodological improvement in designing defect-rich, oxygen incorporated and holey MoS2 nanosheets for highly efficient hydrogen evolution.

NiMo catalysts supported on Al, Nb, Ti or Zr-containing MCM-41 for dibenzothiophene hydrodesulfurization

xMCM-41 materials (x = Al, Nb, Ti or Zr) with nominal x loading of 0.5 mmol/g were prepared by chemical grafting of Al2O3, Nb2O5, TiO2 and ZrO2 precursors and used as supports for NiMo/xMCM-41 catalysts. Small-angle XRD characterization of supports showed typical patterns of solids with hexagonal arrangement of mesopores. After the deposition of Ni and Mo oxide species on the supports a decrease in their long-range pore arrangement was observed. Nevertheless, the prepared NiMo catalysts possessed high specific surface areas and pore volumes. Powder XRD patterns showed the formation of the MoO3 crystalline phase in the NiMo/MCM-41 reference. This phase was not detected in the catalysts supported on xMCM-41 materials. An increase in the dispersion of MoO3 species with the incorporation of alumina, niobia, titania and zirconia in the MCM-41 support was due to the stronger interaction of Mo and Ni oxide species with xMCM-41 materials (H2-TPR and UV–vis DRS). Surface modification of the MCM-41 with different metal oxides increased the dibenzothiophene conversion and pseudo first-order rate constants. This effect was more evident for the NiMo/TiMCM-41 catalyst. Selectivity of the catalysts (product distributions) was also affected by the incorporation of Al-, Zr-, Ti- and Nb-oxide species in the support.

Effect of trimesic acid as chelating agent in sulfided CoMoP/γ-Al2O3 catalyst for hydrodesulfurization of straight-run gas oil

The effect of trimesic acid (TA) on the surface of γ-Al2O3 for CoMoP catalysts has been investigated in the hydrodesulfurization (HDS) of straight-run gas oil. The γ-Al2O3 support was modified by surface impregnation of a solution of TA to afford TA/Co molar ratios (0.5, 1.0 and 2.0) in the final composition. The CoMoP material with atomic ratio of TA/Co = 1.0 displayed the highest HDS activity. FT-IR results suggest that the carboxylic acid moieties (AA) of the TA deposited on the γ-Al2O3 interact with the Mo and Co species. The DRS UV vis revealed the presence of Co species in distorted octahedral symmetry. The MoOh/MoTh ratio varied depending on the amount of the organic additive. TGA results indicated that the TA on the catalyst with TA/Co ratio = 1.0 often decomposes at lower temperature in comparison with the other samples. Thus, a lower temperature decomposition favors the surface concentration of metals species for the sulfurization degree. The interaction of the TA induces moderate metal-support interaction. Raman spectroscopy showed that the presence of TA influenced significantly on the ratio MoO/(MoO + MoOMo + MoO) on the catalyst surface. Raman results also evidenced the highest ratio MoO/(MoO + MoOMo + MoO) for the CoMoP (1.0) sample. Apparently, the augment of the MoO species is related to a major availability of Mo species for the formation of MoS2 for HDS reaction. The XPS and HRTEM results showed higher formation and more dispersed MoS2 and CoMoS species for the catalysts modified by TA compared to that of the reference sample. The CoMoP (1.0) showed higher Moe/Mot ratio in comparison with CoMoP (0.0), which resulted in a higher gas oil HDS activity.

MoO3 supported on ordered mesoporous zirconium oxophosphate: An efficient and reusability solid acid catalyst for alkylation and esterification

A series of molybdenum oxide supported on ordered mesoporous zirconium oxophosphate (MoO3/M-ZrPO) materials with different MoO3 loadings (0–20wt%) and calcination temperatures (500–900°C) have been designed, synthesized and employed as solid acid catalysts in alkylation and esterification. The XRD, TG-DSC, H2-TPR, N2-physisorption and TEM characterizations were taken to investigate the structural properties and states of introduced MoO3 species. The influence of MoO3 loadings and calcination temperatures in catalytic performance was detailedly investigated and optimal catalytic activity was reached at 10wt% MoO3 loadings and treated at 700°C. Moreover, MoO3/M-ZrPO catalysts exhibited outstanding catalytic performance in Friedel-Crafts alkylation of different aromatic compounds and esterification of levulinic acid with 1-butanol. Furthermore, it was noteworthy that the catalyst had superior reusability and no noticeable declines were observed in catalytic performance even after seven runs.

HDO activity of carbon-supported Rh, Ni and Mo-Ni catalysts

This work reports the performance of low metal loading (about 3wt.%) Rh, Ni and Mo-Ni catalysts supported on carbon in the hydrodeoxygenation (HDO) of phenol. The catalytic tests were carried out in a flow microreactor at 310°C and at a total hydrogen pressure of 3MPa. A commercial NiMoP/γ-Al2O3 sulfided catalyst was used as reference. The effect of catalyst pre-treatment (reduction against sulfidation) was investigated in the case of the noble metal catalyst. The thermally treated in inert atmosphere, fresh reduced and spent catalysts have been characterized by several physicochemical techniques: chemical analysis, N2 adsorption-desorption isotherms, Raman spectroscopy, Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HRTEM).The HDO of phenol was found to be favored on the bifunctional Rh/C and Ni/AC catalysts which exhibit a large amount of well dispersed metallic species (from HRTEM). Contrary to a commercial sulfided NiMo/Al2O3 catalyst, the hydrogenation of aromatic ring of phenol was favored being the CO bond hydrogenolysis a minor reaction route. Catalytic HDO of phenol over Rh/C reveal that the catalyst activation by reduction is advantageous compared to that by sulfidation. The partial substitution of Ni by Mo in the Mo-Ni/AC catalyst led to enhance of the catalyst stability but decrease of overall activity occurs due to the decrease of amount of metallic nickel species. The role of the MoO3 species in the inhibition of deactivation by coke is discussed.

Comparison of transesterification and thermal cracking methods on fuel specifications of castor oil biodiesel

A series of NiMo/γ-Al2O3 carbides were synthesized with the temperature programmed carburization method for the tri-reforming of methane. The relationship between the catalytic behavior and the impregnation sequence was investigated by XRD, TG-DSC, XPS, SEM, and so on. It was found that Mo2C species were the active species for the tri-reforming of methane. The amounts of Mo2C species on the fresh NiMo carbides decreased in the order of co-impregnated NiMo carbide > Ni-first NiMo carbide > Mo-first NiMo carbide. In contrast, Mo2C species on the latter two carbides would continue to be formed during the tri-reforming of methane. NiMoO4 species only existed on the co-impregnated NiMo oxidic precursor, exhibiting a strong synergistic effect between Ni and Mo species. NiMoO4 species were reduced more easily than MoO3 species on the step-impregnated NiMo oxides. Ni0 species promoted the dissociation of methane, induced the reduction of molybdenum oxide and supplied active hydrogen and carbon species for the carburization process. The co-impregnation method was conducive to refine the particles.

Effect of impregnation sequence on the catalytic performance of NiMo carbides for the tri-reforming of methane

A series of NiMo/γ-Al2O3 carbides were synthesized with the temperature programmed carburization method for the tri-reforming of methane. The relationship between the catalytic behavior and the impregnation sequence was investigated by XRD, TG-DSC, XPS, SEM, and so on. It was found that Mo2C species were the active species for the tri-reforming of methane. The amounts of Mo2C species on the fresh NiMo carbides decreased in the order of co-impregnated NiMo carbide > Ni-first NiMo carbide > Mo-first NiMo carbide. In contrast, Mo2C species on the latter two carbides would continue to be formed during the tri-reforming of methane. NiMoO4 species only existed on the co-impregnated NiMo oxidic precursor, exhibiting a strong synergistic effect between Ni and Mo species. NiMoO4 species were reduced more easily than MoO3 species on the step-impregnated NiMo oxides. Ni0 species promoted the dissociation of methane, induced the reduction of molybdenum oxide and supplied active hydrogen and carbon species for the carburization process. The co-impregnation method was conducive to refine the particles.

Synthesis of molybdenum-incorporated mesoporous silicates by evaporation-induced self-assembly: Insights into surface oxide species and corresponding olefin metathesis activity

Molybdenum-incorporated mesoporous silicates with different Si/Mo ratios were synthesized via the Evaporation Induced Self-Assembly (EISA) method. SAXS and nitrogen physisorption results confirm the ordered mesoporosity. The BET surface area, pore volume and pore size distribution generally decrease with Mo loading while preserving the mesoporosity. Highly dispersed monomeric and oligomeric MoOx species (Mo6+ oxidation state) were evident from diffuse reflectance UV–Vis and XPS spectra. H2-TPR results confirm the existence of polymeric MoOx and bulk crystalline MoO3 species. At lower loadings, Mo exits in both tetrahedral and octahedral symmetry as established by Mo L3-edge XANES studies. Mo-EISA catalysts with highly dispersed isolated MoOx sites display stable activity for 2-butene + ethylene metathesis that is comparable to those reported for WO3/SiO2 catalysts.

Stable Mo/HZSM-5 methane dehydroaromatization catalysts optimized for high-temperature calcination-regeneration

Dehydroaromatization of methane is a promising reaction to directly convert methane into aromatics and hydrogen. The main drawback of this reaction is the rapid deactivation of the Mo/HZSM-5 catalyst due to coking. Regeneration at high reaction temperature by air calcination is not possible due to extensive dealumination of the zeolite. We investigated the structural and textural stability of HZSM-5 as a function of the Mo loading in air at high temperature (550–700°C) and demonstrated that lowering the Mo loading below 2wt% greatly improves the oxidative stability of Mo/HZSM-5. At low Mo loading (1–2wt% Mo), Mo is predominantly in the zeolite micropores as cationic mono- and dinuclear Mo-oxo complexes irrespective of the calcination temperature. At higher loading, most of the initially aggregated Mo-oxide at the external surface is dispersed into the micropores upon calcination above 550°C, resulting in reaction of mobile MoO3 species with framework Al, aluminum molybdate formation and irreversible damage to the zeolite framework. A DFT-based free energy analysis indicates that water formation from reaction of MoO3 with Brønsted acid sites and high concentration of Mo during MoO3 migration causes aluminum molybdate formation. The high oxidative stability of Mo/HZSM-5 with low Mo loading makes them suitable candidates for a novel isothermal (700°C) reaction – air regeneration protocol of methane dehydroaromatization. Whereas a 5wt% Mo/HZSM-5 rapidly lost its initial activity, an optimized 2wt% Mo/HZSM-5 catalyst retained more than 50% of its initial activity after 100 reaction-regeneration cycles (1week) with a substantially improved total aromatics yield.

Effect of different weight loadings of MoO x /SBA-15 on the oxidative dehydrogenation of n-octane

This study examines the effect of different weight loadings of molybdenum as molybdenum oxide, supported on SBA-15 for the oxidative dehydrogenation of n-octane. The loadings of molybdenum on SBA-15 were performed by wet impregnation method the resultant catalysts were characterised by ICP-OES, BET physisorption studies, PXRD, Raman spectroscopy, TEM and SEM. Raman spectroscopy showed the presence of monomeric MoOx species at 4 wt%, monomeric and polymeric species at 7 wt%, polymeric and crystalline MoO3 species at 10 wt% and only crystalline Mo oxide at 18 wt%. SBA-15 as the catalyst is active but mainly selective to cracked products (33 %) and COx (32 %), whereas the loaded catalysts produced octenes and C8 aromatics. At similar conversion, the highest selectivity to octenes was observed with the 4 wt% catalyst which decreased with an increase in the molybdenum loadings. The highest selectivity to aromatics was observed with the 7 wt% catalyst. When the 10 wt% catalyst was tested over the temperature range of 350–550 °C, the conversion increased and selectivity towards aromatics was promoted. The extent of non-selective oxidation increased with an increase in the oxygen content in the feed while a variable GHSV study revealed that the octenes, cracked products and CO2 are the primary products of the reaction.