Butane Dehydrogenation Reaction on Sulfur Poisoned Group 10 Metal/SiO2 Catalysts

Butane cracking and dehydrogenation reactions on silica supported Ni, Pt, Pd, and S, Pb modified Ni, Pt, Pd catalysts were studied via a fixed bed reaction system. Cracking reaction path prevailed when butane reaction was catalyzed by clean Ni, Pt, Pd and sulfur poisoned Ni catalysts. The addition of sulfur into Pt and Pd catalytic systems can shift the reaction path to dehydrogenation reaction. However, the deactivation problem due to carbonaceous deposit is not improved by the addition of sulfur into the catalytic system. The origin of the sulfur effect on the change of butane reaction pathway is discussed on the basis of the concentrations of Ph and S additives, oxygen perturbation effect, metal loading, carbonaceous deposit and reaction temperatures.     

Highly durable Pd metal catalysts for the oxygen reduction reaction in fuel cells; coverage of Pd metal with silica

Pd cathode catalysts for polymer electrolyte fuel cells have been covered with silica layers a few nanometres thick. The silica-coated Pd catalysts showed high activity and excellent durability for the oxygen reduction under the severe cathode conditions of PEFCs, while Pd catalysts without silica-coating were seriously deactivated under the same conditions. The coverage of Pd metal with silica prevents the diffusion of Pd species out of the silica layers.     

CO Oxidation Activity and Characterization of Ag-Mn、Ag-Ce and Ag-Cu Mixed Oxide Catalysts

Catalytic oxidation is an efficient way to convert CO to CO₂ at low temperature. Precious metal catalysts such as Ft and Pd have been demonstrated to be very effective^[1]. However, attention has also been given to base metals due to the limited availability of precious metals. As a single component base metal catalyst cannot rival a precious metal catalyst, improvement in its activity has been attempted by combining several elements^[2,3]. In the present work, we studied redox and structure of Ag-M(M=Mn、Ce and Cu) catalysts to gain some evidence of the synergism between Ag and base metals, and investigated their catalytic activities.     

Graphene‐Supported Ultrafine Metal Nanoparticles Encapsulated by Mesoporous Silica: Robust Catalysts for Oxidation and Reduction Reactions

Graphene nanosheet‐supported ultrafine metal nanoparticles encapsulated by thin mesoporous SiO₂ layers were prepared and used as robust catalysts with high catalytic activity and excellent high‐temperature stability. The catalysts can be recycled and reused in many gas‐ and solution‐phase reactions, and their high catalytic activity can be fully recovered by high‐temperature regeneration, should they be deactivated by feedstock poisoning. In addition to the large surface area provided by the graphene support, the enhanced catalytic performance is also attributed to the mesoporous SiO₂ layers, which not only stabilize the ultrafine metal nanoparticles, but also prevent the aggregation of the graphene nanosheets. The synthetic strategy can be extended to other metals, such as Pd and Ru, for preparing robust catalysts for various reactions.     

镍族金属团簇在催化加氢过程中的应用

Nanoparticles of precious metals play an important role in many heterogeneous catalytic reactions due to their excellent catalytic performance. As an idealized model, gas phase metal clusters have been extensively utilized to understand catalytic mechanisms at a molecular level. Here we provide an overview of our recent studies on H₂ dissociative chemisorption on nickel family clusters. The structure evolution and the stability of the metal clusters were first compared. H₂ dissociation on the clusters was then carefully addressed to understand the capability of metal clusters to break the H-H bond. Two key parameters, the dissociative chemisorption energy (ΔE_CE) and the H sequential desorption energy (ΔE_DE), were employed to characterize the catalytic activity of metal clusters. Our results show that both ΔE_CE and ΔE_DE decline significantly as the H coverage increases. Since the catalyst is in general covered entirely by H atoms and H₂ molecules in a typical hydrogenation process, and maintained at a pre-determined pressure of H₂ gas, we can rationally use the calculated ΔE_CE and ΔE_DE values at full H saturation to address the activity of metal clusters. Our results suggest that at full H coverage, each Pt atom is essentially capable of adsorbing 4 H atoms, while each Ni or Pd atom can only accommodate 2 H atoms. Considering the similar values of H desorption energies on Pt and Pd clusters, the higher average H capacity per Pt atom could probably lead to a faster reaction rate because more active H atoms are produced on the Pt catalyst particles in the hydrogenation process. Finally, the charge sensitivity of the key catalytic properties of Pt clusters for hydrogenation was systematically evaluated. The results show that the dissociation of H₂ and H desorption are strongly correlated to the charge state of the Pt clusters at low H coverage. However, at high H-capacities, both ΔE_CE and ΔE_DE fall into a narrow range, suggesting that the charge can be readily dispersed and that the Pt-H bonds average the interaction between clusters and H atoms. As a result, the H-capacities on charged clusters were found to be similar as the cluster size increased; in case of sufficiently large clusters, the reactivity of a fully saturated cluster was no longer sensitive to its charge state.     

Viable Photocatalysts under Solar‐Spectrum Irradiation: Nonplasmonic Metal Nanoparticles

Supported nanoparticles (NPs) of nonplasmonic transition metals (Pd, Pt, Rh, and Ir) are widely used as thermally activated catalysts for the synthesis of important organic compounds, but little is known about their photocatalytic capabilities. We discovered that irradiation with light can significantly enhance the intrinsic catalytic performance of these metal NPs at ambient temperatures for several types of reactions. These metal NPs strongly absorb the light mainly through interband electronic transitions. The excited electrons interact with the reactant molecules on the particles to accelerate these reactions. The rate of the catalyzed reaction depends on the concentration and energy of the excited electrons, which can be increased by increasing the light intensity or by reducing the irradiation wavelength. The metal NPs can also effectively couple thermal and light energy sources to more efficiently drive chemical transformations.     

贵金属负载的棒状ZnO复合光催化剂的制备及其提升的光催化性能

以水热制备的ZnO纳米棒为基底,通过乙二醇液相还原法负载不同贵金属颗粒(Pt、Pd、Ru)构筑贵金属负载的ZnO纳米棒复合光催化剂。实验结果表明在制备条件相同时,Pt/ZnO样品中Pt颗粒尺寸较小,分布均匀;Pd/ZnO样品中Pd颗粒尺寸较大且团聚严重;Ru/ZnO样品则几乎没有Ru颗粒负载。在紫外光照射下降解亚甲基蓝的反应中,Pt/ZnO表现出最高的光催化性能,Pd/ZnO样品次之,而Ru/ZnO则表现出与ZnO纳米棒相似的光催化活性;表明小尺寸和大小均匀的贵金属颗粒对ZnO纳米棒的催化性能有着显著的提升作用。对Pt/ZnO来说,当Pt载量为3.2%时Pt/ZnO催化剂的光催化活性最高。     

Synthesis of PtRu nanoparticles from the hydrosilylation reaction and application as catalyst for direct methanol fuel cell

Nanosized Pt, PtRu, and Ru particles were prepared by a novel process, the hydrosilylation reaction. The hydrosilylation reaction is an effective method of preparation not only for Pt particles but also for other metal colloids, such as Ru. Vulcan XC-72 was selected as catalyst support for Pt, PtRu, and Ru colloids, and TEM investigations showed nanoscale particles and narrow size distribution for both supported and unsupported metals. All Pt and Pt-rich catalysts showed the X-ray diffraction pattern of a face-centered cubic (fcc) crystal structure, whereas the Ru and Ru-rich alloys were more typical of a hexagonal close-packed (hcp) structure. As evidenced by XPS, most Pt and Ru atoms in the nanoparticles were zerovalent, except a trace of oxidation-state metals. The electrooxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry and chronoamperometry. The results concluded that some alloy catalysts showed higher catalytic activities and better CO tolerance than the Pt-only catalyst; Pt56Ru44/C have displayed the best electrocatalytic performance among all carbon-supported catalysts.     

Influence of Metallic Modification on Ethylbenzene Dealkylation over ZSM‐5 Zeolites

A series of metal‐modified HZSM‐5 catalysts were prepared by impregnation and were used for ethylbenzene dealkylation of the mixed C8 aromatics (ethylbenzene, m‐xylene and o‐xylene). The effects of different supported metals (Pt, Pd, Ni, Mo) on catalytic performance, including reaction conditions, were investigated. The physicochemical properties of catalysts were characterized by means of XRD, BET, TEM and NH₃‐TPD. Experimental results showed that metallic modification obviously increased the ethylbenzene conversion and reduced the coke deposition, greatly improving the catalyst stability. The distinction of ethylbenzene conversion depended on the interaction between hydrogenation reactivity and acidic cracking of bifunctional metal‐modified zeolites. Compared with Pt and Ni, Pd and Mo were easier to disperse into HZSM‐5 micropores during loading metals. The acidic density of different metal‐modified HZSM‐5 declined in the following order: HZSM‐5>Pt/HZSM‐5>Pd/HZSM‐5>Ni/HZSM‐5>Mo/HZSM‐5. The activity of ethylene hydrogenation decreased with Pt/HZSM‐5>Pd/HZSM‐5>Ni/HZSM‐5>Mo/HZSM‐5. In comparison, Pd/HZSM‐5 showed the best catalytic performance with both high activity and high selectivity, with less cracking loss of m‐xylene and o‐xylene. Moreover, the following reaction conditions were found to be preferable for ethylbenzene dealkylation over Pd/HZSM‐5: 340°C, 1.5 MPa H₂, WHSV 4 h^?1, H₂/C8 4 mol/mol.     

Mixed-metal pt monolayer electrocatalysts for enhanced oxygen reduction kinetics

We have synthesized a new class of electrocatalysts for the O2 reduction reaction, consisting of a mixed monolayer of Pt and another late transition metal (Ir, Ru, Rh, Re, or Os) deposited on a Pd(111) single crystal or on carbon-supported Pd nanoparticles. Several of these mixed monolayer electrocatalysts exhibited very high activity and increased stability of Pt against oxidation, as well as a 20-fold increase in a Pt mass-specific activity, compared with state-of-the-art all-Pt electrocatalysts. Their superior activity and stability reflect a low OH coverage on Pt, caused by the lateral repulsion between the OH adsorbed on Pt and the OH or O adsorbed on neighboring, other than Pt, late transition metal atoms. The origin of this effect was identified through a combination of experimental and theoretical methods, employing electrochemical techniques, in situ X-ray absorption spectroscopy, and periodic, self-consistent density functional theory calculations. This new class of electrocatalysts promises to alleviate some major problems of existing fuel cell technology by simultaneously decreasing materials cost and enhancing performance. Our studies suggest a new way of synthesizing improved ORR catalysts through the modification and control of the surface reactivity of Pt-based mixed monolayers supported on transition metals other than Pt. In addition to improving the ORR catalysts, co-depositing oxophilic metals may be a promising possibility for improving a variety of other catalysts.     

STUDIES ON THE CATALYTIC REACTION OF NITROGEN OXIDE ON METAL MODIFIED ACTIVATED CARBON FIBERS

The catalytic reaction of NO with CO and decomposition of NO over metal modified ACFs were investigated and compared with other carriers supported catalysts. It is demonstrated that Pd/ACF and Pd/Cu/ACF have high catalytic activity for the reaction of NO/CO, while Pt/ACE. Pt/Cu/ACF and Co/Cu/ACF have very low catalytic activity in similar circumstance. Pd-modified ACF possesses high catalytic decomposition of NO at 300℃. Pd/CB and Pd/GAC present good catalytic decomposition abifity for NO only at low [lowrate. Pd/G Pd/ZMS and Pd/A however, do not show any catalytic activity for NO decomposition even at 400 ℃. Catalytic temperature, NO flowrate and loading of metal components affect the decomposition rate of NO. The coexistence of Cu with Pd on Cu/Pd/ACF leads to crystalline of palladium to more unperfected so as to that increase the catalytic activity.     

A new class of electrocatalysts for hydrogen production from water electrolysis: metal monolayers supported on low-cost transition metal carbides

This work explores the opportunity to substantially reduce the cost of hydrogen evolution reaction (HER) catalysts by supporting monolayer (ML) amounts of precious metals on transition metal carbide substrates. The metal component includes platinum (Pt), palladium (Pd), and gold (Au); the low-cost carbide substrate includes tungsten carbides (WC and W(2)C) and molybdenum carbide (Mo(2)C). As a platform for these studies, single-phase carbide thin films with well-characterized surfaces have been synthesized, allowing for a direct comparison of the intrinsic HER activity of bare and Pt-modified carbide surfaces. It is found that WC and W(2)C are both excellent cathode support materials for ML Pt, exhibiting HER activities that are comparable to bulk Pt while displaying stable HER activity during chronopotentiometric HER measurements. The findings of excellent stability and HER activity of the ML Pt-WC and Pt-W(2)C surfaces may be explained by the similar bulk electronic properties of tungsten carbides to Pt, as is supported by density functional theory calculations. These results are further extended to other metal overlayers (Pd and Au) and supports (Mo(2)C), which demonstrate that the metal ML-supported transition metal carbide surfaces exhibit HER activity that is consistent with the well-known volcano relationship between activity and hydrogen binding energy. This work highlights the potential of using carbide materials to reduce the costs of hydrogen production from water electrolysis by serving as stable, low-cost supports for ML amounts of precious metals.     

过渡金属修饰对Pt/M-DMSN催化剂丙烷脱氢性能的影响

以两步法制备了一系列过渡金属(M=Fe, Co, Ni, Cu, Zn)修饰的树枝状介孔二氧化硅纳米粒子(DMSN)负载铂(Pt/M-DMSN)催化剂, 并对该系列催化剂进行了丙烷催化脱氢性能评价. X射线衍射(XRD)、 透射电子显微镜(TEM)、 紫外-可见漫反射光谱(UV-Vis DRS)和氢气程序升温还原(H₂-TPR)表征结果表明, 不同过渡金属在DMSN载体表面分散状态不同,且与Pt的相互作用程度不同. 其中Zn-DMSN载体最有利于Pt的分散, 且反应后催化剂上积碳含量最低; Pt/Fe-DMSN催化剂中Pt与载体的相互作用力较强. 通过活性评价结果可知, Pt/Fe-DMSN催化剂表现出最优的丙烷催化脱氢性能, 丙烷初始转化率为44.2%, 反应6 h后丙烷转化率仍可达36.5%.     

Evaluation of stability of silica-supported Fe–Pd and Fe–Pt nanoparticles in aerobic conditions using thermal analysis

The applications of zerovalent iron nanoparticles (nZVI) exploit their high reactivity which decreases due to oxidation in aerobic conditions during manufacture, application, and storage. In this study, we present the new procedure for estimation of the nZVI stability to oxidation in air. The procedure is suitable for characterization of the novel materials based on the supported nZVI. Nanoscale particles were synthesized inside porous silica supports by incipient wetness impregnation with the metal precursor solutions followed by thermal treatment. The TG–DTA studies revealed the decomposition temperature of the supported precursors, as well as the interaction of Fe and precious metal precursors, which resulted in the formation of alloy nanoparticles. Characterization of the samples by XRD confirmed the formation of the nanoparticles of the metallic Pd, Pt, and Fe phases supported on SiO₂ carriers, as well as the formation of solid solutions based on the structure of precious metals. The new procedure for estimation of the nZVI stability included (1) TPR with hydrogen up to 400–425 °C followed by isothermal reduction at these temperatures; (2) in situ reoxidation with oxygen at room temperature. The samples were reduced “as obtained” and after in situ reoxidation. The results of the TPR studies exhibited that introduction of both Pd and Pt protected the Fe nanoparticles from oxidation with oxygen and air at ambient conditions.     

一维CeO2纳米管载体对Pd纳米粒子团聚的抑制及催化性能的提高

用一维CeO₂纳米管替代非一维结构的商用CeO₂, 用于负载Pd而制得的催化剂在空气气氛下高温煅烧过程中Pd纳米粒子的团聚受到明显抑制, 在选择性有氧氧化苯甲醇生成苯甲醛反应中, 所制CeO₂纳米管负载的Pd催化剂表现出更高的催化活性. 可见, 一维金属氧化物材料有望用作载体以抑制贵金属纳米粒子的团聚, 从而提高其催化性能.     

高分子负载贵金属类催化剂及其在有机反应中的最新应用

高分子负载金属催化剂与传统的均相催化剂相比,具有较高的催化活性、立体选择性、较好的稳定性和重复使用性能,并且后处理简单,在反应完成后可方便地借助固-液分离方法将高分子催化剂与反应体系中其他组分分离、再生和重复使用,可降低成本和减少环境污染。本文综述了近五年来高分子负载贵金属类催化剂在有机反应中的最新应用,根据金属不同将其分为钌、钯、银、金四大类,并分类介绍了其在不同固相反应中的应用。本文介绍的负载贵金属类催化剂中的负载物均为不溶性聚合物,但不包括二氧化硅、可溶性聚合物和树枝状大分子等。     

纳米多孔金属电催化剂在氧还原反应中的应用

燃料电池是将化学能直接转化为电能的能量转换装置,具有绿色、高效、便携等特点。对于大多数使用氧气或者空气为氧化剂的燃料电池而言,其阴极氧还原反应动力学缓慢、稳定性差是阻碍该技术走向商业化的主要因素,因此开发高催化活性和良好稳定性的低成本氧还原催化剂非常重要。基于脱合金法制得的纳米多孔金属是一类新型的宏观尺度纳米结构材料,其独特的开放型孔道结构、优良的导电性和结构的可调控性使其在电催化相关领域具有广泛的应用。本文侧重于讨论纳米多孔金属作为氧还原催化剂时所展示的一系列结构特性,及其在发展新一代高性能一体化燃料电池催化剂中所展示的机会。     

Bamboo‐Like Nitrogen‐Doped Carbon Nanotubes with Co Nanoparticles Encapsulated at the Tips: Uniform and Large‐Scale Synthesis and High‐Performance Electrocatalysts for Oxygen Reduction

In recent years, various non‐precious metal electrocatalysts for the oxygen reduction reaction (ORR) have been extensively investigated. The development of an efficient and simple method to synthesize non‐precious metal catalysts with ORR activity superior to that of Pt is extremely significant for large‐scale applications of fuel cells. Here, we develop a facile, low‐cost, and large‐scale synthesis method for uniform nitrogen‐doped (N‐doped) bamboo‐like CNTs (NBCNT) with Co nanoparticles encapsulated at the tips by annealing a mixture of cobalt acetate and melamine. The uniform NBCNT shows better ORR catalytic activity and higher stability in alkaline solutions as compared with commercial Pt/C and comparable catalytic activity to Pt/C in acidic media. NBCNTs exhibit outstanding ORR catalytic activity due to high defect density, uniform bamboo‐like structure, and the synergistic effect between the Co nanoparticles and protective graphitic layers. This facile method to synthesize catalysts, which is amenable to the large‐scale commercialization of fuel cells, will open a new avenue for the development of low‐cost and high‐performance ORR catalysts to replace Pt‐based catalysts for applications in energy conversion.     

Visible light photochemical synthesis of ultrasmall palladium/copper bimetallic particles at room temperature and its catalytic application in degradation of p-NP

Pt-based metals are very effective catalysts widely adopted in many fields. But the high cost prevents its further industrial application. One of the effective ways to solve the problem is to replace platinum with relatively cheap palladium and its alloy with copper. However, producing Pd/Cu bimetallic catalysts efficiently and economically with controllable particle size and uniform distribution is still challenging, especially when trying to reduce the consumption of precious metals. In this paper, ultrasmall palladium/copper (Pd/Cu) bimetallic catalysts with even dispersion were prepared on multi-walled carbon nanotubes (MWCNTs) by adding polyethylene glycol 400 (PEG 400) as a reducing agent and stabilizer under visible light irradiation at room temperature. The catalytic performance was studied in the catalysis of p-nitrophenol (p-NP) reduction. Of all the bimetallic catalysts produced in different conditions, the best one was obtained under the reaction condition of pH = 7 and violet light irradiation (wavelength 380–435 nm). The average particle size of 0.85 nm, and the apparent rate constant in the catalysis is 1.47 min^?1. This research probes the role of visible light as a key kinetic controlling method in the formation of ultrasmall particles (UPs). It proves the effectiveness of using visible light irradiation as an effective and more “green chemistry” approach to get precious metal UPs as catalysts beyond the traditional ultraviolet or laser photochemistry methods.     

Catalytic Oxidation of Small Molecules in a Gas Phase in the Presence of Heterogenized Platinum and Palladium Complexes with Chemically Different Ligands

This work is devoted to the study of catalytic properties of the metal complexes of platinum and palladium with acetylacetone and N-allyl-N"-propylthiourea heterogenized on the surface of silica in the oxidation reactions of H₂ and CO in a gas phase. We found that the acetylacetonate complexes were not degraded under catalytic reaction conditions, whereas the metal complexes withN-allyl-N"-propylthiourea exhibited a high activity only after partial degradation of the ligand. We demonstrated that the catalytic activity of the grafted metal complexes was higher than that of traditional supported platinum and palladium catalysts with the same metal content. Taking into account the structure of active centers in Pt and Pd complexes grafted on SiO₂ and the interaction of these centers with reactants, we proposed a detailed mechanism for the catalytic action, which adequately describes the entire set of experimental data.