A VOx/meso-TiO2 catalyst for methanol oxidation to dimethoxymethane

Mesoporous TiO₂ was prepared by simply controlling the hydrolysis of Ti(OBu)₄ with the help of acetic acid. The mesoporous TiO₂ had a well-crystallized anatase phase and a high surface area of 290 m² g⁻¹ with a pore size of about 4 nm. The anatase phase and the mesoporous structure were maintained in the VO_x/TiO₂ catalyst with a monolayer dispersion of V₂O₅, however, the surface area decreased to 126 m² g⁻¹. The catalyst was highly active and selective for methanol oxidation, giving about 55% conversion of methanol and 85% selectivity to dimethoxymethane at 423 K.     

甲醇氧化制甲醛铁钼催化剂研究

采用共沉淀法制备了不同Mo与Fe原子比的甲醇氧化制甲醛催化剂,在常压固定床反应器上对催化剂进行活性评价,采用BET、XRD和TEM对制备的催化剂进行表征。结果表明, Mo与Fe原子比为2.2~2.8时,催化剂具有较好的活性,(400~450) ℃焙烧的催化剂具有良好的比表面积、适宜的孔容和孔径,形成了较为稳定的MoO₃和Fe2(MoO₄)₃晶相,使催化剂具有更高的活性和选择性。对甲醇氧化制甲醛反应进行研究,结果表明,在反应温度(265~315) ℃,空速(8 500~13 000) h^-1时,甲醇转化率>98%,甲醛收率>93%, 500 h长周期考核,催化剂表现出良好的活性和稳定性。     

甲醇氧化制甲醛铁钼催化剂表面结构与活性

利用共沉淀法在不同搅拌速度下制备了相同Mo/Fe原子比的甲醇氧化制甲醛催化剂,采用SEM、XRD和拉曼光谱等对催化剂进行表征,在固定床微反上评价催化剂活性和选择性。结果表明,搅拌速度增大,催化剂比表面积增大,催化活性增强,甲醛收率由600 r·min^-1时的73.8%增加到10000 r·min^-1时的95.7%（280℃）。此外,催化剂由片状的MoO₃和颗粒状的Fe₂（MoO₄）₃两部分组成,游离的片状MoO₃无明显催化活性,只有与Fe₂（MoO₄）₃结合时才具有催化活性。     

Selective oxidation of methane to methanol and formaldehyde over V2O5/SiO2 catalysts. Role of NO in the gas phase

The role of nitric oxide incorporation into the reaction feed for the partial oxidation of methane to C₂-hydrocarbons and C₂-oxygenates is evaluated. The addition of NO increases the conversion of methane under all the experimental conditions studied and has a strong effect on the product distribution. At low NO concentration the catalysts yield mainly C₂H_n hydrocarbons, but at higher NO concentrations, carbon oxides dominate. Amongst the C₁-oxygenates produced, methanol is the major compound observed and its proportion increases with increasing NO concentration. The highest C₁-oxygenates yield was 7% at atmospheric pressure. This revised version was published online in July 2006 with corrections to the Cover Date.     

甲烷选择性氧化制甲醛/甲醇多相催化剂研究进展

甲烷是天然气、页岩气等化石能源的主要成分,储量十分丰富.由于甲烷分子结构高度稳定,其高效活化与选择性转化具有很大的挑战性,被认为是催化反应领域的"圣杯",因此,如何在温和条件下实现甲烷选择性氧化为高附加值的含氧化合物(如甲醇、甲醛)成为研究热点.近几十年来,研究者在甲烷选择性氧化催化剂的设计与制备方面开展了大量卓有成效...     

Effect of surface species on activity and selectivity of MoO3/SiO2 catalysts in partial oxidation of methane to formaldehyde

The effect of the nature of surface species on the activity and selectivity of MoO₃/SiO₂ catalysts has been investigated for the partial oxidation of methane to formaldehyde. Characterization techniques including BET surface area, ambient and in situ Raman spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction were used in conjunction with steady-state reaction studies to relate the presence of different surface species to the activity and selectivity of the catalyst. Results of these experiments indicate the presence of a highly dispersed silicomolybdic species with terminal Mo=O sites appearing at lower MoO₃ loadings. As the weight loading increases, these sites are transformed into polymolybdate species, forming more Mo-O-Mo bridging sites at the expense of Mo=O sites. At high weight loadings, crystalline MoO₃ begins to form. The abundance of the Mo=O sites is believed to affect activity and selectivity in the partial oxidation of methane to formaldehyde.     

The effect of the reduction temperature on the structure of Cu/ZnO/SiO2 catalysts for methanol synthesis

The structure of Cu/SiO₂ and Cu/ZnO/SiO₂ catalysts was studied after reduction at 450–1300 K. The influence of the ZnO promoter on the exposed Cu surface area and metal cluster size was determined by N₂O chemisorption and X-ray diffraction. After reduction at 450 K, the metal surface area amounted to 9 m²/g_cat for both catalysts. Oxygen uptake during N₂O chemisorption increased significantly up to reduction temperatures of 800–900 K. This increase was most prominent for the ZnO-promoted catalyst, although no oxygen uptake was observed for a similarly treated ZnO/SiO₂ sample. The behaviour of the promoted catalyst can be explained by formation of Zn⁰, surface alloying, and segregation of ZnO_x species on top of Cu clusters. The high thermostability of the catalysts was confirmed by in situ XRD measurements. The Cu crystallite size in both catalysts was about 4 nm, and did not increase when the reduction temperature was raised to 1100 K for 1 h.     

负载型CeO2/OMS -2催化剂对VOCs的催化氧化性能

采用回流法合成了OMS -2,同时以OMS -2为载体,采用浸渍法负载CeO2制备了Ce/OMS-2催化剂,运用X射线衍射、拉曼光谱、BET、H2 - TPR和NH3 - TPD等方法对催化剂进行表征,并考察CeO2/OMS -2催化剂催化氧化二氯甲烷和乙酸乙酯的性能.结果表明,CeO2的加入并未改变OMS -2较好的八面体分子筛结构,CeO2的晶粒很小且以高分散的形式存在;负载CeO2的OMS -2催化剂比表面积都有增大趋势;随着CeO2负载量的增加,低温和高温的还原峰都先向低温方向偏移再向高温方向偏移;随着CeO2负载量的增加,高温处强酸性峰先向低温方向偏移再向高温方向偏移.反应活性结果表明,CeO2/OMS -2催化剂活性比载体OMS -2的活性好,随着铈负载量的增加,催化活性先升高再降低,其中,CeO2负载质量分数为1.0％(1.0Ce/OMS -2)时催化剂效果最好,这可能是由于铈的加入活化了OMS -2中的氧,影响了整体催化剂的酸性,进而影响反应性能.     

Effect of support synthesis methods on structure and performance of VOx/CeO2 catalysts in low-temperature NH3-SCR of NO

CeO₂ supports were prepared by a citrate (C) or a precipitation method (P) before deposition of vanadia by wet impregnation to obtain supported V/CeO₂ catalysts. The V/CeO₂-P catalyst is more active, reaching ≈ 100% NO conversion and N₂ selectivity already below 225 °C at a space velocity of GHSV = 70,000 h^− 1. XRD, UV-vis-DRS, Raman, pseudo-in-situ-XPS and operando-EPR spectroscopy revealed that this is due to higher surface area and a more effective incorporation of V sites into the support surface, which keeps them in their active valence states + 5 and + 4 and prevents reduction to inactive V^3 + as observed on V/CeO₂-C.     

Potential rare-earth modified CeO2 catalysts for soot oxidation

The physico-chemical properties of ceria (CeO₂) and rare earth modified ceria (with La, Pr, Sm, Y) catalysts are studied and correlated with the soot oxidation activity with using O₂ and O₂ + NO. CeO₂ modified with La and Pr shows superior soot oxidation activity with O₂ compared with the unmodified catalyst. The improved soot oxidation activity of rare earth doped CeO₂ catalysts can be correlated to the increased meso/micro pore volume and the stabilisation of the external surface area. On the other hand, unreducible ions decrease the intrinsic soot oxidation activity of rare earth modified ceria with both O₂ and NO + O₂ due to the decreased amount of redox surface sites. The catalyst bulk oxygen storage capacity is not a critical parameter in determining the soot oxidation activity. The modification with Pr shows the best soot oxidation with both O₂ and O₂ + NO compared with all other catalysts.     

甲醇直接脱氢制甲醛催化剂研究进展

简要叙述了甲醇直接脱氢制甲醛催化剂的研究进展情况,介绍了甲醇脱氢反应所用3类催化剂：金属及其氧化物、碱金属盐和分子筛催化剂。讨论了各类催化剂对甲醇直接脱氢制甲醛的选择性及转化率的影响,并从催化剂的活性、寿命和经济性等方面分析了其优缺点及应用前景。     

Preparation and effect of Mo-V-Cr-Bi-Si oxide catalysts on controlled oxidation of methane to methanol and formaldehyde

Mo-Cr-V-Bi-Si multi-component oxide catalysts were synthesized by three different coprecipitation methods and used in the controlled oxidation of methane to methanol and formaldehyde. It was shown that Mo content in Mo-V-Cr-Bi-Si oxides and the performance of these catalysts were strongly influenced by different coprecipitation methods. The highest methanol and formaldehyde selectivity of 80.2% could be achieved at a methane conversion of 10 % for the catalyst prepared by a particular method. The results of XRD indicated that the crystalline phase structures of catalysts were sensitive to Mo, V and Bi loadings. Bi(III) could combine with V(V) and Mo(VI) to form BiVO₄ and γ-Bi₂MoO₆, whereas Cr seemed to form a single Cr₂O₂ crystalline phase in the presence of Bi. The effects of Mo and Cr loading on controlled methane oxidation were also investigated. Mo(VI) oxide appears to favor the formation of partial oxidation products and Cr(III) oxide seems to enhance the conversion of methane.     

Zn-ZrO2/SiO2非氧化脱氢制无水甲醛的研究

以Zn-ZrO2/SiO2为催化剂,在微型固定床反应器中用甲醇直接非氧化脱氢制备无水甲醛,考察了催化剂组成、反应温度及质量空速对脱氢反应的影响。结果表明,在进料的甲醇体积分数为35%、反应温度为800 K、质量空速为35 mL/(g.s)的反应条件下,甲醇的转化率达到100%,甲醛的选择性达到63%。结合催化剂的活性评价及X射线光电子能谱、热重等技术显示,采用均匀沉淀法制备的Zn-ZrO2/SiO2催化剂,活性组分能均匀分散在载体上,且对甲醇的非氧化脱氢具有高效的催化作用。助剂ZnO的引入可以有效抑制反应过程中催化剂的烧结,极大程度地增强催化剂的稳定性。     

Kinetics of the catalytic oxidation of methanol to formaldehyde

The kinetics of the oxidation of methanol to formaldehyde, over iron molybdate as catalyst, have been studied. The kinetic runs have been performed with a CSTR reactor.The results can be described with a kinetic model derived on the basis of a redox mechanism partially hindered by the adsorption of water. The low temperatures used in the reactor (200–250°C) favour the formation of by-products, as dimetoxymethane, dimethyl ether and methylformate.     

Sodium compounds as catalysts for methanol dehydrogenation to water-free formaldehyde

Formaldehyde is produced industrially from methanol by partial oxidation of oxidative dehydrogenation. In these processes, water is formed as a by-product. Anhydrous formaldehyde is required for many syntheses and, therefore, its production is of potential interest. In the present study, catalysts based on alkali compounds were found to be active in the dehydrogenation of methanol if absence of oxygen. Sodium carbonate doped with indium shows a selective of up to 75% for methanol conversion not exceeding 60%.     

Co改性Na_2WO_4/Mn/SiO_2甲烷催化氧化催化剂结构及性能研究

本文制备了一系列不同Co含量的Na_2WO_4/Co-Mn/SiO_2双功效催化剂,用于甲烷催化转化制备氢甲酰化合成丙醛的原料气。当气体空速GHSV=24 000 h~(-1)、CH_4/O_2=2.5,Co负载量为6%(质量分数)的催化剂上可得到C_2H_4/CO/H_2=1/1/1,且(C_2H_4+CO)总收率达23%。XRD和XPS结果表明,在Na_2WO_4/Co-Mn/SiO_2催化剂上Co只以+2价形式存在,并分散到α-方晶石和/或Na_2WO_4晶相结构中。Mn则以两种化学态共存,即Mn~(3+)和Mn~(4+),且随着Co负载量的增加,更多的Mn~(3+)转化为Mn~(4+)。结果表明,C_2H_4选择性随Co的增加而降低,CO和H_2的选择性及收率则与催化剂表面的Co/W比值近似呈线形关系。     

Comparison of the activity of Au/CeO2 and Au/Fe2O3 catalysts for the CO oxidation and the water-gas shift reactions

We compare the activity and relevant gold species of nanostructured gold–cerium oxide and gold–iron oxide catalysts for the CO oxidation by dioxygen and water. Well dispersed gold nanoparticles in reduced form provide the active sites for the CO oxidation reaction on both oxide supports. On the other hand, oxidized gold species, strongly bound on the support catalyze the water-gas shift reaction. Gold species weakly bound to ceria (doped with lanthana) or iron oxide can be removed by sodium cyanide at pH ≥12. Both parent and leached catalysts were investigated. The activity of the leached gold–iron oxide catalyst in CO oxidation is approximately two orders of magnitude lower than that of the parent material. However, after exposure to H₂ up to 400 °C gold diffuses out and is in reduced form on the surface, a process accompanied by a dramatic enhancement of the CO oxidation activity. Similar results were found with the gold–ceria catalysts. On the other hand, pre-reduction of the calcined leached catalyst samples did not promote their water-gas shift activity. UV–Vis, XANES and XPS were used to probe the oxidation state of the catalysts after various treatments.     

Selective oxidation of methanol to formaldehyde over V–Mg–O catalysts

The results of a complex investigation of V–Mg–O catalysts for oxidative dehydrogenation (ODH) of methanol are presented. The efficiency of vanadium–magnesium oxide catalysts in production of formaldehyde has been evaluated. Strong dependence of the formaldehyde yield and selectivity upon vanadium oxide loading and the conditions of heat treatment of the catalyst were observed. The parameters of the preparation mode for the efficient catalyst were identified. In optimised reaction conditions the V–Mg–O catalysts at the temperature approximate 450 °C ensured the formation of formaldehyde with the yield of 94% at the selectivity of 97%.

No visible changes in the performance of the catalyst (methanol conversion, formaldehyde yield and selectivity) were detected during the 60 h of operation in prolonged runs. Characterization of the catalyst by XRD, IR, and UV methods suggests the formation of species of the pyrovanadate type (Mg₂V₂O₇) with irregular structure on the surface of a V–Mg–O catalyst. These species make the catalyst efficient for methanol ODH.     

Study on catalytic performance of CeO2/CuO catalysts for preferential CO oxidation

采用水热法合成纳米尺寸的CuO,然后采用微乳液法或浸渍法将CeO₂负载在CuO上制备逆负载的CeO₂/CuO催化剂。通过X射线衍射（XRD）、程序升温还原（TPR）、比表面分析（BET）和富氢气中CO优先氧化活性测试等研究手段对催化剂进行了表征。研究发现,CeO₂/CuO催化剂的活性和选择性与CeO₂和CuO颗粒的尺寸密切相关,大颗粒的CuO载体有利于提高催化剂的选择性;小颗粒的氧化铈负载在大颗粒的氧化铜上,可以产生更多两相接触界面,有助于提高催化剂的活性。