Catalytic Activity of Supported Platinum and Metal Oxide Catalysts for Toluene Oxidation

Oxidation of toluene has been investigated over supported platinum as well as over a variety metal oxide (M _x O _y ) catalysts dispersed on high surface area γ-Al₂O₃. Catalysts were characterized with respect to their specific surface area (BET), metal dispersion (selective chemisorption of CO), phase composition and M _x O _y crystallite size (XRD) and reducibility (H₂-TPR). Catalytic performance for the title reaction was investigated in the temperature range of 100–500 °C, using a feed composition consisting of 0.1% toluene in air. For Pt/M _x O _y catalysts, it has been found that catalytic performance depends on the nature of the support, with Pt/CeO₂ being the most active catalyst at low temperatures. The intrinsic reaction rate per surface platinum atom does not depend on Pt loading (0.5–5 wt%), at least for Pt/Al₂O₃. Reducible metal oxides, such as ceria, are active for the title reaction and catalytic performance is improved significantly with increase of specific surface area (SSA). However, the intrinsic reaction rate per unit surface area is invariant with SSA. Dispersion of M _x O _y on high surface area inert supports, such as Al₂O₃, results in materials with relatively high catalytic activity, which seems to correlate well with the reducibility of metal oxides. Catalytic performance of M _x O _y /Al₂O₃ catalysts can be optimized by proper selection of M _x O _y loading. Best performing catalysts of this series include 60% MnO, 90% CeO₂ and 5% CuO on Al₂O₃ which, under the present experimental conditions, are able to completely convert toluene toward CO₂ at temperatures lower than 350 °C. Dispersion of Pt on M _x O _y /Al₂O₃ catalysts improves significantly the catalytic performance of irreducible M _x O _y but does not alter appreciably the activity of reducible M _x O _y /Al₂O₃ catalysts.     

负载型臭氧氧化催化剂研究进展

多相催化臭氧化技术是一种高效的污水净化技术。其中负载型臭氧氧化催化剂因其催化效果好、易分离、重复率用率高等优点而成为研究热点之一。依据不同的载体类型,将负载型臭氧氧化催化剂进行归纳分类,并综述了不同载体的催化剂在催化臭氧氧化水处理中的最新应用。     

Synthesis, Characterization and Catalytic Activity of Supported NiMo Catalysts

A study of NiMo catalysts supported on MCM41 modified with alumina prepared by the sol?Cgel method is presented. Ni?CMo phases were impregnated on the supports using the solution method with the purpose to obtain a material whose hexagonal structure of the MCM41 would not be affected with the addition of these active phases. The impregnation of the metals method used in the present work was outstanding, the textural properties of the catalysts decreased from 42 to 67%. There was a diminution in the textural properties of the catalysts with respect to the supports, nevertheless the prepared materials had more significant textural properties that the conventional catalysts of HDS. The adsorption?Cdesorption isotherms of the catalysts did not change considerably with the support source. By DRX was determined the structural properties of the metallic phases present in the material where phases such as NiMoO₄, MoO₃ and NiO were observed. Support wall thickness was increased with the incorporation of Ni and Mo metals into the materials. By means of Raman spectroscopy, the presence of MoO₃ and Mo₈O₂₆ ^4? species was corroborated. Through UV?Cvis where determined NiO of octahedral symmetry as well as Mo of tetrahedral and octahedral symmetry. The main reaction products were biphenyl (BP), cyclohexylbenzene (CHB) and bicyclohexyl (BCH) when the materials were tested in the HDS of DBT.     

Effect of Pt Dispersion on the Catalytic Activity of Supported Pt Catalysts for Diesel Hydrocarbon Oxidation

The catalytic activity of Pt/Al₂O₃ for the total oxidation of hydrocarbon mixture of n-decane and 1-methylnaphthalene was strongly dependent on the Pt dispersion. The maximum hydrocarbon oxidation activity was achieved for Pt/Al₂O₃ with Pt dispersion (D_Pt) of 0.39. On the other hand, the activity of Pt/ZrO₂ monotonously decreased with decreasing Pt dispersion from 1.00 to 0.09. In situ FT-IR spectroscopy suggested that the presence of plural Pt species in metallic state with slight different electric state, which well catalyze the formation of acrylate species as an intermediate, is responsible for the high catalytic activity of Pt/Al₂O₃ with D_Pt = 0.39.     

Preservation of the Activity of Supported Gold Catalysts for CO Oxidation

Procedures leading to the preservation of activity of supported gold catalysts for CO oxidation are reviewed. The inclusion of iron as Fe(OH)₃ in preparing catalysts using tin oxide, ceria and zirconia as supports gives better activity and much improved stability with time-on-stream. In the case of Au/Fe-SnO₂ (0.5–0.9% Au), the effect is maximal with ~4% Fe. The stability of catalysts based on ceria as support is also much better when small amounts of either iron or lanthanum during preparation of the support by thermal decomposition of nitrates. Au/SnO₂ catalysts often suffer initial deactivation followed by an increase in activity with time-on-stream; a period of refrigeration (7d) induces an excellent stability at high conversion.     

SO2对Y型分子筛选择性催化氧化NO的影响

在Y型分子筛及其负载金属和离子交换催化剂上，考察了低温下SO2对NO催化氧化的影响，发现在分子筛催化剂上SO2对NO氧化同样具有低温活性促进作用，同时也造成了催化剂的失活。本文借实验结果和参考文献，对SO2在分子筛上的活性促进和失活机理提出了初步看法。     

Catalytic Partial Oxidation of Methanol and Methyl Mercaptan: Studies on the Selectivity of TiO2 and CeO2 Supported V2O5 Catalysts

Catalyst samples based on vanadium, cerium and titanium oxides were prepared using sol–gel method and wet impregnation. Several analytical techniques were used to characterize catalysts. The best activity and selectivity in the partial oxidation of methanol and methyl mercaptan were observed for the catalyst sample with the composition of 3 % V₂O₅/Ti_0.1–Ce_0.9O₂.     

Characterization and Catalytic Oxidation of Carbon Monoxide Over Supported Cobalt Catalysts

Three types of supported cobalt catalysts (CoO_x/SiO₂, CoO_x/TiO₂ and CoO_x/Al₂O₃) were prepared by incipient wetness impregnation with aqueous Co(NO₃)₂·6H₂O solution. The phase composition and the interactions of cobalt with supports under different calcined temperatures were investigated using thermogravimetry (TG), N₂-adsorption at −196 °C, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and diffuse reflectance spectroscopy (DRS). Their catalytic activities towards the CO oxidation were further studied in a continuous flow micro-reactor. The results showed that the interaction of cobalt oxide with supports was much stronger in the kinds of Al₂O₃ and TiO₂, while no conclusive evidence of any interaction was found for SiO₂. Besides the crystalline Co₃O₄ which was formed in three supported catalysts, both high-temperature phases CoAl₂O₄ and CoTiO₃ spinel were also detected under XRD, DRS and TPR analysis. The degree of interaction between cobalt oxide and the support not only affected the surface area and reduction behavior of the catalysts, the catalytic activity toward the CO oxidation also affected simultaneously. As the CoAl₂O₄ and CoTiO₃ spinel formed, both the surface area and catalytic activity decreased significantly.     

堇青石蜂窝陶瓷负载CuO/CeO2-ZrO2/TiO2催化氧化含酚废水的性能研究

选取球状堇青石蜂窝陶瓷作为催化剂基体,制备了堇青石蜂窝陶瓷负载CuO/CeO2-ZrO2/TiO2催化剂,采用XRD、BET等方法对其进行了结构表征,测定了其催化湿式氧化含酚废水的活性及抗压强度、脱落率、Cu2+溶出浓度等性能指标.结果表明,CuO/CeO2-ZrO2/TiO2堇青石蜂窝陶瓷催化剂在反应温度180℃、压力5Mpa、搅拌速率为600r/min时,催化湿式氧化反应200minCOD去除率可达92.7％;球状堇青石蜂窝陶瓷CuO/CeO2-ZrO2/TiO2催化剂具有强度高、易装填、易更换、脱落率低特点,Cu2+溶出浓度低于环保排放标准,适合工业化处理含酚废水.     

Preparation, Characterization and Catalytic Activity for CO Oxidation of SiO2 Hollow Spheres Supporting CuO Catalysts

Silica hollow spheres were synthesized by sol–gel process using carbon microspheres as templates, and used as supports for CuO/SiO₂ catalysts. The samples were characterized by TEM, nitrogen adsorption–desorption, XRD and TPR, and furthermore, the catalytic performance for CO oxidation was approached. The results indicated that the catalytic activity of CuO supported on SiO₂ hollow spheres exhibited much higher as compared to that supported on commercial SiO₂. Enhancement of the catalytic activity may be attributed to the fact that the unique hollow spherical texture should facilitate the formation of main active species and gas diffusion in catalysts.     

Deactivation of Gold Catalysts Supported on Sulfated TiO2-ZrO2 Mixed Oxides for CO Oxidation During Catalytic Decomposition of Chlorodifluoromethane (HCFC-22)

Gold deposited on sulfated TiO₂-ZrO₂ with sodium hydroxide existed in the form of isotropic particles of 11 nm or less in diameter, whereas deposition with aqueous ammonia yielded larger anisotropic crystallites. The gold on sulfated TiO₂-ZrO₂ catalyst prepared by deposition with sodium hydroxide was active for the oxidation of carbon monoxide at room temperature in the presence of water vapor. However, the selectivity of the catalysts to carbon dioxide during the decomposition of chlorodifluoromethane in the presence of water vapor was increased by only a small extent compared to those without gold nanoparticles. The gold nanoparticles were deactivated for CO oxidation by HF and HCl formed during the hydrolysis of HCFC-22.     

无机钛硅原料体系TS-1催化环己酮氨氧化反应的研究

研究了自制的无机钛硅原料体系TS - 1催化环己酮氨氧化反应 ,结果表明 :钛进入了分子筛的骨架中 ,构成了TS - 1催化活性中心。考察了以水为溶剂时 ,催化剂用量、氧酮比、氨氧比对氨氧化反应的影响 ,得出了无机钛硅原料体系TS - 1催化环己酮氨氧化反应的最优反应条件。在此条件下 ,环己酮的转化率可达 97%以上 ,环已酮肟的收率可达 96 %     

CeO2掺杂对CuO/沸石催化剂催化氧化VOCs活性的影响

研究CeO2改性得到的CuO/CeO2/沸石催化剂,进行催化氧化（燃烧）销毁乙醇、丙酮、甲苯和苯的实验,并用TPR和XPS对所制备的催化剂进行表征.研究结果表明：使用CuO/CeO2/沸石作为催化剂时,四种VOCs（挥发性有机物）催化燃烧的起燃和完全燃烧温度都明显低于当使用CuO /沸石作为催化剂时四种VOCs催化燃烧的起燃和完全燃烧温度,这表明CuO/CeO2/沸石催化剂的活性明显高于CuO/沸石催化剂的活性.TPR分析表明CeO2的添加有助于增强催化剂中Cu的还原性;XPS表征分析显示,CeO2的添加增加了铜在表面的分布,并且引起Cu 2p3/2的结合能由933.8eV 变到932.8eV 和 933.4eV, 在催化剂表面呈现出Cu2＋和Cu＋的形式.此外,在VOCs催化燃烧过程中,稀土Ce存在有部分还原变价过程（Ce^4 ＋ →Ce^3 ＋ ） ,也使催化剂的活性得到提高.     

ZrO_2负载Cu催化剂对CO低温催化氧化研究

用溶胶-凝胶-超临界干燥法制备了纳米氧化锆。采用沉淀法制备氧化锆负载铜催化剂。制备的催化剂用X-ray射线衍射(XRD),透射电镜(TEM),比表面积(BET)和H2-TPR等进行了表征。研究了催化剂的焙烧温度和负载比例对CO转化效率的影响,其最佳焙烧温度为650℃,Zr与Cu的最佳物质的量比是10:8。获得催化剂在温度为68℃具有催化活性,176℃时CO的转化率达到50%,较好地实现了ZrO2负载Cu在较低温度下对CO的催化。     

Oxidation of SO2over Supported Metal Oxide Catalysts

A systematic catalytic investigation of the sulfur dioxide oxidation reactivity of several binary (M_xO_y/TiO₂) and ternary (V₂O₅/M_xO_y/TiO₂) supported metal oxide catalysts was conducted. Raman spectroscopy characterization of the supported metal oxide catalysts revealed that the metal oxide components were essentially 100% dispersed as surface metal oxide species. Isolated fourfold coordinated metal oxide surface species are present for most oxides tested at low coverages, whereas at surface coverages approaching monolayer polymerized surface metal oxide species with sixfold coordination are present for some of the oxides. The sulfur dioxide oxidation turnover frequencies (SO₂molecules converted per surface redox site per second) of the binary catalysts were all within an order of magnitude (V₂O₅/TiO₂>Fe₂O₃/TiO₂>Re₂O₇/TiO₂∼CrO₃/TiO₂∼Nb₂O₅/TiO₂>MoO₃/TiO₂∼WO₃/TiO₂). An exception was the K₂O/TiO₂catalyst system, which is inactive for sulfur dioxide oxidation under the chosen reaction conditions. With the exception of K₂O, all of the surface metal oxide species present in the ternary catalysts (i.e., oxides of V, Fe, Re, Cr, Nb, Mo, and W) can undergo redox cycles and oxidize sulfur dioxide to sulfur trioxide. The turnover frequency for SO₂oxidation over all of these catalysts is approximately the same at both low and high surface coverages, despite structural differences in the surface metal oxide overlayers. This indicates that the mechanism of sulfur dioxide oxidation is not sensitive to the coordination of the surface metal oxide species. A comparison of the activities of the ternary catalysts with the corresponding binary catalysts suggests that the surface vanadium oxide and the additive surface oxide redox sites act independently without synergistic interactions: the sum of the individual activities of the binary catalysts quantitatively correspond to the activity of the corresponding ternary catalyst. The V₂O₅/K₂O/TiO₂catalyst showed a dramatic reduction in catalytic activity in comparison to the unpromoted V₂O₅/TiO₂catalyst. The ability of potassium oxide to significantly retard the redox potential of the surface vanadia species is primarily responsible for the lower catalytic reactivity.     

Optimizing the Pt-FeOx Interaction over Atomic Pt/FeOx/CeO2 Catalysts for Improved CO Oxidation Activity

The metal-supported CeO₂ catalysts (such as Pt/CeO₂) have been considered as the most promising exhaust-treatment catalyst to meet the future emission standard. However, the Pt-O-Ce interface on Pt/CeO₂ system seems to over-stabilize the Pt sites to cause low activity for CO oxidation. In this work, by adding Fe oxides, the enhanced Pt-FeO_x interaction was formed with the disappearance of the Pt-O-Ce interface, facilitating the electron transfer from the support to the atomically dispersed Pt on the Pt-FeO_x interface for the dramatically CO (preferential) oxidation performance. The single-atom Pt/1.5FeO_x/CeO₂ performed the best catalytic activity with a reaction rate of 0.58 s⁻¹ at 144 °C (T₁₀₀). Such strategy in resorting the special metal-support interaction to tune the active sites can be extended to other metal-oxide systems for further optimized catalysis.     

低负载贵金属催化剂对二甲醚催化燃烧的催化活性

采用浸渍法以g-Al2O3为载体制备了多种低负载量的Pd和Pt催化剂,在微型固定床反应器装置上进行了二甲醚(DME)催化燃烧实验. 考察了不同贵金属负载量的Pd/g-Al2O3和Pt/g-Al2O3催化剂的活性,及浸渍顺序对Pd-Pt/g-Al2O3双金属负载催化剂活性的影响,并测试了贵金属负载摩尔比不同的双金属负载催化剂的活性. Pt负载量0.025%(w)的催化剂在190℃将DME完全燃烧;Pd和Pt共同负载的催化剂[Pd:Pt=2:1(mol), Pt 0.025%(w), Pd 0.027%(w), Pt先负载]性能更好,在175℃将DME完全燃烧;200 h实验后2种催化剂活性降低均小于5%.     

CO Preferential Oxidation Activity of CuO/CeO2 Supported on Zirconium Doped Mesoporous MSU Type Silica

In this paper the comparison of activity of hopcalite (Mn–Cu mixed oxides) modified with noble metals (Pd, Pt and Au) calcined at 300, 400 and 500 °C in oxidation of thiophene was presented. Hopcalite modified with Pd demonstrated the highest activity among the studied samples, thus the results of a more detailed study of the most promising palladium catalyst were also shown. Surface and bulk properties of catalyst were studied with BET, XRD, TPR_H2 and TG-DTA-MS. The redox properties and distribution of active components on the catalyst surface seem to be important factors influencing the modified hopcalite performance in the oxidation reactions. It was found that irreversible changes occurred during thermal treatment in the Pd-modified hopcalite structure, however they have no marked influence on activity of modified catalysts.