Increase In Mo Loading Research Articles

Sulfated TiO2 supported molybdenum-based catalysts for transesterification of Jatropha seed oil: Effect of molybdenum species and acidity properties

A series of sulfated TiO2 supported Mo (xMo/1.5ST) catalysts were synthesized successfully and evaluated for the transesterification of Jatropha seed oil (JO) to biodiesel. Extensive characterization exhibits that the well dispersed Mo oxide species, with Mo6+ and Mo5+ oxidation states, were formed on the surface of the sulfated TiO2. The results indicate the presence of many sulfates species leads to the reduction of Mo6+ species to Mo5+ species. Furthermore, the catalytic activity of the xMo/1.5ST catalysts gradually increases with the increase of Mo-loading, although the sulfates content and the total acid intensity decrease. The transesterification process was fully investigated, and the 10Mo/1.5ST shows the highest yield of biodiesel of up to 97.42%. Additionally, the possible mechanism for the JO transesterification over Mo/1.5ST was described, and the fuel properties of the as-synthesized biodiesel conformed to the current international standards.

Effect of Metal Loading in Unpromoted and Promoted CoMo/Al2O3–TiO2 Catalysts for the Hydrodeoxygenation of Phenol

This paper reports the effects of changes in the supported active phase concentration over titania containing mixed oxides catalysts for hydrodeoxygenation (HDO). Mo and CoMo supported on sol–gel Al2O3–TiO2 (Al/Ti = 2) were synthetized and tested for the HDO of phenol in a batch reactor at 5.5 MPa, 593 K, and 100 ppm S. Characterization results showed that the increase in Mo loading led to an increase in the amount of oxide Mo species with octahedral coordination (MoOh), which produced more active sites and augmented the catalytic activity. The study of the change of Co concentration allowed prototypes of the oxide species and their relationship with the CoMo/AT2 activity to be described. Catalysts were tested at four different Co/(Co + Mo) ratios. The results presented a correlation between the available fraction of CoOh and the catalytic performance. At low CoOh fractions (Co/(Co + Mo) = 0.1), Co could not promote all MoS2 slabs and metallic sites from this latter phase performed the reaction. Also, at high Co/(Co + Mo) ratios (0.3 and 0.4), there was a loss of Co species. The Co/(Co + Mo) = 0.2 ratio presented an optimum amount of available CoOh and catalytic activity since the XPS results indicated a higher concentration of the CoMoS phase than at a higher ratio.

Stable bimetallic Ru-Mo/Al2O3 catalysts for the light alkane combustion: Effect of the Mo addition

A series of Ru-Mo/γ-Al2O3 catalysts containing fixed Ru loading (5 wt.%) and variable Mo contents (1.6, 4.8 and 9.5 wt.%), were synthesized by co-impregnation method using Ru(NO)(NO3)3 and (NH3)6Mo7O24×4H2O as metal precursors and their catalytic characteristics were evaluated for the first time in combustion of propane used as a model compound. The effect of the Ru/Mo atomic ratio (3:1, 1:1 and 1:2) on the structure of the reduced samples was investigated by ICP-AES, BET, XRD, HRTEM, SEM-EDX, H2-TPR and chemisorption of hydrogen and oxygen. The surface properties of the catalysts were detailed studied by XPS spectroscopy. Structural characterization data lead to conclusion that a synergy effect of ruthenium and molybdenum is observed in the Ru-Mo/γ-Al2O3 catalysts. An increase of Mo loading caused the formation of smaller nanoparticles (dav = 1.3, 1.0 and 0.8 nm, respectively) as compared to the monometallic Ru system (dav = 1.4 nm). For low Mo loading (Ru:Mo atomic ratio of 3:1) the H2 uptake was higher (H/Ru = 0.55) than in the Ru/γ-Al2O3 sample (H/Ru = 0.52). This leads to the high activity of the 5%Ru-1.6%Mo catalyst in the propane combustion (TOF = 0.034 (s−1)). Moreover, the catalytic stability was much higher for the bimetallic Ru-Mo systems than for the monometallic Ru catalyst. Despite their high thermal stability under oxygen-rich atmosphere, bimetallic catalyst containing 4.8%Mo (Ru:Mo atomic ratio of 1:1) was less active in propane oxidation (TOF = 0.016 (s−1)) than the Ru system (TOF = 0.029 (s−1)). The lower activity results from partial blocking the active centers on the ruthenium by covering them with an inactive MoOx layer. At the highest Mo content (Ru:Mo atomic ratio of 1:2) the blocking of the active Ru centres increases, much lower H2 chemisorption capacity and a significant increase of the metallic Ru (74%) and metallic Mo (25%) species, resistant to oxidation at low temperature, were observed. This leads to very low activity of the 5%Ru-9.5%Mo catalyst in the propane combustion. Importantly, our studies also revealed that the molybdenum modifies interaction of hydrogen and oxygen with ruthenium in the Ru-Mo catalysts. For hydrogen, the adsorption process becomes activated and Mo species weaken the adsorption strength.

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.

Study on Mo-doped of Li1.18Ni1/3Co1/3Mn1/3O2 Lithium-rich Ternary Cathode Materials

The layered Li1.18(Ni1/3Co1/3Mn1/3)1-xMoxO2 cathode material was prepared by mixing lithium carbonate with precursor-nickel cobalt manganese hydroxide complex which was prepared by co-precipitation method with Mo-doped. The physical and chemical parameters, crystal structure, morphology and electrochemical properties were investigated by ICP analysis, X-ray diffraction, SEM and electrochemical tests, respectively. XRD results showed that doping Mo had no effect on the structure of pristine materials. However, the second phase of Li2MoO4 was dissected until the Mo loading reached 4 at%. The SEM images exhibited that the primary particles size decreased with the increase of Mo loading. Electrochemical measurements showed that the high rate discharge capability and cycle stability of the material can be improved significantly by a small amount of Mo (2 at%). The sample with 2 at% Mo-doped amount exhibited a high initial discharge capacity of 146.3 mAh g-1 at 0.3C rate under the voltage range of 2.5∼4.2V, as well as better cycle stability after 50 cycles. Therefore, Mo-doped is a useful method to improve large current discharge capability of the lithium insertion nickel cobalt manganese oxides.

Dry reforming of methane over nano-Mo2C/Al2O3 catalyst: Effect of carburization conditions on excess carbon deposition

ABSTRACTIn this study, temperature-programmed carburization (TPC) has been used to prepare Mo2C/Al2O3 catalyst for carbon dioxide reforming of methane. Also, the effect of carburization conditions has been examined on excess carbon formation over the prepared catalysts. Minimum excess carbon of 0.51 wt% was obtained in a flow of 12.5 vol% CH4/H2 gas mixture, final carburization temperature of 750°C, and Mo loading of 12.5 wt%. This catalyst exhibited better initial activity due to lower excess carbon and higher carbide dispersion compared with other examined catalysts. However, the results of time on stream performance in the dry reforming of methane (DRM) revealed an increase in durability with an increase in Mo loading.

Electrooxidation of H2/CO on carbon-supported PtRu-MoOx nanoparticles for polymer electrolyte fuel cells

Ternary PtRu-MoOx catalysts with various Mo compositions have been investigated as anode electrocatalytic materials for a polymer electrolyte fuel cell fed with H2/CO mixtures. Electrocatalysts have been prepared using a highly reproducible two step method, which allowed good control over the composition and particle size. All the prepared catalysts record a total metal loading close to 30 wt%, and a Mo load of 0, 1 and 3 wt%, supported on carbon Vulcan XC-72R, keeping the Pt/Ru atomic ratio constant. The incorporation of different amounts of Mo over the PtRu system does not modify structural characteristics such as particle size and crystal phases. However, the surface composition depends largely on the amount of Mo. An increase in the Mo loading to 3 wt% resulted in a decrease of the Pt surface area. The in situ FTIR technique has been used to investigate the CO oxidation process. The extent of CO poisoning was found to be lower for the trimetallic catalysts than for the binary catalyst at a potential below 0.25 V. The fuel cell performance was evaluated at 80 °C in a PEMFC fed with H2/CO (10 ppm). Polarization curves for the catalysts show that activity depends heavily on composition, with catalysts with a small amount of Mo (1 wt%) displaying the highest CO tolerance. An increase in Mo loading (3 wt%) decreases activity of the PtRuMo, although it also reduces CO poisoning. The presence of Mo5+ species must be crucial for reducing the saturation coverage of irreversibly adsorbed CO on Pt surface atoms at very low potentials. However, the surface metal ratio of Pt/Mo (wt%) must be higher than 4, in order to keep the enough surface bare platinum sites, which are required for the dissociative adsorption of molecular H2.

The effect of potassium addition on the state of the components in the oxide precursor of the (Ni)(Mo)/γ-Al 2O 3 water-gas shift catalysts: FT-IR, diffuse reflectance and Raman spectroscopic studies

One-component samples containing K, Ni, and various concentrations of Mo were prepared by incipient wetness impregnation technique. Bi- and tri- component samples have been prepared from the calcined one- and bi-component samples following the same procedure. The samples were characterized by SSA, FT-IR, DRS and Raman measurements. The decrease of the ratio Ni 2+(Td)/Ni 2+(Oh) with the increase of Mo loading and the re-dispersion of Mo phase after the Ni addition on the one-component Mo containing samples proved the occurrence of interactions between these components in the bi-component NiMo-containing samples. Most probably Ni–Mo–O surface species with different number of Mo-oxo and Ni-oxo entities are formed, depending on the Ni/Mo atomic ratio. It may be accepted, that the Ni 2+ ions are partially localized into the molybdate layer without forming well-defined phases. Two kinds of K + ions have been determined in the corresponding samples, interacting (“ bounded” K + ions) and not interacting (“ free” K + ions) with the rest of the supported phases. The potassium deposition increased the dispersion of Mo phase and influenced the coordination state of the Mo 6+ and Ni 2+ ions in the bi-component KMo-, KNi-containing samples and the tri-component KNiMo-containing samples. It provoked partial transformation of the polymeric Mo 6+(Oh) species into monomeric Mo 6+(Td) ones and Ni 2+(Td) species predomination over Ni 2+(Oh) ones. Most probably, new complex K–Ni–Mo–O species were formed on the support surface in the case of the tri-component samples.

Catalytic activities and surface properties of zeolite-supported molybdenum nitrides for NO reduction with H 2

A series of zeolite (H-ZSM-5)-supported molybdenum nitride catalysts with Mo loading ranging from 2 to 30 wt.% were synthesized by temperature-programmed nitridation in a flow of NH 3. The surface properties of the nitride samples were characterized by XPS, H 2-TPR, and XRD techniques and their catalytic activities were evaluated for NO reduction with H 2. For the fresh samples, molybdenum nitrides coexisted with oxides on the zeolite. With the increase of Mo loading from 2 to 30 wt.%, the degree of nitridation increased linearly with the increase of Mo loading. We observed that a catalyst with higher Mo loading exhibited higher initial activities. The nitrided 2 wt.% Mo/H-ZSM-5 catalyst was the most stable and NO conversion to N 2 remained unchanged within a test period of 15 h. For the catalysts with Mo loading above 2 wt.%, catalytic activities decreased with time on stream. After 15 h, the nitrided 2 wt.% Mo/H-ZSM-5 catalyst was the most active among the tested catalysts. The results of H 2-TPR measurements for the used and oxygen-saturated catalysts revealed that catalyst deactivation was a result of oxygen incorporation into the nitride lattices. The strong interaction between the molybdenum species and H-ZSM-5 zeolite as well as the lowering of H 2-reduction temperature of surface oxygen might be the reasons for the good performance of the nitrided 2 wt.% Mo/H-ZSM-5 catalyst for NO reduction with H 2.

Structure and Reactivity of Molybdenum Oxide Catalysts Supported on La2O3-Stabilized Tetragonal ZrO2

A series of molybdenum oxide catalysts with Mo loadings in the range 2.5−12.5 wt % Mo supported on La2O3-stabilized ZrO2 was prepared by impregnation. X-ray diffraction results of the catalysts showed the diffraction patterns of crystalline MoO3 from 10 wt % Mo. Dispersion of molybdena was determined by the oxygen chemisorption method, and it was found to decrease with an increase in Mo loading due to formation of MoO3 crystallites at higher Mo loadings. Temperature-programmed reduction results suggest that the reducibility is found to decrease with Mo loading as a result of the decrease in dispersion. The acidity of the catalysts was found to increase with Mo loading, and the activity of the catalysts also found to increase with the increase in Mo loading up to 7.5 wt % Mo loading. Laser Raman spectra of the catalysts show the Raman bands due to MoO3 from 7.5 wt % Mo at 819 and 997 cm-1. At lower Mo loadings, highly dispersed species were observed. The catalytic properties were evaluated during the ammoxidation of toluene to benzonitrile and were related to the oxygen chemisorption sites on the support surface.

03/01627 Chemical characteristics of coke on Mo/HZSM-5 catalysts for methane dehydroaromatization under nonoxidative conditions by TP techniques: Liu, H.-M. et al. Gaodeng Xuexiao Huaxue Xuehao, 2002, 23, (8), 1556–1561. (In Chinese)

Over Mo/HZSM 5 catalysts, various carbonaceous depositions occurred during the course of methane dehydroaromatization(MDA). These species of surface carbon formed on HZSM 5 zeolite or Mo/HZSM 5 catalysts with different Mo loadings were investigated by means of TPH, TPCO 2 and TPO in combination with thermal gravimetric analysis(TG). The results of TG revealed that, the total amount of coke formed on 6Mo/MCM 22 during TPSR is larger than those formed on HZSM 5 zeolite, 2Mo/HZSM 5 and 10Mo/HZSM 5 catalysts. The TPO profiles recorded during the procedure of coke burning off show two different temperature peaks. The results of TPO and TG after TPH suggested that, the TPH experiments only had an effect on the coke burnt off at a high temperature, but didn′t result in the diminishing of the coke burnt off at low temperature peak. On the other hand, the result of the coked catalyst after succeeding TPCO 2 experiments exhibited an obvious reduction in the areas of both the high and low temperature peaks, particularly in the area of the low temperature peak. The study on the catalysts with different Mo loadings suggested that, the percentage of the coke burnt off at a low temperature turned larger with the increase of Mo loading, respectively. And the change trend of the coke burnt off at a high temperature was opposite exactly. By using the experiments of TPSR, TPH, TPCO 2 and TG, quantitative analysis of the coke and the kinetics of its burning off process have been done. The results show that, either TPH or TPCO 2 can diminish the starting temperature and decrease the activation energy, and there are some differences among the catalysts with various Mo loadings.

Alkylation of phenol with methanol over molybdenum oxide supported on NaY zeolite

A series of MoO 3/NaY catalysts were prepared with Mo loadings ranging from 2 to 16 wt% and characterized by X-ray diffraction (XRD), BET specific surface area and temperature-programmed desorption (TPD) of ammonia. XRD results revealed that the crystallinity of NaY zeolite was found to decrease with increase in Mo loading in the catalysts. The total acidity measured by ammonia TPD of the catalysts was found to decrease with increase in Mo loading. The catalytic properties were evaluated for the vapor phase alkylation of phenol with methanol and the results were correlated with results obtained from different characterization techniques. The conversion of phenol decreases as Mo loading increases in the catalyst. With increase in Mo loading on NaY zeolite the selectivity for the formation of C-alkylated compounds was decreased. However, the selectivity towards the formation of O-alkylated products was increased.

Characterization and reactivity of molybdenum oxide catalysts supported on zirconia

A series of MoO 3/ZrO 2 catalysts with Mo loading varying from 1 to 12 wt.% was prepared. Each catalyst was characterized by oxygen chemisorption, X-ray diffraction (XRD), electron spin resonance (ESR), temperature programmed reduction (TPR), and temperature programmed desorption (TPD) of ammonia. X-ray diffraction patterns indicate the presence of a microcrystalline molybdena phase at higher loadings. Dispersion of molybdena was determined by the oxygen chemisorption at 623 K, using a static method on the samples prereduced at the same temperature. At low Mo loadings, i.e. <7.5%, molybdenum oxide is found to be present in a highly dispersed state. ESR results suggest the presence of Mo 5+ in the reduced catalysts. TPR results suggest that the reducibility of MoO 3 increases with the increase of Mo loading in Mo/ZrO 2 catalysts. TPD of ammonia results suggest that the acidity of the catalysts is increasing with the increase of molybdena loading. The catalytic properties were evaluated for the vapor-phase ammoxidation of 3-picoline to nicotinonitrile and were found to be related to oxygen chemisorption sites.