Promotional effect of hydroxyl on the aqueous phase oxidation of carbon monoxide and glycerol over supported Au catalysts

Gold particles supported on carbon and titania were explored as catalysts for oxidation of CO or glycerol by O₂ at room temperature in liquid-phase water. Although Au/carbon catalysts were not active for vapor phase CO oxidation at room temperature, a turnover frequency of 5 s⁻¹ could be achieved with comparable CO concentration in aqueous solution containing 1 M NaOH. The turnover frequency on Au/carbon was a strong function of pH, decreasing by about a factor of 50 when the pH decreased from 14 to 0.3. Evidently, a catalytic oxidation route that was not available in the vapor phase is enabled by operation in the liquid water at high pH. Since Au/titania is active for vapor phase CO oxidation, the role of water, and therefore hydroxyl concentration, is not as significant as that for Au/carbon. Hydrogen peroxide is also produced during CO oxidation over Au in liquid water and increasing the hydroxyl concentration enhances its formation rate. For glycerol oxidation to glyceric acid (C₃) and glycolic acid (C₂) with O₂ (1–10 atm) at 308–333 K over supported Au particles, high pH is required for catalysis to occur. Similar to CO oxidation in liquid water, H₂O₂ is also produced during glycerol oxidation at high pH. The formation of the C-C cleavage product glycolic acid is attributed to peroxide in the reaction.     

Liquid Phase Oxidation of Glycerol Using a Single Phase (Au–Pd) Alloy Supported on Activated Carbon: Effect of Reaction Conditions

The liquid phase oxidation of glycerol has been studied over gold–palladium nanoparticles supported on activated carbon and synthesized by using a one-protocol synthesis. The effect of pressure, catalyst amount and base has been examined by using an autoclave reactor with molecular oxygen as oxidant at mild conditions. By choosing the appropriate reaction conditions control of selectivity could be possible, whereas activity is strongly dependent on catalyst amount and concentration of base.     

Influence of Distributed Particle Size on the Determination of the Parabolic Rate Constant for Oxidation by the Powder Method

The established analysis for the study of oxidation using powder specimens is based on the assumption of monosized particles. The experiments, however, are conducted on powders with a distributed particle size. Here we present a statistical approach for the calculation of the rate constant for oxidation. The results of the analysis are applied to new data on oxidation studies of dense powders of silicon carbonitride amorphous ceramics. The monosized model requires a wide range of values for the rate constant to fit the short term and the long-term data, leading to considerable ambiguity in the estimate of the parabolic rate constant, k _p, for oxidation. In contrast the statistical model fits over the entire range of data, yielding a much more reliable value for k _p. For example, the monosized approach gave a value in the range 19.7 × 10⁻¹⁸ < k _p < 2.7 × 10⁻¹⁸ m²/s. In contrast, the statistical model yields a specific value of 4.5 × 10⁻¹⁸ m²/s.     

Aerobic Oxidation of Benzene to Biphenyl Using a Pd(II)/Molybdovanadophosphoric Acid Catalytic System

The oxidative coupling reaction of benzene to biphenyl was examined by the use of a Pd(OAc)₂/molybdovanadophosphoric acid/O₂ system under mild conditions. Pd(OAc)₂ combined with two different types of molybdovanadophosphoric acids exhibited the highest catalytic activity for the biphenyl synthesis. The best turn‐over number (TON) of Pd(OAc)₂ and the yield of biphenyl reached 109 and 14.3% based on the benzene used, respectively. The rate‐determining step of the coupling was found to be the reoxidation step of the reduced molybdovanadophosphoric acid by molecular oxygen.     

催化剂粒径对水合异丁烯反应的影响

在半连续浆态搅拌釜中,使用NKC-9离子交换树脂细粉作为催化剂,考察了颗粒粒径对异丁烯水合反应速率的影响。试验结果表明,催化剂颗粒在105μm以上时内扩散影响较严重。在30μm以下,速率随颗粒粒径减小而加快的趋势较为明显。     

Effect of Particle Size on the Hydrothermal Stability and Catalytic Activity of Polycrystalline Beta Zeolite

The effect of particle size in the range of 0.2–0.9 μ m on the hydrothermal stability of polycrystalline beta zeolites was investigated in terms of changes in BET surface areas, percent crystallinity, and framework aluminum atoms. It was found that the hydrothermal stability of beta zeolite increased with increasing particle size while the catalytic activities decreased. However, the XRD results have revealed that percent crystallinity of the hydrothermally treated beta zeolite remained relatively high (> 95%) although dealumination occurred in most cases. This high stability is due probably to small amount of Al atoms present in the unit cell of this zeolite.     

Effect of Pore Size and Particle Size Distribution on Granular Bed Filtration and Microfiltration

Abstract

The paper reviews the effect of particle size distribution and pore size distribution on granular bed filter and crossflow microfiltration performance. The experimental results of the granular bed filter with pollen particles in suspension showed that the presence of large particles improved the filter efficiency of smaller particles in suspension. Microfiltration results with bi and tri‐modal latex suspensions showed that the permeate flux and the quality were significantly affected by the particle size and its distribution, especially when the particle size was smaller than the pore size of the membrane. The mathematical model simulation results of granular bed filtration show that media pore size distribution is an important parameter of filtration for the particle removal and pressure drop across the filter.     

颗粒粒径和膜孔径对陶瓷膜微滤微米级颗粒悬浮液的影响

通过测定颗粒悬浮液通过陶瓷微滤膜时的参透通量及污染阻力,确定了陶瓷膜处理微米级颗粒悬浮液时,颗粒粒径和膜孔径对微滤过程的影响和膜污染机理,获得了微米级颗粒悬浮液微滤过程中膜孔径的选择方法。     

Exhaust Gas Catalysts for Heavy-Duty Applications: Influence of the Pd Particle Size and Particle Size Distribution on the Combustion of Natural Gas and Biogas

In this study, an experimental investigation concerning exhaust gas catalysts for heavy-duty diesel engines fuelled by natural gas or biogas is presented. Miniature monoliths, 2.5 wt% Pd/Al₂O₃, have been prepared, characterised and tested. Various methods have been used in order to obtain different palladium particle sizes, including incipient wetness and microemulsion technique. Crystallite sizes between 2 and 40 nm were obtained. We observed that the metal particle size influences the activity for methane oxidation. Moreover, the homogeneity of the active material was found to affect the reaction rate.     

Influences on the Particle Size Distribution of Diesel Particulate Emissions

Particulates give great concern for mankind health. Especially the nano size particles are under discussion. Therefore, the particle size distribution from the combustion chamber to tail pipe emissions are of great interest. With the aim of scanning mobility particle sizer the number weighted particle size distributions were measured in the combustion chamber as well as in the exhaust gas up and downstream of aftertreatment systems. Using the identical particle measurement technique results can be compared without changing the particle size definition. The particles in the cylinder of a modern serious DI diesel engine were sampled with a time resolved fast gas sampling valve. The Soot particles formed in the cylinder during the early combustion phase are oxidized by about 99% in the late combustion/early expansion phase, whereas the soot particle sizes distribution in the cylinder at the end of the expansion phase are equal to that in the tail pipe. DI diesel engines with high pressure injection system emit less numbers of particle with in tendency greater sizes compared to IDI diesel engines. Oxidation catalysts do not influence particle size distribution but particulate traps reduce particle number by up to two orders of magnitude. Detail analysis shows that an increase of nano size particle number downstream of an aftertreatment device results from artifacts.     

乙氧基镁催化剂粉末粒度及粒度分布测定的研究

用乙醇做分散介质,用激光粒度测定仪测定四个乙氧基镁催化剂粉末试样的粒度及粒度分布,测试快速、准确。试验结果显示乙氧基镁（德国）催化剂粉末粒度最小,粒度分布集中,在四个样品中质量最好,试验结果令人满意。     

氢氧化铝粒度对干法氟化铝生产的影响

根据生产实践。总结分析了氢氧化铝粒度对千法氟化铝生产产品产量、产品质量、流化床工况和设备的影响。认为选用粗颗粒氢氧化铝生产的优越性在于能更好地保持流态化、有利于流化床的正常稳定操作,延长设备使用寿命,提高产品产量、质量,提高产品粒度,增加效益,并受电解铝厂用户的欢迎。     

沉淀反应工艺条件的变化对纳米二氧化硅宏观粒径的影响

文章采用化学沉淀法,以蛇纹石酸浸滤饼碱浸所制备的硅酸钠溶液为原料、硫酸为沉淀剂,以所制得二氧化硅样品的宏观粒径为主要考察指标,通过单因素条件实验和正交实验,分别考察了表面活性剂用量等因素的变化对所制备的纳米二氧化硅样品宏观平均粒径的影响,所确定的优化工艺条件下的重复实验结果表明:所制备的二氧化硅样品的微观粒径约为25nm,宏观平均粒径均小于1.30μm。     

阴离子聚氨酯乳液的粒径及粒子形态的研究

讨论了用二羟甲基丙酸制备阴离子聚氨酯乳液,二羟甲基丙酸的量,反应程度,扩链剂的用量对乳液的稳定性、粒径大小和分布及粒子形态的影响。     

粒径对磨屑粉填充EPDM胶料性能的影响

研究了4种不同粒径的PMMA磨屑粉填充的EPDM性能的变化.力学性能试验表明:EPDM以粒径为47μm的磨屑粉填充时,拉伸强度最高;以粒径为190μm的磨屑粉填充时,断裂伸长率最高.扫描电镜(SEM)形貌观察分析表明:随着磨屑粉粒径越小,磨屑粉与EPDM之间的界面结合越强.     

不同因素对氢氧化镁粒径的影响程度

以氨水为沉淀剂与氯化镁反应,直接沉淀法制备氢氧化镁,探讨了反应温度、氯化镁浓度、氨水浓度、氨水加入流量、氨镁比、反应时间对制备超细氢氧化镁阻燃剂的影响程度。通过正交实验,选用L25(56)正交试验表,进行了25次实验,其中有9次实验均生产出了D(50)1.00μm的氢氧化镁产品。得出各影响因素的影响程度依次为:镁离子浓度氨镁比反应温度氨水加入速度氨水浓度反应时间。     

超声波清洗对石英砂粒度和白度影响的研究

利用超声波仪在不同的条件下对凤阳县不同粒度湿法石英砂进行清洗,结果显示所有石英砂的粒度减小、白度增加,其中粒度和白度改变最大的是80～100目石英砂.在清洗过程中,超声波的频率和功率、草酸浓度、石英砂的粒度、清洗时间、清洗温度、搅拌器转速等参数对石英砂的粒度和白度都会产生影响,其中超声波的频率和草酸浓度对试验结果影响最大.利用扫描电子显微镜对清洗前后石英砂的形貌进行了观察和分析,结果显示清洗后的石英砂表面吸附的杂质颗粒比清洗前明显减少,有裂痕的石英砂颗粒都被粉碎,清洗后的石英砂表面出现了“微坑”,说明超声波清洗对石英砂有粉碎作用,从而使石英砂的粒度和白度发生变化,试验数据显示,在超声波频率(20～40 kHz)和功率(180～300 W)一定的条件下,超声波使石英砂粒度减小1.15％-5.69％,白度增加2.01％～6.98％.     

颗粒分布、比表面积、化学组成对水泥强度的影响

水泥的化学组成、细度决定着水泥的力学性能.根据已有的关于水泥颗粒的粒度分布和比表面积的数学模型,对4个不同水泥厂的水泥数据进行了分析,发现这些数据与模型之间没有很好的对应.利用120组数据建立了水泥颗粒的粒度分布与比表面积新的数学模型及28 d抗压强度与4种矿物组成的数学关系式,并把水泥的抗压强度用水泥颗粒大小、比表面积和化学组成表示出来了.     

Effect of Carbon Deposits on Reactivity of Supported Pd Model Catalysts

Alumina-supported Pd model catalysts were prepared by Pd evaporation onto a thin alumina film grown on a NiAl(110) substrate. Adsorption and co-adsorption of ethene, CO and hydrogen on Pd/Al₂O₃/NiAl(110) covered by carbon species, formed by ethene dehydrogenation at 550 K, was studied by temperature programmed desorption (TPD). TPD results show that carbon deposits do not prevent adsorption but inhibit dehydrogenation of di- bonded ethene. Carbon species suppress CO adsorption in the highly coordinated sites and also suppress the formation of hydrogen ad-atoms on the surface. The ethene hydrogenation reaction performed by co-adsorption of hydrogen and ethene is inhibited by the presence of carbon deposits. The inhibition is independent of particle size studied (1-3 nm). The effects are rationalized in terms of a site-blocking behavior of carbon species occupying highly coordinated sites on the Pd surface.