Roles of interaction between components in CZZA/HZSM-5 catalyst for dimethyl ether synthesis via CO2 hydrogenation

The roles of interaction between two catalyst components in CuO–ZnO–ZrO₂–Al₂O₃ (CZZA)/HZSM-5 bifunctional catalyst for dimethyl ether (DME) synthesis via carbon dioxide hydrogenation were investigated. It was found that CZZA catalyst showed excellent stability during methanol (MeOH) synthesis for 100 h, while there was a severe loss of catalytic activity in the bifunctional catalyst for DME synthesis. Hence, the effects of different degrees of intimacy of two catalyst components were studied for DME synthesis, including mixed and separated modes. For the mixed mode, the particle size of catalysts and the amount of reaction intermediates were proven to influence the catalyst deactivation. For the separated mode, the catalysts showed rapid deactivation within a short time. Various characterizations indicated that the remarkable deactivation of separated mode was mainly caused by the decrease of copper active centers (e.g., sintering and oxidation) and blockage of acid sites via increased coke deposition on HZSM-5.     

Microwave-Assisted Solution Combustion Synthesis of Spinel-Type Mixed Oxides for Esterification Reaction

Environmentally benign production of biodiesel using heterogeneous catalysts is an important issue that requires the preparation of catalysts with high activity and reusability by a simple procedure. In this study, pure alumina and zinc oxide- and copper oxide-modified alumina were tested for the esterification of oleic acid to its methyl ester. The microwave-assisted solution combustion (MSC) method was used to prepare the catalyst samples that were characterized by X-ray diffraction (XRD), Fourier transform infra-red (FTIR), Brunauer–Emmett–Teller (BET) surface area measurement, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The spinel-type zinc aluminate was successfully synthesized, but CuO-modified alumina particles were clearly observed. Whereas in the alumina, much lower activity was observed than the doped alumina, zinc aluminate showed higher activity than copper oxide-alumina due to its smaller particle size, higher BET surface area, larger average pore size, and higher acidity. Finally, after the reaction conditions for the conversion of oleic acid were optimized for the case of spinel ZnAl₂O₄ as nanocatalyst, a yield of higher than 94% was obtained at 180°C, 9 methanol/oleic acid molar ratio, 3?wt% of catalyst for 6?h. Furthermore, the catalyst deactivation was not observed after four reaction cycles at the optimal reaction conditions, indicating the feasibility of the proposed method for the preparation of industrial catalysts.     

磺酸功能化MIL-101(Cr)固体酸催化降解纤维素为葡萄糖

以葡萄糖为原料,发烟硫酸为磺酸化试剂,MIL-101(Cr)为载体制备了碳基磺酸化固体酸催化剂C-SO3H/MIL-101(Cr).通过SEM、酸碱滴定、FT-IR和XRD等手段对催化剂进行表征;并考察了其催化降解纤维素为葡萄糖的水解反应性能.结果表明,磺酸化48 h的C-SO3 H(48)/MIL-101(Cr)固体...     

Deactivation of CuZn Catalysts Used in Glycerol Hydrogenolysis to Obtain 1,2-Propanediol

Different CuZn catalysts were prepared by coprecipitation method with Cu/Zn atomic ratio of 0.2, 0.4, 1.0, 2.5 and 6.0. Monometallic Zn and Cu catalysts and a bimetallic catalyst (Cu/Zn?=?2.5) prepared by physical mixture of the precursors were also studied. These catalysts were tested in the glycerol hydrogenolysis reaction and the higher yields to 1,2-propanediol were achieved for Cu/Zn atomic ratio?≥?1 samples. The deactivation of a representative catalyst (Cu/Zn?=?1) was evaluated and its yield to 1,2 propanediol decreases until ca 40% after five runs. To explain this behavior, fresh and used catalysts were characterized by different techniques. Chemical analysis of solid catalysts and liquid reaction medium confirmed the leaching of Zn species under our reaction conditions. This process promotes Cu sintering which is proposed as the actual reason of the observed deactivation in the glycerol hydrogenolysis for this catalytic system.     

Mesoporous Tin-Triflate Based Catalysts for Transesterification of Sunflower Oil

Unimodal porous system (denoted as SnTf-MCM-41) and bimodal porosity (denoted as SnTf-UVM-7) were prepared in a two-step synthesis. The triflic acid was incorporated into previously synthesized Sn-containing porous silicas. Chemical analysis was carried out by electron probe microanalysis (EPMA), textural properties were determined by transmission electron microscopy (TEM) and from nitrogen adsorption–desorption isotherms (77 K), while structural characterization by X-ray absorption near-edge structure (XANES), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements. The structural characterization provided evidences on the direct interaction of triflate with incorporated tin species. The acidity of these catalysts was determined from the ammonia chemisorption measurements. The catalysts have been tested for transesterification of sunflower oil under both microwave and ultrasound activation. These experiments showed a direct reaction between the acidity of the catalysts and catalytic performances. No leaching of the triflate species or catalyst deactivation have been detected over several runs.     

Adsorption and Deactivation Characteristics of Cu/ZnO-Based Catalysts for Methanol Synthesis from Carbon Dioxide

The adsorption and deactivation characteristics of coprecipitated Cu/ZnO-based catalysts were examined and correlated to their performance in methanol synthesis from CO₂ hydrogenation. The addition of Ga₂O₃ and Y₂O₃ promoters is shown to increase the Cu surface area and CO₂/H₂ adsorption capacities of the catalysts and enhance methanol synthesis activity. Infrared studies showed that CO₂ adsorbs spontaneously on these catalysts at room temperature as both mono- and bi-dentate carbonate species. These weakly bound species desorb completely from the catalyst surface by 200 °C while other carbonate species persist up to 500 °C. Characterization using N₂O decomposition, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy with energy-dispersive X-ray spectroscopy analysis clearly indicated that Cu sintering is the main cause of catalyst deactivation. Ga and Y promotion improves the catalyst stability by suppressing the agglomeration of Cu and ZnO particles under pretreatment and reaction conditions.     

Study on deactivation of Cu–Zn–Al catalysts in the synthesis of N-ethylethylenediamine

The performance of a Cu–Zn–Al catalyst employed in the synthesis of N-ethylethylenediamine from ethylenediamine and ethanol was studied. The results showed that the activity of the Cu–Zn–Al catalyst decreased with time-on-stream. Fresh and deactivated catalysts were characterized by XRD, XPS, N₂ adsorption–desorption and TEM. It was found that the crystallite size of Cu and ZnO in the deactivated catalyst were much bigger than those for the fresh catalyst. In addition, channels in the deactivated catalyst were blocked by carbonaceous deposits, so the surface area and pore volumes of the deactivated catalyst were much smaller than in the fresh catalyst. Therefore, it was concluded that the deactivation of the Cu–Zn–Al catalyst was mainly caused by the growth in the Cu and ZnO crystallite sizes and carbonaceous deposits.     

SURFACE MORPHOLOGY AND CATALYTIC ACTIVITY OF THE CONTACT MASS IN ORGANOSILANE SYNTHESIS

The contact mass in the Rochow reaction was analyzed to understand catalyst deactivation during the reaction. Changes in crystalline structure, particle surface morphology, and the elemental composition of the contact mass were measured by XRD, SEM, EDX, and XRF, respectively, at four different reaction conversions. The results indicate that the main reason for contact-mass deactivation is copper enrichment on the surface of silicon. Coke deposition may hamper Cu diffusion and result in the copper enrichment.     

SURFACE MORPHOLOGY AND CATALYTIC ACTIVITY OF THE CONTACT MASS IN ORGANOSILANE SYNTHESIS

The contact mass in the Rochow reaction was analyzed to understand catalyst deactivation during the reaction. Changes in crystalline structure, particle surface morphology, and the elemental composition of the contact mass were measured by XRD, SEM, EDX, and XRF, respectively, at four different reaction conversions. The results indicate that the main reason for contact-mass deactivation is copper enrichment on the surface of silicon. Coke deposition may hamper Cu diffusion and result in the copper enrichment.     

氯化亚铜催化四氯化硅和硅耦合加氢的机理研究

以氯化亚铜为催化剂、使用固定床反应器,对四氯化硅和硅耦合加氢反应进行反应历程中固体催化物种活性变化的机理研究。利用程序升温策略使Cu3Si在反应前完全生成,开启反应后观察到包含诱导期、稳定期、失活期的反应活性曲线,对诱导期的成因进行了讨论,认为Cu3Si在反应气氛下的氯化是形成活性中心的必要条件。使用惰性气体吹扫降温法制备了不同反应阶段的颗粒样品。利用SEM-EDS、XRD、XRF等研究了反应历程中表面形貌、晶型及体相组成的演化规律,提出了反应失活模型,认为颗粒表面形貌组成的变化导致扩散速率下降是失活的原因。     

用于低温液相合成甲醇的Cu/MgO/ZnO催化剂

采用并流共沉淀法制备了不同Cu:(Mg+Zn)及Mg:Zn摩尔比的铜基催化剂Cu/MgO/ZnO,用于低温液相甲醇的合成,并对比了Cu/ZnO及Cu/MgO催化剂,分析了催化剂中载体MgO的作用. 结果表明,MgO的引入有利于催化剂中Cu+的生成并均匀分散在载体中,可提高催化剂的催化活性. 以合成气CO+H2为原料,在443 K和5.0 MPa条件下,采用液体石蜡作溶剂,考察了催化剂的催化性能. 结果表明,Cu/MgO/ZnO催化剂的活性优于Cu/ZnO和Cu/MgO催化剂,且当Cu:Mg:Zn=2:1:1时催化性能最好,此时合成气中CO的转化率为63.56%,甲醇的选择性为99.09%,时空收率为5.413 mol/(kg×h). 分析了Cu/MgO催化剂在高温反应条件下的失活现象,认为铜烧结是其失活的主要原因.     

Fischer–Tropsch Synthesis: Characterization Rb Promoted Iron Catalyst

Rubidium promoted iron Fischer–Tropsch synthesis (FTS) catalysts were prepared with two Rb/Fe atomic ratios (1.44/100 and 5/100) using rubidium nitrate and rubidium carbonate as rubidium precursors. Results of catalytic activity and deactivation studies in a CSTR revealed that rubidium promoted catalysts result in a steady conversion with a lower deactivation rate than that of the corresponding unpromoted catalyst although the initial activity of the promoted catalyst was almost half that of the unpromoted catalyst. Rubidium promotion results in lower methane production, and higher CO₂, alkene and 1-alkene fraction in FTS products. Mössbauer spectroscopic measurements of CO activated and working catalyst samples indicated that the composition of the iron carbide phase formed after carbidization was χ-Fe₅ C₂ for both promoted and unpromoted catalysts. However, in the case of the rubidium promoted catalyst, ?′-Fe_2.2C became the predominant carbidic phase as FTS continued and the overall catalyst composition remained carbidic in nature. In contrast, the carbide content of the unpromoted catalyst was found to decline very quickly as a function of synthesis time. Results of XANES and EXAFS measurements suggested that rubidium was present in the oxidized state and that the compound most prevalent in the active catalyst samples closely resembled that of rubidium carbonate.     

Zn(Al)O复合氧化物负载Au催化剂催化氧化甘油制备1,3-二羟基丙酮

以尿素为沉淀剂,采用均匀沉积沉淀法制备了Zn(Al)O复合氧化物负载Au催化剂,并用于无碱条件下催化氧化甘油制备1,3-二羟基丙酮（DHA）反应,值得注意的是随着载体中Zn/Al摩尔比的不同,负载Au催化剂的催化活性和产物DHA的选择性呈现明显差距。结合X射线衍射（XRD）、X射线光电子能谱（XPS）、透射电镜（TEM）、CO吸附傅里叶变换红外光谱（CO吸附FTIR）等表征手段,发现载体Zn(Al)O复合氧化物中Zn/Al摩尔比会影响表面氧物种的含量并进一步会影响催化剂的催化活性和选择性。当Zn/Al摩尔比为7∶1、反应温度为80℃、氧气压力为10bar、反应2h时获得最佳的甘油转化率（58.5%）和DHA的选择性（95.3%）。同时,还考察了反应温度、反应时间、反应压力及载体的焙烧温度对催化性能的影响,并发现反应条件对催化剂的催化活性和选择性均有不同程度的影响。此外,以Au/Zn(Al)O-7∶1催化剂为基准考察了催化剂的稳定性,并通过表征手段分析了催化剂失活的主要原因。     

流化床甲醇合成催化剂的制备及其性能

采用碳酸钠共沉淀法制备了5种不同组成的铜基甲醇合成催化剂,并对其进行了活性评价和形貌及抗磨损性能表征. 结果表明,氧化锆可使催化剂的耐磨损强度显著提高,磨损指数(AJI)可达0.056;催化剂的活性和稳定性较好,CO转化率约40%,260℃高温下长达50 h基本不失活. 氧化铝与铜锌发生复合使催化剂的活性显著下降,CO转化率仅有10%,对催化剂的强度提高作用不明显,AJI值达0.103. 组成为铜锌锆的催化剂较适用于流化床中甲醇的合成.     

乙二醇为原料制备乙二醇乙醚用催化剂及其失活

以硫酸铵浸渍改性的HZSM-5为催化剂催化乙二醇和乙醇合成乙二醇乙醚和乙二醇二乙醚时催化剂效率很高,乙二醇转化率能达到69.1%,乙二醇乙醚选择性达到72.9%,乙二醇二乙醚的选择性为25.3%。但催化剂在重复使用时催化活性降低较快,因此分别采用X射线衍射仪（XRD）,NH3-TPD,扫描电子显微镜（SEM）,电子能谱（EDS）,比表面积及孔径测定仪和热重/差热分析仪（TG）对催化剂改性及使用前后晶型结构,表面酸强和酸量,表面吸附物,催化剂形貌,表面元素变化,比表面积,孔径大小等对催化剂失活原因及再生条件进行研究。结果表明,在使用后未对催化剂处理情况下,催化剂失活主要是由于表面积碳导致催化剂孔道堵塞造成的。经多次使用后催化剂缓慢失活主要是由于催化剂表面负载的S流失造成的,在整个过程中催化剂晶型结构未发生变化。     

Fluidized bed synthesis of carbon nanotubes: Reaction mechanism,rate controlling step and overall rate of reaction

Carbon nanotubes have been synthesized from acetylene and methane in a fluidized bed by using ferrocene as the catalyst dispersed over carbon black support material. The agglomerate size of carbon black, loading of catalyst, total gas flow rate, partial pressure of reactant gas, temperature of synthesis, and time of synthesis have been varied to understand their effects on the yield of carbon nanotubes. A reaction mechanism consisting of eleven steps and the rate equations for these steps have been proposed. Formation of carbon molecules on the catalyst surface was found to be the rate controlling step in the temperature range of 700–807°C, with an activation energy 47 kJ mol^?1, while diffusion through pores in the carbon black was found to be the rate controlling step in the temperature range of 807–1000°C with an activation energy of 7.6 kJ mol^?1. A continuous deactivation of the catalyst, represented by an exponential decay, was observed. The products have been characterized by thermogravimetry, electron microscopy, and Raman spectroscopy. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2882–2892, 2014     

铜基石墨烯复合催化剂的合成与表征

采用原位水热法制备了Cu/r GO催化剂并引入对苯二甲酸(TPA)对Cu基石墨烯复合材料进行改性研究,探究了不同溶剂、水热时间、沉淀p H对引入TPA的Cu/r GO催化剂材料微观结构特性的影响。通过XRD、FT-IR、XPS和SEM表征技术分析了催化剂的形貌结构及物化性质。考察了催化剂用于二乙醇胺脱氢的催化性能。在V(乙醇)∶V(水)=1∶1为溶剂,沉淀p H为13.0,160℃水热10 h,制备的催化剂性能最好,亚氨基二乙酸收率为86.55%,与没有添加TPA的Cu/r GO催化剂相比收率提高20%。TPA的加入,增强了GO片层间的相互作用,增加了GO片层间的有机官能团,稳定Cu2O并使其结晶度较好,增加催化剂活性位点,以提高反应速率。且粒径约为10 nm左右的Cu纳米粒子均匀分布在褶皱状片层结构的r GO表面,提高催化剂抗烧结性能。     

Selective kinetic deactivation model for methanol synthesis from simultaneous reaction of CO2 and CO with H2 on a commercial copper/zinc oxide catalyst

A kinetic model for the deactivation of copper/zinc oxide catalyst during the methanol synthesis has been developed. This model is of the Langmuir-Hinshelwood-Hougen-Watson type and considers two types of active sites for the deactivation of catalyst. One of the site types on copper is allocated for the deactivation of the catalyst due to carbon dioxide while another type is assigned for the deactivation of the catalyst due to carbon monoxide. The parameters of the deactivation rate equations based on the above concept have been determined using the experimental data of Hoffmann (1993). The validity of the deactivation model has been checked by comparing the results predicted by the model with experimental data different than of those used to evaluate the parameters of the model. The good agreement that noticed in this comparison confirmed the idea that CO and CO₂ are responsible at different extent for the deactivation of Cu/ZnO catalyst during methanol synthesis.     

Deactivation of a Pd/Al2O3 catalyst used in hydrodechlorination reactions: Influence of the nature of organochlorinated compound and hydrogen chloride

The deactivation of a 0.5 wt.% Pd on alumina catalyst used for the hydrodechlorination of tetrachloroethylene (TTCE), chlorobenzene (CBZ) and dichloromethane (DCM) in organic matrix in gas phase has been studied in this work. Experiments were carried out in a continuous fixed bed reactor, at a pressure range of 0.1–2 MPa. It was found that the reactivity and stability of the catalyst increases as pressure increases. Different compounds present quite different deactivation patterns: fast initial deactivation followed by a plateau for DCM and CBZ, continuous moderate deactivation for TTCE.The effect of hydrogen chloride was studied by adding to the reactor feed different amounts of hydrogen chloride, working at 225–300 °C.Fresh and used catalysts were characterised by nitrogen porosimetry, X-ray diffraction, transmission electronic microscopy, scanning electronic microscopy, thermogravimetry and temperature-programmed oxidation. Results indicate that carbonaceous deposits play a key role in the catalyst deactivation, being this phenomenon promoted by the presence of HCl.