Modified iron-molybdate catalysts with various metal oxides by a mechanochemical method: enhanced formaldehyde yield in methanol partial oxidation

A mechanochemical method was employed to prepare modified iron molybdate catalysts with various metal salts as precursors. The physicochemical properties of the iron molybdate catalysts were characterized, and their performances in catalyzing the reaction from methanol to formaldehyde (HCHO) were evaluated. Iron molybdate catalysts doped with Co(NO₃)₂·6H₂O and Al(NO₃)₃·9H₂O resulted in high HCHO yields. Compared with a commercial catalyst, the HCHO yields in the reaction with the modified catalyst at an optimal Co/Mo molar ratio reached 97.37%. According to chemical state analysis, the formation of CoO and the efficient decrease in the MoO₃ sublimation rate could be important factors enhancing the HCHO yield in reactions catalyzed with iron molybdate doped with different Co/Mo mole ratios.     

Surface Segregation in Iron Molybdate Catalysts

The high selectivity of iron molybdate catalysts for the production of formaldehyde from methanol is somewhat surprising in view of the very different behaviour of the individual oxides of Fe and Mo for this reaction. The former, on its own, is a complete combustor of methanol, whereas the latter is highly selective. Here we use STEM (scanning transmission electron microscopy) at high resolution to image the surface of small particles of the catalyst and to show that this high selectivity is due to the dominance of the surface region by molybdenum oxide.     

Recent progress in the use of in situ X-ray methods for the study of heterogeneous catalysts in packed-bed capillary reactors

Synchrotron-based X-ray techniques, such as Diffraction and Absorption Spectroscopy (XAS), can be readily employed to study catalysts in action, thereby offering great potential for revealing the mechanism and behaviour of catalytic solids both during preparation and reaction. The continued advancement of X-ray generation and collection mean that it is now possible to obtain high quality data from catalysts under reaction conditions with second/sub-second time resolution. In this paper, we describe in detail a specific setup which can be used to obtain transmission in situ data. It is able to mimic industrial preparation/reaction environments and has been developed to such an extent that such measurements are now routine. To illustrate its applicability, we present time-resolved diffraction data obtained from an iron molybdate-based catalyst under pseudo industrial operating conditions revealing its bulk solid-state chemistry and stability, and further show how the catalyst behaviour changes as a function of the Fe/Mo ratio. We also illustrate the versatility of this setup in obtaining data using simultaneous multiple techniques (including non-X-ray-based methods, e.g. UV–vis) from an iron molybdate catalyst under methanol/air-flow. We conclude with a brief outlook towards the future, in which we identify new possibilities for studying catalysts in action which could yield insight into their preparation and behaviour.     

Molybdenum ZSM-5 zeolite catalysts for the conversion of methane to benzene

This paper describes characterization studies of Mo-HZSM-5 zeolite catalysts active for the non-oxidative conversion of methane to benzene. FTIR, and NMR evidence is presented for migration of molybdenum into the zeolite pores during catalyst calcination at high temperatures. Mo K-edge EXAFS confirms that calcination produces highly dispersed oxomolybdenum or molybdate species which are converted to a molybdenum carbide phase under reaction conditions. Factors determining catalyst performance are discussed.     

Iron catalyst supported on carbon nanotubes for Fischer-Tropsch synthesis: Effects of Mo promotion

Our studies on the application of carbon nanotubes (CNTs) as support have shown that iron catalysts supported on CNTs are active and selective catalysts for Fischer-Tropsch synthesis (FTS). However, these catalysts experienced deactivation as a result of active site agglomerations. In order to control the agglomeration of active site, which is an important step in developing a novel catalyst supported on carbon-based supports, the effects of Mo promotion on deactivation behavior of iron catalysts supported on CNTs were studied. In this work the properties and catalytic performance of unpromoted iron catalysts were compared with a promoted catalyst with different Mo contents (0.5, 1, 5, and 12 wt%). Based on TEM and XRD analyses, promotion of the catalysts with Mo resulted in production of smaller metal particles compared to the unpromoted iron catalyst. According to XRD analysis, Mo species were deposited in their amorphous structure. TPR analyses showed that addition of Mo increased reduction temperature significantly. Based on TEM and XRD analyses, the particle size of the iron oxides in the unpromoted catalyst increased from 16 to 25 nm under FT operating conditions, while the particle size of the iron oxide in the Mo promoted catalysts (∼12-14 nm) did not change noticeably under the same operating conditions. Activity, selectivity and stability of the unpromoted and Mo promoted catalysts showed that addition of 0.5-1 wt% Mo resulted in a more stable catalyst. Higher contents of Mo (5 and 12 wt%) decreased the activity of the catalysts due to catalytic site coverage and lower extent of reduction. Mo promotion (0.5-12 wt%) increased the selectivity of the catalysts toward lighter hydrocarbons. The promotion of the iron catalyst with 0.5 wt% of Mo stabilized the activity of the catalyst with minimal increase (2%) in methane selectivity.     

Hydrogenation of a brown coal pretreated with water-soluble nickel/molybdenum and cobalt/molybdenum catalysts

Loy Yang brown coal treated with cobalt acetate/ammonium molybdate (Co/Mo) gave lower conversions than the very high values obtained for the same coal treated with nickel acetate/ammonium molybdate (Ni/Mo) when reacted with hydrogen at 400°C. The difference in conversions obtained between the two catalyst systems decreased with increasing time. Addition of sulphur as carbon disulphide (CS₂) eliminated the difference between the Co/Mo and Ni/Mo catalyst systems, but neither system was more active than a sulphided Mo catalyst. Addition of a hydrogen donor solvent, tetralin, to a reaction in the absence of sulphur decreased conversion for the Ni/Mo catalysed system, but increased that for the Co/Mo system. The order of activity in reactions without solvent or added sulphur for the coal treated with the individual metals was CoMo < Ni. In the presence of sulphur the order was Co Ni < Mo; the addition of sulphur led to no significant improvement with Co catalysts.     

Determination of Optimum Conditions and the Kinetics of Methanol Oxidation

In this study, the catalytic oxidation of methanol to formaldehyde was investigated in a laboratory‐scale fixed‐bed catalytic reactor, under a large number of different conditions. Iron‐molybdate catalysts supported by silica or alumina with a molybdenium/iron (Mo/Fe) ratio of 1.5, 3 and 5 were studied for the gas phase reaction. In order to obtain the optimum conditions, six different temperatures in the range of 250–375 °C and three different space times of 50.63, 33.75 and 20.25 g/(mol/h) were investigated. After determining the optimum conditions for this reaction, experiments aimed at understanding the reaction kinetics, were carried out. These experiments were performed on the catalyst favoring the formation of formaldehyde, which has a (Mo/Fe) ratio of 5 on a silica support. Seven reaction models derived by the mechanisms cited in the literature were tested to elucidate the kinetics of the reaction and the surface reaction controlling model was found to be the most suitable reaction mechanism.     

Effects of iron precursors on the structure and catalytic performance of iron molybdate prepared by mechanochemical route for methanol to formaldehyde

Mechanochemical synthesis has been applied for many novel material preparations and gained more and more attention due to green and high-efficiency recently. In order to explore the influences of iron precursors on structure and performance of iron molybdate catalyst prepared by mechanochemical route, three typical and cheap iron precursors have been used in preparation of iron molybdate catalyst. Many characterization methods have been employed to obtain the physical and chemical properties of iron molybdate catalyst. Results indicate that iron precursors have the significant impact on the phase composition, crystal morphology and catalytic performance in the conversion of methanol to formaldehyde. It is hard to regulate the phase composition by changing Mo/Fe mole ratios for Fe_2(SO_4)_3 as iron precursor. In addition, as for Fe_2(SO_4)_3, the formaldehyde yield is lower than that from iron molybdate catalyst prepared with Fe(NO_3)_3·9H_2O due to the reduction in Fe_2(MoO_4)_3 phase as active phase. Based on mechanochemical and coprecipitation method, the solvent water could be a key factor for the formation of MoO_3 and Fe_2(MoO_4) for FeCl_3·6H_2O and Fe_2(SO_4)_3 as precursors. Iron molybdate catalyst prepared with Fe(NO_3)_3·9H_2O by mechanochemical route, shows the best methanol conversion and formaldehyde yield in this reaction.     

Effect of high temperature treatment on the properties of fe-mo oxide catalysts

In this study the structural and compositional changes that Fe-Mo oxide catalysts undergo during treatment at elevated temperatures were investigated. Commercial and laboratory prepared catalysts were examined. The changes in catalyst properties were determined by low temperature nitrogen adsorption, scanning electron microscopy, X-ray diffraction, X-ray fluorescence and thermogravimetric analysis. The activities of the catalysts for the oxidation of methanol in air to formaldehyde were measured using an integral bed reactor. The results showed that treatment at elevated temperatures resulted in the growth and segregation of Fe₂(Mo0₄)₃ and Mo0₃ crystals resulting in a loss of specific surface area. The changes in specific activity can be explained in terms of molybdenum depletion from a molybdenum rich iron molybdate phase.     

Potassium-modified molybdenum-containing SBA-15 catalysts for highly efficient production of acetaldehyde and ethylene by the selective oxidation of ethane

Mo-incorporated SBA-15 (Mo-SBA-15) catalysts with different Mo:Si molar ratios were synthesized by a direct hydrothermal method, and SBA-15-supported Mo catalysts (Mo/SBA-15 and K-Mo/SBA-15) were prepared by an incipient-wetness impregnation method. The structures of the catalysts were characterized by means of N₂ adsorption–desorption, XRD, TEM, FT-IR, and UV-Raman, and their catalytic performance for the oxidation of ethane was tested. Turnover frequency and product selectivity are strongly dependent on the molybdenum content and catalyst preparation method. Furthermore, the addition of potassium promotes the formation of isolated tetra-coordination molybdenum species and potassium molybdate. The K/Mo-SBA-15 catalysts possess much higher catalytic selectivity to acetaldehyde in the selective oxidation of ethane than the supported molybdenum catalysts (Mo/SBA-15 or K-Mo/SBA-15). The highest selectivity of CH₃CHO + C₂H₄ 68.3% is obtained over the K/Mo-SBA-15 catalyst. Analysis of kinetic results supports the conclusion that ethane oxidation is the first-order reaction and ethane activation may be the rate-determining step for the oxidation of ethane. Ethylene is a possible intermediate for acetaldehyde formation.     

Soot oxidation catalyzed by a Cu/K/Mo/Cl catalyst: evaluation of the chemistry and performance of the catalyst

Several non-supported oxidic compounds potentially present in a Cu/K/Mo/Cl catalyst (copper molybdates, potassium molybdates, and a mixed copper-potassium molybdate (K₂Cu₂(MoO₄)₃)) have been tested individually on their activity in the oxidation of a model soot (Printex-U, which non-catalytically oxidizes at 875 K). These oxidic compounds are active between 665 and 720 K, but only after establishment of ‘tight contact’ between the catalyst and soot in a ball mill. Without the ball mill procedure (‘loose contact’) these oxides are less active (the soot oxidation temperature is shifted to about 790 K), while a ZrO₂ supported Cu/K/Mo/Cl catalyst still shows a high activity around 670 K. Hence, the ‘loose contact’ activity of the supported Cu/K/Mo/Cl catalyst is not explained by the presence of an active oxidic compound. DRIFT and XRD analyses have shown that addition of KCl to CuMoO₄ (two compounds present within the Cu/K/Mo/Cl catalysts) followed by calcination at 950 K in air, eventually results in the formation of a mixed potassium-copper molybdate. Simultaneously several volatile copper, potassium and chlorine containing compounds (e.g. K₂CuCl₄) are formed. These copper and chlorine containing compounds possess a high ‘loose contact’ soot oxidation activity between 600 and 690 K. A catalytic cycle, involving Cu₂OCl₂, is proposed to explain the high ‘loose contact’ activity of copper chlorides and supported Cu/K/Mo/Cl catalysts. The activity of the latter catalyst will be maintained as long as Cu₂OCl₂ can be reformed by reaction of copper molybdates with KCl, which serves as a chlorine supplier.     

煤的一段加氢液化的催化剂

煤的一段加氢液化使用的催化剂有可弃性催化剂,铁和钼氧化物及溶于水或油的催化剂和浸渍催化剂,其中以Co-Mo/Al_2O_3,Ni-Mo/Al_2O_3和钼酸铵为最广泛;黄铁矿能促进煤向油的转化,但却降低了脱硫率:Fe(OH)3-MoO_3-S在较低和较高温度下都是一种较活泼的催化剂;SnMo混合物明显优于纯SnO_2或无助催化剂的MoO_3/Al_2O_3;硫化的Mo(CO)_6是一种性能很好的煤加氢液化催化剂。     

Study of ternary-component bismuth molybdate catalysts by 18O2 tracer in the oxidation of propylene to acrolein

Participation of lattice oxide ions of ternary-component bismuth molybdate catalysts MBiMo O (M = Ni, Co, Mg, Mn, Ca, Sr, Ba, and Pb) was investigated using the ¹⁸O₂ tracer in the selective oxidation of propylene to acrolein. The participation of the lattice oxide ions in the oxidation is prominent on every catalyst but the extent of the participation varies significantly depending on the structure of the catalyst. Only lattice oxide ions in the bismuth molybdate phase are incorporated into the oxidized products on the catalysts (M = Ni, Co, Mg, and Mn) where M have smaller ionic radius than Bi³⁺; catalyst particles are composed of a shell of bismuth molybdates and a core of MMoO₄. On the other hand, whole oxide ions in the active particles are involved in the oxidation on catalysts having a scheelite-type structure (M = Ca, Sr, Ba, and Pb) where M has a comparable ionic radius to Bi³⁺.     

Aromatization of Methane Over Mo-Fe/ZSM-5 Catalysts

Two groups of samples were studied for the aromatization of methane over Mo-Fe/ZSM-5 catalysts. The first group contains fixed loading (5 wt%) and variable Mo/Fe ratio. The second group was prepared with fixed Mo/Fe ratio and variable loading. The samples were characterized by TGA, S _BET, XRD, NH₃-TPD and TPO analysis. NH₃-TPD results indicate that the strength of strong acid sites increases when Mo/Fe ratio decreases for samples with fixed loading. The amount of strong sites decreases and new intermediate acid sites appear on samples containing both Mo and Fe. XRD results show the presence of iron molybdate for samples impregnated with both Mo and Fe. The catalytic properties of these samples were related not only to the amount and strength of acid sites but also to the iron molybdate phase.     

Low‐temperature oxidation of methane to form formaldehyde: role of Fe and Mo on Fe–Mo/SiO2 catalysts, and their synergistic effects

The partial oxidation of methane with molecular oxygen was performed on Fe–Mo/SiO₂ catalysts. Iron was loaded on the Mo/SiO₂ catalyst by chemical vapor deposition of Fe₃(CO)₁₂. The catalyst showed good low‐temperature activities at 723–823 K. Formaldehyde was a major condensable liquid product on the prepared catalyst. There were synergistic effects between iron and molybdenum in Fe–Mo/SiO₂ catalysts for the production of formaldehyde from the methane partial oxidation. The activation energy of Mo/SiO₂ decreased with the addition of iron and approached that of the Fe/SiO₂. The concentration of isolated molybdenum species (the peak at 1148 K in TPR experiments) decreased as the ion concentration increased and had a linear relationship with the selectivity of methane to formaldehyde. The role of Fe and Mo in the Fe–Mo/SiO₂ catalyst was proposed: Fe is the center for the C–H activation to generate reaction intermediates, and Mo is the one for the transformation of intermediates into formaldehyde. Those phenomena were predominant below 775 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mo/HZSM-5上甲烷无氧芳构化催化剂制备因素的考察

采用Mo/HZSM-5作为甲烷无氧芳构化催化剂,考察了催化剂制备部分影响因素.结果表明,采用较低的nSi:nAl时(25)载体制备的催化剂活性和稳定性较好;浸渍法优于固相反应法;Mo担载的质量分数为4%时,催化剂表现出最高活性;分子筛预先经碱处理,能够明显改善催化剂稳定性.     

Catalytic conversion of urea to biuret: A catalyst screening study

Biuret was synthesized from urea in a batch reactor using various homogeneous and heterogeneous catalysts, with the aim of searching for efficient catalyst in converting non-catalytic reaction to catalytic reaction. For this purpose, zeolite, heteropolyacid, organic acid and base, multicomponent bismuth molybdate, and multicomponent bismuth molybdate-alumina mixed catalysts were tested. It was revealed that the performance of catalytic reaction was better than that of non-catalytic reaction in the synthesis of biuret from urea. Among the homogeneous acid and base catalysts tested, thionyl chloride (SOCl₂) showed the best catalytic performance. Among the heterogeneous catalysts tested, on the other hand, a mixed catalyst comprising multicomponent bismuth molybdate (Co₈Fe₃Bi₁Mo₁₂O₅₀) and alumina showed the best catalytic performance.     

Mo/REHY催化剂的加氢脱硫性能

将钼酸按溶液与REHY等体积浸渍和焙烧,制备了Mo/REHY催化剂,采用XRD和NH3-TPD对其进行表征.以质量分数0.6%的二苯并噻吩/正癸烷溶液为模型反应物评价其加氢脱硫性能.结果表明,不同焙烧温度制备的Mo/REHY催化剂,归属于REHY的晶相峰保持完好,金属活性组分Mo进入REHY体相超笼,引起REHY分子筛...     

Mo oxide modified catalysts for direct methanol, formaldehyde and formic acid fuel cells

Pt black and PtRu black fuel cell anodes have been modified with Mo oxide and evaluated in direct methanol, formaldehyde and formic acid fuel cells. Mo oxide deposition by reductive electrodeposition from sodium molybdate or by spraying of the fuel cell anode with aqueous sodium molybdate resulted in similar performance gains in formaldehyde cells. At current densities below ca. 20 mA cm⁻², cell voltages were 350–450 mV higher when the Pt catalyst was modified with Mo oxide, but these performance gains decreased sharply at higher current densities. For PtRu, voltage gains of up to 125 mV were observed. Modification of Pt and PtRu back catalysts with Mo oxide also significantly improved their activities in direct formic acid cells, but performances in direct methanol fuel cells were decreased.