Dibenzothiophene hydrodesulfurization by noble metal supported catalysts

The hydrodesulfurization of dibenzothiophene (DBT) is investigated at 240°C, under one atmosphere pressure of H₂ + DBT, in a DBT conversion range giving rise to a H₂S concentration between 30 and 200 ppm. The turnover number (TN) of platinum slightly decreases as the dispersion of platinum (Ptins) to Pt ratio = D (Pt)) increases from 0.01 to 0.7, whatever support (α-Al₂0₃, SiO₂, chlorinated γ-Al₂O₃, SiO₂-Al₂O₃, montmorillonite) was used. Furthermore, the TN is much lower for highly dispersed Pt/γ-Al₂O₃-C1 (D(Pt) = 0.9; ø (Pt) = 1.0 nm). Pt/TiO₂ (D(Pt) = 0.06 or D(Pt) = 0.34) reduced or re-reduced at 240°C has a higher TN than the preceding catalysts. Reduction or re-reduction of Pt/TiO₂, at 500°C results in only a relatively small decrease in the catalytic activity, in spite of the appearance of a strong metal-support interaction observed by several workers. For different supported metals on Al₂O₃, the TN follows the sequence: Pt > Ir > Ru > Re. Alloying Ir or Ru (25 to 30 at %) with Platinum results in a relatively small decrease in the TN (per one (Pt_s + Ir_s or Ru_s ) atom).The activity, per unit weight of catalyst, of an industrial Co-Mo/γ-Al₂O₃ sulfided catalyst (HR 306) is equivalent to that of 1 % Pt/γ-Al₃0₃ (D(Pt) = 0.7). The present platinum supported catalysts have a very low selectivity in hydrogenation (production of phenylcyclohexane, PCH < 1 %), except when supported by silica, SiO₂-Al₂O₃ or montmorillonite; the Co-Mo/γ-Al₂0₃ catalyst has a selectivity which is intermediate between Pt/γ-Al₂O₃ and Pt/SiO₂-Al₂O₃ or montmorillonite. The deactivation (decrease in activity versus the time en-stream) is lower for Co-Moγ-Al₃0₃ than for Pt/γ-Al₃O₃, but the addition of Ge to Pt/γ-Al₂O₃ gives rise to a more stable catalyst.     

Catalytic wet oxidation of p-chlorophenol over supported noble metal catalysts

Heterogeneous catalytic wet oxidation of aqueous p-chlorophenol (p-CP) solution was investigated at 453 K and 2.6 MPa in a slurry reactor. The performance of noble metal catalysts was compared with that of traditional manganese catalysts. Activated carbon supported catalysts showed significant higher activities for total organic carbon (TOC) reduction than those supported on alumina or cerium oxide. Pt was found to be the most active metal for p-chlorophenol oxidation. The activities of noble metal catalysts were found to correlate with heat of formation of metal oxides. CO₂ is the predominant oxidation product with formation of minor p-benzoquinone and acetic acid as intermediate compounds. Possible reaction pathway was also discussed.     

贵金属分子筛催化剂的润滑油脱蜡反应研究

制备了硅铝比不同、载体分别为ZSM-5和β分子筛的贵金属Pd催化剂,并对催化剂进行孔结构和酸性表征。以正十二烷为模型化合物分别评价该系列催化剂的加氢反应性能,同时以含蜡润滑油为原料,考察催化剂对润滑油的加氢脱蜡效果,结果表明,酸性和孔径适宜的ZSM-5贵金属催化剂具有较好的脱除长链大分子蜡的能力。     

Modification of the catalytic properties of supported noble metal catalysts by carrier doping

The influence of altervalent cation doping of TiO₂ carriers on the chemisorptive and catalytic properties of supported Pt and Rh crystallites has been investigated. It was observed that doping of the carrier with higher valence cations leads to suppression of the H₂ and CO chemisorption capacity of Pt catalysts, while their activity in hydrogenation and oxidation reactions is significantly reduced. The opposite effects were observed in the case of Rh catalysts supported on higher valence doped TiO₂. These catalysts were found to possess higher activity in CO and CO₂ hydrogenation, in aromatics hydrogenation and in CO and C₂H₄ oxidation. Their stability characteristics were also found to be superior to those of the undoped Rh/TiO₂ catalyst. These effects are believed to originate from an electronic type interaction at the metal-support interface, induced by doping, which results in electron transfer from the support to the metal crystallites.     

Impedance measurements in catalysis: charge transfer in titania supported noble metal catalysts

Hydrogen treatment of Pt/TiO₂ leads to an exceptional increase in electric conductivity even at moderate temperature presumably due to the formation of donor electrons during a superficial reduction process. Interestingly, after cooling to lower temperatures that are typically applied for catalytic reactions the observed high conductivity was largely preserved. The enhanced charge carrier density in titania is assumed to cause a considerable charge transfer between support and metal. In this work we show that this charge transfer is correlated with typical catalytic parameters (e.g. hydrogen adsorption capacity and catalytic activity for a hydrocarbon skeleton reaction). Based on these observations we suggest and discuss a modified charge transfer mechanism in addition to the decoration mechanism as a possible reason for the SMSI effect occurring during hydrogen treatment already at moderate temperatures. Dedicated to Konrad Hayek.     

Direct conversion of triglycerides to olefins and paraffins over noble metal supported catalysts

Deoxygenation of methyl esters and triglycerides was studied for production of either α-olefins or diesel components. The reactions were carried out in a reactive distillation fashion in which products are quickly removed from the reaction mixture in flowing He. The effects of He flow rate, reaction temperature, active component and support were studied. PtSnK supported on silica was found to be the best catalyst for selective production of α-olefins. Palm kernel oil and coconut oil were also deoxygenated to produce α-olefins or diesel components, depending on reaction conditions.     

Catalytic wet air oxidation of stearic acid on cerium oxide supported noble metal catalysts

Catalytic wet air oxidation (CWAO) of stearic acid was carried out in a batch reactor over noble metals (Ru, Pd, Pt, Ir) catalysts supported on ceria. The influence of reaction conditions such as temperature, oxygen pressure and stearic acid concentration were investigated. The reaction occurs via a complex mechanism. The molecule of stearic acid can be oxidized by successive carboxy–decarboxylation (R_nCOOH + O₂ → R_n−1COOH +CO₂) yielding essentially CO₂ (route A). It may also be oxidized after CC bond rupture within the alkyl chain, which gives rise to significant amounts of acetic acid besides CO₂ (route B). Pt/CeO₂ is a very active catalyst in the conversion of stearic acid and extremely selective to carbon dioxide (route A), while the mechanism via CC bond splitting is much more marked on Ru/CeO₂. The catalyst characterization indicates that both noble metal and CeO₂ particles remain stable during the reaction.     

Production of hydrogen for fuel cells by steam reforming of ethanol over supported noble metal catalysts

The catalytic performance of supported noble metal catalysts for the steam reforming (SR) of ethanol has been investigated in the temperature range of 600–850 °C with respect to the nature of the active metallic phase (Rh, Ru, Pt, Pd), the nature of the support (Al₂O₃, MgO, TiO₂) and the metal loading (0–5 wt.%). It is found that for low-loaded catalysts, Rh is significantly more active and selective toward hydrogen formation compared to Ru, Pt and Pd, which show a similar behavior. The catalytic performance of Rh and, particularly, Ru is significantly improved with increasing metal loading, leading to higher ethanol conversions and hydrogen selectivities at given reaction temperatures. The catalytic activity and selectivity of high-loaded Ru catalysts is comparable to that of Rh and, therefore, ruthenium was further investigated as a less costly alternative. It was found that, under certain reaction conditions, the 5% Ru/Al₂O₃ catalyst is able to completely convert ethanol with selectivities toward hydrogen above 95%, the only byproduct being methane. Long-term tests conducted under severe conditions showed that the catalyst is acceptably stable and could be a good candidate for the production of hydrogen by steam reforming of ethanol for fuel cell applications.     

Advanced metal oxide (supported) catalysts: Synthesis and applications

A variety of metal oxides catalysts are used in heterogeneous catalysis for chemical processes and have now been developed for their catalytic performance and durability. The heterogeneous catalysis is the most important technology in chemical industry as well as other environmental, energy applications, etc. This review examines recent advances at the preparation and applications of metal oxide particles, especially pertaining to catalytic enhancements for current and future chemical process such as Fischer–Tropsch process, alkylation, and transesterification and environmental applications such as the oxidation of volatile organic compounds and the reduction of NO_x.     

硫化铂族金属加氢催化剂的研究进展

硫化铂族金属催化剂为可提高有机液相加氢反应选择性的高效催化剂,能提高含羰基、羟基和卤素等官能团化合物催化加氢反应的选择性,应用广泛。综述了国内外负载型Pt和Pd等硫化贵金属催化剂的制备方法,包括采用H_2S和Na_2S无机硫化以及Ph_2S和DMSO(二甲基亚砜)等有机硫化剂进行硫化;综述了Pt和Pd硫化贵金属催化剂在有机液相催化加氢体系中的应用;并对硫化Pt族金属催化剂的硫化机理和催化机理进行探讨,展望了硫化贵金属催化剂的应用前景。     

Stability of supported metal and supported metal oxide combustion catalysts

Catalysts used for high-temperature combustion of light hydrocarbons must maintain high activity over long time intervals by avoiding excessive sintering and deactivation in the hot and corrosive combustion environment. The sintering resistance and chemical stability of catalytically active phases is a key technical problem that must be solved for the development of commercially viable combustion catalysts. All noble metals and transition metal oxides that are catalytically active rapidly sinter at temperatures required for high combustion rates. Advanced materials used in the development of stable catalysts include highly sintering-resistant hexaaluminate supports for dispersion of noble metals, chemically and thermally stable supporting oxides for active transition metal oxides, and single-phase, substitutionally activated, sintering-resistant complex metal oxides. This paper will review deactivating phenomena, such as sintering and vapor transport and assess recent progress in the development of durable combustion catalysts.     

Hydrodeoxygenation of guaiacol on noble metal catalysts

Hydrodeoxygenation (HDO) performed at high temperatures and pressures is one alternative for upgrading of pyrolysis oils from biomass. Studies on zirconia-supported mono- and bimetallic noble metal (Rh, Pd, Pt) catalysts showed these catalysts to be active and selective in the hydrogenation of guaiacol (GUA) at 100 °C and in the HDO of GUA at 300 °C. GUA was used as model compound for wood-based pyrolysis oil. At the temperatures tested, the performance of the noble metal catalysts, especially the Rh-containing catalysts was similar or better than that of the conventional sulfided CoMo/Al₂O₃ catalyst. The carbon deposition on the noble metal catalysts was lower than that on the sulfided CoMo/Al₂O₃ catalyst. The performance of the Rh-containing catalysts in the reactions of GUA at the tested conditions demonstrates their potential in the upgrading of wood-based pyrolysis oils.     

Preparation of highly effective ferric hydroxide supported noble metal catalysts for CO oxidations: From gold to palladium

Ferric hydroxide supported Pd catalyst prepared by a simple co-precipitation method without calcinations at elevated temperatures and only reduced at 50 °C possessed unexpectedly higher activity for CO oxidations even compared with that of supported Au catalysts. XRD and TEM results showed that the support was mixture of Fe(OH)_x and Fe₃O₄ and Pd was highly dispersed on it. XPS results showed that Pd existed as mixture of oxidation and metal state. The large amount of OH group on the supports may play an important role in O adsorption and activation.     

Catalytic decomposition of nitrous oxide over perovskite type solid oxide solutions and supported noble metal catalysts

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been investigated over various solid oxide solutions (SOS), La_0.8Sr_0.2MO_3– (M=Cr, Fe, Mn, Co or Y), La_1.8Sr_0.2CuO_4– and supported Pd, Pt catalysts. The reaction was carried out in a gradientless recycle reactor at 1 atm pressure with a feed gas containing about 0.5% N₂O (in helium). Among the various solid solutions, La_0.8Sr_0.2CoO_3– showed a maximum N₂O conversion of 90% at 600C. The order of activity observed for N₂O decomposition was La_0.8Sr_0.2CoO_3–>La_0.8Sr_0.2FeO_3–>La_1.8Sr_0.2CuO_4–> La_0.8Sr_0.2MnO_3–La_0.8Sr_0.2CrO_3–La_0.8Sr_0.2YO_3–. The activity of La_0.8Sr_0.2CoO_3– was compared with supported Pd, Pt and also with unsubstituted LaCoO₃ catalysts under similar reaction conditions. Among all the catalysts tested in this study, Pd/Al₂O₃ showed the lowest light-off temperature for N₂O decomposition. The activity of La_0.8Sr_0.2CoO_3– was found to be comparable to Pd/Al₂O₃ catalyst at temperatures above 500 C. The influence of added oxygen (about 4%) in the feed was examined over La_0.8Sr_0.2CoO_3– and Pd/Al₂O₃ catalysts and only in the case of cobalt catalyst was the conversion of N₂O decreased by 13%. By choosing varied sintering conditions, La_0.8Sr_0.2CoO_3– of different BET surface areas were prepared and the light-off temperature was found to decrease with increase in surface area. The results obtained over solid solutions are discussed on the basis of the cation mixed valency and oxygen properties of the catalyst.     

乙炔氢氯化反应无汞贵金属催化剂的研究进展

受“水俣公约”和环境保护政策约束,研究和开发新型无汞催化剂是保障我国乙炔法制备聚氯乙烯未来发展的核心环节。无汞催化剂包括贵金属催化剂、非贵金属催化剂和非金属催化剂,其中贵金属催化剂被认为是最具有工业化应用前景的催化剂。本文概述了近年来国内外乙炔氢氯化贵金属Au、Ru、Pd和Pt催化剂的研究进展,重点综述了不同催化剂的活性组分、催化机理及催化剂的改性方法等方面的研究,分析了不同改性方法的作用机制及不同催化剂改性的研究方向。研究表明,添加助剂或多金属复配、配体和离子液体的使用及载体改性均使贵金属催化剂的催化活性和稳定性得到一定程度提高,从而进一步增加了贵金属催化剂工业化应用的可能性。     

乙炔氢氯化反应贵金属无汞催化剂研究进展

概述近年来国内外乙炔氢氯化反应贵金属无汞催化剂的研究进展,主要探讨了催化剂的活性组分、载体及其对催化活性的影响,简要介绍催化剂失活原因与再生手段.多种贵金属的协同催化、载体处理方法的多样化、制备过程的条件优化是贵金属无汞催化剂未来的发展方向.     

Influence of ammonia on thiophene HDS at high pressures over noble metal catalysts for deep HDS applications

The thiophene hydrodesulfurization (HDS) activity of Pt/ASA, Pt/SiO₂, Ir/ASA and Ir/SiO₂ catalysts at thiophene concentrations of 300 ppm has been studied at 573 K and 20 bar. Pt/ASA showed the highest HDS activity. Nitrogen tolerance was investigated by co-feeding ammonia in gas phase concentrations from 10 to 1000 ppm. The amorphous silica alumina (ASA) supported catalysts were similarly strongly inhibited by the presence of ammonia, with even 10 ppm of ammonia causing a significant drop in activity, despite widely different dispersions. The SiO₂ supported catalysts were less severely affected by the presence of ammonia.     

负载型金属配合物催化硅氢加成反应研究进展

硅氢加成反应是有机硅化学中制备含Si-C化合物的一类重要反应。综述了硅氢加成反应中负载型金属配合物催化剂的种类、催化性能及催化机理,并展望了此类反应的研究前景,表明探索价廉高效的硅氢加成催化体系将是这一领域的主要研究方向。     

纳米贵金属催化剂制备的研究进展

介绍了化学还原法、电化学法、化学气相沉积法、微波辅助法和模板法等纳米贵金属催化剂的制备方法,论述了各种方法的制备过程和研究进展,指出纳米贵金属催化剂现有的制备技术还不够成熟,较难实现工业化;纳米催化剂性能稳定控制技术尚未掌握,在空气中极易被氧化、吸湿和团聚,性能不够稳定等问题。需要在提高催化反应效率、优化反应途径和提高反应速率等方面进行广泛深入研究和探讨,尽早使纳米贵金属催化剂实用化。     

Hydrotreatment of jatropha oil over noble metal catalysts

Jatropha oil is a promising nonedible feedstock for producing renewable diesel. In this work, the hydrotreatment processing of jatropha oil was investigated. Instead of using conventional alumina-supported Co–Mo, Ni–Mo, and Ni–W catalysts that need sulfidation pretreatment, noble metals such as Pd and Ru were chosen. Trials were performed in an isothermal trickle-bed reactor and the reaction conditions were as follows: temperature 603–663?K, weight hourly space velocity (WHSV) 1 to 4/h, pressure 1.5–3?MPa, and H₂/oil ratio 200–800 (v/v). Yield of n-C₁₅ to n-C₁₈ hydrocarbons was maximized (70.3 and 43.8% for Pd/Al₂O₃ and Ru/Al₂O₃, respectively) at the following conditions: T?=?663 K, WHSV?=?2/h, P?=?3?MPa, and H₂/oil ratio?=?600 (v/v). Since Ru favored cracking reactions to a larger extent than Pd, the yield of C₁₅ to C₁₈ hydrocarbons over Ru/Al₂O₃ was lowered. Using simple first-order plots for oil conversion, activation energies for the hydrotreating process over Pd/Al₂O₃ and Ru/Al₂O₃ were found and they were equal to 109 and 121?kJ/mol, correspondingly.