Preparation and Study of Pd Catalysts Supported on Activated Carbon Cloth (ACC) for Direct Synthesis of H2O2 from H2 and O2

Activated carbon cloths (ACCs) were used as supports for Pd catalysts. The catalyst preparation was carried out by the impregnation method using acidic solution of palladium dichloride (PdCl₂) as metal precursor. The effects of the oxidation state of the loaded metal, heat treatment of the catalysts in different atmosphere (H₂, air) at different temperatures and surface chemistry of the support on the catalyst characterizations and the catalytic activities were investigated. Wet oxidation of ACC was done by nitric acid in order to induce oxygen-containing surface functional groups. Surface chemistry of the support and oxidation state of the metallic phase was investigated by means of XPS, TPD, SEM, DTA and TGA tests. Direct synthesis of hydrogen peroxide from H₂ and O₂ was performed batch wise in a stainless steel autoclave. The reactions were conducted under high pressure (38 bar) at 0 °C and methanol was used as reaction medium. The direct synthesis results showed that the oxygen-containing surface functional groups increase the selectivity of the catalysts by reducing the rate of water production. Existence of the oxidized state of Pd (PdO) also makes the catalyst more selective than the corresponding zerovalent state (Pd0). PdO affected on selectivity by increasing the rate of H₂O₂ production and reducing the amount of production of water, simultaneously.     

Role of Feed Composition on the Performances of Pd-Based Catalysts for the Direct Synthesis of H2O2

The role of feed composition, in particular the O₂ to H₂ ratio and the concentration of CO₂, has been investigated on two Pd/N-CNT and PdAu/N-CNT catalysts. There is a significant influence on the catalytic behavior, but the effect is complex, and cannot be analyzed in terms of conventional kinetic approaches, due to the presence also of a change in the catalyst characteristics as a function of time on stream (in the fresh samples). Depending on the O₂ to H₂ feed and catalyst nature, the trend of productivity and selectivity varies differently with the time on stream. A simplified kinetic model has been developed which well accounts for the observed behavior. The model is based on the concepts that (i) the selective sites are associated to small Pd terraces covered by chemisorbed O₂ with limited sites for H₂ chemisorption, and (ii) during the reaction, due to catalyst modifications, a change of available chemisorbed H₂ for unselective parallel formation of H₂O and H₂O₂ hydrogenolysis occurs. The changes during time on stream are related to (i) the removal of PVA capping agent, with an initial increase of available Pd surface area leading also to an increase of the H₂ chemisorption sites for unselective parallel conversion and consecutive H₂O₂ hydrogenolysis, and (ii) for the longer times on stream aggregation of some Pd nanoparticles leading to some decrease in the available Pd surface area. The isolation of Pd ensembles by Au (PdAu/N-CNT) influences this trend of productivity and selectivity to H₂O₂ as a function of the O₂ to H₂ ratio in the feed. The change is consistent with the model indicated above.     

Supported Pd and PdAu Nanoparticles on Ti-MCM-41 Prepared by a Photo-assisted Deposition Method as Efficient Catalysts for Direct Synthesis of H2O2 from H2 and O2

An efficient methodology to synthesize highly active Pd nanoparticles using a single-site photocatalyst under UV-light irradiation has been developed for the synthesis of hydrogen peroxide (H₂O₂) from H₂ and O₂. By the photo-assisted deposition (PAD) method, Pd precursor can be deposited directly on the photo-excited tetrahedrally coordinated metal-oxide moiety within the silica frameworks, and subsequently transformed into Pd nanoparticles by H₂ reduction. The mean diameter of the deposited Pd particles determined by CO adsorption and the catalytic activities in the direct synthesis of H₂O₂ were strongly dependent on the preparation method and kind and/or amount of metal-oxide moieties. Here, the use of Ti-containing mesoporous silica (Ti/Si = 0.01) acted as a most efficient support for the above reaction. The PAD method also provides PdAu bimetallic nanoparticles from an aqueous solution of mixture of PdCl₂ and HAuCl₄. The PdAu/Ti-MCM-41 catalyst prepared by the PAD method was shown to perform significantly better activity than the pure Pd/Ti-MCM-41.     

H_3O_(40)PW_(12)/SiO_2固体酸催化剂的合成与性能研究

采用溶胶-凝胶法合成H3O40PW12/SiO2固体酸催化剂,通过正交实验,考察磷钨酸(H3O40PW12)负载量、水与正硅酸乙酯的物质的量之比、乙醇与正硅酸乙酯的物质的量之比、水解温度四个主要影响因素对负载型H3O40PW12/SiO2固体酸催化剂合成的影响,结果表明,乙醇与正硅酸乙酯的物质的量之比对催化剂活性影响最大,依次水与正硅酸乙酯的物质的量之比、磷钨酸的负载量、水解的温度。通过FTIR、XRD、TGA法对H3O40PW12/SiO2固体酸催化剂的性能进行表征,结果表明,磷钨酸均匀的负载在SiO2上,仍保持原有杂多酸的结构,催化剂的活性较高。     

氢氧直接合成过氧化氢催化剂研究进展

从性组分和载体两方面,总结了近年来氢氧直接合成过氧化氢催化剂的研究进展,重点介绍了Au-Pd、Pt-Pd双金属催化剂在氢氧直接合成过氧化氢中的应用研究。指出负载型纳米双金属催化剂将是氢氧直接合成过氧化氢催化剂研究的发展方向。摘要：从活性组分和载体两方面，总结了近年来氢氧直接合成过氧化氢催化剂的研究进展，重点介绍了Au—Pd、Pt—Pd双金属催化剂在氢氧直接合成过氧化氢中的应用研究。指出负载型纳米双金属催化剂将是氢氧直接合成过氧化氢催化剂研究的发展方向。     

Reactivity Aspects of SBA15-Based Doped Supported Catalysts: H2O2 Direct Synthesis and Disproportionation Reactions

Pd and PdAu catalysts supported on SBA15 and SiO₂ were prepared and investigated for H₂O₂ direct synthesis in a batch autoclave (10 °C and 17.5 bar) and in the absence of halides and acids. The SiO₂ supported catalysts exhibited inferior performances compared to the mesoporous ordered SBA15. A good control of both the catalysts dispersion and nanoparticle stability was achieved using SBA15. Catalysts were doped with bromine, a promoter in the H₂O₂ direct synthesis. Productivity and selectivity decreased when bromine was incorporated in the catalysts, thus indicating a possible poisoning due to the grafting process. A synergetic effect between Pd and Au was observed both in presence and absence of bromopropylsilane grafting on the catalyst surface. Three modifiers of the SBA15 support (Al, CeO₂ and Ti) were chosen to elucidate the influence of the surface properties on metal dispersion and catalytic performance. Higher productivity and selectivity were achieved incorporating Al into the SBA15 framework, whereas neither Ti nor CeO₂ improved H₂O₂ yields. The enhanced performance observed for the Prau/Al–SBA15 catalysts was attributed to the increased number of Brønsted acid sites. A modification of this catalyst with bromine was confirmed to impair both productivity and selectivity, possibly due to the broader particle size distribution and the poor stability of the metal nanoparticles, as demonstrate by transmission electron microscopy (TEM) images. H₂O₂ disproportionation was also investigated. A much slower reaction rate was observed compared to the H₂O₂ production, suggesting that the major contributor in the process of H₂O₂ destruction must be connected to the hydrogenation reaction.     

Direct Oxidation of H2 to H2O2 and Decomposition of H2O2 Over Oxidized and Reduced Pd-Containing Zeolite Catalysts in Acidic Medium

Both the conversion and H₂O₂ selectivity (or yield) in direct oxidation of H₂-to-H₂O₂ (using 1.7 mol% H₂ in O₂ as a feed) and also the H₂O₂ decomposition over zeolite (viz. H-ZSM-5, H-GaAlMFI and H- ) supported palladium catalysts (at 22 °C and atmospheric pressure) are strongly influenced by the zeolite support and its fluorination, the reaction medium (viz. pure water, 0.016 M or 1.0 M NaCl solution or 0.016 M H₂SO₄, HCl, HNO₃, H₃PO₄ and HClO₄), and also by the form of palladium (Pd⁰ or PdO). The oxidized (PdO-containing) catalysts are active for the H₂-to-H₂O₂ conversion and show very poor activity for the H₂O₂ decomposition. However, the reduced (Pd⁰-containing) catalysts show higher H₂ conversion activity but with no selectivity for H₂O₂, and also show much higher H₂O₂ decomposition activity. No direct correlation is observed between the H₂-to-H₂O₂ conversion activity (or H₂O₂ selectivity) and the Pd dispersion or surface acidity of the catalysts. Higher H₂O₂ yield and lower H₂O₂ decomposition activity are, however, obtained when the non-acidic reaction medium (water with or without NaCl) is replaced by the acidic one.     

Hydrogen Spillover in Ga2O3–Pd/SiO2 Catalysts for Methanol Synthesis from CO2/H2

The hydrogenation of CO₂ was investigated on Ga₂O₃-promoted Pd/SiO₂ catalyts and mechanical mixtures of Ga₂O₃/SiO₂ and Pd/SiO₂ catalysts (H₂/CO₂ = 3; P = 3.0 MPa; T = 523 K). By means of the latter it was possible to demonstrate that atomic hydrogen, H_s, can be generated by Pd⁰ far from Ga₂O₃, and move (spill-over) there to reach the other reactive species (formates) and complete the reaction cycle. The reaction results indicate that (as also evidenced by in situ FTIR) the Ga₂O₃-Pd/SiO₂ catalyst works as a true bi-functional system. The metal-promoter intimacy is not decisive in terms of the catalytic chemistry of the system, but the closeness between the Pd crystallites and the Ga₂O₃ surface patches boost the activity, owing to a minimized effort in the H_s supply to the latter.     

Direct Decomposition of N2O over Cesium-doped CuO Catalysts

A series of Cs promoted copper oxide catalysts were prepared by co-precipitation method and tested for the direct decomposition of nitrous oxide (N₂O). The Cs promoted catalysts were more active particularly with a molar ratio of Cs/Cu at 0.1 compared to bulk CuO. Methods of XRD, BET, XPS, H₂-TPR, and N₂O-TPD were used to characterize these catalysts to evaluate structure activity relationship. The characterization results indicated that the addition of Cs could improve the reduction of Cu²⁺–Cu⁰ by facilitating the desorption of adsorbed oxygen species, during the N₂O decomposition. The influences of oxygen and steam on N₂O decomposition over these catalysts were also studied.     

Decomposition of H2O2 by Iron Centered Catalysts

The kinetics and mechanism of the catalytic decomposition of H₂O₂ by Fe³⁺ ion, haemin and catalase are discussed. A general mechanism is set up. The kinetic features of the three catalytic systems are discussed in terms of this mechanism.     

The Active Phase in the Direct Synthesis of H2O2 from H2 and O2 over Pd/SiO2 Catalyst in a H2SO4/Ethanol System

In an effort to determine the active state of supported palladium for the direct formation of H₂O₂ from H₂ and O₂, the catalytic behavior of Pd⁰/SiO₂, PdO/SiO₂ and partially reduced PdO/SiO₂ was determined. The results obtained in an ethanol slurry, with chloride ions and H₂SO₄ being present, showed that the PdO/SiO₂ catalyst was almost completely inactive for the formation of H₂O₂ at 10 °C. The Pd⁰/SiO₂ catalyst exhibited the highest activity for H₂O₂ formation, and the PdO/SiO₂ material, reduced under very mild conditions, exhibited an intermediate activity. The state of Pd on the three catalysts was characterized by XRD, TEM and XPS methods. Only Pd⁰ (the metal phase) and PdO were observed on Pd⁰/SiO₂ and PdO/SiO₂, respectively. As expected, with the partially reduced PdO/SiO₂ catalyst, both Pd⁰ and PdO phases were evident. The TEM results revealed that the Pd⁰ particles decorated the larger PdO particles. The results reported here support the role of metallic palladium, rather than the oxide, as the active phase for the direct formation of H₂O₂.     

制备钴镍黄铁矿作为固体氧化物燃料电池的耐硫阳极

硫钴化合物具有优良的光学、电学和磁学性能,是近几年的研究热点,本文以(Co,Ni)8S9-MoS_2为阳极催化剂制备的固体氧化物燃料电池在800℃H_2-H_2S中不仅能稳定运行,而且与纯H2相比,当阳极气体中含有25μg/g的H_2S时电池的性能有明显的提升,说明H_2S的存在能提升阳极的电化学活性。     

Bi2O3电极的制备及其选择性氧化苯甲醇性能研究

采用滴凃法和电沉积法制备了Bi2O3薄膜电极,运用场发射扫描电子显微镜和X射线衍射仪对其进行了表征。在水相中以苯甲醇选择性氧化合成苯甲醛为模型反应,研究Bi2O3薄膜的催化性能。其中电沉积法制备的Bi2O3薄膜电极在水相溶液中表现出优异的电催化选择性氧化性能,苯甲醇的转化率最高,并且在外加偏压为2 V时达到了最高的苯甲醛选择性和苯甲醛收率。     

Metal Exchanged ZSM-5 Zeolite Based Catalysts for Direct Decomposition of N2O

Co+Pt/ZSM-5 and Ag+Pt/ZSM-5 type catalysts were prepared by ion exchange method followed by calcination. These Co and Ag based catalysts, promoted by a small amount of Pt have been studied for their catalytic activity towards N₂O decomposition. Both the catalysts show high catalytic activity, however, cobalt–platinum based catalyst shows relatively better activity at higher temperature. At 550 °C almost 100% conversion of N₂O is achieved over Co+Pt/ZSM-5 with a maximum of 0.08479 mmole of N₂O decomposed per gram of the catalyst per unit time. These catalytic materials have been characterized for their structure, composition, morphology and other details, using XRD, SEM, EDX, ICP, BET techniques. Much improved catalytic activity for the bimetallic zeolite than the mono-metal containing compositions clearly demonstrate the synergistic effect of these transition metals, while high surface area of ZSM-5 is also responsible for the improved N₂O decomposition activity.     

一步法合成二甲醚双功能催化剂的研究进展

从一步法制二甲醚双功能催化剂的结构出发,综述了传统复合型和新型双层结构、核壳结构催化剂的制备、结构和性能的研究进展,并展望了双功能催化剂的发展趋势。     

H3PW12O40/Al2O3催化合成丙烯醛

采用等体积浸渍法制备了具有Keggin结构的杂多酸H3PW12O40/Al2O3催化剂,用IR、XRD、BET等方法对催化剂进行了表征。同时利用常压连续流动的固定床反应器考察该催化剂对甘油制备丙烯醛的工艺条件,重点考察了催化剂的种类、杂多酸的负载量、反应温度等条件对反应的影响。结果表明,由甘油制备丙烯醛的较优条件为：当催化剂为H3PW12O40/Al2O3,负载量为40%,反应温度为330℃时,丙烯醛的选择性可达83.7％,甘油的转化率为100％。     

Synthesis and Structural Characterization of SiO2-Supported PtFe Catalysts Prepared from PtFe2(C8H12)(CO)8

Fourier transform infrared (FTIR) and extended X-ray absorption fine structure (EXAFS) spectroscopies were used to characterize the species formed following deposition of a PtFe₂(COD)(CO)₈ cluster on SiO₂ and removal of the organic ligands. The results indicate that the PtFe₂(COD)(CO)₈ cluster initially adsorbs weakly on the SiO₂ surface but loses a fraction of the organic ligands during aging under N₂ and thus becomes bonded to the surface. The PtFe₂ cluster core remains nearly intact during this process. The organic ligands can be further removed from freshly impregnated species by thermal treatments in either He or H₂ at 350 °C. Both treatments lead to the formation of bimetallic surface species with average dimensions on the order of 1 nm. However, these PtFe bimetallic species undergo substantial structural changes under CO oxidation conditions.     

H_3PW_(12)O_(40)/TiO_2催化合成对羟基苯甲酸丁酯的研究

采用溶胶-液相法制备了H3PW12O40/TiO2复合催化剂,用FT-IR分析方法对催化剂进行了结构表征。以对羟基苯甲酸和正丁醇为原料合成了对羟基苯甲酸丁酯,考察了反应物配比、催化剂用量、反应时间及催化剂的重复使用性能对产品收率的影响。实验结果表明,合成对羟基苯甲酸丁酯的较优反应条件为:对羟基苯甲酸0.1 mol,n(对羟基苯甲酸)∶n(正丁醇)=1.0∶5.0(摩尔比),催化剂的用量为1.2 g,反应时间4.0 h。上述条件下,对羟基苯甲酸丁酯的收率可达85.0%以上。     

Combinatorial Design of Al2O3 Supported Au Catalysts For Preferential CO Oxidation

Multi-component Au/Al₂O₃ catalysts were designed and tested for PROX reaction using holographic research strategy. On the bases of our previous study Pb has been selected as the main modifier of the Au. In addition to Au and Pb the catalysts library contained V, Ba, Ce, Sm, Ag and Cu resulting in multi component catalysts tailored for PROX reaction. After preparation and testing of 173 catalysts within five generations new catalyst compositions with excellent performance have been obtained. Upon using the best catalyst CO could be removed almost completely and the selectivity of oxygen towards the CO oxidation was around 75%. In the course of catalyst library design it has been revealed that the selection of the objective function (OF) has high impact both on the rate of optimization and the performance of catalysts designed. The complex OF was created from two single desirability functions related to CO conversion and oxygen selectivity towards CO oxidation. In order to maintain high optimization rate there was a need to change the weights of single desirability functions in the course of catalyst library design. The results show that Pb, Sm, Cu and Ag are the key modifiers for PROX reaction under experimental conditions applied.