Reactivity and surface properties of silica supported molybdenum oxide catalysts for the transesterification of dimethyl oxalate with phenol

A series of MoO₃/SiO₂ catalysts were prepared with Mo loadings ranging from 1 to 16 wt% and applied to the transesterification of dimethyl oxalate (DMO) with phenol. The results showed that the catalyst of MoO₃/SiO₂ with 1 wt% Mo content performed best, giving 54.6% conversion of DMO and 99.6% selectivity to target products, methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO). The surface properties were investigated by means of X-ray diffraction (XRD), X-ray photoelectron (XPS), BET specific surface area, temperature-programmed desorption (TPD) of ammonia, and FTIR analysis of adsorbed pyridine. XPS and XRD analyses indicated that Mo(VI) species was highly dispersed at low Mo loading and MoO₃ of the crystal structure appeared at higher loading. NH₃-TPD characterization and FTIR analysis of adsorbed pyridine demonstrated that only Lewis weak acids were present on catalyst surface and the amount of Mo loading has little effect on the strength of the surface acid on MoO₃/SiO₂. The catalytic results exhibited that the synergetic effect of Mo active centers with weak Lewis acid sites catalyzed transesterification of DMO with phenol.     

Preparation and characterization of Ni-B/SiO2sol amorphous catalyst and its catalytic activity for hydrogenation of nitrobenzene

Supported Ni-B/SiO₂sol amorphous alloy catalyst was prepared by a sol-gel and impregnation-chemical reduction method, and the effects of the tetraethyl orthosilicate (TEOS) and ammonia ratio, and the nickel loading amount on the nitrobenzene hydrogenation were also investigated. The results showed that Ni-B amorphous alloy catalyst supported on the silica sol increased the specific surface area of catalysts, improved the catalytic activity of Ni-B amorphous alloy catalyst, and the Ni species on the surface existed in the form of Ni²⁺. The optimal TEOS and ammonia ratio and nickel loading amount was 1.0 and 10%, respectively, and when using this optimal Ni-B/SiO₂sol catalyst, the nitrobenzene conversion was 99.9% with an aniline selectivity of 99.8%, and after 5 recycles, the Ni-B/SiO₂sol maintained a good stability.     

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

A series of MoO₃/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.     

Influence of reduction temperature and metal loading on the performance of molybdenum phosphide catalysts for dibenzothiophene hydrodesulfurization

Two series of alumina-supported molybdenum phosphide (MoP) catalysts with low and high metal loadings were prepared by temperature-programmed reduction of the oxidic catalyst precursors in hydrogen to different temperatures (823, 923, 1023 and 1123 K, respectively). Effects of reduction temperature and metal loading on the surface distribution and the type of species formed were studied by TPR, S_BET, XRD, HRTEM, ³¹P NMR, ²⁷Al NMR and in the reaction of dibenzothiophene (DBT) hydrodesulfurization (HDS) performed in a flow reactor at 553 K and total hydrogen pressure of 3.4 MPa. HRTEM and ³¹P NMR confirmed formation of MoP phase on all catalysts. The 9.9 wt% Mo catalyst activated at lowest reduction temperature (823 K) was found to be most active among the catalysts studied. The presence of a low amount of Mo⁰ species on the surface of this catalyst does not appear to be a drawback for the catalytic activity. The increase in both metal loading (from 9.9 to 15 wt% Mo and from 3.2 to 4.8 wt% P) and reduction temperature (from 823 to 1123 K) was found to be detrimental for HDS activity due to sintering of active phase, and also to decrease in specific area and formation of phosphate species.     

CH4 reforming with CO2 for syngas production over nickel catalysts supported on mesoporous nanostructured γ-Al2O3

Nanostructured γ-Al₂O₃ with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, BET, TPR, TPH, SEM and TPO techniques. The BET analysis showed a high surface area of 204m²g^?1 and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The results revealed that an increase in nickel loading from 5 to 15 wt% decreased the surface area of catalyst from 182 to 160 m²g^?1. In addition, the catalytic results showed an increase in methane conversion with increase in nickel content. TPO analysis revealed that the coke deposition increased with increasing in nickel loading, and the catalyst with 15 wt% of nickel showed the highest degree of carbon formation. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Increasing CO₂/CH₄ ratio increased the methane conversion. The BET analysis of spent catalysts indicated that the mesoporous structure of catalysts still remained after reaction.     

The effect of promoters on the CO<Subscript>2</Subscript> reforming activity and coke formation of nanocrystalline Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts prepared by microemulsion method

Mesoporous nanocrystalline nickel-alumina promoted catalysts with high surface area were prepared by microemulsion (ME) method and employed in dry reforming of methane reaction. The catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller surface area analysis (BET), temperature programmed reduction (TPR) and temperature programmed oxidation (TPO) techniques. The results showed that the prepared catalysts had high porosity with great surface area and small crystallite size. Among the K₂O, MgO, CaO and BaO promoters, the MgO promoter showed considerable effect on catalytic performance and coke suppression of catalyst.     

Performance of Ni catalyst supported on La-hexaaluminate in CO<Subscript>2</Subscript> reforming of CH<Subscript>4</Subscript>

CO₂ reforming of CH₄ was performed using Ni catalyst supported on La-hexaaluminate which has been an well-known material for high-temperature combustion. La-hexaaluminate was synthesized by sol-gel method at various conditions where different amount of Ni (5–20 wt%) was loaded. Ni/La-hexaaluminate experienced 72 h reaction and its catalytic activity was compared with that of Ni/Al₂O₃, Ni/La-hexaaluminate shows higher reforming activity and resistance to coke deposition compared to the Ni/Al₂O₃ model catalyst. Coke deposition increases proportionally to Ni content. Consequently, Ni(5)/La-hexaaluminate(700) is the most efficient catalyst among various Ni/La-hexaaluminate catalysts regarding the cost of Ni in Ni(X)/La-hexaaluminate catalysts. BET surface area, XRD, EA, TGA and TPO were performed for surface characterization. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Effect of vanadium surface density and structure in VOx/TiO<Subscript>2</Subscript> on selective catalytic reduction by NH<Subscript>3</Subscript>

We investigated the correlation between vanadium surface density and VOx structure species in the selective catalytic reduction of NOx by NH₃. The properties of the VOx/TiO₂ catalysts were investigated using physicochemical measurements, including BET, XRD, Raman spectroscopy, FE-TEM, UV-visible DRS, NH₃-TPD, H₂-TPR, O₂-On/Off. Catalysts were prepared using the wet impregnation method by supporting 1.0-3.0 wt% vanadium on TiO₂ thermally treated at various calcination temperatures. Through the above analysis, we found that VOx surface density was 3.4 VOx/nm², and the optimal V loading amounts were 2.0-2.5 wt% and the specific surface area was 65-80m²/g. In addition, it was confirmed that the optimal VOx surface density and formation of vanadium structure species correlated with the reaction activity depending on the V loading amounts and the specific surface area size.     

C<Subscript>2</Subscript>H<Subscript>6</Subscript>/CO<Subscript>2</Subscript> oxidative dehydrogenation (ODH) reaction on nanostructured CrAPSO-34 catalyst: One-pot hydrothermal vs. conventional hydrothermal/impregnation catalyst synthesis

A series of Cr incorporated SAPO-34 catalysts varying in Cr content and a Cr supported SAPO-34 catalyst were prepared by one-pot hydrothermal and incipient-wetness impregnation methods, respectively. The synthesized materials were characterized by XRD, FESEM, TEM, BET, EDX dot mapping, TPD-NH₃ and FTIR, and tested in ethane dehydrogenation with CO₂ reaction. The incorporation of Cr³⁺ into the SAPO-34 framework and impregnation of Cr species were proved by TEM technique. With increase in the incorporated Cr content, smaller cubic crystals and amorphous particles were obtained. However, the extra-framework species probably appeared. Chromium impregnation led to micropore blockage and surface coverage partly, resulting in morphology change somewhat, significant decrease of surface area and acidity as evidenced by FESEM, TEM, BET and TPD-NH₃ analysis. However, one-pot synthesis not only preserved the structure of SAPO-34 but also allowed higher surface area, more effective surface acidity and better chromium dispersion to be achieved, features that account for superior catalytic performance and stability of directly synthesized Cr rich catalyst. The Cr incorporated SAPO-34 catalyst containing rich amount of Cr exhibited the best catalytic activity, showing 38% ethylene yield at 700 °C even after 5 h on-stream operation.     

Surface properties and catalytic behavior of MoO3/SiO2 in esterification of acetic acid with ethanol

A series of MoO₃/SiO₂ catalysts was prepared by an impregnation method with Mo loadings ranging from 1 to 50 wt%. The original and calcined samples at 400 °C were characterized by thermogravimetry (TG), differential thermogravimetry (DTG), differential scanning calorimetry (DSC), X‐ray diffraction (XRD), Fourier transform infra‐red (FTIR) spectroscopy, and nitrogen adsorption measurements. The surface acidity and basicity of the catalysts were investigated by the dehydration–dehydrogenation of isopropanol and the chemisorption of pyridine. The catalytic esterification of acetic acid with ethanol was carried out at 220 °C in a conventional fixed‐bed reactor at 1 atm using air as a carrier gas. The results clearly revealed that silica–molybdena catalysts were active and selective towards the formation of ethyl acetate. Moreover, the catalyst containing 20 wt% MoO₃ was the most active and selective one. The results emphasize the importance of the surface acid sites together with the specific surface area of the prepared catalyst, towards ester formation. Copyright © 2005 Society of Chemical Industry     

Support effect on the properties of iron–molybdenum hydrodesulfurization catalysts

Two series of Mo and Fe containing catalysts have been prepared over alumina and titania supports using H₃PMo₁₂O₄₀ heteropolyacid (HPMo) and Fe salt of HPMo. Catalysts have been characterized by BET, SEM, IR, TPR, XPS methods and by their HDS activity in the reaction of thiophene conversion. The TiO₂-supported catalysts with low Mo concentration (6 wt%) show higher HDS activity than the catalyst with 12 wt% Mo. Iron promoting effect (Fe/Mo ~ 0.1) is observed with both, the alumina- and titania-supported catalysts. Iron supported over alumina increases Mo reducibility and decreases it on TiO₂-supported catalysts. Compared to alumina-supported catalysts, the TiO₂-supported catalysts show higher surface concentration of Mo⁶⁺ and Mo⁵⁺ in octahedral coordination – Mo(Oh). Iron increases the Mo(Oh) concentration even more. After sulfidation the Fe-containing catalysts show formation of different Mo valence states (Mo⁴⁺, Mo⁵⁺, Mo⁶⁺), Fe–P, Mo–P and/or Fe–Mo–P bonds, which affect the HDS catalytic activity.     

还原终温对磷化物催化剂加氢脱硫反应性能的影响

以全硅MCM-41为载体,制备负载Ni2P和Mop型催化剂,考察了还原终温对催化剂制备和加氢脱硫反应性能的影响.对于Ni2P/MCM-41,NiO负载质量分数为12%,通过XRD和加氢脱硫反应评价得出最佳还原终温为500℃;对于MoP/MCM-41,MoO3负载质量分数为40%,通过XRD和加氢脱硫反应评价得出最佳还原...     

Studies on physico-chemical characterization and catalysis on high surface area titania supported molybdenum hydrotreating catalysts

A series of titania supported molybdenum catalysts were prepared by incipient wetness impregnation method and characterized by BET surface area, XRD, TPR, FTIR, ESCA, and low temperature oxygen chemisorption. Thiophene, cyclohexene and tetrahydrofuran were taken as model compounds for evaluating catalytic activities for hydrodesulfurization (HDS), hydrogenation (HYD), and hydrodeoxygenation (HDO) reactions, respectively. XRD results indicate that molybdenum oxide species are dispersed as a monolayer on the support up to 8 wt.% Mo and the formation of crystalline MoO₃ is observed above this loading. FTIR and TPR results showed that molybdenum oxide species were present predominantly in tetrahedral form at lower loading and polymeric octahedral forms are dominant at higher loading. Both oxygen chemisorption and rates of reaction were found to increase with increasing Mo loading up to 8 wt.% and then decrease with further increase in loading. HDS and HYD activities are more or less same but HDO activity is two times higher than HDS and HYD activities. The results are also interpreted with the help of other parameters, like dispersion, equivalent molybdenum surface area, surface coverage, crystalline size, quasi-turnover frequencies and intrinsic activities. ESCA results suggest that electron transfer is taking place from support to metal.     

Hydrotreating of gas oil on SBA-15 supported NiMo catalysts

The siliceous and the metal substituted (B or Al)-SBA-15 molecular sieves were used as a support for NiMo hydrotreating catalysts (12 wt.% Mo and 2.4 wt.% Ni). The supports were characterized by X-ray diffraction (XRD), scanning electron microscopy and N₂ adsorption–desorption isotherms. The SBA-15 supported NiMo catalysts in oxide state were characterized by BET surface area analysis and XRD. The sulfided NiMo/SBA-15 catalysts were examined by DRIFT of CO adsorption and TPD of NH₃. The HDN and HDS activities with bitumen derived light gas oil at industrial conditions showed that Al substituted SBA-15 (Al-SBA-15) is the best among the supports studied for NiMo catalyst. A series of NiMo catalysts containing 7–22 wt.% Mo with Ni/Mo weight ratio of 0.2 was prepared using Al-SBA-15 support and characterized by BET surface area analysis, XRD and temperature programmed reduction and DRIFT spectroscopy of adsorbed CO. The DRIFT spectra of adsorbed CO showed the presence of both unpromoted and Ni promoted MoS₂ sites in all the catalysts, and maximum “NiMoS” sites concentration with 17 wt.% of Mo loading. The HDN and HDS activities of NiMo/Al-SBA-15 catalysts were studied using light gas oil at temperature, pressure and WHSV of 370 °C, 1300 psig and 4.5 h⁻¹, respectively. The NiMo/Al-SBA-15 catalyst with 17 wt.% Mo and 3.4 wt.% of Ni is found to be the best catalyst. The HDN and HDS activities of this catalyst are comparable with the conventional Al₂O₃ supported NiMo catalyst in real feed at industrial conditions.     

Preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hollow spheres and their activity in methylene blue photodecomposition

PSA [poly-(styrene-methyl acrylic acid)] latex particle has been taken into account as template material in SiO₂ hollow spheres preparation. TiO₂-doped SiO₂ hollow spheres were obtained by using the appropriate amount of Ti(SO₄)₂ solution on SiO₂ hollow spheres. The photodecomposition of the MB (methylene blue) was evaluated on these TiO₂-doped SiO₂ hollow spheres under UV light irradiation. The catalyst samples were characterized by XRD, UV-DRS, SEM and BET. A TiO₂-doped SiO₂ hollow sphere has shown higher surface area in comparison with pure TiO₂ hollow spheres. The 40 wt% TiO₂-doped SiO₂ hollow sphere has been found as the most active catalyst compared with the others in the process of photodecomposition of MB (methylene blue). The BET surface area of this sample was found to be 377.6 m²g⁻¹. The photodegradation rate of MB using the TiO₂-doped SiO₂ catalyst was much higher than that of pure TiO₂ hollow spheres.     

Mn、Ce负载顺序对催化剂Mn-Ce/TiO2低温脱硝活性的影响

采用溶胶凝胶法制备了一系列Mn-Ce/TiO₂催化剂样品, 并用比表面积及孔径分析仪(BET)、X射线衍射仪(XRD)和扫描电子显微镜(SEM)等对催化剂进行了表征, 考察了活性组分Mn、Ce负载顺序对催化剂结构的影响, 并在固定床连续流动反应器上对其催化活性进行了评价。结果表明, 催化剂晶相均为锐钛矿型结构, Mn、Ce活性组分在载体表面高度分散或形成了无定形结构;Mn、Ce同时负载时催化剂表面活性组分分布均匀, 比表面积最大, 为97.6m²/g, 且催化剂孔径分布以中孔为主;Mn、Ce同时负载时催化剂活性最好, 反应温度为200℃时, NO转化率达到90%以上。     

Hierarchical ordered meso/macroporous H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>/SiO<Subscript>2</Subscript> catalysts with superior oxidative desulfurization activity

A series of phosphotungstic acid (HPW)/SiO₂ materials with hierarchical meso/macroporous structure were synthesized by evaporation-induced self-assembly method (EISA), using nonionic surfactant (P123) and polystyrene (PS) spheres as templates. SEM images displayed uniform macropores with an average pore size of 210 nm. TEM, small-angle XRD and N₂ adsorption–desorption isotherms confirmed the existence of the ordered mesoporous structures, embedded in the wall of macropores. The wild-angle XRD and FT-IR spectra proved Keggin-type HPW dispersed homogeneously in the silica framework. With the amount of added PS spheres, the density of the macropores increased, the hierarchically ordered porous HPW/SiO₂ possessed two-dimensional (2D) hexagonal (p6mm) mesostructures and uniform periodic macropores. The ODS catalytic activity of these samples were tested, the result showed that the meso/macroporous HPW/SiO₂ catalyst with proper PS beads usage displayed much higher catalytic activity than other catalysts. In addition, the reusability of the meso/macroporous HPW/SiO₂ catalyst was investigated, the activity of catalyst has not obviously decreased even after eight times.     

TiO2–ZrO2 mixed oxide as a support for hydrotreating catalyst

Pure TiO₂, ZrO₂ and TiO₂–ZrO₂ mixed oxides are prepared by urea hydrolysis. Hydrotreating catalysts containing 12 wt% molybdenum are prepared using these oxides and characterized by BET surface area, pore volume, XRD and oxygen chemisorption. It is observed that oxides produced by the method of urea hydrolysis have higher surface area as compared to those available commercially. With increasing zirconia content in the mixed oxide, the surface area increases and a maximum value is obtained for a mixed oxide having Ti and Zr molar ratio of 65/35. XRD results indicate that mixed oxides are poorly crystalline in nature. Thiophene hydrodesulfurization, cyclohexene hydrogenation and tetrahydrofuran hydrodeoxygenation are taken as model reactions for evaluating catalytic activities. It is found that both O₂ uptake and catalytic activities increase with increasing zirconia content in mixed oxide and reach maximum values for the 12 wt% Mo/TiO₂–ZrO₂ (65/35) catalyst. With further increases in zirconia content, O₂ uptake and catalytic activities decrease and the lowest values are observed for the pure ZrO₂ supported catalyst.     

CO and CO<Subscript>2</Subscript> Methanation Over Ni/SiC and Ni/SiO<Subscript>2</Subscript> Catalysts

Ni/SiC and Ni/SiO₂ catalysts prepared by both wet impregnation (WI) and deposition–precipitation (DP) methods were compared for CO and CO₂ methanation. The prepared catalysts were characterized using N₂ physisorption, temperature-programmed reduction with H₂ (H₂-TPR), H₂ chemisorption, pulsed CO₂ chemisorption, temperature-programmed desorption of CO₂ (CO₂-TPD), transmission electron microscopy, and X-ray diffraction. H₂-TPR analysis revealed that the catalysts prepared by DP exhibit stronger interaction between the nickel oxides and support than those prepared by WI. The former catalysts exhibit higher Ni dispersions than the latter. The catalytic activities for both reactions over Ni/SiC and Ni/SiO₂ catalysts prepared by WI increase on increasing the Ni content from 10 to 20 wt%. The Ni/SiC catalyst prepared by DP shows higher catalytic activity for CO and CO₂ methanation than that of the Ni/SiC catalyst prepared by WI. Furthermore, it exhibits the highest catalytic activity for CO methanation among the tested catalysts. The high Ni dispersion achieved by the DP method and the high thermal conductivity enabled by SiC are beneficial for both CO and CO₂ methanation.     

Surface Properties and Reactivity of Al2O3-Supported MoO3 Catalysts in Ethane Oxidative Dehydrogenation

The effect of MoO₃ loading on the properties and the catalytic performance of a series of alumina-supported molybdena catalysts (0–30 wt% MoO₃) was investigated in the oxidative dehydrogenation of ethane. The molybdena species on alumina were found to be amorphous at submonolayer coverages. At higher loadings, the formation of Al₂(MoO₄)₃ crystallites was detected by XRD. XPS revealed the existence of both Mo(VI) and Mo(V) sites on the catalyst surface, the concentration of which depends on the MoO₃ loading. In terms of catalytic performance, the activity increases with increasing loading in the submonolayer regime, decreasing for higher loadings. High selectivity to ethene is obtained even at relatively high conversion levels for catalysts exceeding monolayer coverage.