二甲基二硫醚对Ni/Al_2O_3催化剂加氢性能的影响

考察了二甲基二硫醚(CH3SSCH3)对Ni/Al2O3催化剂上苯、环己烯和苯乙烯加氢活性的影响,并采用BET、XRD、H2-TPR、XPS、SEM和EA等手段对催化剂进行表征。实验结果表明,在CH3SSCH3存在下,Ni/Al2O3催化剂对苯和环己烯加氢迅速失活,且环己烯加氢对CH3SSCH3的耐硫性要略强于苯加氢,而苯乙烯中共轭烯烃的加氢转化率则维持100%长时间不变。CH3SSCH3的影响顺序为芳环单烯烃共轭烯烃。此外,通过设计实验研究了CH3SSCH3对催化剂的毒化机理,发现CH3SSCH3分子首先吸附在催化剂的表面,并发生氢解生成甲烷随尾气逸出,故CH3SSCH3分子中碳对催化剂的失活影响较小,而留下的硫原子则与镍活性组分发生相互作用,毒化催化剂。     

醋酸仲丁酯加氢反应中Cu/B/Ca/Al_2O_3催化剂的失活及再生

Cu/B/Ca/Al2O3催化剂在长达1 118 h的催化醋酸仲丁酯加氢反应中出现了明显的失活.经过对比分析反应前、后和再生催化剂的组成、形貌和结构,发现金属铜粒子在长时间反应后无明显聚集,醋酸仲丁酯加氢反应中部分氧化钙向醋酸钙转变而引起催化剂结构的改变以及有机物种在催化剂表面的沉积是其失活的根本原因.失活后的催化剂经过350℃空气焙烧再生能够有效消除表面沉积的醋酸钙和有机物种,基本恢复催化剂的结构及其催化醋酸仲丁酯加氢反应的性能.     

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.     

Heavy Atom Effects in Tellurapyrylium Dyes Useful in Photodynamic Therapy and Catalytic Generation of H2O2

Abstract

The large rate of intersystem crossing between singlet and triplet states of tellurapyrylium dyes leads to efficient generation of singlet oxygen in irradiated airsaturated aqueous solutions containing these dyes. One reaction of tellurapyrylium dyes with singlet oxygen and water is the formation of dihydroxy tellurane [tellurium(IV)] species. We have found that the photochemical generation of dihydroxy telluranes is reversible thermally. The tellurapyrylium dye is regenerated while a molecule of hydrogen peroxide is produced. The thermal generation of hydrogen peroxide coupled with a photochemical generation of singlet oxygen allows a catalytic cycle to be devised for the conversion of oxygen and water to hydrogen peroxide. The dihydroxy telluranes are efficient two-electron oxidizing agents and can be used as catalysts to accelerate reactions using hydrogen peroxide as a two-electron oxidizing agent. Examples of tellurapyrylium dye-mediated reactions of hydrogen peroxide include reactions of leucodyes normally oxidized by horseradish peroxidase and hydrogen peroxide. These processes lead to thermal and photochemical reactions that are potentially cytotoxic following the generation of singlet oxygen in photodynamic therapy. The regeneration of the original catalyst allows repeated treatment from a single dose.     

Direct synthesis of hydrogen peroxide from H2/O2 using Pd/Al2O3 catalysts

Pd/Al₂O₃ catalysts were prepared by the impregnation method and were used for the direct formation of hydrogen peroxide from H₂ and O₂. The H₂O₂ concentration and selectivity were strongly dependent on the solubility of hydrogen in the reaction medium. The modification of the support by halogenate has a beneficial effect on the selectivity. The state of the active Pd on Pd/Al₂O₃ catalysts was studied using X-ray photoelectron spectroscopy, and Pd(0) was found to be active.     

Effect of N2O pretreatment on fresh and regenerated Pd-Ag/α-Al2O3 catalysts during selective hydrogenation of acetylene

N₂O pretreatment has shown to result in enhancement of the performance of fresh commercial Pd-Ag/α-Al₂O₃ catalyst during selective acetylene hydrogenation. However, it showed no effect for the used and regenerated catalysts probably due to changes int he metal arrangement on the catalyst surface after regeneration.     

合成气制乙醇Rh-Nb2O5/SiO2催化剂中的SMPI和助催剂作用本质的研究

使用负载型催化剂由合成气制乙醇是一碳化学研究的一个重要发展。本实验室前已报道用化学反应法检验出Rh-Nb_2O_5/SiO_2表面上除了铑位外同时还存在氧化铌位。本文为兰部分工作所组成: (1)进一步用氢还原过的Nb_2O_5/SiO_2催化乙炔聚合成聚乙炔的化学方法推断Rh-Nb_2O_5/SiO_2上可能存在着Nb—H键。(2)用FTIR法检测上述催化剂的红外光谱吸收带, 1740(w) cm~(-1)为V_(Rh-H), 1560 cm~(-1)(broad, m)、1269 cm~(-1)(s)为与Nb—H有关的吸收, 后者可能属于桥式Rh—H—Nb的吸收。(3)XPS检测出合成气处理的Rh-Nb_2O_5/SiO_2表面上存在Rh~0、Rh~Ⅰ、Nb~Ⅴ、Nb~Ⅳ和两种不同的沉积碳。根据这些结果, 提出活性中心可能为A(参见正文图3)简写为B(见图3), CO转化的主要途径是而后C—O还原断裂生成=CH_2***, 再与CO偶联为CH_2=C=O, 最后还原为乙醇或乙醛。根据实验结果对本体系催化剂中SMPI和助催剂作用的实质作了讨论。     

MIL-100(Fe) Supported Pt−Co Nanoparticles as Active and Selective Heterogeneous Catalysts for Hydrogenation of 1,3-Butadiene

Superior catalytic performance for selective 1,3-butadiene (1,3-BD) hydrogenation can usually be achieved with supported bimetallic catalysts. In this work, Pt−Co nanoparticles and Pt nanoparticles supported on metal–organic framework MIL-100(Fe) catalysts (MIL=Materials of Institut Lavoisier, PtCo/MIL-100(Fe) and Pt/MIL-100(Fe)) were synthesized via a simple impregnation reduction method, and their catalytic performance was investigated for the hydrogenation of 1,3-BD. Pt1Co1/MIL-100(Fe) presented better catalytic performance than Pt/MIL-100(Fe), with significantly enhanced total butene selectivity. Moreover, the secondary hydrogenation of butenes was effectively inhibited after doping with Co. The Pt1Co1/MIL-100(Fe) catalyst displayed good stability in the 1,3-BD hydrogenation reaction. No significant catalyst deactivation was observed during 9 h of hydrogenation, but its catalytic activity gradually reduces for the next 17 h. Carbon deposition on Pt1Co1/MIL-100(Fe) is the reason for its deactivation in 1,3-BD hydrogenation reaction. The spent Pt1Co1/MIL-100(Fe) catalyst could be regenerated at 200 °C, and regenerated catalysts displayed the similar 1,3-BD conversion and butene selectivity with fresh catalysts. Moreover, the rate-determining step of this reaction was hydrogen dissociation. The outstanding activity and total butene selectivity of the Pt1Co1/MIL-100(Fe) catalyst illustrate that Pt−Co bimetallic catalysts are an ideal alternative for replacing mono-noble-metal-based catalysts in selective 1,3-BD hydrogenation reactions.     

Effects of the preparation methods on the properties of Ni-La2O3-SiO2 catalysts for m -dinitrobenzene hydrogenation

Ni-La₂O₃-SiO₂ catalysts were prepared by wetness impregnation and sol-gel method followed by conventional drying and supercritical drying, respectively. Their physico-chemical properties and activity for the hydrogenation of m-dinitrobenzene to m-phenylenediamine were investigated by BET, XRD, TPR, H₂-TPD and activity tests. The results showed that the structural and catalytic properties of the Ni-La₂O₃-SiO₂ catalysts obviously depended on the preparation method and the drying mode. The catalyst prepared by the sol-gel method in combination with conventional drying exhibited the highest catalytic activity among the catalysts tested, attributable to its well-dispersed nickel particles and larger active nickel surface area.     

积碳失活催化剂的再生

催化反应常伴随着积碳的生成,而积碳又可以通过覆盖催化剂酸性位点或者堵塞催化剂孔道而引起催化剂失活,表现为产物选择性的降低.根据不同的失活机理可以将催化剂失活分为永久性失活和可逆性失活,而积碳失活一般是可逆的,可以通过再生的方式来除去积碳并恢复催化剂活性.对于工业生产而言,为了保证反应的连续运行,失活催化剂的及时再生是非常必要的.尽管前人已经做了大量的研究,并尝试不同的再生方法来除去催化剂积碳,但发展一种操作简单、高效和经济的再生方法仍然是一个巨大的挑战.目前工业催化剂积碳失活后最常用的再生手段是氧化再生,其主要以空气或氧气为再生气体,将积碳转化为一氧化碳、二氧化碳和水等.但空气或氧气氧化再生为强放热反应,放出的大量热量及生成的水蒸气会对催化剂的组分及结构带来一定的影响.虽然以臭氧和氮氧化物为再生气体可以有效降低再生温度,但是作为有毒有害气体,它们的排放受到严格的限制,这也阻碍了其进一步工业化应用.与氧化再生相比,二氧化碳或水蒸气气化再生可以有效降低再生过程中的放热量,并将无价值的积碳转化为高品质的合成气,同时减少二氧化碳的排放.但由于二氧化碳和水蒸气的氧化性较弱,需要较高的再生温度,对催化剂的水热稳定性提出了更高的要求.此外,在氢气气氛下,可以通过加氢裂解除去积碳,但同样需要较高的再生温度或压力.通过添加金属或金属氧化物等添加剂,可以有效降低再生温度并增加再生速率,但也可能会引起催化剂中毒,造成催化剂的永久性失活,所以需要严格控制添加剂的含量.本文分析了目前常用的几种再生方法的优缺点及面临的挑战,并对未来的研究重点及研究方向进行了展望.     

Ni2P和MoS2催化剂在喹啉加氢脱氮反应中的协同效应

设计实验证明了Ni₂P和MoS₂催化剂在喹啉加氢脱氮反应中存在协同效应,该协同效应能够用氢溢流遥控模型理论解释。Ni₂P//MoS₂的协同因子随反应温度升高而减小,并且略微大于相同反应条件下NiS_x//MoS₂的协同因子。Ni₂P产生的溢流氢能够提高MoS₂催化剂上加氢活性位的数量,促使Ni₂P//MoS₂催化体系增加1,2,3,4-四氢喹啉和5,6,7,8-四氢喹啉加氢生成十氢喹啉的速率,提高其脱氮活性;因此,Ni₂P对MoS₂催化剂是很好的助剂。     

Effect of precursor, dispersity and water vapor treatment on structure-insensitive hydrogenation reactions on Rh/silica

The hydrogenation of 2-cyclohexen-1-one and cyclohexene were studied in liquid phase over Rh/SiO₂ catalysts. The turnover frequency for both reactions is independent of the dispersity for each set of catalysts prepared with organic or chloride rhodium precursors. An effect of the precursor was observed: the chlorinated catalysts showed a higher activity than the non-chlorinated ones. However, the highest activity was observed when the catalysts were thermally treated with hydrogen saturated with water vapor (HWV).     

Effect of substitution of Fe3+ in CuCr2O4 matrix for the hydrogenation of nitrobenzene

The hydrogenation of nitrobenzene to aniline over reduced Cu(Fe_xCr_2–x)O₄ series of catalysts (where x=0, 0.2, 0.4, 0.6, 0.8 and 1.0) has been studied at 250°C in a fixed bed flow type reactor. All the catalysts were characterized by XRD, IR and DRS analysis and by measurements of electrical conductivity and surface area. The conversion of nitrobenzene to aniline is maximum over the catalysts with composition x=0.4. By comparing the results of reversible and irreversible adsorption of carbon monoxide with hydrogenation activity, it can be concluded that univalent copper at octahedral sites is more active for hydrogenation than metallic copper. The second cations [Cr(III) or Fe(III)] develop their catalytic activity by sharing anionic vacancies.     

Ni-Mo/Al_2O_3催化剂上硫转移反应的研究

制备了以γ-Al2O3为载体的Ni-Mo催化剂,并用于FCC汽油的加氢硫转移反应。对Ni-Mo/Al2O3催化剂上的硫转移反应机理进行了研究,考察了不同反应条件对硫转移反应的影响。实验结果表明,硫醇与烯烃的反应在催化剂表面的加氢活性位上进行,小分子的硫醇发生加氢脱硫,生成吸附态H2S,吸附态的H2S与烯烃反应,生成大分子硫醇和硫醚;另外小分子硫醇还可直接与烯烃发生反应,生成硫醚。提高反应温度、压力、氢油比或降低空速,均可提高催化剂的硫转移反应活性,轻质硫转化率得到明显提高,且单烯选择性还能维持在98%左右。     

Highly chemoselective hydrogenation of 2-ethylanthraquinone to 2-ethylanthrahydroquinone catalyzed by palladium metal dispersed inside highly lipophilic functional resins

Most hydrogen peroxide is currently produced by the selective hydrogenation of 2-ethylanthraquinone (EAQ) to 2-ethylanthrahydroquinone (EAHQ), followed by treatment with dioxygen; this produces hydrogen peroxide and regenerates 2-ethylanthraquinone. We have developed novel catalysts for this process that are based on palladium supported on very lipophilic functional resins and that are able to promote a chemoselectivity for EAHQ slightly but definitely superior to that provided by an industrial catalyst under identical conditions. This finding demonstrates the potential of variations of the lipophilic/hydrophilic character of the support as a tool for the improvement of the chemoselectivity of resin-based metal catalysts.     

The Effect of Particle Size and the Modifier on the Properties of Palladium Catalysts in the Synthesis of Hydrogen Peroxide by the Anthraquinone Method

The effect of the composition of the catalytic system and the size of particles on the properties of palladium catalysts in 2-ethyl-9,10-anthraquinone hydrogenation was studied. It was shown that, depending on the nature of a reducing agent (H₂, AlEt₃), palladium species formed in the absence of a modifying agent catalyze various side processes to a substantial extent together with 2-ethyl-9,10-anthraquinone hydrogenation: mostly hydrogenolysis (in the case of H₂ as a reducing agent) and hydrogenation of aromatic rings in 2-ethyl-9,10-anthrahydroquinone (in the case of AlEt₃ as a reducing agent). Elementary phosphorus was found to have a promoting effect on the selectivity of palladium catalysts in the synthesis of hydrogen peroxide by the anthraquinone method. The main factors that make it possible to control the selectivity of palladium catalysts were discussed.     

NiO–ThO2 mixed catalysts in hydrogen peroxide decomposition and influence of ionizing radiation

Some physico-chemical and catalytic properties of NiO–ThO₂ catalysts containing various amounts of components in the range 0–100 wt% of one component have been studied before and after 1 MGy gamma or 1 and 3 MGy accelerated electron irradiation in air or in water using the hydrogen peroxide decomposition as a test reaction. The γ-irradiation of pure NiO led to significant changes in surface oxidative ability as well as in catalytic activity of the oxide. Dramatic changes in catalytic activity of the NiO (and partially also of the samples containing an excess of NiO) were caused by reduction of the samples with hydrogen.     

纳米负载型V2O5-WO3/TiO2催化剂碱中毒及再生研究

实验制备了陶瓷颗粒为骨架的纳米级V₂O₅-WO₃/TiO₂(C)催化剂。采用浸渍法模拟碱金属中毒,研究了中毒及再生对催化剂脱硝活性的影响,运用XRD、FT-IR、H₂-TPR、XPS技术表征分析了碱金属对催化剂的失活作用。实验表明,碱金属能使催化剂活性降低,钾的毒性大于钠。FT-IR结果显示,催化剂以Lewis酸作为活性酸位。H₂-TPR、XPS结果表明,钾的加入降低了催化剂的氧化能力,主要影响了催化剂表面的吸附氧。采用单纯的水洗方法并不能提高催化剂活性,而酸洗再生后催化剂在较高反应温度下活性得到较好的恢复。     

Formation of C4 Oligomers in Hydrogenation of Acetylene over Pd/Al2O3 and Pd/TiO2 Catalysts

Selectivity of product formation has been tested in hydrogenation of acetylene over 0.3 wt.% Pd/-alumina and 0.5 wt.% Pd/TiO₂catalysts. Non-steady-state regime of catalyst operation was tested in pulse-flow experiments. Significant carbon poisoning appears to be a necessaryrequisite for selective formation of ethylene. The effect of hydrogen and acetylene partial pressure has been tested on the selectivity of C₄products. At 273–298 K the catalysts showed 26–35% selectivity for C₄ hydrocarbons and <2.5% for ethane production at conversionsof 30–40%. Deuterium distribution in ethylene and 1,3-butadiene and the deuterium content of the surface hydrogen pool have been compared and mechanismof diene formation has been discussed.     

贵金属负载TiO2对光催化还原CO2选择性的影响

利用光沉积方法在TiO₂表面分别负载1%(质量分数) Pt、Pd、Au和Ag助催化剂.用TEM、XRD、UV-vis等技术对催化剂进行了表征,并利用连续瞬态电流时间响应和线性扫描伏安法等电化学方法,对贵金属负载的TiO₂光催化剂在光照条件下的电流响应强度及电催化析氢电位等特性加以测试.分析了贵金属助催化剂对光催化还原CO₂性能的差异.结果表明,负载贵金属助催化剂能显著加速光生电子空穴的分离,降低复合率;另外,助催化剂对还原CO₂选择性的顺序为Ag>Au>Pd>Pt.贵金属助催化剂还原CO₂的加氢选择性和析氢过电位存在相关性,即越不利于析氢过程的助催化剂,其催化CO₂加氢还原产物的选择性越高.