不同价态五氧化二钒吸附水和氨的机理研究

为研究不同价态的V_2O_5(V_6O_(15)及V_6O_(15)~+)吸附H_2O和NH_3的反应机理,应用量子化学得到反应物、中间体、过渡态和产物的几何构型,对比分析反应过程中优化结构的势能、反应能垒、键长和吸附能等数据.结果表明:V_6O_(15)和V_6O_(15)~+均可吸附H_2O生成V—OH,但是对于后者整个反应表现为放热,而且反应能垒更低,说明V_6O_(15)~+更容易与H2O反应生成BrФnsted酸位;NH_3在V_6O_(15)~+上的吸附能更大,更容易形成可与NO反应的—NH4~+;在SCR脱硝反应中阳离子团簇V_6O_(15)~+比中性团簇V_6O_(15)活性更大.     

SCR催化剂表面NH3和NO吸附实验与机理研究

选择性催化还原(SCR)技术被广泛应用于大型燃煤机组烟气氮氧化物脱除中,脱硝效率达到90%以上。烟气温度下降会导致SCR系统的催化剂受损,在停机之前会停止向SCR系统喷氨,导致此期间的NO_x排放超标。采集并计算了某电厂停炉过程中排放NO的数据,实验发现NO排放量在此过程中仍会有不同幅度的降低。运用密度泛函理论(DFT)基于V_2O_5团簇模型研究了NO和NH_3在催化剂不同吸附位上的吸附机理。研究结果表明:NO不会稳定吸附在催化剂的表面;NH_3既能吸附在钒基表面的Lewis酸性位,又可吸附在Br?nsted酸性位,而且更稳定。由此可知,停机后由于吸附在催化剂表面的NH_3与烟气中的NO反应,使得出口处的NO量降低。     

V2O5/TiO2的钾、钠、钙复合中毒及改性研究

以V2O5/TiO2催化剂及在其基础上改良得到的VSbNbTi催化剂为研究对象,研究了碱金属K、Na和碱土金属Ca的氧化物及氯盐对两种催化剂以NH3选择催化还原NO反应的影响。研究结果表明,三种金属中,无论以氧化物或氯盐的形式存在,K对催化剂的毒化作用都是最强的;同时掺入两种氧化物时,两种组分之间的相互作用会弱化单组分对催化剂的毒化作用,且这种弱化作用以CaO最为明显;VSbNbTi催化剂具有良好的抗K、Na、Ca三种元素的氧化物或氯盐中毒的能力。     

SCR催化剂再生中去除中毒物质的实验研究

针对传统钒系SCR催化剂的再生方式,分别研究了水洗、酸洗处理对催化剂性能的影响。结果表明,水洗可以去除14%的中毒元素Na,酸洗几乎能去除全部的Na,但与此同时也洗去大约22.6%的V。Na中毒使催化剂的氧化能力与表面酸位对NH3的吸附能力大幅下降,水洗、酸洗工艺处理后可以使中毒催化剂的氧化能力与NH3吸附能力提高。此外中毒和再生处理过程对催化剂的物理结构影响较小。     

纳米级V_2O_5/TiO_2的活性特征及对碳烟氧化的催化作用

采用浸渍法制备了不同钒负载量的纳米级V_2O_5/TiO_2催化剂,通过扫描电镜(scanning electron microscope,SEM)、X射线衍射仪(X-ray diffractomer,XRD)和傅里叶红外光谱(Fourier transform infrared spectrometer,FT-IR)测试手段对催化剂的物化特性进行表征。以Printex-U碳黑作为实际发动机颗粒的替代物,利用热重分析法探究V_2O_5负载量对催化氧化碳烟活性的影响,并基于Flynn-Wall-Ozawa法定量表征碳烟催化氧化反应过程。研究结果表明:较低钒负载量时,活性组分钒氧物种处于高度分散状态,基本呈现单层分布。当负载量较高(40%)时,部分钒氧物种开始团聚并以结晶态析出,催化剂表面出现明显的柱状晶结构。随着钒负载量的增加,在碳烟氧化过程中催化剂活性呈递增趋势。在一系列样品中,负载量20%的V_2O_5/TiO_2催化剂表现出最佳催化活性,与无触媒状态相比,碳烟氧化的起燃温度Ti、失重峰值温度Tp和燃尽温度Tf等特征温度的降幅最大。当负载量达40%时,V_2O_5主要以结晶相存在,占据大量活性位,降低催化效果。由FWO法热力学分析得到颗粒氧化的活化能的顺序为EPMEV5EV10EV40EV20。     

飞灰未燃尽碳吸附(HgS)n及(HgO)n的量化分析

为研究飞灰中未燃尽碳对(HgS)_n及(HgO)_n(n=1~4)的吸附机理,构建了三碳环石墨烯结构作为未燃尽碳分子表面模型,应用密度泛函理论在B3LYP/6-31G(d)水平上进行结构优化,在PWPB95/def 2-Tzvp水平上计算了体系的单点能。研究表明:HgS及HgO团簇在未燃尽碳表面的吸附形式为化学吸附,吸附能为-646.546~-105.116 k J/mol;HgS及HgO团簇以解离和非解离形式吸附于未燃尽碳表面,更倾向于稳定的解离吸附;相同情况下HgO团簇的吸附稳定性高于Hg S团簇;团簇数量的增加对吸附能几乎无影响,当吸附位点增多时,吸附能绝对值显著增加,吸附稳定性提高。     

二维碳载Au4Pd2催化剂的构建及其电催化性能

贵金属纳米团簇由于精确的结构和明确的化学组成而受到广泛的关注.该工作采用具有精准的颗粒大小和精确的结构双金属金属纳米团簇,研究其电子结构、几何结构对催化反应的影响,同时利用杂原子与主原子间的强电子耦合作用调控催化性能.首先制备4个金原子与2个钯原子组成的金钯纳米团簇,并分散至二维材料上得到单团簇分散的金钯基纳米复合材料催化剂;通过XPS测试可知,AuPd与载体之间存在较强的协同作用,有助于促进其氧还原(ORR)与析氢反应(HER)的稳定性;调节贵金属比例得到最佳比例的金钯催化剂,在0.1 mol/L KOH氧饱和电解液中,起始电位为0.95 V,半波电位为0.81 V,其ORR性能优于商业Pd/C.该催化剂也具有良好的HER性能,在0.5 mol/L H2SO4电解液中,电流密度为10 mA/cm2下的过电位为129 mV;利用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电镜(TEM)对催化剂结构进行表征分析,解释其结构与性能间的联系.优化贵金属团簇掺杂比例得到具有优异氧还原与析氢性能的双功能催化剂,为高效稳定的电催化剂的开发提供了新方向.     

CuO与负载间相互作用的密度泛函理论

通过密度泛函理论(DFT)模拟了不同负载对Cu基氧载体反应性能和抗烧结性能的影响.首先通过DFT模拟计算得出了CuO纳米团簇在4种不同负载(TiO_2、ZrO_2、CuAl_2O_4和MgAl_2O_4)上的吸附能分别为-2.96eV、-5.14eV、-4.25eV和-5.42eV,其中TiO_2的吸附能最低,不利于氧载体颗粒的抗烧结性,但CuO在ZrO_2、CuAl_2O_4和Mg Al2O4上的高吸附能有助于抑制氧载体的烧结.通过计算不同负载下团簇释氧过程的能量势垒来比较负载对氧载体释氧性能的影响.结果表明,氧气分子从表面的脱附过程是整个释氧过程的速控步骤.不同负载(TiO_2、ZrO_2、CuAl_2O_4和MgAl_2O_4)下CuO纳米团簇总的释氧能量势垒分别为3.45eV、3.33eV、3.28eV和3.41eV,其中负载于CuAl_2O_4的CuO释氧能量势垒最低,反应活性最高.     

金属盐催化剂对木粉半焦CO_2气化反应性的影响

在热重分析仪上进行了几种金属盐(K、Na、Ca、Mg、Fe)对杉木粉半焦CO_2催化气化反应特性的研究;利用XRD和SEM技术对半焦样品的碳化程度、晶相结构及表面形貌进行了表征。研究表明:5种金属盐均提高了半焦样品的反应活性;且反应活性指标显示其催化效果顺序为KNaCaFeMg。XRD结果显示:Na和Ca在制焦过程中形成了明显的晶相结构;Mg增强了半焦中碳的有序化程度。SEM结果表明:5种金属盐均在半焦表面形成了"斑点"状的活化中心点且在碱金属半焦的部分表面观测到疏松片状结构。     

当量比对稻壳气化及碱金属K释放迁移特性的影响

文章基于气化气成分、气化效率和炭转化率等参数研究了当量比对稻壳气化特性的影响;采用化学分馏法和电感耦合等离子体发射光谱分析仪测量了气化炉产生的飞灰中的碱金属K总含量和各赋存形态的碱金属K含量,进而计算出碱金属K的释放和转化比例。研究结果表明:当量比对稻壳气化特性及碱金属K释放迁移特性影响较大,且当量比对稻壳气化特性及碱金属K释放迁移特性的影响存在最优值;在低温阶段(700℃),KCl会与焦炭基体中的羧基官能团反应生成可离子交换态钾;随着反应温度的逐渐升高,可离子交换态钾开始氧化分解成无机钾(如K_2CO_3)和焦炭结合钾(char-K),随后K_2CO_3与水蒸气(H_2O)反应生成气态的原子K(g)或KOH(g);在O_2气氛下,K(g)会与SiO_2,O_2和Al_2O_3反应生成不溶钾。     

Recent research progress of metal compounds as anode materials for sodium-ion batteries

钠离子电池具有钠资源存储丰富、价格低廉等优点,是一种极具发展前景的储能装置,因此成为当下研究热点。钠离子电池的电化学性能主要取决于正负极材料。但是,钠离子较大的半径使其在电极材料中可逆地嵌入/脱出更为困难。而金属化合物材料作为储钠负极材料时,遵循转化反应机制,并表现出较高的理论比容量,因而受到研究人员的广泛关注。本文综述了金属氧化物、金属硫化物、金属磷化物等几种金属化合物负极材料的储钠机制和研究进展,探讨了金属化合物材料的储钠性能,阐明了金属化合物作为理想的储钠负极材料的优势,最后对金属化合物材料的研究前景进行了展望。     

纳米金属及氧化物对污染处理的影响研究进展

纳米金属及氧化物在日常生活中应用广泛,它们会通过各种途径进入环境,因此需要对它们的环境和健康风险进行评估。纳米金属及氧化物具有独特的物理化学性质。综述了纳米金属及氧化物对污染去除过程中微生物的毒性方面的文献,特别关注了其对污染处理过程(污水处理、固体废弃物处理)的影响,并阐述了可能的毒性机制。在此基础上,探讨了纳米金属及氧化物的微生物毒性的研究目前存在的问题和未来研究的展望。     

Hybrid of AgInZnS and MoS2 as efficient visible-light driven photocatalyst for hydrogen production

We present a simple two-step hydrothermal method to prepare AgInZnS/MoS₂ nanocomposite. The morphology and compositional characteristics of the sample were investigated by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The as-synthesized heterostructures exhibited superior photocatalytic activity for hydrogen evolution under visible-light irradiation and the optimum loading amount of MoS₂ is at 0.5 wt%. In an attempt to explain this phenomenon, a possible mechanism was also proposed. The enhanced photocatalytic activities toward water splitting arise from the boosted active sites for hydrogen generation and the enhanced charge transfer. This work may contribute to the design and construction of highly efficient visible-light responsive photocatalyst for sustainable energy harvesting and conversion.     

Unidirectional sensing characteristics of structured Au–GaN–Pt diodes for differential-pair hydrogen sensors

A new metal-semiconductor-metal (MSM) hydrogen sensor was proposed to avoid (or to reduce) false alarms due to temperature drift when it is used in differential-pair hydrogen-sensing systems. A GaN semiconductor layer together with Pt as catalytic metal and Au as Schottky metal was employed to structure an Au–GaN–Pt MSM sensor. In particular, the structured Au–GaN–Pt MSM sensor can function as an active sensor and a reference sensor, depending on the polarity of applied voltage, in a differential-pair sensing circuit. Possible sensing mechanisms associated with the Au–GaN–Pt MSM sensor were described first to include band diagrams and graphical analysis. Experimental results reveal that an active sensor by forward-biasing the Au–GaN–Pt MSM sensor responses well to hydrogen-containing gases (50, 500, and 5000 ppm H₂/N₂) at various temperatures (25 °C, 50 °C, 70 °C, and 90 °C). High sensing current gains over 10⁴ were obtained. Further, the Au–GaN–Pt MSM sensor can also be reverse-biased to act as a reference sensor which shows negligible responses to hydrogen-containing gases. The differential-pair sensing circuit with the proposed Au–GaN–Pt MSM sensor reduces false alarms due to ambient temperature variation while it provides a short detection time.     

高浓度含盐有机废液焚烧技术

介绍了有机废液焚烧处理的国内外现状、焚烧工艺及焚烧设备,比较了各自的处理效果及优缺点,针对有机废液中的碱金属和碱土金属盐在焚烧过程中容易形成低熔点的共晶体,造成焚烧炉的结焦、结渣、流化失败等危害,着重分析了含盐有机废液的焚烧处理技术,最后提出了采用蒸发结晶技术对有机废液进行脱盐处理的可行性。     

Liquid phase reforming of woody biomass to hydrogen

This work concentrates on the production of H₂ directly from raw biomass through liquid phase reforming in the presence of a liquid base and a solid catalyst. Both precious metal and base metal catalysts were found to be active for the liquid phase hydrolysis and reforming of wood. Pt-based catalysts, particularly Pt–Re, were shown by atomistic modeling to be more selective toward breaking C–C bonds, resulting in a higher selectivity to hydrogen versus methane. Ni-based catalysts were found to prefer breaking C–O bonds, favoring the production of methane. The results showed that at a constant wood concentration, increasing the concentration of base (base to wood ratio) in the presence of Raney Ni catalysts resulted in greater selectivity toward hydrogen. The amount of wood converted to gas was lower due to increased production of undesirable organic acids from the wood at higher base concentrations. It was shown that by modifying Ni-based catalysts with dopants, it was possible to reduce the base concentration while maintaining the selectivity toward hydrogen and increasing wood conversion to gas versus organic acids.     

准东五彩湾煤中碱/碱土金属含量及迁移特性试验研究

了解新疆准东煤中碱金属不同赋存形态的含量及其在燃烧过程的迁移特性对于了解准东煤燃烧过程中的沾污结渣特性具有重要意义。采用以去离子水、醋酸铵溶液、盐酸为萃取剂的有序萃取法测量准东五彩湾煤中不同赋存形态的K、Na、Ca、Mg,研究了不同萃取时间、粒径下煤燃烧过程中碱/碱土金属的迁移特性。结果表明,采用有序萃取法测量煤中Na、Ca和Mg含量的推荐测量时间为12 h,而K的则应大于24 h;从大粒径准东五彩湾煤中萃取得到的水溶性Na、Ca、Mg含量相对较少,醋酸铵溶性、盐酸溶性和不溶性含量受粒径影响不大;煤中Ca含量较高,Na、Mg含量次之,K含量较低;可溶性Na占煤中Na的质量分数为90%。Ca和Mg主要以醋酸铵溶性成分存在,可溶性成分占比高达90%;准东五彩湾煤在900℃温度下,约有一半可溶性Na迁移到了气相中,可溶性K同样有较明显的迁移量,但Ca、Mg的迁移量较少。     

Metal-based direct hydrogen generation as unconventional high density energy

Metals are unconventional hydrogen production materials which are of high energy densities. This paper comprehensively reviewed and digested the latest researches of the metal-based direct hydrogen generation and the unconventional energy utilization ways thus enabled. According to the metal activities, the reaction conditions of metals were generalized into three categories. The first ones refer to those which would violently react with water at ambient temperature. The second ones start to react with water after certain pretreatments. The third ones can only react with steam under somewhat harsh conditions. To interpret the metal-water reaction mechanisms at the molecular scale, the molecule dynamics simulation and computational quantum chemistry were introduced as representative theoretical analytical tools. Besides, the state-of-the-art of the metal-water reaction was presented with several ordinary metals as illustration examples, including the material treatment technologies and the evaluations of hydrogen evolution performances. Moreover, the energy capacities of various metals were summarized, and the application potentials of the metal-based direct hydrogen production approach were explored. Furthermore, the challenges lying behind this unconventional hydrogen generation method and energy strategy were raised, which outlined promising directions worth of further endeavors. Overall, active metals like Na and K are appropriate for rapid hydrogen production occasions. Of these metals discussed, Al, Mg and their alloys offer the most promising hydrogen generation route for clean and efficient propulsion and real-time power source. In the long run, there exists plenty of space for developing future energy technology along this direction.     

焊缝金属的机械性能试验

阐述了焊缝金属的各种试验方法 ,并对试样形状 ,尺寸 ,应用范围 ,允许偏差及试样截取部位做了详细说明。由此推出熔注金属重的理论计算公式。     

压力容器焊接工艺评定规划

依据新出版的NB/T47014-2011《承压设备焊接工艺评定》和多次压力容器取、换证的经验,结合制造企业的发展定位,笔者认为对焊接工艺评定试件的接头形式、母材牌号、母材厚度以及焊接方法的选择进行合理规划,可以有效地防止焊接工艺评定项目过多做或漏项,更好地满足压力容器生产的需要。