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.     

基于焦化除尘灰和无纺布的活性炭布制备研究

以焦化除尘灰基活性炭和无纺布为原料制成一种活性炭布。活性炭布的成形工艺采用浸渍涂布法。研究了活性炭质量分数和粘结剂质量分数对活性炭布的载炭量及碘吸附值的影响。活性炭布的载炭量随着活性炭质量分数和粘结剂质量分数的增大而增大。当活性炭质量分数为20%、粘结剂质量分数为30%时,活性炭布的碘吸附值高达291.3541 mg/g。     

活性炭负载[Rh(COD)Cl]2催化剂的制备及其催化性能

以氧化活性炭(OAC)为载体、自制[Rh(COD)Cl]_2为活性组分,制备了负载型催化剂[Rh(COD)Cl]_2/OAC(COD为1,5-环辛二烯),用XPS、N2吸-脱附、FTIR等对其结构进行了表征与分析,以β-蒎烯加氢反应为探针反应,考察了载体种类、氧化剂HNO3浓度、[Rh(COD)Cl]_2与OAC质量比对负载型催化剂[Rh(COD)Cl]_2/OAC性能的影响,在此基础上优化了β-蒎烯加氢工艺条件,并测定了催化剂([Rh(COD)Cl]_2/OAC)的重复使用性。结果表明,催化剂的最佳制备条件为:氧化活性炭为较佳载体,HNO3浓度为7.23mol/L,[Rh(COD)Cl]_2与OAC质量比为1∶8.3,此时β-蒎烯转化率均值为99.94%;顺式蒎烷选择性(以只生成蒎烷计,下同)均值为88.64%;顺式蒎烷收率均值为88.59%;β-蒎烯加氢工艺的最佳条件为:反应温度50℃,反应压力3.5 MPa,催化剂用量为β-蒎烯质量的3.5%,反应时间4.0 h,此条件下β-蒎烯转化率均值为99.88%;顺式蒎烷选择性均值为89.00%;顺式蒎烷收率均值为88.90%,[Rh(COD)Cl]_2/OAC催化剂在β-蒎烯加氢反应中表现出较佳的催化活性。催化剂重复使用4次后,β-蒎烯转化率仍可达89.64%,活性组分Rh的流失是造成催化剂失活的主要原因。     

结构化纳米碳纤维载体的制备与应用

研究了通过气相沉积法裂解甲烷在TiO2表面生长纳米碳纤维层,制备具有中孔孔径结构的结构化纳米碳纤维的方法。利用SEM-EDS和BET对该载体进行了表征。结果发现,该结构化纳米碳纤维载体的纳米碳纤维层厚度1.5～2.0μm,比表面积60.3 m2/g,其中外表面积为51.1 m2/g,只有很少的内表面积;平均孔径为5nm。在肉桂醛加氢反应中,该载体负载Pd催化剂能明显降低内扩散对反应选择性的影响,肉桂醛转化率低于56%时,氢化肉桂醛选择性达98%,明显高于常规活性炭负载型Pd催化剂。     

活性炭固载钛酸异丙酯催化剂的制备

研究了新型固载钛酸异丙酯催化剂的制备方法，该催化剂活性高，选择性好，可成为绿色酯化工艺用催化剂。     

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.     

Methanol Synthesis from CO2 Under Atmospheric Pressure over Supported Pd Catalysts

Pd/ZnO catalyst exhibits high activity and selectivity for methanol synthesis in the hydrogenation of CO₂ under atmospheric pressure. PdZn alloys are formed upon reduction of the Pd/ZnO catalyst at high temperatures. The catalytic activity and selectivity are greatly enhanced upon the formation of such PdZn alloys. The turnover frequency and selectivity of methanol formation are markedly larger than those of a Cu/ZnO type control catalyst.     

负载型钌炭加氢催化剂的工艺研究

通过对负载型钌炭催化剂的制备工艺的研究,分析讨论了载体种类、制备工艺中的负载和还原操作对钌炭催化剂性能的影响。研究结果表明:在催化剂的制备过程中,活性炭载体、负载方式和还原操作对表面活性金属的分散度有影响,从而造成催化剂的性能差异。选择椰壳炭为载体、沉淀法进行活性金属的负载,经过液相法硼氢化钠还原得到的催化剂表面活性金属的分散度高,催化剂在苯部分加氢反应中具有高活性和高选择性,环己烯的收率达到55%。     

兰炭基活性炭负载TiO2光催化剂的制备及性能研究

以兰炭为原料,采用物理化学法制备了兰炭基活性炭,以钛酸丁酯、硝酸铁为主要试剂并采用泥浆法制备了不同煅烧温度的Fe3+-TiO2/AC复合材料,并将其用于光催化降解酸性橙溶液,考察了反应时间、催化剂用量、酸性橙初始质量浓度、溶液pH及光源功率对其光催化性能的影响.结果表明:制备的兰炭基活性炭具有发达的孔隙结构和良好的吸附性能,以其为载体制备的Fe3+-TiO2/AC复合材料在光降解时间为3 h、催化剂用量为0.8 g、酸性橙初始质量浓度为40 mg?L-1、溶液pH值为9、光源功率为650 W的条件下,酸性橙溶液降解性能最好,降解率达到96.8％.该研究成果对兰炭制备活性炭应用于TiO2光降解实验的研究具有一定的指导意义.     

Effect of Carbon Deposits on Reactivity of Supported Pd Model Catalysts

Alumina-supported Pd model catalysts were prepared by Pd evaporation onto a thin alumina film grown on a NiAl(110) substrate. Adsorption and co-adsorption of ethene, CO and hydrogen on Pd/Al₂O₃/NiAl(110) covered by carbon species, formed by ethene dehydrogenation at 550 K, was studied by temperature programmed desorption (TPD). TPD results show that carbon deposits do not prevent adsorption but inhibit dehydrogenation of di- bonded ethene. Carbon species suppress CO adsorption in the highly coordinated sites and also suppress the formation of hydrogen ad-atoms on the surface. The ethene hydrogenation reaction performed by co-adsorption of hydrogen and ethene is inhibited by the presence of carbon deposits. The inhibition is independent of particle size studied (1-3 nm). The effects are rationalized in terms of a site-blocking behavior of carbon species occupying highly coordinated sites on the Pd surface.     

AlCl3/活性炭催化甲基三氯硅烷与低沸物再分配反应研究

甲基三氯硅烷(M1)与低沸物(LBR)是工业上"直接法"生产二甲基二氯硅烷单体过程中产生的副产物,两者之间通过再分配反应可转化为高价值的有机硅单体.以活性炭为载体,采用浸渍蒸发煅烧法制备了负载型AlCl3固体酸催化剂,在固定床反应器中进行甲基三氯硅烷与低沸物的再分配反应,制得二甲基二氯硅烷和三甲基氯硅烷.考察了活性炭载体预处理方式及反应条件对再分配反应的影响.结果表明,经过高温扩孔处理的活性炭载体负载的AlCl3催化剂具有较好的反应活性;优化的反应条件为:W(M1/LBR)为2.0～3.0,反应温度为310℃,LHSV为1.5 h-1;该催化剂的制备过程简单,催化反应条件温和且表现出良好的催化稳定性.     

Activated Carbon Supported Metal Catalysts for Nitrate and Nitrite Reduction in Water

Ten monometallic and 13 bimetallic catalysts supported on activated carbon were assessed, the former in the reduction of nitrate or nitrite and the latter in the nitrate reduction. Under the conditions used, nitrite was shown to be reduced by monometallic catalysts. With exception of Ru, only some of the bimetallic catalysts were able to reduce nitrate. Rh–Cu shows the highest conversion, but Pd–Cu is the most promising catalyst if selectivity into nitrogen is also considered.     

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.     

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.     

双氧水处理活性碳修饰碳糊电极测水中Pb（Ⅱ）

实验研究了用双氧水处理的活性碳修饰碳糊电极测定水中的Pb（Ⅱ）。对富集电位、富集时间、支持电解质及其酸度、修饰剂用量及超声处理时间进行了研究和优化,并研究了部分干扰离子的影响。结果表明在优化条件下对铅的检测线性范围为4.0×10-8～2.0×10-5 mol/L,检测限为1.0×10-8。用该修饰电极检测了护城河水样中的铅离子,平均回收率为101%。     

Pd Nanoparticles Supported on Hierarchically Porous Carbon Nanofibers as Efficient Catalysts for Phenol Hydrogenation

Catalysis Letters - One-step hydrogenation of phenol is a preferable and economic route for preparing cyclohexanone. The development of catalysts with high catalytic performance and easy recovery...     

Comparison of H2Adsorption,O2Adsorption,H2Titration,and O2Titration on Supported Palladium Catalysts

Four different methods for Pd dispersion measurement are compared: H₂adsorption, O₂adsorption, H₂titration, and O₂titration. A correct comparison requires the knowledge of H/Pd_sand O/Pd_sstoichiometries. The H/Pd_sstoichiometry is discussed by reviewing published results, which lead us to the conclusion that H/Pd_s=1. Our experimental results demonstrate that the relative O/H stoichiometry is independent of Pd concentration, type of carrier, and preparation method, O/H=1; thus O/Pd_s=1. If correctly performed, the four methods give the same Pd dispersion, but those based on direct adsorption have less applicability, because they require the complete removal of hydrogen used for reduction from the metal surface. A method to evaluate residual hydrogen is given.     

Methane Transformation in Presence of Carbon Dioxide on Activated Carbon Supported Nickel–calcium Catalysts

The objective of the present work was to study the catalytic reformation of methane in presence of carbon dioxide on activated carbon-supported nickel and calcium catalysts. Results are very promising ones because they suggests that it is possible to transform methane on these catalysts by using mild reaction conditions.