Anaerobic oxidation of isobutane: Catalytic properties of MgV2O6 and Mg2V2O7 prepared by the molten method

The catalytic activity of MV₂O₆ and M₂V₂O₇ type oxides prepared by the molten method (MM) for anaerobic oxidation of isobutane was studied in order to construct a system for the selective oxidation of isobutene using a thin layer reactor. Isobutene, CO and CO₂ were formed by every catalyst tested. The activities for isobutene formation were CuV₂O₆ > ZnV₂O₆, NiV₂O₆, CoV₂O₆ > MgV₂O₆ > MnV₂O₆  CaV₂O₆. Isobutene was a major product over M₂V₂O₇ (MM). Co₂V₂O₇ showed the highest activity and high isobutene selectivity exceeded 90%, demonstrating that Co₂V₂O₇ is a suitable oxide for a thin layer reactor for anaerobic oxidation of isobutane. Partial substitution of Mg by Cu in Mg₂V₂O₇ (MM) improved the activity. It is shown by the oxidation at low O₂ concentration as 2–3% that two types of oxidations occurred simultaneously: isobutene formation by the lattice oxygen ions diffused from the bulk, and CO and CO₂ formation by the oxygen species derived from molecular oxygen in the gas phase.     

复合仿生催化体系的构建与高效有氧氧化芳基烷烃

直接活化氧气氧化碳氢化合物是件挑战性的研究工作。根据生物酶很容易在温和条件下实现上述反应,以Keggin-型杂多酸[CuPW_(11)O_(39)]5-(简写为CuPW_(11))与金属-有机框架材料HKUST-1形成的复合材料Cu PW_(11)@HKUST-1为催化剂,以N-羟基邻苯二甲酰亚胺为助催化剂,构建模拟酶催化氧化反应体系。其中,CuPW_(11)@HKUST-1中的杂多酸作为氧化还原中心,N-羟基邻苯二甲酰亚胺作为电子供体。该复合模拟酶催化体系在催化活化氧气氧化芳基烷烃的反应中表现出了类似生物酶催化的性质,具有反应条件温和、转化率高、转化数高和选择性高等特点,其中产物产率与转化数分别高达99%和17700,为实现在温和条件下高效活化氧气氧化惰性有机物分子提供了一条切实可行的路线。     

O2对燃煤烟气中As2 O3均相反应生成途径影响研究

应用量子化学密度泛函理论研究了燃煤烟气中As和AsO与O_2均相生成As_2O_3的反应机理。首先计算确定了各反应物、中间体、过渡态和产物的结构和能量,然后运用热力学和动力学方法对As_2O_3均相生成过程进行分析。结果表明,由As和AsO与O_2均相生成As_2O_3的最大反应能垒分别为32.9和157.2kJ/mol,在烟气中由As转化为As_2O_3更为容易进行。在500-1900 K下,各反应的正逆反应速率常数均随温度的提高而增大,但不同反应过程受温度影响的程度不同。As与O_2反应生成AsO和AsO_2的两个反应过程的平衡常数在所研究的温度范围内均大于10~5,能完全反应,可以认为是单向反应。AsO与O_2反应生成AsO_2的过程平衡常数在所研究的温度范围内小于10~5,反应不完全,转化率低。AsO与AsO_2生成As_2O_3(D3H)构型的平衡常数极低,反应难以进行,而生成As_2O_3(GAUCHE)构型反应能垒低,可自发进行。     

不同气氛下煤连续热解产物的分配规律及产品品质分析

在连续进出料的流化床中研究了热解温度为850 ℃时,含有O₂、H₂、CO、CO₂、CH₄的反应气氛对热解产物分配规律及产品组成的影响。采用Raman、BET等测试方法对不同热解气氛下制得半焦的品质进行了评价,结合热重分析了影响半焦反应活性的因素。结果表明,无O₂气氛下,H₂与CO₂存在时降低了焦油产率,而CO与CH₄促进了焦油的生成。CH₄的裂解析碳使半焦产率上升。O₂的加入使CO₂、CO含量明显增加,半焦及焦油产率降低。N₂中引入O₂时,PAHs含量降低。CH₄促进了烷基萘与苯类的生成,CO则抑制酚类裂解生成苯类。CO₂的气化作用促进了微孔的生成,相应地,半焦的比表面积快速增加,半焦的反应活性也最高。CO歧化与CH₄热裂解产生的析碳堵塞了部分孔道,降低了比表面积。H₂与CH₄所产生的氢自由基能渗透到半焦内部,引起半焦结构的缩聚,进而影响氧化反应活性。     

Se掺杂对单层MoS2电子能带结构和光吸收性质的影响

基于密度泛函理论的第一性原理方法,计算了Se掺杂单层MoS₂能带结构和光吸特性,并分析了对其光解水性质的影响。结果表明：本征单层MoS₂为直接带隙结构,禁带宽度为1.740 eV,导带底电位在H⁺/H₂还原势之上0.430 eV,价带顶电位在O₂/H₂O的氧化势之下0.080 eV,具有可见光催化分解水的能力,但氧化和还原能力不均衡,导致单层MoS₂作为光催化剂分解水的效率不高。通过Se掺杂计算发现,单层MoS₂的禁带宽度变为1.727 eV,相应的光吸收谱变化幅度几乎不变,且体系的形成能较低,表明其热力学稳定性良好。然而,导带底电位调整到H⁺/H₂还原势之上0.253 eV,价带顶电位处于O₂/H₂O的氧化势之下0.244 eV,平衡了氧化与还原能力,单层MoS₂可见光催化分解水的效率得到提高。     

Ab initio study on the adsorption and oxidation of HCHO with Ag2 cluster

We present an ab initio study on the adsorption and oxidation of HCHO on the Ag₂ dimer. HCHO is found to weakly adsorb on the neutral Ag₂ cluster and the adsorption energy increases when the Ag₂ cluster is positively charged. The adsorption of HCHO on Ag₂ is promoted by pre-adsorbed OH species while coadsorbed H has no effect. The formation of η²-methylendioxy is inhibited if the Ag₂ cluster is positively and properly charged, which enhance the selectivity of the partial oxidation of methanol. These results provide insight into the reaction mechanism of HCHO on silver surfaces and may guide the design of novel catalysts.     

利用硫酸氧钒制备钒炭催化剂用于烟气脱硫

利用硫酸氧钒制备钒炭催化剂用于烟气脱硫。研究发现,负载在活性炭上的硫酸氧钒极易被氧化为五价钒硫酸盐,这些五价钒硫酸盐具有很高的氧化SO₂的活性,极大地促进了SO₂在活性炭上的脱除。而且,通过煅烧可以将五价钒硫酸盐分解为五价钒氧化物,最佳煅烧温度为500℃,由于煅烧后用于储存硫酸的微孔孔容增加,SO₂的吸附容量得到了进一步提高,由此表明,利用硫酸氧钒可以制备传统的V₂O₅/AC催化剂。为了获得完全氧化的钒物种,对煅烧后的催化剂进行了空气中预氧化,但由于含氧官能团的形成、炭载体的烧蚀以及钒的还原,预氧化不利于脱硫。此外,研究中得到初步证据证明脱硫过程中V₂O₅/AC催化剂中五价钒氧化物转变成了五价钒硫酸盐,结合五价钒硫酸盐所表现出的氧化SO₂的能力,推测SO₂在V₂O₅/AC上的脱除遵循以下机理:五价钒氧化物先转变为五价钒硫酸盐,后者催化氧化SO₂为硫酸。     

负载型Pd-Cu催化剂的制备及富氢气氛下CO优先氧化性能

分别以Al₂O₃, SiO₂和C₃N₄为载体, 通过简单浸渍法制备了3种负载型Pd-Cu催化剂(PC-Al₂O₃, PC-SiO₂, PC-C₃N₄), 考察了其在室温下富氢气氛中CO优先氧化反应性能. 采用X射线衍射(XRD)、 傅里叶变换红外光谱(FTIR)、 氮气物理吸附仪(N₂-physisorption)、 氢气程序升温还原(H₂-TPR)、 二氧化碳程序升温脱附(CO₂-TPD)、 X射线光电子能谱(XPS)和原位漫反射傅里叶变换红外光谱(In situ DRIFTS)等手段对其进行了表征. 结果表明, 与PC-SiO₂和PC-C₃N₄相比, PC-Al₂O₃具有更高的CO优先氧化性能. 这是由于PC-Al₂O₃上形成了大量与Pd物种具有强相互作用的Cu₂Cl(OH)₃物种; 而PC-SiO₂中仅有少量的Cu₂Cl(OH)₃, 且与Pd物种相互作用较弱; PC-C₃N₄中Cu物种则更易与C₃N₄基质配位, 由此削弱了Pd, Cu之间的相互作用. 在反应气氛下PC-Al₂O₃表面还易形成具有更强CO活化能力的Pd⁺物种, 通过与大量Cu⁺物种紧密相互作用, 在一定程度上抑制Pd⁺被过度还原为Pd⁰, 从而维持了其催化活性. 与SiO₂和C₃N₄相比, Al₂O₃更适合负载Pd-Cu用于富氢气氛下CO优先氧化反应.     

C_6H_2(OH)_3CH_3氧化成羟基苯甲酸反应路径的DFT研究

运用密度泛函(DFT)理论,采用Materials Studio 8.0,用GGA/BP方法研究了C_6H_2(OH)_3CH_3氧化成羟基苯甲酸的反应路径。结果表明,甲基上的氢原子被氧化成羟基以及羟基被氧化为醛基及醛基被氧化成羧基均为放热过程。分子C_6H_2(OH)_3CH_3中甲基氧化成羧基的主路径为三个氢原子氧化反应路径,其路径为C_6H_2(OH)_3CH_3+3O→C6H2(OH)3C(OH)3→C6H2(OH)3COOH+H2O,该路径受限于羟基直接被氧化成羧基过程,需克服130 k J/mol的反应势垒,反应速率常数对数ln(k)为-22.96 s-1;醛基、羟基优先被氧化成羧基的顺序为:-CHO-C(OH)3-HC(OH)2-H2C(OH);提高反应温度、氧气浓度均有利于羟基苯甲酸的生成,适当的催化剂有利于促进整个反应的进行。     

Synthesis of Cu^Ⅱ/ZIF-8 Metal-organic Framework Catalyst and Its Application in the Aerobic Oxidation of Alcohols

The tliree-dimensional copper-doped zeolitic imidazolate framework ZIF-8(Cu^Ⅱ/ZIF-8) was prepared by a metal ion exchange process, using reaction of three different copper salts, zinc nitrate hexahydrate[Zn(NO)3·6H2O] and 2?methylimidazole(2-MelM) under nitrogen atmosphere at the room temperature. The TEM and PXRD results indicated that the morphology of Cu^Ⅱ/ZIF-8 was rhombic dodecahedron and the structure was intact after copper was doped into the porous ZIF-8. The synthesized Cu(NO3)2/ZIF-8 heterogeneous catalyst showed an excellent activity for tlie aerobic oxidation of primary alcohols employing molecular oxygen as oxidant. Moreover, tlie Cu(NO3)2/ZIF-8 heterogeneous catalyst can cycled 15 times without leaching of copper.     

Syntheses of low-valent nitrosyl complexes of rhenium and X-ray structure oftrans-[ReCl(NO)(Ph2PCH2CH2PPh2)2][NO3]2 with nitrosyl derived nitrates

The nitrosyl complexes trans-[ReCl(NO)(dppe)₂]A₂ (1; A = BF₄ or NO₃; dppe = Ph₂PCH₂CH₂₋PPh₂) and trans-[ReCl(NO)(dppe)₂][BF₄] (2) have been prepared from the reactions of NO[BF₄] or NO with trans-[ReCl(N₂)dppe)₂]. An unusual facile oxidation of NO to nitrate is involved in the formation of (1, A = NO₃), the X-ray structure of which is reported.     

Au单晶电极上H2O2的氧化反应研究

本文利用旋转圆盘电极系统研究了酸性介质中H₂O₂在Au(100)和Au(111)电极表面的电化学行为. 实验发现在Au电极上H₂O₂难以发生还原,但是当电位稍微正于H₂O₂氧化为O₂的平衡电势时即可发生氧化. 在Au(111)上H₂O₂氧化的起始电位比在Au(100)正0.1 V左右. Au(100)上的双桥位位点能增强反应中间体*OOH的吸附,可能是导致Au(100)上H₂O₂氧化反应超电势比Au(111)低的主要原因. 在较正电位区(E>1.2 V), 当电极表面被氧物种覆盖时,H₂O₂在两个电极上的氧化都会受到一定程度的抑制,这种影响在Au(111)上比Au(100)上更加明显,这与Au(111)上氧物种的生成与逆向还原可逆性差的趋势一致. 最后还将Au与Pt单晶电极上H₂O₂氧化的行为进行了对比分析.     

Hydroxyl radical formation upon dark oxidation of reduced iron minerals: Effects of iron species and environmental factors

Dark oxidation of reduced iron minerals can produce hydroxyl radical under ambient conditions.     

SCR脱硝过程中SO2催化氧化的原位红外研究

采用工业用V₂O₅-WO₃/TiO₂催化剂,基于傅里叶原位红外光谱(FT-IR)技术考察SO₂的氧化过程及烟气组分对SO₂氧化行为的影响;结果表明,SO₂在催化剂表面氧化主要是首先吸附在催化剂表面V₂O₅活性位上,占据其O原子,以SO^2-₃形式存在,后与催化剂表面V⁵⁺-OH发生反应,生成金属硫酸盐(VOSO₄)中间产物,O₂重新氧化催化氧化过程中由于被SO₂夺取O原子而被还原的V₂O₅物种,使V⁴⁺转化为V⁵⁺,促进金属硫酸盐(VOSO₄)向SO₃转化;SO₂与NO、NH₃的竞争吸附阻碍SO₂在V₂O₅活性点位上的氧化;在SCR中,NO的脱除与SO₂的氧化是相互抑制的关系。     

Fe2O3/Al2O3氧载体用于甲烷化学链燃烧：负载量与制备方法的影响

以不同方法制备了系列Fe₂O₃/Al₂O₃氧载体,采用XRD、H₂-TPR、CH₄-TPR、O₂-TPD和BET等分析技术对氧载体进行了表征。研究了不同Fe₂O₃负载量氧载体的甲烷化学链燃烧性能,考察了不同制备方法对Fe₂O₃/Al₂O₃氧载体结构、反应性和产物选择性的影响。结果表明,Fe₂O₃负载量对氧载体活性及产物中CO₂选择性的影响较大,负载量较低时氧载体活性较低且引起甲烷部分氧化产物CO含量增加。制备方法亦对氧载体与甲烷的反应活性有所影响,整体上共沉淀法制备的质量分数60％Fe₂O₃/Al₂O₃氧载体具有较高的氧化活性和化学链循环稳定性。其在反应温度850℃、反应时间15 min、30次循环后甲烷转化率及产物中CO₂选择性均未见明显降低。     

Pd/γ-Al2O3-TiO2催化剂上乙醇乙醛的催化氧化性能研究

采用混胶法和机械混合等方法制备了Pd质量分数为1%的Pd/γ-Al₂O₃-TiO₂催化剂,并对其催化活性、影响条件进行了考察。结果说明,由混胶法制备的Pd/γ-Al₂O₃-TiO₂催化剂对乙醇和乙醛的完全氧化表现出优异的催化性能,其活性明显高于单一载体催化剂Pd/TiO₂和Pd/Al₂O₃,150℃时乙醇和乙醛的转化率分别达到98.9%和98.5%。在较宽温度范围内和高空速条件下表现出良好的稳定性。同时运用XRD、TEM和FT-IR等技术对催化剂进行了表征。结果表明,在Pd/γ-Al₂O₃-TiO₂催化剂中Al₂O₃与TiO₂之间存在着较强的相互作用,使γ-Al₂O₃-TiO₂的比表面积和孔容积均调变到一个适中的数值,同时在催化剂表面Al₂O₃参与形成了有利于其催化活性的表面结构。     

SO2水溶液的光催化选择氧化和氢转移

ＳＯ_２水溶液的光催化选择氧化和氢转移王增华,洪剑斌,庄启星（厦门大学化学系,厦门,３６１００５）关键词二氧化硫,光催化,选择氧化,氢转移,光溢流以一定ｐＨ的ＳＯ２水溶液为反应液、Ｐｔ／Ｃｄｓ为光催化剂,在封闭体系中用可见光辐照进行选择氧化反应：以自?..     

C/Fe-Bi_2WO_6光催化氧化诺氟沙星废水的效能及其机理

采用树脂碳化和水热两步法制备C/Fe-Bi_2WO_6光催化剂,对不同光催化剂光催化降解诺氟沙星溶液的去除效果进行对比研究。考察了条件因素对诺氟沙星(NOR)溶液在模拟太阳光下光催化氧化降解的影响规律。结果表明,在实验条件下,NOR光催化氧化降解符合L-H拟一级反应动力学模型,在NOR溶液初始浓度10 mg/L、溶液p H=7.0、催化剂用量0.75 g/L、H_2O_2浓度为200 mg/L、500 W氙灯照射60 min条件下,NOR完全分解,表观速率常数K_(app)为0.0751 min-1。采用分子荧光光谱法,对C/Fe-Bi_2WO_6光催化氧化去除NOR体系中羟基自由基生成规律进行研究,并推测了反应机理。结合LC-MS的分析结果,推测了NOR可能的降解路径和中间产物。     

CeO2的添加对柴油车氧化催化剂Pt/SiO2-Al2O3的NO氧化性能提高的影响

The catalytic activities for NO oxidation achieved by different amounts of CeO₂-modified Pt/SiO₂-Al₂O₃ catalysts Pt/SiO₂-Al₂O₃-wCeO₂ (the mass fraction w being 0%, 5%, 10%, 15%, 30%), prepared using step-wise impregnation, were investigated in the presence and absence of CO and C₃H₆. The results showed that the NO oxidation activity could be efficiently improved by modification of CeO₂, wherein the 15%-CeO₂-modified catalyst exhibited the maximum NO conversion of 61% even in the presence of CO and C₃H₆, which were proved to inhibit NO₂ formation in this study. A series of characterization methods were performed over the as-prepared samples to correlate their surface and structural characteristics with their enhanced NO oxidation activities. CO-chemisorption illustrated that appropriate CeO₂-loading was effective for enhancing Pt dispersion, thus enhancing Pt surface-to-volume ratio, confirmed by transmission electron microscope (TEM) images. X-Ray Diffraction (XRD) further suggested that ceria addition could suppress the growth of the Pt crystal, resulting in higher surface Pt atomic ratio. Further, H₂ temperature-programmed reduction (H₂-TPR), together with TEM results, implied that the presence of ceria could enhance the interaction between metal and supports, thus facilitating reducibility of both active platinum and ceria. Hence, this study displays that ceria could act as a dispersion promoter and a reducibility booster, both of which are beneficial to NO oxidation activity. The improved NO oxidation activity is significant for the efficient purification of diesel integrated catalytic system.     

Structural and catalytic investigation of vanadia supported on ceria promoted with high surface area rice husk silica

Rice husk silica was utilized as the promoter of ceria for preparing supported vanadia catalysts. Effect of vanadium content was investigated with 2–10 wt.% V₂O₅ loading over the support. Structural characterization of the catalysts was done by various techniques like energy dispersive X-ray (EDX), X-ray diffraction (XRD), BET surface area, thermal analysis (TGA/DTA), FT-infrared spectroscopy (FT-IR), UV–vis diffused reflectance spectroscopy (DR UV–vis), electron paramagnetic spectroscopy (EPR) and solid state magnetic resonance spectroscopies (²⁹Si and ⁵¹V MASNMR). Catalytic activity was studied towards liquid-phase oxidation of benzene. Surface area of ceria enhanced upon rice husk silica promotion, thus makes dispersion of the active sites of vanadia easier. Highly dispersed vanadia was found for low V₂O₅ loading and formation of cerium orthovanadate (CeVO₄) occurs as the loading increases. Spectroscopic investigation clearly confirms the formation of CeVO₄ phase at higher loadings of V₂O₅. The oxidation activity increases with vanadia loading up to 8 wt.% V₂O₅, and further increase reduces the conversion rate. Selective formation of phenol can be attributed to the presence of highly dispersed active sites of vanadia over the support.