Characterization and reactivity of MoO3/SiO2 catalysts in the selective catalytic oxidation of ammonia to N2

Silica-supported MoO₃ catalysts with MoO₃ loadings up to 21% w/w were prepared, characterized and tested in the selective catalytic oxidation (SCO) of ammonia to N₂ under dilute conditions. It is found that the catalysts are active and selective in the reaction, and that the catalytic performance increases on increasing the Mo loading. Crystalline MoO₃, detected over the silica support, is supposed to be the active species in the reaction. The reactivity of the catalysts is depressed by water addition to the feed at low temperatures and is enhanced by the presence of selected promoters, like Bi and Pb.     

ZrO2/SiO2- and La2O3/Al2O3-supported platinum catalysts for CH4/CO2 reforming

Surface-phase ZrO₂ on SiO₂ (SZrOs) and surface-phase La₂O₃ on Al₂O₃ (SLaOs) were prepared with various loadings of ZrO₂ and La₂O₃, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH₄/CO₂ reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al₂O₃ and Pt/SiO₂ catalysts. CO₂ or CH₄ pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides.

The zirconia can be homogeneously dispersed on SiO₂ to form a stable surface-phase oxide. The lanthana cannot be spread well on Al₂O₃, but it forms a stable amorphous oxide with Al₂O₃. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO₂ and Pt/Al₂O₃ by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO₂ and Pt/Al₂O₃ catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO₂ adsorbed on the basic sites of SZrOs and SLaOs.     

CO2吸附强化CH4/H2O重整制氢催化剂研究进展

CO_2吸附强化CH_4/H_2O重整制氢是提供低成本高纯氢气和实现CO_2减排的方法之一。其中,催化剂和吸附剂是该工艺的重要组成部分,其活性与选择性制约了反应速率和产率,寿命长短关系到生产成本。综述了CO_2吸附强化CH_4/H_2O重整制氢催化剂和吸附剂的研究现状及存在的问题,机械混合的催化剂与吸附剂在反应过程中存在吸附产物包覆催化活性位点的问题,导致催化剂活性迅速下降。针对该问题,进一步探讨了不同结构双功能复合催化剂的结构特性、研究现状及其在循环-再生过程中存在的问题,核壳型双功能催化剂具有吸附组分与催化剂组分相对独立、催化组分分散分布和比表面积大等优点,在吸附强化制氢中有进一步研究的潜力。利用双功能催化剂的结构特点,实现反复循环再生过程中催化与脱碳反应的匹配,是推动CO_2吸附强化CH_4/H_2O重整制氢技术工业化发展的关键。     

Solid state protonic conductor NH4PO3–(NH4)2Mn(PO3)4 for intermediate temperature fuel cells

A new proton-conductive composite of NH₄PO₃–(NH₄)₂Mn(PO₃)₄ was synthesized and characterized as a potential electrolyte for intermediate temperature fuel cells that operated around 250 °C. Thermal gravimetric analysis and X-ray diffraction investigation showed that (NH₄)₂Mn(PO₃)₄ was stable as a supporting matrix for NH₄PO₃. The composite conductivity, measured using impedance spectroscopy, improved with increasing the molar ratio of NH₄PO₃ in both dry and wet atmospheres. A conductivity of 7 mS cm⁻¹ was obtained at 250 °C in wet hydrogen. Electromotive forces measured by hydrogen concentration cells showed that the composite was nearly a pure protonic conductor with hydrogen partial pressure in the range of 10²–10⁵ Pa. The proton transference number was determined to be 0.95 at 250 °C for 2NH₄PO₃–(NH₄)₂Mn(PO₃)₄ electrolyte. Fuel cells using 2NH₄PO₃–(NH₄)₂Mn(PO₃)₄ as an electrolyte and the Pt–C catalyst as an electrode were fabricated. Maximum power density of 16.8 mW/cm² was achieved at 250 °C with dry hydrogen and dry oxygen as the fuel and oxidant, respectively. However, the NH₄PO₃–(NH₄)₂Mn(PO₃)₄ electrolyte is not compatible with the Pt–C catalyst, indicating that it is critical to develop new electrode materials for the intermediate temperature fuel cells.     

Effect of SiO2/Al2O3 ratio on the conversion of methanol to olefins over molecular sieve catalysts

A series of SAPO-34 molecular sieves with different SiO₂/Al₂O₃ ratios have been synthesized for the methanol-to-olefin (MTO) reaction. Their physico-chemical properties are characterized by various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR) and N₂ adsorption-desorption. The results are compared with those of the commercial HZSM-5, which show that the crystallinity and particle diameter of SAPO-34 as well as HZSM-5 increase with SiO₂/Al₂O₃ ratio. The variation of BET surface area of SAPO-34 is different from that of HZSM-5 and the sample with SiO₂/Al₂O₃ ratio of 0.4 exhibits the highest BET surface area. FT-IR spectra indicate that HZSM-5 has both Br?nsted and Lewis acid sites and Br?nsted acid sites are stronger, whereas SAPO-34 samples are dominated only by Lewis acid sites. When the SiO₂/Al₂O₃ ratio increases, propylene and butylenes become the predominant product of the MTO reaction over HZSM-5. In contrast, the main products of this reaction catalyzed by SAPO-34 are ethylene and propylene. According to the product distribution, the reaction mechanism over HZSM-5 catalysts is proposed.     

助剂对Ni/SiO2催化剂1,4-丁炔二醇加氢性能的影响

通过分步浸渍法在Ni/SiO 2催化剂中分别引入Zn、Cu、La、Mo、Co金属助剂,结合N 2物理吸附-脱附、XRD、H 2-TPR和NH 3-TPD等表征手段研究金属助剂对1,4-丁炔二醇加氢性能的影响。结果发现,Mo的引入使Ni/SiO 2催化剂的初始活性大幅增加,但反应2 h后活性下降,归因于催化剂表面酸中心使催化剂积炭失活;引入Cu、La及Co后的催化剂活性较低,推测是由于催化剂表面产生强吸附氢物种,不利于1,4-丁炔二醇加氢反应进行;与其他样品相比,Zn的引入使催化剂保持了Ni/SiO 2催化剂高的1,4-丁炔二醇加氢活性,同时可有效降低产物中2-羟基四氢呋喃副产物含量,提高目标产物1,4-丁二醇收率。     

Synthesis, characterization and evaluation of NiMo/SiO2–Al2O3 catalysts prepared by the pH-swing method

NiMo/(X)SiO₂–Al₂O₃ catalysts were synthesized with various SiO₂ contents (X = 0, 10, 25 and 50 wt%) using the pH-swing method. In order to find the optimum SiO₂ content, the catalysts were evaluated in the hydrodesulfurization of 4,6-DMDBT, hydrogenation of naphthalene and hydrodenitrogenation of carbazole. Kinetic parameters of Langmuir–Hinshelwood type equations for all the reaction systems were estimated. FTIR analysis of CO adsorption for the sulfided catalysts shows that the amount of coordinatively unsaturated Mo sites promoted by nickel (CUS-NiMoS) follows the order NiMo/10ASA > NiMo/25ASA > NiMo/0ASA. This tendency agrees with the results obtained in catalytic activity.     

Preparation, characterization and catalytic properties of Co–Nb2O5–SiO2 catalysts

Co–Nb₂O₅–SiO₂ catalysts were prepared using three different sol–gel procedures: (i) the colloidal sol–gel method using NbCl₅ and SiCl₄ as precursors; (ii) the polymeric sol–gel method using niobium ethoxide and tetraethyl-orthosilicate (TEOS); (iii) an intermediate procedure between the colloidal and polymeric sol–gel method in which the precursors were those utilized in the CSG but dissolved in a mixture of anhydrous ethanol and CCl₄. In all procedures, the elimination of the solvent carried out between 80 and 110°C was followed by a reduction in hydrogen flow (30 ml min⁻¹) at 773 K. Following these procedures, samples containing 10 wt.% Co and 15 wt.% niobium oxide (expressed as Nb₂O₅) were obtained. The characterization of the catalysts was performed using various techniques: N₂ adsorption and desorption curves at 77 K, NH₃- and H₂-chemisorption, TPO, XPS, XRD, and solid state ¹H MAS-NMR. Hydrogenolysis of butane was evaluated. The low reaction rates are assigned to the effect of the metal size, whereas the isobutane selectivity as well as the relatively high stability is due to the acidity of the support.     

PW/SiO2-Al2O3负载型催化剂用于萘异丙基化反应性能研究

以自制PW/SiO_2-Al_2O_3为催化剂,研究载体及其负载量对萘异丙基化反应转化率和选择性的影响,并考察反应时间、活化温度和反应温度对催化剂性能的影响。结果表明,以异丙醇和萘[n(异丙醇)∶n(萘)=2]为原料,环己烷为溶剂,在活化温度和反应温度均为250℃及反应时间5 h条件下,磷钨酸(PW)负载质量分数40%时,PW/SiO_2-Al_2O_3负载型催化剂对萘异丙基化反应的催化效果最好,萘转化率87. 97%,DIPN选择性41. 41%,DIPN中β,β-DIPN占比达到59. 82%。     

Formation of isocyanic acid during the reaction of mixtures of NO, CO and H2 over supported platinum catalysts

On-line infrared spectroscopy has been used to show that isocyanic acid, HNCO, is a substantial primary product of the reaction between NO, CO and H₂ over a Pt/SiO₂ catalyst. At 230°C it accounts for more than 40% of the CO converted. No isocyanic acid is seen when Al₂O₃ is placed downstream of Pt/SiO₂, or when using a Pt/Al₂O₃ catalyst under the same conditions, due to rapid hydrolysis of HNCO on the alumina. Isocyanic acid may exist as a trace intermediate in automobile catalytic converters during their warm-up phase but it is unlikely to emerge from the pore system of aluminabased catalysts.     

CO, H2 or C3H8 assisted catalytic combustion of methane over supported LaMnO3 monoliths

The effect of the addition of a second fuel such as CO, C₃H₈ or H₂ on the catalytic combustion of methane was investigated over ceramic monoliths coated with LaMnO₃/La-γAl₂O₃ catalyst. Results of autothermal ignition of different binary fuel mixtures characterised by the same overall heating value show that the presence of a more reactive compound reduces the minimum pre-heating temperature necessary to burn methane. The effect is more pronounced for the addition of CO and very similar for C₃H₈ and H₂. Order of reactivity of the different fuels established in isothermal activity measurements was: CO>H₂≥C₃H₈>CH₄. Under autothermal conditions, nearly complete methane conversion is obtained with catalyst temperatures around 800 °C mainly through heterogeneous reactions, with about 60–70 ppm of unburned CH₄ when pure methane or CO/CH₄ mixtures are used. For H₂/CH₄ and C₃H₈/CH₄ mixtures, emissions of unburned methane are lower, probably due to the proceeding of CH₄ homogeneous oxidation promoted by H and OH radicals generated by propane and hydrogen pyrolysis at such relatively high temperatures.

Finally, a steady state multiplicity is found by decreasing the pre-heating temperature from the ignited state. This occurrence can be successfully employed to pilot the catalytic ignition of methane at temperatures close to compressor discharge or easily achieved in regenerative burners.     

g-C3N4/Bi2MoO6/Ag3PO4复合材料制备及其可见光催化性能

以三聚氰胺、二水合钼酸钠和五水合硝酸铋为原料,采用溶剂热法制备了g-C3N4/Bi2MoO6前驱体,然后通过共沉淀法将Ag3PO4纳米粒子负载在前驱体上,得到g-C3N4/Bi2MoO6/Ag3PO4复合材料。通过XRD、FTIR、XPS、SEM、UV-Vis DRS等对复合材料进行表征。结果表明,g-C3N4、Bi2MoO6和Ag3PO4之间形成了异质结结构,促进光生电子-空穴对的有效分离。以盐酸四环素（TC）为目标降解物,分析材料的光催化活性。在可见光照射下,30 mg g-C3N4/Bi2MoO6/Ag3PO4在50 min内对40 mL 10 mg/L的TC溶液的降解率达到93%。降解速率常数为0.033 min-1,分别是g-C3N4、Bi2MoO6和Ag3PO4降解速率常数的33倍、3.6倍和1.5倍;g-C3N4/Bi2MoO6/Ag3PO4对TC进行降解,循环利用4次后,对TC的降解率为71%,说明g-C3N4/Bi2MoO6/Ag3PO4具有较好的稳定性。自由基捕获实验结果表明,g-C3N4/Bi2MoO6/Ag3PO4光催化降解TC的主要活性物种为·OH和·O2-。最后提出了TC可能的降解机理和降解路径。     

Direct conversion of methane into methanol over MoO3/SiO2 catalyst in an excess amount of water vapor

Well-dispersed MoO₃ on SiO₂ showed a high activity for partial oxidation of methane (mixed with oxygen in a molar ratio of 9:1) into methanol and formaldehyde at 873 K in an excess amount of water vapor, which is attributed to the formation of silicomolybdic acid (SMA) on the catalyst surface during reaction. One of the roles of SMA for the partial oxidation of methane is proved to depress the successive oxidation of methanol and formaldehyde into carbon oxides.     

Preparation of Cu/ZrO2 catalysts for methanol synthesis from CO2/H2

Cu/ZrO₂ catalysts for methanol synthesis from CO₂/H₂ were respectively prepared by deposition coprecipitation (DP) and solid state reaction (SR) methods. There is an intimate interaction between copper and zirconia, which strongly affects the reduction property and catalytic performance of the catalysts. The stronger the interaction, the lower the reduction temperature and the better the performance of the catalysts. Surface area, pore structure and crystal structure of the catalysts are mainly controlled by preparation methods and alkalinity of synthesis system. The conversion of CO₂ and selectivity of methanol are higher for DP catalysts than for SP catalysts.     

O2 reduction at the Pt/Nafion interface in 85% concentrated H3PO4

The kinetics of oxygen electroreduction have been studied on a smooth platinum electrode coated with Nafion® in concentrated 85% H₃PO₄. The effects of Nafion® coatings of different thickness on O₂ electroreduction at a smooth Pt rotating disk electrode with 85% phosphoric acid as the bulk electrolyte were examined. The kinetic current increases with increasing Nafion® film thickness while the diffusion limiting current decreases with increasing Nafion® film thickness. A O₂ concentration profile model for the Pt/Nafion®/bulk electrolyte has been established, and this model can be used to explain the O₂ reduction polarization results. The performance of Nafion®-modified, high surface area Pt/carbon air cathodes for use in the H₂–air concentrated phosphoric acid fuel cell was also studied.     

SiO2/Al2O3对仿铜金属光泽釉面的性能影响

通过单因素实验探讨了SiO2/Al2O3摩尔比对仿铜金属釉的影响,研制了一种釉面耐磨性较高且呈现仿铜金属效果的生料金属釉。实验结果表明:随着SiO2/Al2O3摩尔比的增加,由于釉中析出的晶体种类和数量不同,从而导致釉面光泽度和色泽不一。当SiO2/Al2O3摩尔比为5.6时,釉中析出了CuMn2O4尖晶石晶体,从而使釉面呈现最佳的仿铜金属光泽,该釉面硬度为894.65Kg/mm2。     

Carbon reduction reaction in the Y2O3–SiO2 glass system at high temperature

In order to assess the role of carbon with respect to the grain boundary chemistry of Si₃N₄-based ceramics model experiments were performed. Y₂O₃–SiO₂ glass systems with various amount of carbon (from 1 to 30 wt.%) were prepared by high-temperature treatment in a graphite furnace. High carbon activity of the furnace atmosphere was observed. EDX analysis proved the formation of SiC by the carbothermal reduction of SiO₂ either in the melt or in the solid state. The melting temperature of the Y₂O₃–SiO₂ system is strongly dependent on the amount of reduced SiO₂. XRD analysis of the products documented the presence of Y₂Si₂O₇, Y₂SiO₅ and Y₂O₃ crystalline phases in that order with an increasing amount of free C in the starting mixture. The reduction of Y₂O₃ was not confirmed.     

Catalytic reduction of NOx with H2/CO/CH4 over PdMOR catalysts

Conversion of NO_x with reducing agents H₂, CO and CH₄, with and without O₂, H₂O, and CO₂ were studied with catalysts based on MOR zeolite loaded with palladium and cerium. The catalysts reached high NO_x to N₂ conversion with H₂ and CO (>90% conversion and N₂ selectivity) range under lean conditions. The formation of N₂O is absent in the presence of both H₂ and CO together with oxygen in the feed, which will be the case in lean engine exhaust. PdMOR shows synergic co-operation between H₂ and CO at 450–500 K. The positive effect of cerium is significant in the case of H₂ and CH₄ reducing agent but is less obvious with H₂/CO mixture and under lean conditions. Cerium lowers the reducibility of Pd species in the zeolite micropores. The catalysts showed excellent stability at temperatures up to 673 K in a feed with 2500 ppm CH₄, 500 ppm NO, 5% O₂, 10% H₂O (0–1% H₂), N₂ balance but deactivation is noticed at higher temperatures. Combining results of the present study with those of previous studies it shows that the PdMOR-based catalysts are good catalysts for NO_x reduction with H₂, CO, hydrocarbons, alcohols and aldehydes under lean conditions at temperatures up to 673 K.     

锂离子电池正极材料磷酸钒锂制备方法研究进展

单斜结构的磷酸钒锂[Li₃V₂（PO₄）₃]材料与其他锂离子电池正极材料相比具有较高的工作电压（3.0~4.8 V）、良好的离子迁移率和优良的热稳定性,是一种具有竞争优势和发展前景的大功率锂离子电池正极材料,成为了近年来研究的热点。综述了锂离子电池正极材料磷酸钒锂的结构特点及其充放电机理。磷酸钒锂的常用合成方法有碳热还原法、水热法、溶胶-凝胶法及流变相法等,着重阐述了磷酸钒锂的不同合成方法对所制备样品的形貌和电化学性能的影响。分析总结了不同合成方法的改进方法,以改善磷酸钒锂正极材料电子导电性和锂离子扩散系数较低的问题。最后,针对磷酸钒锂正极材料在锂离子电池的应用中所存在的问题展望了该材料未来可能的发展方向和研究热点。指出需要优化材料的制备方法以改善材料的颗粒形貌、提高电子导电率和扩散系数等,进而改善材料的循环性能、倍率性能和充放电性能等;需要改进制备流程、提高实验的安全性、简化反应流程和减少制备成本等,以实现磷酸钒锂正极材料的工业化应用。     

Conditioning of Rh/α-Al2O3 catalysts for H2 production via CH4 partial oxidation at high space velocity

Experimental evidence and literature indications suggest that the process of methane partial oxidation over Rh catalysts is structure sensitive. Crystal phases and Rh cluster size are thus expected to affect the final catalytic performance. In this work, it is observed that outstanding performances are obtained when the as-prepared catalysts are conditioned through repeated runs at increasing temperature and O₂/CH₄ = 0.56. Catalysts slowly activate, that is CH₄ conversion and synthesis gas selectivity progressively grow with time on stream. On the basis of TPO and CH₄ decomposition measurements, this phenomenon is herein explained as the result of a surface reconstruction driven by the repeated exposition to the reaction at high temperature; it is thought that such reconstruction tends to eliminate defect sites and disfavors C-deposition reactions (extremely fast over steps and kinks). Conditioning with O₂-enriched feed streams makes conditioning faster, since the accumulation of surface C-species is suppressed; however, the catalyst is eventually less active than a catalyst conditioned with standard feed mixtures. As an alternative, accumulation of carbon can be suppressed and surface reconstruction proceeds faster if the catalyst is directly exposed to the reaction at high temperature for several hours.