Characterization of C12A7-O- Catalyst and Mechanism of Phenol Formation by Hydroxylation of Benzene

The benzene conversion and phenol selectivity from C6H6/O2/H2O over Ca24Al28O644+·4O-(C12A7-O-) catalyst were investigated using a flow reactor. The benzene conversion increases with the increase of temperature, and the phenol selectivity mainly depends on both reaction temperature and the composition of the mixtures. The changes of the catalyst structure before and after the reactions and the intermediates on the catalyst surface and in the bulk were investigated by XRD, EPR and FT-IR. The catalytic reactions do not cause any damage to the structure of the positively charged lattice framework C12A7-O-, but part of the O- and O2- species in the bulk of C12A7-O- translate to OH- after the reactions. The neutral species and anion intermediate were investigated by Q-MS and TOF-MS respectively. It is suggested that the active O- and OH- species played a key role in the process of phenol formation.     

Adsorption/desorption studies of NOx on well-mixed oxides derived from Co-Mg/Al Hydrotalcite-like compounds

CoxMg3-x/Al hydrotalcite-like compounds (where x=0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0) were synthesized by the coprecipitation method and characterized by the XRD and TGA techniques. Incorporation of Co for x=0.0-3.0 gradually decreased the transformation temperature of the hydrotalcites to the corresponding oxides from 444 to 246 degrees C and also decreased the surface area from 162.7 to 21.6 m2/g upon calcination at 800 degrees C for 4 h in air. The resultant oxide was generally composed of a poor MgO phase and a spinel phase, with more spinel phase at higher Co incorporation. The derived oxides were tested as the storage/reduction catalysts for NOx adsorption/desorption. The storage capacity for NOx was highly dependent on the catalyst composition and storage temperature. In general, more NOx was stored at lower temperature (100 degrees C) than that at higher temperature (300 degrees C), and tertiary catalysts (x=0.5-2.5) stored more NOx than binary catalyst (x=0.0 or 3.0). The catalytic conversion of NO to NO2 and the catalytic decomposition of NOx were observed on the tertiary catalysts during NOx adsorption at 300 degrees C, which was highly related to the loading of cobalt. The reducibility of catalysts was determined by TPR experiments, and the reduction of cobalt cations started at 150-200 degrees C in H2. In situ IR spectra of catalysts adsorbing NOx revealed that the major NOx species formed on the catalysts were various kinds of nitrites and nitrates, together with some forms of dimers, such as N2O2(2-) and N2O4 (or NO+NO3-). The storage/reduction mechanism and the function of Co in the mixed oxides are proposed and discussed on the basis of these observations.     

NO2 adsorption on ultrathin theta-Al2O3 films: formation of nitrite and nitrate species

Interaction of NO2 with an ordered theta-Al2O3/NiAl(100) model catalyst surface was investigated using temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The origin of the NO(x) uptake of the catalytic support (i.e., Al2O3) in a NO(x) storage catalyst is identified. Adsorbed NO2 is converted to strongly bound nitrites and nitrates that are stable on the model catalyst surface at temperatures as high as 300 and 650 K, respectively. The results show that alumina is not completely inert and may stabilize some form of NO(x) under certain catalytic conditions. The stability of the NO(x) formed by exposing the theta-Al2O3 model catalyst to NO2 adsorption increases in the order NO2 (physisorbed or N2O4) < NO2 (chemisorbed) < NO2- < NO3-.     

以金属氧化物及钙钛矿结构化合物为活性组分的ZSM-5催化剂上NOx选择性还原研究

研究了在水蒸汽存在条件下,以ＮＨ３为还原剂,金属／ＺＳＭ－５催化剂和负载于ＺＳＭ－５上的钙钛矿结构催化剂上的ＮＯｘ选择性催化还原（ＳＣＲ）性能。实验结果表明,当反应气中通入水蒸汽时,各样品的催化活性均下降,同时伴随着Ｎ２选择性的增加。而Ｃｕ－ＺＳＭ－５样品却表现出独特的性能,在所有测定样品中具有最高的ＮＯｘ转化率（在４５０℃时达到６９％）,当有水蒸汽存在时,其活性没有下降,反而有所增加,４５０℃时     

富氧条件下 Mn/ZSM-5 选择催化 CH4 还原 NO

 考察了富氧条件下 Mn/ZSM-5 催化剂上 CH₄ 选择催化还原 NO 反应, 并采用 H2程序升温还原、SO2程序升温表面反应和 NO程序升温脱附等手段对催化剂进行了表征. 结果表明, 催化剂活性与制备方法和 Mn 负载量密切相关. 离子交换法制备的 Mn/ZSM-5 催化剂活性明显优于浸渍法制备的催化剂; NO 转化率随着 Mn 负载量的增加而增加, 至 2.06% 时达到最大值 (57.3%), 然后随着 Mn 负载量的增加而降低. 采用离子交换法或较低 Mn 负载量 (≤ 2.06%) 抑制了催化剂中非化学计量的 MnO_x (1.5 < x < 2) 物种的形成, 减缓了 CH₄ 的氧化燃烧反应, 因而 CH₄ 还原 NO 的选择性提高. 在含 SO₂ 体系中, Mn/ZSM-5 活性在 550 ^oC 以下时明显下降, 但在 600 ^oC 以上基本不受影响. 这是由于在 550 ^oC 以下时 SO₂ 在 Mn/ZSM-5 表面形成了稳定的吸附硫物种, 覆盖了部分活性位, 导致催化剂活性降低; 而在 600 ^oC 以上时含硫物种基本脱附完全, 因而对催化剂活性影响不大.     

SiO2骨架支撑MoOx催化剂用于正庚烷异构化反应

 采用SEM，XRD，EDS及N2吸附－脱附方法研究了骨架型MoOx－SiO2催化剂和负载型MoOx／SiO2催化剂的物理化学结构，并在常压固定床流动反应器上考察了两种催化剂对正庚烷异构化反应的催化性能．结果表明，在MoOx－SiO2催化剂中，44．6％的SiO2即可起到很好的骨架支撑作用；MoOx晶相以足够大的空间区域聚集包裹在SiO2骨架中，形成类似MoOx催化剂的独特的中孔结构．与MoOx催化剂相比，MoOx－SiO2催化剂显著提高了机械强度，并维持了MoOx催化剂较高的活性和选择性．由于钼物种和载体之间的相互作用，负载型MoOx／SiO2催化剂表现出较低的比活性．脉冲注入H2S实验结果表明，MoOx－SiO2催化剂具有较好的抗硫性能．     

Pd/Mg(Al)O催化剂上NOx的储存 还原

采用共沉淀-浸渍法制备了催化剂Pd/Mg(Al)O，并用XRD、TPD等手段进行了表征。考察了催化剂的NOx储存 还原性能。结果表明，NO在Pd/Mg(Al)O上的主要储存途径是Pd促进NO氧化生成NO2，NO2与Mg(Al)O作用成盐，放出NO；Pd对NO2吸附成盐影响不大。NO在Pd/Mg(Al)O上吸附储存的适宜温度为350℃。350℃下Pd/Mg(Al)O催化剂经15次储存 还原（以H2为还原剂），NOx储存量变化不超过8％，维持在300μmol·g－1以上，N2选择性维持在94％以上。     

Effect of dispersion and distribution of tungsten on W/HZSM-5 for selective catalytic reduction of NO by acetylene

Catalytic performance of W/HZSM-5 in selective catalytic reduction of NO by acetylene was investigated in a reaction system with 1600 ppm of NO, 800 ppm of C2H2, and 9.95% of O2 in He. It was found that promotional effect of tungsten on the reaction is strongly affected by catalyst preparation conditions and Si/Al ratio of the parent zeolite. A better dispersion of tungsten on HZSM-5 and relatively more monomeric tungsten species were found on 8%W/HZSM-5 prepared by impregnation of the zeolite with lower SiO2/A1203 ratio （25） in ammonic ammonium tungstate solution and calcination of the resulting material at higher temperature （550 ℃）. The highest NO conversion to N2 of 86.3% in the reaction system was obtained at 350 ℃ over the catalyst thus prepared. The mechanism of monomeric tungsten species improving the C2H2-SCR can be attributed to accelerating the formation of active nitrate species.     

NO2 adsorption on BaO/Al2O3: the nature of nitrate species

Temperature programmed desorption, infrared spectroscopy, and (15)N solid state NMR spectroscopy were used to characterize the nature of the nitrate species formed on Al(2)O(3) and BaO/Al(2)O(3) NO(x) storage/reduction materials. Two distinctly different nitrate species were found: surface nitrates that are associated with a monolayer BaO on the alumina support, and a bulk-like nitrate that forms on this thin BaO layer. The surface nitrates desorb as NO(2) at lower temperatures than do the bulk-like nitrates, which decompose as NO+O(2) at higher temperatures. The amount of NO(x) stored in the monolayer nitrate is proportional to the surface area of the catalyst, while that in the bulk nitrate increases with BaO coverage.     

Role of adsorbed NO in N2O decomposition over iron-containing ZSM-5 catalysts at low temperatures

Transient response and temperature-programmed desorption/reaction (TPD/TPR) methods were used to study the formation of adsorbed NO(x) from N2O and its effect during N2O decomposition to O2 and N2 over FeZSM-5 catalysts at temperatures below 653 K. The reaction proceeds via the atomic oxygen (O)(Fe) loading from N2O on extraframework active Fe(II) sites followed by its recombination/desorption as the rate-limiting step. The slow formation of surface NO(x,ads) species was observed from N2O catalyzing the N2O decomposition. This autocatalytic effect was assigned to the formation of NO(2,ads) species from NO(ads) and (O)(Fe) leading to facilitation of (O)(Fe) recombination/desorption. Mononitrosyl Fe2+(NO) and nitro (NO(2,ads)) species were found by diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) in situ at 603 K when N2O was introduced into NO-containing flow passing through the catalyst. The presence of NO(x,ads) does not inhibit the surface oxygen loading from N2O at 523 K as observed by transient response. However, the reactivity of (O)(Fe) toward CO oxidation at low temperatures (<523 K) is drastically diminished. Surface NO(x) species probably block the sites necessary for CO activation, which are in the vicinity of the loaded atomic oxygen.     

Nitrogen doped tin oxide nanostructured catalysts for selective electrochemical reduction of carbon dioxide to formate

Tin/tin oxide materials are key electrocatalysts for selective conversion of CO_2 to formate/formic acid.Herein we report a tin oxide material with nitrogen doping by using ammonia treatment at elevated temperature. The N doped material demonstrated enhanced electrocatalytic CO_2 reduction activity, showing high Faradaic efficiency(90%) for formate at -0.65 V vs. RHE with partial current density of 4 mA/cm~2.The catalysis was contributed to increased electron negativity of N atom compared to O atom. Additionally, the N-doped catalyst demonstrates sulfur tolerance with retained formate selectivity. The analysis after electrolysis shows that the catalyst structure partially converts to metallic Sn, and thus the combined Sn/N-SnO_2 is the key for the active CO_2 catalysis.     

富氧条件下Cu/Al2O3催化剂上C3H6选择性还原NO的研究

以Cu/Al2O3为催化剂,对富氧条件下C3H6为还原剂选择性催化还原NO反应进行了研究.活性评价结果表明,与高活性的Ag/Al2O3催化剂相比,Cu/Al2O3催化剂选择性还原NO的活性较低,NO的最高转化率仅为40%.在所考察的温度范围(473～723K)内,红外谱图中不存在有机含氮化合物(R—ONO和R—NO2)的特征振动吸收峰.作为反应中间体—NCO的前驱体,有机含氮化合物在Cu/Al2O3催化剂表面难以生成是造成催化剂选择性还原NO活性低的直接原因.在Cu/Al2O3催化剂上,NO2吸附能够优先发生,并以NO3-物种的形式覆盖在大部分催化剂表面.动态原位红外光谱实验发现,这种NO3-表面物种与C3H6的反应性较差,使生成有机含氮化合物的关键反应难以发生,但此时的催化剂表面有利于C3H6和O2的完全氧化反应,这是导致Cu/Al2O3催化剂选择性较低的根本原因.     

Changing morphology of BaO/Al2O3 during NO2 uptake and release

The changes in the morphology of Ba-oxide-based NO(x)() storage/reduction catalysts were investigated using time-resolved X-ray diffraction, transmission electron microscopy, and energy dispersed spectroscopy. Large Ba(NO(3))(2) crystallites form on the alumina support when the catalyst is prepared by the incipient wetness method using an aqueous Ba(NO(3))(2) solution. Heating the sample to 873 K in a He flow results in the decomposition of the Ba(NO(3))(2) phase and the formation of both a monolayer BaO film strongly interacting with the alumina support and nanocrystalline BaO particles. Upon NO(2) exposure of these BaO phases at room temperature, small (nanosized) Ba(NO(3))(2) crystals and a monolayer of surface nitrate form. Heating this sample in NO(2) results in the coalescence of the nanocrystalline Ba(NO(3))(2) particles into large crystals. The average crystal size in the reformed Ba(NO(3))(2) layer is significantly smaller than that measured after the catalyst preparation. Evidence is also presented for the existence of a monolayer Ba(NO(3))(2) phase after thermal treatment in NO(2), in addition to these large crystals. These results clearly demonstrate the dynamic nature of the Ba-containing phases that are active in the NO(x)() storage/reduction process. The proposed morphology cycle may contribute to the understanding of the changes observed in the performances of these catalysts during actual operating conditions.     

WO3/CeO2-ZrO2, a promising catalyst for selective catalytic reduction (SCR) of NOx with NH3 in diesel exhaust

A WO3/CeO2-ZrO2 catalyst system was discovered for selective catalytic reduction of NOx with NH3; the catalyst (10 wt% WO3 loading) showed nearly 100% NOx conversion in a temperature range of 200-500 degrees C, at a space velocity of 90 000 h(-1) in a simulated diesel exhaust containing 550 ppm NOx (NO : NO2 feed ratio at 1.0), 10 vol% H2O and 10 vol% CO2; the catalyst also exhibited high temperature stability.     

Selective photoreduction of nitric oxide to nitrogen by nanostructured TiO2 photocatalysts: role of oxygen vacancies and iron dopant

Conventional TiO(2)-based photocatalysts oxidize NO(x) to nitrate species, which do not spontaneously desorb and therefore deactivate the catalyst. We show that the selectivity of this reaction can be changed by creating a large concentration of oxygen vacancies in TiO(2) nanoparticles through thermal reduction in a reducing atmosphere. This results in the photoreduction of nitric oxide (NO) to N(2) and O(2), species which spontaneously desorb at room temperature. The activity of the photoreduction reaction can be greatly enhanced by doping the TiO(2) nanoparticles with Fe(3+), an acceptor-type dopant that stabilizes the oxygen vacancies. Moreover, the photoinduced reduction of Fe(3+) to Fe(2+) provides a recombination pathway that almost completely suppresses the formation of NO(2) and thus enhances the selectivity of the reaction for N(2) formation. Gas chromatography confirms that N(2) and O(2) are formed in a stoichiometric ratio, and the activity for NO decomposition is found to be limited by the concentration of oxygen vacancies. A series of internally consistent reaction equations are proposed that describe all experimentally observed features of the photocatalytic process. The observed influence of oxygen vacancies on the activity and selectivity of photoinduced reactions may lead to new routes toward the design of highly selective photocatalysts.     

介孔Ce1-xZrxO2负载的Cu基催化剂在富氢条件下催化CO选择性氧化

采用多元醇为模板剂合成了介孔Ce1-xZrxO2(x=0.2,0.35,0.5)固溶体材料,并以其为载体负载CuO制备了Cu基催化剂.应用透射电子显微镜、X射线衍射、程序升温还原、程序升温脱附和N2吸附-脱附等技术对载体及催化剂进行了表征,并研究了Zr的取代比例x值对载体和Cu基催化剂性能的影响.结果表明,所有Ce1-xZrxO2样品均为介孔材料,其中Ce0.5-Zr0.5O2载体样品有较大的比表面积(181m2/g),CuO/Ce0.5Zr0.5O2催化剂样品在富氢条件下有较高的催化CO选择性氧化反应的活性和选择性.与其他催化剂样品相比,CuO/Ce0.5Zr0.5O2催化剂样品中形成的活性中心更多,分散性更好,对CO的吸附量更大,CO脱附温度更低,活性组分与载体的相互作用更强。     

Bis-dimethylaminobenzaldehyde Schiff-base cobalt(II) complex as a neutral carrier for a highly selective iodide electrode.

A new solvent polymeric membrane electrode based on N,N'-bis-(dimethylaminobenzaldehyde)-glycine cobalt(II) [Co(II)-BDMABG] as a neutral carrier is described, which displays a preferential potentiometric response to iodide ion and an anti-Hofmeister selectivity sequence in the following order: I- > ClO4- > Sal- > SCN- > NO2- > Br- > NO3- > Cl- > SO3(2-) > SO4(2-). The electrode exhibits a near-Nernstian potential linear range of 9.0 x 10(-7)-1.0 x 10(-1) M with a detection limit of 6.8 x 10(-7) M and a slope of -53.0 mV/decade in pH 2.0 of a phosphate buffer solution at 20 degrees C. The response mechanism is discussed in view of the A.C. impedance technique and the UV spectroscopy technique. The electrode was successfully applied to the determination of iodide in Jialing River and Spring in Jinyun Mountains with satisfactory results.     

One-step synthesis of phenol by O- and OH- emission material

A novel approach to the direct synthesis of phenol from benzene was obtained with high benzene conversion (30%) and phenol selectivity (approximately 90%) by using a microporous material [Ca24Al28O64]4+.4O-(C12A7-O-) as catalyst with oxygen and water; active O- and OH- anions are proposed to play important roles in the formation of phenol by hydroxylating the aromatic ring of benzene.     

温控相转移配体及催化(ⅩⅥ)──Rh/PETPP催化的水/有机两相邻氯硝基苯CO还原反应动力学的研究

首次将具有"温控相转移催化"功能的非离子表面活性水溶性膦/铑配合物用于以CO为还原剂的水/有机两相芳香硝基物选择还原反应.以邻氯硝基苯为底物考察了反应温度、CO压力、底物浓度、催化剂浓度和水/有机两相体积比等对反应转化率和选择性的影响.结果表明,当反应条件为150℃和4MPa,反应32h时,邻氯硝基苯的转化率为98%,邻氯苯胺的选择性接近100%.动力学研究表明,底物浓度和催化剂浓度分别对反应速率呈一级,反应的表观活化能E_a=131.13kJ/mol.     

银在甲烷选择性催化还原NOx反应中不同催化行为的研究

 采用XRD,TEM和UV－Vis方法研究了Ag－HZSM－5催化剂中活性组分银的价态和结构变化,并将这种变化与其在CH4选择性催化还原NOx反应中的活性和选择性相关联．结果表明,惰性气氛下高温处理使交换到分子筛阳离子位上的Ag＋自还原为Ag0,并在热的作用下聚集成纳米尺度的银颗粒Agn．纳米银颗粒Agn的形成提高了银催化剂在CH4选择性催化还原NOx反应中的活性,但它的长大又促进了CH4和O2的直接燃烧,使CH4选择性催化还原NOx反应的选择性降低．氧气气氛下高温预处理抑制了银颗粒的长大,并且氧气的氧化作用使银颗粒带有一定电荷,形成小的荷电纳米银粒子Agy＋x．荷电纳米银粒子的形成使催化剂的活性降低,但提高了CH4选择性催化还原NOx反应的选择性．