Preparation and Characterization of Forsterite (Mg2SiO4) Xerogels

Mg2SiO4 gels were prepared from alkoxide precursors, and the formation of the forsterite crystal phase was studied after heat treatments up to 1200°C. Prehydrolyzed TEOS in solution with 2-methoxyethanol was mixed with Mg(OEt)2, and the solution was hydrolyzed using excess water. The resultant gels were dried at 100°C to form xerogels which were subsequently powdered. These powders were characterized using thermal analysis (DTA and TGA), surface area analysis (BET), X-ray diffraction (XRD) and transmission electron microscopy (TEM).DTA and XRD indicated that forsterite crystallized at 770°C, and by 1000°C the powders were predominantly crystalline. BET gave powder surface areas between 400 and 550 m2 g–1. TEM revealed angular particles with sizes between 0.2 and 2 m. The low temperature of crystallization of forsterite indicates a high degree of intimate mixing between the precursor alkoxides, although XRD indicated some degree of inhomogeneity.     

SiO2-PEG凝胶体系织构特性的研究

采用溶胶-凝胶法,以正硅酸乙酯(TEOS)为前驱体,以不同分子量的聚乙二醇(PEG)为改性剂,制备结构可控的多孔SiO₂干凝胶.结果表明:PEG限制了TEOS的水解反应,进而对溶胶粒子的表面进行修饰,形成“粒子团-PEG”聚集体及短程有序的环状网络结构,由此对SiO₂干凝胶的结构性质进行调控.经真空热处理后,PEG等有机残留物被脱除的同时,SiO₂-PEG干凝胶柔性骨架得到加强,孔分布更趋集中,干凝胶结构的热稳定性得到进一步提高.     

SiO2-AEO凝胶体系的织构特性

采用溶胶 凝胶法 ,以正硅酸乙酯 (TEOS)为前驱体 ,用脂肪醇聚氧乙烯醚 (AEO)为改性剂制备结构可控的多孔SiO2 干凝胶.结果表明 :通过调节添加量和聚合度以及溶胶老化时间可以对SiO2 干凝胶织构性质进行有效的调控 ;采用不同的环境气氛对SiO2 AEO干凝胶进行热处理 ,则AEO表现出不同的热稳定性 ;经热处理后 ,AEO等有机残留物被脱除的同时 ,SiO2 AEO干凝胶柔性骨架得到加强 ,孔分布更趋集中 ,干凝胶结构的热稳定性得到进一步提高.     

Nucleation Phenomenon in Silica Xerogels and Pd/SiO2, Ag/SiO2, Cu/SiO2 Cogelled Catalysts

Pd/SiO₂, Ag/SiO₂ and Cu/SiO₂ xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Pd, Ag and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS). It appears that, in cogelled samples, the metal complex acts as a nucleation agent in the formation of silica particles. The resulting catalysts are then composed of completely accessible metallic crystallites with a diameter of about 3 nm located inside silica porous particles with a monodisperse microporous distribution. Xerogels without metal synthesized with EDAS and TEOS (C. Alié, R. Pirard, A.J. Lecloux, and J.-P. Pirard, J. Non-Cryst. Solids 289, 88 (2001)) verify this hypothesis of nucleation by EDAS.     

负载型Ni-B非晶态合金催化剂的表征

作为一种新型的催化加氢材料 ,非晶态合金具有高的活性及选择性 ,近年来引起了人们的注意［１］．尤其将非晶态合金负载化 ,可以提高其表面积和热稳定性 ,抑制非晶态合金的晶化 ,增加了非晶态合金催化剂的工业应用前景．文献已报导了对负载型非晶态合金催化剂的制备、化学及结构修饰、催化性能、催化剂的失活及抗硫性能的研究［２,３］．应该说 ,相比于淬冷法和化学还原法制备的超细微粒非晶态合金 ,负载化有效地提高了非晶态合金的热稳定性．但是 ,当负载型非晶态合金催化剂应用于催化反应时 ,仍存在着结构逐渐变化的过程［４］．本文以Ｎ…     

负载型非晶态Cu／SiO2催化剂局域结构的研究

采用ＸＰＳ和ＥＸＡＦＳ方法，研究了以ｓｏｌ－ｇｅｌ法制得的超累粉体ＳｉＯ２为载体，用化学还原沉积法制备的负载型非晶态Ｃｕ／ＳｉＯ２催化剂在甲酸甲酯氢解反应前后的表面结构和局域结构。结果表明，非晶态样品中的铜原子以零价铜的形式存在，但配位数却大幅度地低于铜樯档，意味着铜原子在高比表面超细ＳｉＯ２载体上处于高分散的非晶状态，表面悬空键显著增多，表面能增大，导致配位键收缩。     

Co/SiO2催化剂的表征和吸附量热研究

用溶胶-凝胶法制备了Co/S iO2系列的担载型催化剂,采用SBET、TPR、XRD、O2滴定及室温H2、O2、CO和C2H4微量吸附量热等技术进行了研究.结果表明:Co很好分散,S iO2的含量越高,样品的SBET越大;Co是经由Co3 →Co2 →Co0的还原过程;Co/S iO2系列催化剂上,CO、H2、O2和C2H4的初始吸附热数值均比较接近、饱和覆盖度以50Co/50S iO2最高,O2为多层吸附而H2、CO和C2H4为单层吸附,CO为线式吸附并发生歧化反应生成了C和CO2,C2H4吸附解离生成了H2、乙川(C2H3)和C2H6.     

Characterization of Pore Structure and Coordination of Titanium in TiO(2) and SiO(2)-TiO(2) Sol-Pillared Clays

Titania sol-pillared clay (TiO(2) PILC) and silica-titania sol-pillared clay (SiO(2)-TiO(2) PILC) were synthesized by the sol-gel method. Supercritical drying (SCD) and treatment with quaternary ammonium surfactants were used to tailor the pore structure of the resulting clay. It was found that SCD approach increased the external surface area of the PILCs dramatically and that treatment with surfactants could be used to tailor pore size because the mesopore formation in the galleries between the clay layers follows the templating mechanism as observed in the synthesis of MCM-41 materials. Highly mesoporous solids were thus obtained. In calcined TiO(2) PILC, ultrafine crystallites in anatase phase, which are active for photocatalytic oxidation of organics, were observed. In SiO(2)-TiO(2) PILCs and their derivatives, titanium was highly dispersed in the matrix of silica and no crystal phase was observed. The highly dispersed titanium sites are good catalytic centers for selective oxidation of organic compounds. Copyright 2001 Academic Press.     

SiO2-AEO凝胶体系的织构特性

采用溶胶－凝胶法,以正硅酸乙酯（ＴＥＯＳ）为前驱体,用脂肪醇聚氧乙烯醚（ＡＥＯ）为改性剂制备结构可控的多孔ＳｉＯ２干凝胶。结果表明：通过调节添加量和聚合度以及溶胶老化时间可以对ＳｉＯ２干凝胶织构性质进行有效的调控;采用不同的环境气候对ＳｉＯ２－ＡＥＯ干凝胶进行热处理,则ＡＥＯ表现出不同的热稳定性;经热处理后,ＡＥＯ等有机残留物被脱除的同时,ＳｉＯ２－ＡＥＯ干凝胶柔性骨架得到加强,孔分布更趋集中,干     

Al2（SO4）3／SiO2催化甲醇脱水合成二甲醚

采用浸渍法制备了不同负载量的Al2（SO4）3／SiO2催化剂．使用BET、XRD、FT—IR、异丙醇探针反应、NH3吸附量热和NH3吸附红外等手段对催化剂进行了表征,并测试了其在甲醇脱水合成二甲醚反应中的活性．BET、XRD和FT-IR结果表明,载体SiO2的表面积较高,随着Al2（SO4）3负载量的增加,样品的表面积逐渐降低,当Al2（SO4）3负载量高于20％时,样品表面开始出现晶相Al2（SO4）3．NH3吸附量热和NH3吸附红外结果表明,载体SiO2的酸性很弱,负载了Al2（SO4）3后,样品酸性大大增强,且酸性随着Al2（SO4）3负载量的增加先增强后减弱．样品表面同时存在B酸中心和L酸中心,但以B酸中心为主．Al2（SO4）3负载量为3％的样品的表面酸性最强,因而在甲醇脱水反应中表现出最高的反应活性,533K,甲醇转化率为83．5％,二甲醚选择性100％．     

二氧化碳在Pd/SiO2和La-Pd/SiO2上的催化氢化反应

对CO₂在附载型Pd催化剂上的氢化反应的研究迄今报道不多^[1,2],且都在加压条件下进行,对常压下助催剂如何改善Pd的催化行为未见报道。本文探讨了Pd/SiO₂催化剂,未加与掺加助催剂La(NO₃)₃后,其Pd粒大小、CO₂的吸附性能及CO₂/H₂催化活性等方面都有显著差异。     

V2O5/TiO2 Catalyst Xerogels: Method of Preparation and Characterization

This work describes a modified sol-gel method for the preparation of V₂O₅/TiO₂ catalysts. The samples have been characterized by N₂ adsorption at 77 K, X-ray Diffractometry (XRD), Scanning Electronic Microscopy (SEM/EDX) and Fourier Transform Infrared Spectroscopy (FT-IR). The surface area increases with the vanadia loading from 24 m² g^–1 for pure TiO₂ to 87 m² g^–1 for 9 wt% of V₂O₅. The rutile form is predominant for pure TiO₂ but becomes enriched with anatase phase when vanadia loading is increased. No crystalline V₂O₅ phase was observed in the diffractograms of the catalysts. Analysis by SEM showed heterogeneous granulation of particles with high vanadium dispersion. Two species of surface vanadium were observed by FT-IR spectroscopy: a monomeric vanadyl and polymeric vanadates. The vanadyl/vanadate ratio remains practically constant. Ethanol oxidation was used as a catalytic test in a temperature range from 350 to 560 K. The catalytic activity starts around 380 K. For the sample with 9 wt% of vanadia, the conversion of ethanol into acetaldehyde as the main product was approximately 90% at 473 K.     

Co/HMS和Co/SiO2催化剂的表征及在费-托合成反应中的催化性能

 HMS介孔分子筛经水热处理得到无定形SiO2,分别以无定形SiO2和HMS为载体,用浸渍法制得了15%Co/SiO2和15%Co/HMS催化剂. 研究表明: 氧化态Co/SiO2和Co/HMS催化剂中的钴物种以Co3O4形式存在,且Co3O4晶粒粒径均较相应催化剂的孔径大,故有部分钴物种存在于催化剂外表面; 氧化态Co/HMS催化剂中的钴物种堵塞孔道较为严重; Co/HMS催化剂中存在较强的金属-载体相互作用,因此Co/HMS催化剂较Co/SiO2催化剂难还原; Co/HMS催化剂还原后具有较高的钴分散度,使其具有优异的费-托合成反应性能.     

Characterization of low molecular weight components of [(ViMe2SiO1/2)x(PhSiO3/2)y(SiO4/2)z], [(ViMe2SiO1/2)x(SiO4/2)y], and [(SiO4/2)x(HO1/2)y(tBuO1/2)z] silsesquioxanes by electrospray ionization fourier transform mass spectrometry (ESI-FTMS)

This paper describes the characterization of low molecular weight components of four materials using electrospray ionization Fourier transform mass spectrometry (ESI-FTMS). The materials in the current study are [(ViMe₂SiO_1/2)_x(PhSiO_3/2)_y(SiO_4/2)_z] (MTQ), [(ViMe₂SiO_1/2)_x(SiO_4/2)_y] (MQ), and [(SiO_4/2)_x(HO_1/2)_y(^tBuO_1/2)_z] (Q) silsesquioxanes. Accurate mass measurements coupled with knowledge of resin chemistry afforded siloxane composition determination that was used to propose specific structures for the oligomers. Branched or linear (T_nQ_mM_n+2m+2), and monocyclic (T_nQ_mM_n+2m) structures are predominant structures for the low molecular weight species in MTQ. For MQ and Q, more condensed structures, such as partially opened cage structures (Q_mM_2m?6 and Q_mM_2m?8), were identified. The differences between MQ, Q, and MTQ are likely attributed to differences in intrinsic structure and reactivity of T and Q building blocks. The structural information obtained for these oligomeric species will ultimately provide a better understanding of new resin materials and their associated physical properties.     

Pd-Ag/C@TiO_2核壳结构纳米棒阵列的制备及对NaBH_4电氧化的催化性能

通过热蒸发结合恒电位沉积法制备了具有核壳结构的Pd-Ag/C@Ti O2催化剂.利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等对所制备样品的形貌和结构进行了表征,利用线性伏安扫描和计时电流技术研究了Pd-Ag/C@Ti O2电极对Na BH4的电氧化性能.结果表明,Pd-Ag/C@Ti O2电极具有三维纳米核壳结构,在电化学反应过程中有利于燃料与催化剂充分接触.催化剂中Pd与Ag的原子比为0.37∶0.17的Pd-Ag(2∶1)/C@Ti O2催化剂的效果最佳,在3.0 mol/L Na OH+0.20 mol/L Na BH4溶液中电流密度达到672 m A/cm2,在1200 s测试时间内计时电流曲线衰减很小,说明该Pd-Ag/C@Ti O2电极对Na BH4电氧化具有很高的电化学活性和稳定性.     

TiO2纳米管负载Pd-Ag催化1,2-二氯乙烷的选择性加氢脱氯

以二氧化钛纳米管为载体,分别采用光沉积法和浸渍法制备负载Pd和Ag的双金属催化剂,并考察它们对1,2-二氯乙烷选择性加氢脱氯的行为。催化剂的UV-Vis,XRD,XPS等表征结果显示,在Ag负载量相近的情况下,光沉积法制备的催化剂较浸渍法制备的催化剂具备更显著的Ag富集现象。催化剂对1,2-二氯乙烷活性评价的结果表明,在Ag负载量相近时,光沉积法制备的催化剂对乙烯具有更高的选择性,且随着Ag负载量的提高,催化剂对乙烯选择性也逐渐增强。     

Preparation and Characterization of the Nanocomposites SiO2/H-Bond Hydrogensulphate (Hydrogenselenate)

The nanocomposites representing interesting H-bond compounds (Na₃H(SO₄)₂, RbHSO₄, RbHSeO₄, and Rb₃H(SeO₄)₂) in the silica matrix were prepared by the sol-gel method. Resulting samples were characterised by X-ray diffraction, IR spectroscopy and electron microscopy. Transition temperatures of the nanocomposites were determined using DSC and compared with the T _C of the pure bulk active compounds. The shifts of the T _C towards lower temperatures or the disappearing of the certain effects in the case nanocomposites were observed. A possible explanation of these phenomena was proposed using the analogy with the superparamagnetic compounds.     

Preparation and Characterization of SiO2/Co and C/Co Nanocomposites as Fisher-Tropsch Catalysts for CO2 Hydrogenation

To fabricate high-density cobalt-based catalysts, we first synthesized SiO₂/C composites via a hydrothermal method and removed C and SiO₂ by two different methods, respectively. The as-prepared SiO₂ and C supports then reacted with cobalt acetylacetonate and N,N-dimethylformamide(DMF) under hydrothermal conditions to prepare SiO₂/Co and C/Co nanocomposite catalysts. The catalysts were characterized by X-ray diffraction(XRD), scanning electron microscope(SEM), transmission electron microscopy(TEM), inductively coupled plasma mass spectrometry(ICP), energy dispersive X-ray fluoresence spectrometer(EDX), and nitrogen adsorption. It was found that hexagonal cobalt nanocrystals were successfully integrated with the mesoporous silica or carbon nanotube supports. SEM and TEM results show that SiO₂/Co composites with a hollow/mesoporous sphere structure and C/Co composites with a tubular structure have been successfully synthesized. Both composite samples show superparamagnetism exhibiting an S-type hysteresis loop, which originated from the cobalt nanoparticles in the samples. Nitrogen adsorption/desorption curves suggest that the SiO₂ and C supports have well-developed pore structures and large specific surface areas, and the loading and good dispersity of cobalt nanoparticles on the supports were proven by ICP and EDX. Moreover, the samples exhibited good and stable catalytic activity, demonstrating that the two composites are suitable catalysts for Fischer-Tropsch CO₂ hydrogenation.     

负载型Pd/TiO2和Pd-Ag/TiO2催化剂的乙炔选择性加氢催化性能

利用程序升温还原(TPR)、X-射线衍射(XRD)、CO吸附-红外光谱(CO-IR)、电子顺磁共振(EPR)和微型催化反应评价等手段, 研究了负载Pd/γ-Al2O3, Pd/TiO2和Pd-Ag/TiO2催化剂的结构和乙炔选择性加氢催化性能. 结果表明, Pd/TiO2催化剂具有较Pd/γ-Al2O3催化剂更优良的乙炔选择性加氢催化性能, 这与Pd-TiO2之间的强相互作用密切相关. Pd-TiO2之间的强相互作用不仅使负载型钯金属催化剂具有较高的乙炔加氢催化选择性, 而且具有较高的乙炔加氢催化活性. Pd/TiO2催化剂中添加Ag 组分后, Pd金属可促进Ag+的还原并可能形成Pd-Ag合金, 催化剂的乙烯选择性虽有所增加, 但乙炔转化率和乙烯收率下降.     

TiO_2纳米管负载Pd-Ag催化1,2-二氯乙烷的选择性加氢脱氯

以二氧化钛纳米管为载体,分别采用光沉积法和浸渍法制备负载Pd和Ag的双金属催化剂,并考察它们对1,2-二氯乙烷选择性加氢脱氯的行为。催化剂的UV-Vis,XRD,XPS等表征结果显示,在Ag负载量相近的情况下,光沉积法制备的催化剂较浸渍法制备的催化剂具备更显著的Ag富集现象。催化剂对1,2-二氯乙烷活性评价的结果表明,在Ag负载量相近时,光沉积法制备的催化剂对乙烯具有更高的选择性,且随着Ag负载量的提高,催化剂对乙烯选择性也逐渐增强。