溶胶-凝胶法制备NixCo1-xCoAlO4尖晶石型复合氧化物及其催化分解N2O性能

用溶胶凝胶法制备了一组Ni<sub>xsub>Co<sub>1-xsub>CoAlO<sub>4sub>尖晶石型复合氧化物,并采用表面润湿浸渍K<sub>2sub>CO<sub>3sub>溶液进行了K掺杂改性,用于有氧气氛下的N<sub>2sub>O催化分解反应.采用N<sub>2sub>物理吸附、X-射线衍射(XRD)、扫描电镜(SEM)、H<sub>2sub>-程序升温还原(H<sub>2sub>-TPR)等技术对催化剂进行了表征,考察了催化剂组成、母液pH值、K负载量等制备参数对其催化活性的影响.结果表明,母液pH值为3、K/(Ni+Co)物质的量比为0.1的K/Ni<sub>0.15sub>Co<sub>0.85sub>CoAlO<sub>4sub>催化剂具有较高的N<sub>2sub>O分解活性,450 ℃ N<sub>2sub>O可完全分解.助剂K的加入弱化了催化剂表面金属氧键,提高了催化剂的还原性、催化活性和抗水性.     

臭氧氧化结合湿法喷淋对玻璃窑炉烟气同时脱硫脱硝实验研究

采用臭氧氧化结合湿法喷淋对模拟玻璃窑炉烟气开展了同时脱硫脱硝实验研究.采用不同溶液(NaOH、Na<sub>2sub>S)进行了喷淋实验.结果表明,保证溶液pH值在10以上,NaOH浓度对NO<sub>xsub>脱除效率无影响,SO<sub>2sub>的存在促进了NO<sub>xsub>吸收.当O<sub>3sub>/NO物质的量比为1.6、溶液NaOH浓度为0.5%时,NO<sub>xsub>脱除效率可达70%,SO<sub>2sub>脱除效率在99%以上.往喷淋液中添加Na<sub>2sub>S,NO<sub>xsub>脱除效率随Na<sub>2sub>S浓度增加而提高,SO<sub>2sub>的存在对NO<sub>xsub>脱除效率无影响.当O<sub>3sub>/NO物质的量比为1.2、溶液中NaOH浓度为0.5%、添加剂Na<sub>2sub>S浓度为0.6%时,NO<sub>xsub>脱除效率可达70%,SO<sub>2sub>脱除效率在95%以上.60 min长时间运行实验证明,模拟烟气中的NO<sub>xsub>经碱液和添加剂吸收后主要以NO^-<sub>2sub>的形式存在于喷淋液中,且NO<sub>xsub>脱除效率不随溶液pH值的变化而变化.     

贵金属负载TiO2对光催化还原CO2选择性的影响

利用光沉积方法在TiO<sub>2sub>表面分别负载1%(质量分数) Pt、Pd、Au和Ag助催化剂.用TEM、XRD、UV-vis等技术对催化剂进行了表征,并利用连续瞬态电流时间响应和线性扫描伏安法等电化学方法,对贵金属负载的TiO<sub>2sub>光催化剂在光照条件下的电流响应强度及电催化析氢电位等特性加以测试.分析了贵金属助催化剂对光催化还原CO<sub>2sub>性能的差异.结果表明,负载贵金属助催化剂能显著加速光生电子空穴的分离,降低复合率;另外,助催化剂对还原CO<sub>2sub>选择性的顺序为Ag>Au>Pd>Pt.贵金属助催化剂还原CO<sub>2sub>的加氢选择性和析氢过电位存在相关性,即越不利于析氢过程的助催化剂,其催化CO<sub>2sub>加氢还原产物的选择性越高.     

大气压下甲烷火花放电制乙炔和合成气

用大气压下火花放电方法和发射光谱原位诊断技术, 对CH<sub>4sub>直接转化制乙炔和间接转化制合成气进行了研究, 并与介质阻挡放电进行了比较。结果表明, 火花放电具有能量效率高的突出优点, 能够高效地将CH<sub>4sub>活化成C原子、H原子和C<sub>2sub>等活泼物种。当CH<sub>4sub>单独进料时, 能得到以C<sub>2sub>H<sub>2sub>为主的烃类产物。当CH<sub>4sub>与CO<sub>2sub>和O<sub>2sub>共进料时, 能得到H<sub>2sub>/CO比值可调的合成气产物。在用火花放电转化CH<sub>4sub>和CO<sub>2sub>制合成气时, 添加O<sub>2sub>能够避免反应器的结炭问题, 反应温度只需225 ℃, 与常规催化法相比具有明显的低温优势。     

不同碱处理制备多级孔HZSM-5催化剂及噻吩烷基化性能研究

用Na<sub>2sub>CO<sub>3sub>、TPAOH和TPA⁺/CO<sub>3sub>^2-混合碱分别处理HZSM-5分子筛,采用FT-IR、XRD、XRF、N<sub>2sub>吸附脱附、SEM、NH<sub>3sub>-TPD及Py-FTIR表征手段对各类碱处理前后的HZSM-5分子筛进行表征。结果表明,3种类型的碱处理HZSM-5分子筛后,均能形成微孔-介孔多级孔道的HZSM-5(A)催化剂,并能调变催化剂的酸性,其中,TPA⁺/CO<sub>3sub>^2-混合碱处理得到的HZSM-5(TPA⁺/CO<sub>3sub>^2-)催化剂,比表面积最大,介孔数量最多。在小型固定床反应器上,考察了HZSM-5和HZSM-5(A)催化剂的噻吩烷基化性能,结果表明,HZSM-5(TPA⁺/CO<sub>3sub>^2-)催化剂因为具有适当的多级孔孔道和较多的B酸中心而表现出较高的噻吩转化率和1-己烯对噻吩的选择性。     

Lattice Boltzmann method for the fractional sub‐diffusion equation

A lattice Boltzmann model for the fractional sub‐diffusion equation is presented. By using the Chapman–Enskog expansion and the multiscale time expansion, several higher‐order moments of equilibrium distribution functions and a series of partial differential equations in different time scales are obtained. Furthermore, the modified partial differential equation of the fractional sub‐diffusion equation with the second‐order truncation error is obtained. In the numerical simulations, comparisons between numerical results of the lattice Boltzmann models and exact solutions are given. The numerical results agree well with the classical ones. Copyright © 2015 John Wiley & Sons, Ltd.     

Generation of sub‐terahertz repetition rates from a monolithic self‐mode‐locked laser coupled with an external Fabry‐Perot cavity

A novel scheme to multiply the repetition rate of a monolithic self‐mode‐locked laser for generating sub‐terahertz pulse sources is successfully demonstrated. A coated Yb:KGW crystal is designed to achieve a self‐mode‐locked operation at a repetition rate of 24 GHz with an average output power exceeding 1.0 W at a pump power of 4.8 W. A partially reflective mirror is utilized to combine with the output surface of the gain medium to constitute an external Fabry‐Perot cavity. It is theoretically and experimentally verified that adjusting the external cavity length to satisfy the commensurate condition can lead to the frequency spacing to be various order harmonics of the mode spacing of the monolithic cavity. The maximum pulse repetition rate of the laser output can be up to 216 GHz and the pulse duration is as short as 330 fs. More importantly, the overall characteristics of the first‐order temporal autocorrelation traces obtained by sequentially scanning the external cavity.length display an intriguing phenomenon of temporally fractional revivals, similar to the feature of spatial Talbot revivals.

     

Multiple solutions of semilinear degenerate elliptic boundary value problems

The purpose of this paper is to study a class of semilinear elliptic boundary value problems with degenerate boundary conditions which include as particular cases the Dirichlet problem and the Robin problem. The approach here is based on the super‐sub‐solution method in the degenerate case, and is distinguished by the extensive use of an L^p Schauder theory elaborated for second‐order, elliptic differential operators with discontinuous zero‐th order term. By using Schauder's fixed point theorem, we prove that the existence of an ordered pair of sub‐ and supersolutions of our problem implies the existence of a solution of the problem. The results extend an earlier theorem due to Kazdan and Warner to the degenerate case. © 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

金属醇盐法制备Ta2O5气凝胶

 以乙醇钽为前驱物,采用金属醇盐溶胶-凝胶技术,获得了Ta<sub>2sub>O<sub>5sub>湿凝胶,分析了不同条件下的溶胶-凝胶过程,并初步探讨了凝胶过程机理。Ta<sub>2sub>O<sub>5sub>的溶胶-凝胶过程主要受到水量、催化剂用量及钽源浓度等因素的影响：体系在强酸性条件下凝胶,且随着酸性的增强,体系凝胶时间明显缩短;当水量较少时,凝胶时间随水量的增加而增加,但当水量增加到一定程度时,体系凝胶时间基本不变;实验证明,通过增大溶剂用量,体系凝胶时间延长,气凝胶理论密度降低。通过对溶胶-凝胶过程的控制,结合超临界干燥技术,获得了密度低至44 mg/cm³的Ta<sub>2sub>O<sub>5sub>气凝胶样品。     

铁酸镍用于热化学循环反应CO2分解制CO的研究

采用共沉淀法制备了NiFe<sub>2sub>O<sub>4sub>和NiFe<sub>2sub>O<sub>4sub>/ZrO<sub>2sub>催化剂,用TGA考察了其热化学法,CO<sub>2sub>高温分解反应性能。通过对反应前后催化剂的表征发现,反应高温使两种催化剂都发生了明显的烧结,导致在热还原反应中形成的还原态氧化物不能完全被CO<sub>2sub>氧化从而降低了催化剂的反应性能;ZrO<sub>2sub>的加入对于提高催化剂的热稳定性以及循环反应稳定性具有重要的作用。在高温反应炉中考察了NiFe<sub>2sub>O<sub>4sub>/ZrO<sub>2sub>的CO<sub>2sub>分解实验,结果表明,提高热还原温度可以提高CO产量,然而,随着循环次数的增加CO的产量降低得更明显。