Partial oxidation of propane on Nafion supported catalytic membranes

Nafion supported catalytic membranes were found to be effective in the partial oxidation of propane to oxygenates with H₂O₂ in the presence of Fe²⁺ under mild conditions. The influence of [Fe²⁺] and [H₂O₂] on the reaction rate and product distribution in the temperature range 80–110°C has been ascertained. A reaction pathway involving the electrophilic activation of propane on superacid sites and subsequent reaction of the activated propane molecules with OH radicals generated by Fe²⁺/H₂O₂ Fenton system is discussed.     

The influence of sulfur dioxide on propane oxidation activity over supported platinum and palladium

Earlier studies have shown that sulfur dioxide and metal-support interaction can strongly influence propane oxidation over platinum. In particular, oxidation activity is enhanced when platinum is supported on sulfated -alumina or zirconia compared to -alumina. Therefore, it is of interest to compare the performance of palladium under the same experimental conditions. Four model catalysts were examined: Pt/-alumina, Pt/zirconia, Pd/-alumina and Pd/zirconia. The metal loading was kept at or below 0.05 wt% to emphasize changes in activity attributable to metal-support interaction. Reaction rates were measured with and without sulfur dioxide. Surface sulfation was analyzed by measuring acid strength and evaluating spectra obtained by Fourier-transform infrared spectroscopy. In contrast to platinum, sulfation does not promote propane oxidation on Pd/-alumina, and Pd/zirconia is less active than Pd/-alumina.     

Short channeled Zr-Ce-SBA-15 supported palladium catalysts for toluene catalytic oxidation

Short channeled Zr-Ce-SBA-15 (ZCS) mesoporous materials were synthesized through hydrothermal routes without addition of mineral acids. 0.5 wt.% palladium was loaded on ZCS and SBA-15 via an ethanol reduction approach. Pd/ZCS possesses unique hexagonal platelet morphologies with short channels running parallel to the thickness in the range of 400–500 nm, while Pd/SBA-15 has a fibrous macrostructure with channels at the micrometer scale. Palladium species present in supports as well dispersed PdO nanocrystals with diameter of ca. 5–6 nm. Comparing with Pd/SBA-15, Pd/ZCS shows enhanced catalytic activity for toluene oxidation, which is ascribed to short channeled supports facilitating the molecular diffusion.     

Catalytic dehydrogenation of propane on chromia,palladium and platinum supported catalysts

The dehydrogenation of propane to propylene over Cr₂O₃/Al₂O₃, Pd/Al₂O₃ and Pt/SiO₂ has been investigated in the temperature range 580–618°C. Runs were performed on propane, alone or in the presence of nitrogen (as a diluent), with complete analysis of the reaction products. The reaction was carried out in a fixed bed reactor at space velocities from 450–800 h^?1 which are close to industrial values and at pressures from 0.3 to 1 atm. A set of runs was made over a commercial chromia-alumina catalyst (10% Cr₂O₃) and over a promoted catalyst prepared in the laboratory by impregnation (16.8% Cr₂O₃ + 2% K₂O). The latter catalyst showed high selectivity and stability even when subjected to continuous cycles of dehydrogenation, regeneration and purging. Of the two noble metal supported catalysts used, reduced Pd/Al₂O₃ showed higher activity than Pt/SiO₂ at 618°C. The former catalyst gave a propylene yield of around 98% at 20% conversion level.     

Surface structure and catalytic performance of niobium oxides supported on titania

The surface structure and activity of catalytic systems based on niobium oxide supported on titania were investigated. A series of catalysts with Nb content up to 3.6 atoms/nm² was prepared by incipient wetness impregnation of the titania support with niobium oxalate solutions. Characterization of the system by X-ray diffraction (XRD) and Raman spectroscopy studies did not show evidence of niobium oxide formation. Surface analysis was performed by X-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), Raman and infrared spectroscopy. These results were correlated with Brønsted acidity and catalytic activity determined in our previous study. A direct correlation between the catalytic activity and the abundance of Brønsted acid sites had been observed. Analysis of the surface structure by infrared spectroscopy showed a similar evolution for the intensity of the band attributed to polymerized NbO_x.     

Preparation of novel titania supported palladium catalysts for selective hydrogenation of acetylene to ethylene

Novel titania supports have been designed and elaborated with the hydrolysis precipitation method, by adjusting and controlling of the main preparation parameters, such as pH value, adding rate of tetrabutyl titanate Ti(OBu)₄, and calcining temperature of precursor during support preparation. The new titania supported Pd catalysts were prepared and investigated for selective hydrogenation of acetylene to ethylene. The catalyst samples have been characterized by temperature programmed reduction (TPR), XRD and BET techniques. The experimental results indicated that with MgO modification, the improved catalyst (0.5%Pd–MgO/TiO₂) showed better performance of high and stable activity.     

AgBiVMo oxide catalytic membrane for selective oxidation of propane to acrolein

A metal ions (Ag, Bi, V, Mo) modified sol–gel method was used to prepare a mesoporous Ag_0.01Bi_0.85V_0.54Mo_0.45O₄ catalytic membrane which was used in the selective oxidation of propane to acrolein. By optimizing the preparation parameters, a thin and perfect catalytically active membrane was successfully prepared. SEM results showed that the membrane thickness is 5 μm. XRD results revealed that Ag_0.01Bi_0.85V_0.54Mo_0.45O₄ with a Scheelite structure, which is catalytically active for the selective oxidation of propane to acrolein, was formed in the catalytic membrane only when AgBiVMoO concentrations were higher than 40%. Catalytic reaction results demonstrated that the selective oxidation of propane could be controlled to a certain degree, such as to acrolein, in the catalytic membrane reactor (CMR) compared to the fixed bed reactor (FBR). For example, a selectivity of 54.85% for acrolein in the liquid phase was obtained in the CMR, while only 8.31% was achieved in the FBR.     

催化湿式氧化中负载型催化剂制备

采用浸渍法制备了负载型催化剂CuO/γ-Al_2O_3和Fe_2O_3/γ—Al_2O_3,以甲基橙为代表化合物,考察了制备因素对催化活性的影响,结果表明,CuO/γ-Al_2O_3的活性高于Fe_2O_3/γ-Al_2O_3,催化湿式氧化甲基橙2 h,脱色率接近100%。正交试验和稳定性研究表明,焙烧温度对催化活性影响较大,350℃焙烧,催化剂活性组分Cu溶出较少,且重复使用情况较好。采用SEM和XRD等手段对CuO/γ-Al_2O_3进行表征,发现其活性组分分散度良好。     

Relationship between oxidation states of copper supported on alumina and activities for catalytic combustion of NH3

The relationship between the oxidation state of Cu supported on an alumina catalyst (Cu/Al₂O₃) and the activity for combustion of NH₃ was investigated. Combustion of NH₃ on the catalyst treated in hydrogen at 800°C occurred at lower temperature than on the catalyst treated in air. It was also much better than Pt and Rh catalysts for the conversion of NH₃ to N₂. Characteristics of the catalyst were investigated by XRD, XPS, and the N₂O pulse injection method to understand the reason of its high catalytic activity. The reason of the high activity of the catalyst treated in hydrogen at the high temperature was attributed to the lower oxidation state of Cu in the catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Remarkable activity enhancement in the catalytic combustion of methane on supported palladium catalysts

The activity of supported palladium catalysts for the combustion of methane has been determined. It has been observed that the activity increases with time on stream irrespective of whether the catalysts are pre-calcined or pre-reduced. Careful re-reduction experiments have shown that the enhanced activity is maintained. It is concluded that the increase in activity with time on stream is not attributable to slow variations in the chemical state of the palladium particles, but to changes in the morphology of the palladium crystallites under reaction conditions. The possible role of dissolved carbon in stabilising the reconstructed crystallites against reduction is discussed.     

Structural organization of catalytic functions in Mo-based oxides for propane selective oxidation

Several single phasic MoVO-based mixed oxides, all of which have a layer structure in the direction of c-axis and a high dimensional arrangement of metal octahedra in a–b plane, were synthesized by hydrothermal method and their catalytic performance in the selective oxidation of propane to acrylic acid were compared in order to elucidate structure effects on catalytic property and roles of constituent elements. It was clearly demonstrated that the catalyst with the particular arrangement of MO₆ (M = Mo, V) octahedra forming slabs with pentagonal, hexagonal and heptagonal rings in (0 0 1) plane of orthorhombic structure was exclusively superior both in the propane oxidation activity and in the selectivity to acrylic acid to the other related Mo- and V-based layer oxide catalysts consisting of either pentagonal or hexagonal ring unit. The role of constituent elements was clarified by the comparison of catalytic performance of MoVO, MoVTeO and MoVTeNbO, all of which have the same orthorhombic structure. Mo and V, which were indispensable elements for the structure formation, were found to be responsible for the catalytic activity for propane oxidation. Te located in the central position of the hexagonal ring promoted the conversion of intermediate propene effectively, resulting in a high selectivity to acrylic acid. The introduced Nb occupied the same structural position of V and the resulting catalyst clearly showed the improved selectively to acrylic acid particularly at high conversion region, because the further oxidation of acrylic acid to CO_x was suppressed.     

交联腐植酸负载钯催化剂对Heck反应催化性能研究

通过简单的方法制得了环氧氯丙烷交联腐植酸负载钯配合物催化剂,并通过IR、TG进行表征。该催化剂能够成功地催化芳基卤和不同取代芳基卤与丙烯酸、苯乙烯和丙烯酰胺的Heck反应。进一步研究显示:环氧氯丙烷交联腐植酸负载钯催化剂还能够催化溴苯与丙烯酸、苯乙烯和丙烯酰胺的反应,产率都达到95%以上;在62℃及催化剂钯含量为0.038%的条件下也能很好地催化碘苯与丙烯酸的反应。催化剂经过简单的分离处理重复使用7次仍然可以得到75.6%的产率。     

制备抗硫性负载钯甲烷低温氧化催化剂的研究进展

介绍了耐硫性负载钯甲烷氧化催化剂的研究现状,比较了3种不同的提高催化剂耐硫性的方法。其中,重点介绍了钯硫化物催化剂。该方法是对传统抗硫方法的一次突破,通过以Pd_xS_y组分取代PdO活性相使催化剂具备真正意义上的抗硫性。重点对气相、液相硫化方法进行了概述,并对该领域的研究前景进行了展望。     

Partial oxidation of light paraffins on supported superacid catalytic membranes

Superacid-supported catalytic membranes were found to be active and very selective in the partial oxidation of light paraffins (C₁–C₂) with H₂O₂ under mild conditions (T_R: 80–110°C; P_R: 1.4 bar) in a three-phase catalytic membrane reactor (3PCMR). Among different catalytic membranes investigated, Nafion-based ones showed the best performance in terms of both activity and selectivity. Addition of Fe²⁺ ions in the liquid phase enhances the reaction rate, however, a volcano-shaped trend between reaction rate and concentration of Fe²⁺ was observed. Reaction temperature drastically affects both reaction rate and product distribution. A reaction pathway based on the electrophilic hydroxylation of the C–H bond on superacid sites and subsequent reaction of the activated paraffin with OH radicals has been proposed.     

硫化处理对负载钯催化剂甲烷低温催化燃烧性能的影响

采用浸渍法制备氧化硅负载钯催化剂,考察硫化气氛和硫化时间对催化剂性能的影响,并采用XRD对催化剂进行表征。结果表明,硫化后形成的Pd4S物种可以提高催化剂抗硫中毒性能,同时催化剂表面的SPd4S/SPd对催化活性有重要影响,改变硫化气氛和硫化时间可以调节Pd4S物种的形成和SPd4S/SPd。     

Synthesis and catalytic activity of SBA-15 supported catalysts for styrene oxidation

Cu(II) and Mn(II) metals embedded on mesoporous SBA-15 were synthesized by co-precipitation technique.The support and catalysts were characterized by SEM–EDX,TEM,BET,XRD and ICP-AES methods.The catalytic activity of these catalysts was evaluated for styrene oxidation at various reaction conditions such as styrene to TBHP mole ratio,temperature,catalyst amount by using TBHP as an oxidizing agent.Major reaction products were styrene oxide and benzaldehyde and highest styrene conversion(97.3%) was observed at styrene to TBHP mole ratio of 1:4,temperature at 80 °C and 20 mg of catalyst.Further,the recyclability of the catalysts was observed and found that they can be recycled three times without major loss in their activity and selectivity.     

Catalytic activity of copper and palladium based catalysts for toluene total oxidation

In this study, catalysts containing 0.5 wt.% of palladium or 5 wt.% of copper were compared towards toluene total oxidation using FAU Zeolite and ZrO₂ supports. A 0.5%Pd/NaFAU and 5%Cu/ZrO₂ were found to be promising catalysts for this reaction. Palladium presented then a better affinity for FAU zeolite and copper oxide had a better affinity for zirconia. The performances of Pd based catalysts were correlated to interaction between the active phase and the support whereas the activity of copper oxide was related to oxygen mobility property of the support leading to copper oxide particles easily reducible. Support modifications, yttrium addition for ZrO₂ and cation exchange for the zeolite FAU, still enhanced the catalytic activity. Therefore, 0.5%Pd/CsFAU and 5%Cu/Zr₉₅Y₅ samples were found to be interesting catalysts for total VOC oxidation.