Combined polymerization catalysis of nickel complex and zirconocene for branched polyethylene

The polymerization behavior of 2-(2′-pyridyl) quinoxaline nickel dibromide/Cp₂ZrCl₂/MAO system was investigated in three ways: the Ni catalyst was added first, followed by addition of Zr catalyst (method I); the Ni and Zr catalysts were added simultaneously (method II); and the Zr catalyst was added first, followed by addition of Ni catalyst (method III). Results of GC-MS, GPC,¹³C NMR and DSC investigations indicated that the properties of resulting polyethylene were greatly varied by changing feeding orders of the two catalysts. Decreasing Ni/Zr molar ratio or increasing polymerization temperature gave corresponding polyethylenes with less branches and higher melting point. Compared to the procedure using Cp₂ZrCl₂ catalyst only, the activity of Zr catalyst in those combined system decreased because of the competition of ethylene between the [Ni−C] and [Zr−C] active centers. In addition, other zirconocenes were also employed as copolymerization catalysts in the combined system with nickel complex. compared to Cp₂ZrCl₂ case, the ethyl-bridged Zr catalyst performed better for polymerization of ethylene while the Si-bridged Zr catalyst showed better copolymerization ability.     

超声改性的CuO/Al2O3-MgO催化剂结构 及其超低浓度甲烷催化燃烧性能

采用普通浸渍和超声改性的方法分别制备了CuO/Al₂O₃-MgO催化剂,用于超低浓度甲烷的催化燃烧,并利用SEM、XRD、XPS、H₂-TPR等技术对催化剂进行表征,研究了超声改性作用对催化剂的结构和性能的影响.结果表明,与普通浸渍法制备的催化剂相比,在超声改性的CuO/Al₂O₃-MgO催化剂上,甲烷的转化率得到提高,燃烧特征温度降低.随着超声时间的延长和超声功率的增加,催化剂的催化活性均呈现先增大后减小的趋势;催化剂制备的最佳超声工况为功率150 W、时间20 min.超声改性可使催化剂的比表面积和孔容积增大,表面催化活性较高的Cu⁺浓度增加,活性组分CuO由晶相向非晶相转变、分散度增大,晶粒粒径变小、分布更均匀;这使得甲烷催化燃烧的表观活化能下降、催化剂活性得到增强.     

Deactivation and regeneration of the B2O3/TiO2-ZrO2 catalyst in the vapor phase Beckmann rearrangement of cyclohexanone oxime

The deactivation and regeneration of B₂O₃/TiO₂-ZrO₂ catalyst for the vapor phase Beckmann rearrangement of cyclohexanone oxime to -caprolactam were studied. The fresh, deactivated and regenerated catalysts were characterized by using adsorption of nitrogen, X-ray diffraction (XRD), thermogravimetry (TG) and NH₃-temperature-programmed desorption (NH₃-TPD) techniques. The crystal structure and pore size distribution of the catalyst were retained after reaction, but the number of acid sites decreased significantly. There was a relationship between the amount of coke deposited on the catalyst and the decline in catalytic activity. These results suggest that the coke deposition on the surface of catalyst is mainly responsible for the catalyst deactivation. The catalytic activity can be recovered completely after calcining the deactivated catalyst in air flow at 600 °C for 8 h.     

中空管状g-C3N4/Ag3PO4复合催化剂的制备及其可见光催化性能

采用化学沉淀法制备中空管状 g-C₃N₄/Ag₃PO₄复合催化剂。通过 X射线衍射(XRD)、扫描电子显微镜(SEM)、紫外可见漫反射光谱(UV-Vis DRS)和荧光光谱对其结构、形貌和光学性能进行了表征。结果表明：Ag₃PO₄纳米颗粒均匀地分散在中空管状g-C₃N₄表面,两者紧密结合形成异质结。研究复合催化剂在可见光照射下降解盐酸四环素(TC)的光催化活性。结果显示：复合催化剂在80 min内对TC的降解率为98%,其降解反应速率常数是纯相Ag₃PO₄的3倍。经过5次循环实验后复合催化剂对于TC的降解率仍保持87%,具有优良的循环稳定性。捕获实验表明空穴(h⁺)和超氧负离子(·O₂^ˉ)是光催化反应过程中的主要活性物种。根据能带理论,提出了复合催化剂异质结的Z型光催化机理。     

Al含量对Pt-SO2-4 /ZrO2-Al2O3固体超强酸催化

通过向SO^2-₄ /ZrO₂催化剂中同时引入适量的Pt和Al₂O₃, 制备出了具有较高催化性能和稳定性的Pt-SO^2-₄ /ZrO₂-Al₂O₃型固体超强酸催化剂. 以正戊烷异构化反应为探针, 考察了Al含量对催化剂性能的影响; 并采用X射线衍射(XRD)、比表面积测定(BET)、红外(IR)光谱、程序升温还原(TPR)、热重-差热分析(TG-DTA)和氨-程序升温脱附(NH₃-TPD)手段对催化剂进行了表征. 结果表明, Al能够提高ZrO₂的晶化温度, 抑制硫的分解, 增加催化剂的比表面积, 增强硫氧键的结合, 提高催化剂的还原性能, 增加催化剂的酸强度和酸总量. 当Al₂O₃含量(质量分数, w)为5.0%时, Pt-SO^2-₄ /ZrO₂-Al₂O₃固体超强酸催化剂的催化活性最好, 在100 h内异戊烷收率可稳定在52.0%以上, 选择性在98.2%以上.     

Yb(OTf)3催化苯乙酮、芳香醛和芳香胺的Mannich反应: 三组分“一锅法”合成β-氨基酮衍生物

报道了稀土化合物Yb(OTf)₃催化的苯乙酮、芳香醛和芳香胺Mannich反应, 三组分“一锅法”合成了一系列的β-氨基酮衍生物. 该方法操作简单、条件温和、产率较高、催化剂可重复使用, 且对环境友好.     

Catalytically Promoted NOx Sorption by ZrO2-Based Oxides

Metal promoted zirconia-based oxide sorbents, such as Pt–ZrO₂/Al₂O₃ for NO _x have been investigated. To clarify the role of the catalyst component, sorption of NO and NO₂ was compared using the samples with and without Pt. The catalytic oxidation of NO to NO₂ and successively to nitrate ions is an important role for the Pt catalyst. The experimental results indicate that a high-temperature calcination is essential to remove residual Cl from Pt–ZrO₂–Al₂O₃ prepared from H₂PtCl₆ in order to provide more active NO _x sorption sites. Of M–ZrO₂–Al₂O₃ samples investigated, ruthenium as well as Pt demonstrated relatively good performance as a catalyst component in the sorbent. The FT-IR spectra after sorption of NO and NO₂ demonstrated a strong band attributed to stored nitrate ions. The Pt catalyst was more resistant to sulfur poisoning than a base metal catalyst. However, the NO _x sorptive capacities of the Pt–ZrO₂/Al₂O₃ sorbents were expected to be deteriorated in dilute SO₂ as far as observed from FT-IR spectra.     

Zr0.5Ti0.5O2的添加对超临界裂解RP-3催化剂性能的影响

采用共沉淀法制备了Zr_0.5Ti_0.5O₂载体材料,将其掺杂在CeO₂-Al₂O₃ (CA)基催化剂中, 并对其催化活性进行了超临界裂解测试, 采用全自动吸附仪、X射线衍射(XRD)、透射电镜(TEM)、程序升温脱附(TPD)等方法对催化剂进行了表征. 实验结果表明, 催化剂能够明显降低裂解反应的温度, 600 ℃ CA基催化剂产气率是热裂解的2.8倍, 掺杂Zr_0.5Ti_0.5O₂载体材料的CA基催化剂是热裂解的4.0倍, 650 ℃时, 掺杂Zr_0.5Ti_0.5O₂载体材料的CA基催化剂热沉提高了0.55 MJ·kg^-1. BET结果表明, 掺杂Zr_0.5Ti_0.5O₂载体后催化剂出现双孔结构, 部分小孔的出现使得乙烯的选择性提高; NH₃-TPD结果表明, 掺杂Zr_0.5Ti_0.5O₂载体材料后, 催化剂强酸位的酸量增加了4.0倍,催化剂表现出更强的表面酸性和更集中的强酸酸中心密度, 有利于裂解多产烯烃.     

多孔SiO_2·xH_2O负载RuB纳米粒子催化喹啉加氢反应

通过水解,聚乙烯吡咯烷酮(PVP)保护,NaOH刻蚀等方法制备了多孔及富含表面羟基的SiO2·xH2O负载的RuB催化剂RuB/SiO2·xH2O,并用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、傅里叶变换红外(FT-IR)光谱和BET(Brunauer-Emmett-Teller)等手段对该催化剂进行了表征.结果表明该催化剂具有良好的抗中毒能力,在3.0MPa的H2压力和80℃的温和反应条件下,喹啉的转化率高于95%,生成1,2,3,4-四氢喹啉的选择性高于97%.并系统研究了表面羟基和溶剂对催化剂性能的影响,发现以水为溶剂时,RuB/SiO2·xH2O对喹啉加氢反应展示出较高的活性和对1,2,3,4-四氢喹啉较高的选择性,催化剂能够多次循环使用.这一体系的优异催化性能归属于载体表面羟基和水的协同作用.     

Selective oxidation of octadecan-1-ol to octadecanoic acid over Co3O4/SiO2 catalysts

Factors (reaction temperature, reaction time, flow rate of oxygen, amount of catalyst, etc.) influencing the catalytic properties of Co₃O₄/SiO₂catalyst in the oxidation octadecan-1-ol to octadecanoic acid were investigated. The catalysts were characterized by means of XRD, FT-IR and N₂-adsorption. The experimental results indicate that under the optimal condition the selectivity to octadecanoic acid reached 97.5 % over 5 % Co₃O₄/SiO₂ catalyst.This revised version was published online in December 2005 with corrections to the Cover Date.     

Application of Li2SiO3 as a heterogeneous catalyst in the production of biodiesel from soybean oil

Biodiesel was synthesized from soybean oil by transesterification over Li₂SiO₃ catalyst.The Li₂SiO₃ can be used for biodiesel production directly without further drying or thermal pretreatment,no obvious difference in the FAME conversion（92.4-96.7%） between the air-exposed catalyst（24-72 h） and the fresh one（94.2%）.This leads to important benefits when considering industrial applications of Li₂SiO₃ as a solid catalyst for storing and handling catalyst without taking special actions.     

磁性Fe3O4/石墨烯Photo-Fenton催化剂的制备及其催化活性

采用共沉淀法制备磁性Fe3O4/GE(石墨烯)催化剂,实现Fe3O4纳米颗粒生长和氧化石墨烯还原同步进行,采用FTIR、XRD、TEM及低温氮吸附-脱附等对Fe3O4/GE纳米催化剂的物相、颗粒粒径及比表面积进行了表征。在H2O2存在条件下,以亚甲基蓝为目标降解物,考察了在模拟太阳光下Fe3O4/GE的催化活性,当氧化石墨烯与Fe3O4的质量比为1∶10时,经过2 h催化反应,在pH=6条件下,对亚甲基蓝的降解率达到98.7%,经过10次循环使用后对染料溶液的降解率仍保持在95.7%以上,明显优于纯的Fe3O4。     

Efficient synthesis of xanthenedione derivatives using cesium salt of phosphotungstic acid as a heterogeneous and reusable catalyst in water

Cs_2.5H_0.5PW₁₂O₄₀ has been reported to be an efficient catalyst for the synthesis of 1,8-dioxo-octahydroxanthene from aldehydes and 1,3-cyclohexanedione/dimedone in water. This approach is environmentally benign with clean synthetic procedure, short reaction time, easy workup procedure, excellent yield, and regeneration of catalyst, which made this protocol efficient and safe.     

Study of the selectivity of a V2O5?ZrO2 catalyst for partial oxidation ofo-xylene at high temperatures

It has been established that at high temperatures (above 450°C) the V₂O₅−ZrO₂ catalyst exhibits a higher selectivity in the oxidation ofo-xylene to phthalic anhydride than does the conventional V₂O₅−TiO₂(a) catalyst. The catalyst selectivity is found to increase with respect to partial oxidation ofo-xylene, the valuable by-product maleic anhydride being obtained. Studies by different physicochemical methods have shown that V₂O₅−ZrO₂ undergoes no significant phase and structural changes under high-temperature conditions.     

Effect of 3% Re2O7/60%Al2O3 - 40%SiO2 Catalyst Alkylation Time and Temperature Using Et4Pb on Methyl Erucate Conversion

A study of the alkylation of 3% Re₂O₇/60%Al₂O₃-40%SiO₂ catalyst using tetraethyllead (Et₄Pb)(TEL) shows that the reaction time and temperature affect the catalyst activity and selectivity in the methyl erucate metathesis reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

改性SCR催化剂对Hg0催化氧化性能的研究

采用一系列金属氧化物对商用SCR催化剂进行掺杂改性,筛选出最优Ce掺杂SCR催化剂,模拟实际烟气组分,考察了Ce改性催化剂对烟气中Hg⁰氧化的影响。实验结果表明,Ce掺杂比例适当可显著提高其催化活性,Ce最佳负载量为9%时,Hg⁰的催化氧化效率比未掺杂SCR催化剂提高近40%,BET和XRD也显示,CeO₂在催化剂表面分散程度较好,未出现聚集现象。烟气工况对Hg⁰的催化氧化具有重要影响,其中,烟气组分HCl显著促进了Ce改性催化剂对Hg⁰的氧化,在一定温度范围内,Hg⁰的氧化效率随着温度升高而增加,在最佳空速、温度和烟气组分浓度时,Hg⁰的催化氧化效率可达95.11%。此外,掺杂CeO₂之后SCR催化剂的脱硝性能并未受到影响。     

A Radioisotope Flow-Circulation Tracer Method for Determination of Sulfur Uptake and Exchange

A combined radioactive flow-circulation tracer method has been developed and applied to a CoMo/Al₂O₃ catalyst for measurement of sulfur uptakes and of catalyst - gas phase sulfur exchange in the H₂S partial pressure range of 2–47 kPa and the temperature range of 373–673 K. Equilibrium between gas-phase and catalyst sulfur species was rapidly achieved. A substantial part of the sulfur uptake was retained as adsorbed (reversible) sulfur species. The exchange of sulfur increased with increase in temperature up to 573 K and in H₂S partial pressure up to 4 kPa.     

Nano-TiO2: An Efficient and Reusable Heterogeneous Catalyst for Ring Opening of Epoxides Under Solvent-Free Conditions

Nano-TiO₂ is an effective heterogeneous catalyst for the ring opening of epoxides with aromatic amines to afford β-amino alcohols in good to excellent yields at room temperature under solvent-free conditions. It was found that the catalyst is recyclable, and the activity of the catalyst was not weakened markedly even after several reaction cycles. In addition, the catalytic activity of TiO₂ strongly depends on particle size or surface area.     

Vapor phase hydrofluorination of acetylene to vinyl fluoride over La2O3-Al2O3 catalysts

A series of La-doped Al₂O₃ catalysts were prepared and tested for the vapor phase hydrofluorination of C₂H₂ to vinyl fluoride (CH₂CHF, VF). It was found that the La-doped catalyst gave a stable catalytic performance and a higher selectivity to the desired VF and a lower selectivity to coke deposition compared with the pure Al₂O₃ catalyst. The enhancement in VF selectivity on the La-doped catalyst was due to the elimination of acidic sites on the Al₂O₃ surface by the addition of La₂O₃, evidenced by NH₃-TPD results, which could also explain the declined selectivity to coke deposition on the catalyst. Raman result indicated there were two different vibration forms of CH distortion and CC expansion for the coke deposition.     

The effects of silica gel (carrier) on the activity (hydrogen yield) of photocatalytic decomposition of water over [pol-Ti(OBu)4 + CH3OH]-complex

A significant effect of pore size has been found on the yield of photolysis of water to hydrogen, ozone (oxidising product) and methane (decomposing product of catalyst or solvent) using [pol-Ti(OBu)₄ + CH₃OH]-complex/SiO₂. The pore structure of silica gel has been found to provide good conditions for forming this type of catalyst.