An integrated system of biological and catalytic oxidation for the removal of o-xylene from exhaust

Biofiltration is an efficient technology for treatment of gaseous waste. Its disadvantages, however, include large volume of bioreactor and slow adaptation to fluctuating concentrations in waste gas. Catalytic oxidation offers a high destructive efficiency at relatively low operating temperature and small unit. A bench scale system integrated with a biofilter and a catalytic oxidation unit for the treatment of gases containing o-xylene was investigated in this study. The catalytic oxidation unit was packed with Cu/Al₂O₃ catalyst. The results showed that 90% of o-xylene could be removed in the biofilter at the load below 38.2 g m⁻³ h⁻¹. High o-xylene concentration in inlet gas resulted in an overload of the biofilter. Using the Cu/Al₂O₃ catalytic oxidation unit, the concentration of o-xylene could be reduced evidently. The combination of the chemical and microbial processes not only led to a high and stable efficiency of o-xylene conversion, but also improved capacity resisting the shock loads. The Cu/Al₂O₃ was studied for o-xylene oxidation in temperature range of 90–320 °C. The o-xylene conversion was improved correspondingly with the increasing of oxidation temperature. The reaction mechanism of o-xylene oxidation on Cu/Al₂O₃ was also investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS).     

Gas-phase selective oxidation of toluene on TiO2–sepiolite supported vanadium oxides: Influence of vanadium loading on conversion and product selectivities

Gas-phase selective oxidation of toluene has been carried out on vanadium oxide systems (5–20 wt.% of V₂O₅, equivalent to 0.4–1.7 theoretical monolayers) supported on TiO₂–sepiolite (with titania loading around the theoretical monolayer, 12 wt.%) and on sepiolite. A study has been made on both the influence of vanadia loading and of the support on the catalytic behaviour of the supported vanadium systems. The reducibility by H₂ TPR was also studied as well as the acid and basic/redox sites from the results of conversion of the 2-propanol test reaction of the solids. Benzaldehyde, benzoic acid and several coupling products were the main ones detected, attaining over 50% selectivity towards the benzaldehyde and benzoic acid products at a total conversion around 10%. The activity and selectivity to the selective products exhibited by vanadium systems supported on mixed support were superior to those exhibited by the systems supported on sepiolite and increased notably in both series with the increase in vanadium loading. The best catalytic behaviour exhibited by the vanadium systems supported on mixed support, which also exhibited the highest density of sites capable of being reduced (as well as their reducibility) and of those responsible for propanone formation, could be attributed not only to the different balance of the vanadia species existing in the two supports (monomeric + oligomeric/polymeric), but also to such other factors as the nature of the support and, concretely, its chemical composition.     

表面引发剂对熔融铝合金直接氧化生长的影响

为了控制熔融铝合金直接氧化法制备Al2O3/Al复合材料的氧化生长,采用ZnO,SiO2和MgO3种表面引发剂,研究它们对Al-Si-Zn合金氧化生长过程及Al2O3/Al复合材料组织形貌的影响.结果表明:与未使用引发剂时相比,使用SiO2,ZnO或MgO表面引发剂制备的粉末都能显著地缩短Al-Si-Zn合金的氧化生长孕育期,提高合金氧化生长速率,改善复合材料的胞状生长方式,提高复合材料的组织均匀度和致密度,为实际生产应用提供了依据.实验发现:ZnO表面引发剂的使用效果最为突出,其最佳添加量为12mg/cm2.     

Synthesis and activation of Pt nanoparticles with controlled size for fuel cell electrocatalysts

Well-dispersed Pt nanoparticles with controlled size and narrow size distribution were prepared by polyalcohol reduction of platinum acetylacetonate, using oleylamine as a capping agent. The particle size was varied from 3.5 nm to 11.5 nm by decreasing the amount of oleylamine added in the synthesis. Size selection of the as-prepared particles by solvent fractionation yielded nearly monodispersed Pt particles. The as-prepared particles were loaded on a carbon support by physical deposition, but showed no electrocatalytic activity due to the oleylamine bound to the particle surface. The particles were activated for electrocatalysis after heating the particles in air at 185 °C for 5 h, conditions that gave no particle-sintering and no oxidation. Cyclic voltammetry showed that the particles after the heat treatment in air were electrocatalytically active for methanol oxidation. The smaller 3.5 nm and 4.0 nm Pt particles had a higher intrinsic activity for methanol oxidation, but a lower tolerance to CO poisoning, compared with 6.0 nm, 9.5 nm and 11.5 nm particles. CO-stripping results suggest that CO is more easily oxidized on larger Pt particles.     

亚硫酸钙氧化为石膏的研究

进行了亚硫酸钙氧化为二水石膏的研究 ,考察了初始 p H值、反应温度、空塔气速、固含量和停留时间对氧化率的影响 ,给出了适宜的反应条件 .在这些条件下 ,氧化率达 96 %以上     

Studies on Catalytic Side-Chain Oxidation of Nitroaromatics to Aldehydes with Oxygen

The side-chain oxidation of 2-nitrotoluene in liquid phase in the presence of catalytic amount of manganese sulfate and stoichiometric amount of potassium hydroxide with oxygen was studied. In the most favorable conditions, over 80% of conversion of 2-nitrotoluene and 50% of selectivity to 2-nitrobenzaldehyde was achieved. Effects of the reaction parameters on the conversion of the reactant and the selectivity of the product were examined. These results, together with EPR spectroscopic study, show that a benzyl anion was formed in the early stage of the reaction, which was then converted to the final product via a free radical mechanism.     

Chemistry and Physics of Alkali Metals on MoS2 Surfaces

The interaction of alkali metal with surfaces has been of great interest to the community of catalysis since alkali metal can play an important role as a promoter. On alkali-doped MoS₂, such a promotion effect of alkali metal has been exemplified in the direct synthesis of linear alcohols from CO and H₂, where the alkali-doping switches the catalyst selectivity from methanation to alcohol synthesis. This paper reviews recent high-resolution X-ray photoelectron spectroscopy experiments that have provided direct observation of electron transfer from alkali metals to a model single crystal MoS₂ and the capture of the supra-valence electrons in the subsequent oxidation reactions.     

天然气制液态烃新工艺

丰富的天然气资源,特别是边远地区分散的中小天然气田和油气共生的油气田的天然气,由于产量达不到管线长输的规模效益,又远离消费市场,很难开发利用.为此,作者在天然气两段催化氧化制合成气和费-托合成研究的基础上,提出了一种流程较短、投资和操作费用较低的天然气合成液态烃新工艺,可将丰富的天然气资源,特别适合将边远地区分散的中小天然气田的天然气转化为无硫、无氮、无芳烃、无重金属污染和便于输运的优质石蜡基液态产品.该产品可经轻度加氢改质得到高品质的柴油掺合组分、润滑油基础油高等附加值产品.该工艺副产的燃料气可用于发电,或作为燃料气使用.     

A novel laboratory bench for practical evaluation of catalysts useful for simultaneous conversion of NOx and soot in diesel exhaust

This study deals with the development of a laboratory bench for the practical evaluation of catalysts that are useful for the direct conversion of NO_x and soot in the exhaust of diesel engines. The employed model exhaust is generated by using a diffusion burner with additionally dosing some gaseous components to the burner gas to obtain a realistic feed composition. The produced soot is extensively characterized by employing thermogravimetry, transmission electron microscopy, N₂ physisorption and temperature programmed techniques. The results of the different characterization methods show that the present soot is suitable for the intended catalytic investigations. The simultaneous conversion of NO_x and soot is examined like in practice, i.e. the soot is separated from the tail gas by a diesel particulate filter (DPF) that is coated with the catalyst. The deposited soot is then catalytically converted by NO_x and O₂ to form N₂ and CO₂. The conversions of NO_x and soot are measured by exclusively applying gas analysers, whereby a special experimental procedure is developed to determine the soot removal. Hence, additional soot related analytics are not required. To show the suitability of the constructed bench a Pt/Fe₂O₃/β-zeolite sample is taken as test catalyst that is reported to be very active in NO_x/soot reaction. The measurements performed with and without catalyst clearly show the effect of the used sample in simultaneous NO_x/soot conversion. We therefore consider the constructed laboratory bench to be a useful tool for testing and ranking catalytic materials.     

Promising alloys for intermediate-temperature solid oxide fuel cell interconnect application

The formation of a low Cr-volatility and electrically conductive oxide outer layer atop an inner chromia layer via thermal oxidation is highly desirable for preventing chromium evaporation from solid oxide fuel cell (SOFC) metallic interconnects at the SOFC operation temperatures. In this paper, a number of ferritic Fe–22Cr alloys with different levels of Mn and Ti as well as a Ni-based alloy Haynes 242 were cyclically oxidized in air at 800 °C for twenty 100-h cycles. No oxide scale spallation was observed during thermal cycling for any of these alloys. A mixed Mn₂O₃/TiO₂ surface layer and/or a (Mn, Cr)₃O₄ spinel outer layer atop a Cr₂O₃ inner layer was formed for the Fe–22Cr series alloys, while an NiO outer layer with a Cr₂O₃ inner layer was developed for Haynes 242 after cyclic oxidation. For the Fe–22Cr series alloys, the effects of Mn and Ti contents as well as alloy purity on the oxidation resistance and scale area specific resistance were evaluated. The performance of the ferritic alloys was compared with that of Haynes 242. The mismatch in thermal expansion coefficient between the different layers in the oxide scale was identified as a potential concern for these otherwise promising alloys.