不同载体对Pt-Sn催化剂丙烷催化脱氢性能影响

分别以Hβ分子筛和γ-Al₂O₃为载体,采用浸渍法制备不同Sn含量的负载型Pt-Sn双组分丙烷催化脱氢催化剂。在固定床微反装置上对制备的催化剂进行活性评价,并采用NH₃-TPD方法测定催化剂表面酸量和酸强度分布。结果表明,负载型Pt-Sn/Hβ和Pt-Sn/γ-Al₂O₃催化剂对丙烷催化脱氢反应性能与Sn含量密切相关,弱酸中心的存在对丙烷催化脱氢反应有利,对于特定的Pt-Sn体系,γ-Al₂O₃为载体的催化剂性能优于Hβ分子筛为载体的催化剂,当负载Sn质量分数为0.9时,Pt-Sn/γ-Al₂O₃催化剂性能最好。     

Model oxide supports for studies of catalyst sintering at elevated temperatures

Sintering is one of the most important causes for loss of catalytic activity when catalysts are subjected to elevated temperatures, as in automotive exhaust or during catalytic combustion. Herein we report a novel form of model catalyst for sintering studies at elevated temperatures. These model catalysts based on disks of SiO₂ (quartz) and Al₂O₃ (sapphire) allow sintering temperatures of > 900 °C to be studied. High resolution scanning electron microscopy (SEM) was used for the study of these catalysts. Using modern in-lens backscatter electron detection operating at low voltages, high contrast images can be obtained of the metal catalyst on these model oxide supports. Model catalysts make it possible to observe the same area of the sample, before and after sintering, which is essential to gain mechanistic insights into the sintering phenomena. Our results show that while Ostwald ripening is the dominant mechanism for Pd sintering at 900 °C, we see evidence for the migration of particles as large as 50 nm on the alumina surface.     

Characterization and activity of Pt-Sn/Al2O3 catalysts of different preparation: coimpregnation and new Pt-Sn precursor

A new bimetallic Pt-Sn compound [Pt(NH₃)₄][SnCl₆] has been used as precursor for the preparation of supported Pt-Sn/Al₂O₃ catalysts. A comparison of a dried sample with that prepared by coimpregnation displays different behaviour in TPR, chemisorption. The initial catalytic activity properties were checked in the reactions of cyclohexane dehydrogenation and cyclopentane ring opening, whilen-hexane skeletal reactions were used to probe the quasisteady-state activity. The catalyst prepared via the Pt-Sn complex precursors exhibited some-what lower specific activity. This fact, together with enhanced olefin formation fromn-hexane was taken as an indication of lower amount of contiguous Pt atoms and some electronic interaction between Pt and Sn in that catalyst.On leave from Fachhochschule Ostfriesland, D-26723 Emden, Germany.     

IR studies of Re2O7 metathesis catalysts supported on alumina and phosphated alumina

FTIR data from Re₂O₇/-Al₂O₃ metathesis catalysts indicate that a low Re contents ReO₄ ions have predominantly reacted with basic surface OH groups, while at higher Re₂O₇ loadings they have also reacted with neutral and more acidic OH groups.On phosphated -Al₂O₃ the phosphate has reacted with the more acidic OH groups on the -Al₂O₃; in catalysts based on this support, the ReO₄ ^– ions have also reacted with the phosphorus-bonded OH groups already at low Re₂O₇ loadings, resulting in more active catalysts.     

Thermal stability of palladium on ceria-doped alumina

Several palladium on alumina and ceria/alumina catalysts were prepared and oxidized in air between 400 and 1000°C. The metal dispersion was determined by hydrogen titration of adsorbed oxygen. Dispersions above 50% were maintained on 0.2% Pd/Al₂O₃ up to 900°C. Adding 5.0% ceria, or increasing the metal loading to 2.5%, greatly reduces the thermal stability of the palladium, such that the dispersion falls rapidly at 600°C. The rates of methane oxidation (moles of CO₂/g Pd h) at 250°C and 5% excess oxygen are nearly equal on 0.22–2.50% Pd/3.5–5.2% CeO₂/Al₂O₃, dispersion 14–42%, and 0.20–0.46% Pd/Al₂O₃, dispersion 59–86%, but are 10 to 20 times lower than the rate on 2.3% Pd/Al₂O₃, dispersion 11%. The lower rate of methane oxidation on ceria-promoted and highly dispersed palladium on alumina might be due to the conversion of the palladium into less active palladium oxide during reaction.     

Recovery of high surface area alumina from aluminium dross tailings

Aluminium dross tailings (ADT), a chemical waste from a factory producing aluminium in Egypt, was used for the recovery of the aluminium content in the form of alumina (Al₂O₃). Extraction of the aluminium was carried out via atmospheric‐ and high‐pressure leaching with caustic soda. Then, it was separated from the sodium aluminate solutions thus obtained, using six different precipitation methods. The precipitates were filtered, washed, dried and calcined at 600 °C to produce the test aluminas. The precipitates and the calcination products were analysed for their chemical and crystalline phase compositions. The calcination products (aluminas) were subjected to sorpometry for surface area determination, and to particle sizing. The results indicated that highly pure (SiO₂ < 0.53% and Na₂O < 0.14%), well‐defined crystalline γ‐aluminas of high surface areas (>200 m² g⁻¹) and uniform small crystallite sizes (60–70 Å) could be efficiently recovered from ADT. Optimal recovery conditions were examined and determined. © 2000 Society of Chemical Industry     

活性氧化铝在FCC催化剂中的应用研究

采用N^₂吸附法、IR和XRD等手段研究了活性氧化铝用于催化裂化(FCC )催化剂中的性能。结果表明,在FCC催化剂制备及应用条件下,活性氧化铝保持比较稳定的比表面积、孔容和酸性等性能。磷易与活性氧化铝作用,分子筛与磷的作用存在一个逐步平衡的过程;氧化铝有利于改善基质的孔结构;对以铝溶胶为粘结剂制备的催化剂进行磷改性处理,催化剂基质与活性组分分子筛上的磷含量基本相当。     

溶胶-凝胶法制备丙烷脱氢Pt-Sn/Al2O3催化剂性能

采用溶胶-凝胶法和浸渍法制备了不同Sn组分含量的Pt-Sn/Al₂O₃催化剂, 通过XPS、TEM和H₂吸附等物化表征手段对催化剂进行了表征,考察了无H2存在下的催化剂丙烷脱氢性能。结果表明,采用溶胶-凝胶法导致一部分Sn组分被包埋,减少高温还原条件下Sn组分的析出而提高催化脱氢活性。在550 ℃反应 6.5 h的条件下,丙烯收率36.3%,丙烯选择性达98.8%。     

高铝粉煤灰负载锰基催化剂的催化氧化NO性能研究

氮氧化物催化氧化是烟气脱硝技术的一个重要发展方向。本工作以具有球形镂空结构的预处理后高铝粉煤灰为载体,以硝酸锰为活性组分源,采用溶胶凝胶法制备锰基NO氧化催化剂,采用扫描电镜(SEM)、X射线衍射仪(XRD)、N2物理吸附、H2程序升温还原分析仪(H2-TPR)和X射线光电子能谱(XPS)等分析测试手段对催化剂的NO催化氧化性能进行深入研究。结果表明,载体粒径、锰负载量、硝酸锰凝胶煅烧温度以及NO催化氧化温度对催化剂催化活性均有较大影响。当载体粒径在100~200目(150~75 μm)、锰负载量为8wt%、硝酸锰凝胶煅烧温度为500℃、NO催化氧化温度290℃时,NO催化氧化效果最好,氧化率达到77.8%。SEM结果显示,溶胶凝胶法制备的氧化锰粒子在100~200 nm,且相对均匀负载在载体上。N2-物理吸附表明,催化剂的孔结构主要为介孔,并呈现H3型回滞环。锰基催化剂上化学吸附氧Oβ的占比和Mn4+浓度随着锰负载量的增加先增大后减小,此趋势与NO催化性能变化趋势一致,表明Oβ和Mn4+是影响NO催化氧化效果的决定因素。     

The electro-oxidation of carbon monoxide, hydrogen/carbon monoxide and methanol in acid medium on Pt-Sn catalysts for low-temperature fuel cells: A comparative review of the effect of Pt-Sn structural characteristics

The electrocatalytic activity for CO, H₂/CO and CH₃OH oxidation of Pt-Sn catalysts has been extensively investigated for a possible use as anode materials for low-temperature fuel cells. This paper presents an overview of the relationship between the structural characteristics of the catalysts (catalyst composition, degree of alloying, presence of oxides) and their electrocatalytic activity for the oxidation of the different fuels.     

高表面积高分散度铜基催化剂的制备及其性能研究

本文对传统共沉淀法进行改进，成功制备出高表面积（383.87 m2/g）高分散度（42.74%）的新型Cu-O-Al骨架结构催化剂，表征结果表明，改进后的制备方法可以有效增大催化剂比表面积和孔容，并使得催化剂上铜物种的颗粒更小、分散度更高，进而表现出较高的催化活性。同时由于形成了Cu-O-Al骨架结构，可以显著抑制铜物种的移动，进而提高催化剂的稳定性。本文以成本较低的空气作为氧源，在典型催化剂（CuAl3）上反应温度300 ℃、较高液时空速2 h-1下，MOP最佳转化率为85.2%，MOA选择性为55.7%，且稳定运行32 h，而该空速下传统浸渍法制备的催化剂已基本无催化活性。     

规整填料型加氢脱硫催化剂的制备及性能评价

用电化学方法制备多孔氧化铝膜,并负载Mo-Co活性组分制得了金属支撑-多孔层规整填料型加氢催化剂。采用BET和SEM技术表征了多孔性氧化铝膜的物理结构,并考察了电解及后处理条件的影响。结果表明,电解液浓度、氧化时间、水封时间、水封温度等对多孔氧化铝膜的比表面积影响显著。采用二次氧化的方法,在质量分数为4%的草酸电解液、氧化时间1 h、80℃水封3 h条件下,所制备的多孔氧化铝膜具有相对较大的比表面积。汽油重馏分加氢反应结果表明该类催化剂具有较高的催化活性和选择性。     

Textural properties evolution of Ir and Ru supported on alumina catalysts during hydrazine decomposition in satellite thruster

Ir/Al₂O₃, Ru/Al₂O₃, and Ir-Ru/Al₂O₃ catalysts with total metallic contents of 30% in mass were prepared by an incipient wetness method. The characterization of these materials, before and after their use for hydrazine decomposition in a satellite thruster, was performed by measurement techniques of specific surface area, volume and pores size distribution, H₂ chemisorption, TEM and basic chemical analysis. An average decrease of 11% in the BET surface area was observed, independent of the catalyst composition. The total specific pore volume remained unchanged because the volume reduction in the size range diameters between 1.0 and 10 nm was compensated by the increase in the diameters size range between 10 and 100 nm. A reduction of the H₂ quantity adsorbed on the Ir/Al₂O₃ catalyst can be explained by the metal loss through erosion as well as by its partial occlusion within the pores of the alumina support. On the other hand, catalysts containing Ru showed an increase of H₂ chemisorbed amount, attributed to a more complete reduction of this material after hydrazine decomposition, in spite of the erosion and occlusion losses. Such observations were confirmed by TEM, which showed a great stability of the distributions of the metallic particle sizes in all catalysts.     

Preparation of alumina–silica bimodal pore catalysts for Fischer-Tropsch synthesis

The bimodal pore structure support has excellent advantages in solid catalysis reaction because the large pores provide pathways for rapid molecular transportation and small pores provide a large active surface, contributing to high diffusion efficiency and high dispersion of supported metal simultaneously, A multi-functional bimodal pore catalyst support, alumina-silica bimodal pore support, was prepared from polymer complex solution and silica gel. The obtained bimodal pore support had two kinds of main pores, decreased pore volume and enlarged specific surface area, comparing the original silica gel. This kind of bimodal pore support was applied in slurry phase Fischer-Tropsch synthesis, where cobalt was supported as active metal. Alumina-silica bimodal pore catalyst exhibited high catalytic activity and favorite selectivity, due to the spatial effects of bimodal pore structure and chemical effects of coexisting alumina, which formed the new small pores of bimodal pore support.     

Hydrogen sulphide oxidation over teflon treated activated alumina and titanium dioxide catalysts

Commercial activated alumina and titanium dioxide catalysts were treated with Teflon to reduce the negative effects of water vapour on the oxidation of hydrogen sulphide by sulphur dioxide (Claus Reaction) near the sulphur dew point. The tests were conducted at 200°C and 130°C (108 kPa), with and without 30% water vapour in the feed gas. An alumina/Teflon composite catalyst was found to be superior to both untreated commercial catalysts at 130°C. This improvement was probably due to an increase in macroporosity rather than to a wetproofing effect. At 200°C, the performance of the composite was similar to that of the untreated titanium dioxide which in turn was superior to the untreated activated alumina.     

铅/氧化铝催化剂的制备研究

工业上应用最广的合成吡啶的催化剂是Pb/ZSM-5催化剂.研究了在铅/氧化铝(Pb/Al2O3)催化剂上的醛氨缩合生成吡啶的反应,考察了不同氧化铝载体、铅负载量、催化剂焙烧温度对催化剂性能的影响,并对催化剂进行了XRD表征.结果表明:在氧化铝载体比表面170～185 m2/g、孔容1.6～2.0 cm3/g、平均孔径34 nm,铅负载量在质量分数2.5%～4.0%,催化剂焙烧温度在500～550℃时,制备的催化剂性能最好,烷基吡啶的收率可达90%.     

Silica–alumina catalysts for polymerization of cyclic siloxanes

Silica–alumina catalysts of varying acidity were used for polymerization of hexamethyl cyclotrisiloxane and octamethyl cyclotetrasiloxane monomers (cyclic trimer and tetramer, respectively). Acidic sites of silica–alumina are responsible for the polymerization and variation in the acidity of the catalyst were shown to influence the polymerization significantly. Mordenite type zeolites with low silica-to-alumina ratio (∼5) gave low yields of polymer from tetramer and zeolite ZSM-5 with a much higher silica-to-alumina ratio (∼40) was found to be a very efficient catalyst for polymerization. Studies on the effect of water on the polymerization suggested that the polymerization (rate and yield) depended to some extent on the amount of water present in the system. The products were characterized using FTIR, ¹H-NMR, ²⁹Si-NMR, and GPC techniques. A plausible mechanism for polymerization of cyclic siloxane monomers on silica–alumina catalysts was proposed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 629–635, 1998     

Comparison of metathesis activity of catalysts prepared by anchoring of MoO2(acac)2 on various supports

The properties and olefin metathesis activity of molybdena–alumina, molybdena–silica–alumina and molybdena–silica catalysts prepared by anchoring of MoO₂(acac)₂ complex were compared. The specific activity obtained for molybdena–silica–alumina system is higher than that of molybdena–alumina and molybdena–silica catalysts. This statement concerns also the catalysts treated with tetramethyltin     

低碳烷烃脱氢催化剂的研究进展

叙述了低碳烷烃脱氢研究的发展现状。介绍了低碳烷烃脱氢的方法,包括无氧脱氢法和有氧脱氢法。用于低碳烷烃脱氢的Pt基催化剂主要缺点是稳定性差、选择性低。分别介绍了Pt基催化剂的活性组分、载体及不同助剂添加对Pt-Sn催化剂性能的影响。简单介绍了铬系催化剂以及国外低碳烷烃脱氢的技术工艺。最后对低碳烷烃脱氢催化剂的发展趋势做了展望。     

Propane Dehydrogenation over a Commercial Pt-Sn/Al2O3 Catalyst for Isobutane Dehydrogenation: Optimization of Reaction Conditions

The applicability of a commercial Pt-Sn/Al₂O₃ isobutane dehydrogenation catalyst in dehydrogenation of propane was studied. Catalyst performance tests were carried out in a fixed-bed quartz reactor under different operating conditions. Generally, as the factors improving propane conversion decrease the propylene selectivity, the optimal operating condition to maximize propylene yield is expected. The optimal condition was obtained by the experimental design method. The investigated parameters were temperature, hydrogen/hydrocarbon (H₂/HC) ratio and space velocity, being changed in three levels. Constrains such as the susceptibility of the catalyst components to sintering or phase transformation were also taken into account. Activity, selectivity and stability of the catalyst were considered as the measured response factors, while the space-time-yield (STY) was considered as the variable to be optimized due to its commercial interest. A STY of 16 mol·kg^-1·h^-1 was achieved under the optimal conditions of T 620℃, H₂/HC 0.6 and, weight hourly space velocity (WHSV) 2.2 h^-1. Single carbon-carbon bond rupture was found to be the main route for the formation of lower hydrocarbon byproducts.