掺杂Co对CNTs负载Pt催化剂上肉桂醛选择性催化加氢性能的影响

研究了Co的掺杂对Pt/CNTs催化剂催化加氢肉桂醛反应性能的影响。结果发现, Co的掺杂对Pt/CNTs催化剂催化加氢活性起到明显促进作用, 并有利于C＝O基团的选择性加氢。Pt-0.17% Co/CNTs催化剂显示了较高的肉桂醇加氢选择性, 在反应条件为70℃、2 MPa和1.5 h时, 肉桂醛的加氢转化率达到97.1％,生成肉桂醇的选择性达到93.6％。同时, 初步研究了该催化剂上肉桂醛催化加氢反应动力学, 催化反应的活化能为26.5 kJ•mol^-1。     

氮掺杂介孔碳纳米球负载铂催化剂在肉桂醛选择性加氢中的催化性能研究

以多巴胺为碳源和氮源、F127为软模板制备氮掺杂有序介孔碳纳米球（NOMCS）,并以其为载体制备Pt催化剂（Pt/NOMCS）。通过TEM、XPS、OEA、Raman和N₂吸附等手段对材料进行表征。将制备的Pt/NOMCS用于肉桂醛（CAL）选择性加氢模型反应,并研究其催化性能。结果表明,与商用介孔炭（MC）和活性炭（AC）负载Pt催化剂（Pt/MC和Pt/AC）相比,Pt/NOMCS在CAL选择性加氢中显示出较高的催化活性(反应速率常数k=（0.37±0.02） h^-1)和选择性（转化率为90%时的肉桂醇选择性约为75%）。循环实验4次后,Pt/NOMCS显示出较好的可回收性能。     

原子层沉积制备Pt/TiO_2催化剂及其在肉桂醛加氢中的应用

利用原子层沉积技术在载体TiO_2上沉积尺寸均一的Pt纳米粒子得到Pt/TiO_2催化剂,研究了不同还原温度对其催化肉桂醛加氢性能的影响。结果表明,与未经高温还原的Pt/TiO_2相比,经700℃还原的催化剂Pt/TiO_2-700对肉桂醛的加氢活性提高了29.2%,对肉桂醇的选择性提高了40.5%。通过TEM、XPS和XRD等分析手段对催化剂的形貌、电子状态及晶体结构等进行表征,结果表明,高温还原有利于增大Pt纳米粒子和改变电子状态,从而提高其催化性能。     

Pt/Fe_3O_4@C磁响应核壳催化剂上肉桂醛选择性加氢性能

采用溶剂热法合成了Pt/Fe3O4@C磁响应核壳催化剂,以扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)和超导量子干涉磁强计(SQUID)对催化剂的结构和磁性质进行了表征。研究发现Pt颗粒均匀地分散在碳层上,Pt/Fe3O4@C催化剂显示了良好的超顺磁性。研究了Pt/Fe3O4@C磁响应催化剂上肉桂醛(CAL)的选择性加氢反应,结果显示催化剂具有良好的C=O加氢活性,在考察的条件下,肉桂醛转化率在60%左右时,肉桂醇选择性可达96%以上。催化剂在外加磁场作用下可以高效地从液相反应体系中分离,经多次循环使用后仍具有良好的催化性能。     

碱基调控Pt纳米晶构型及其催化加氢性能

贵金属纳米晶对加氢反应具有良好的催化性能,特别是Pt纳米晶,其催化活性和选择性与纳米晶的纳米结构(形貌和尺寸)密切相关。由Gibbs-Wulff晶体生长定律可知,通过加入特定结构的封端剂可以有效控制纳米晶的形貌和尺寸。本文采用Na BH4在水溶液中还原Pt的前体H2Pt Cl6制备Pt纳米晶,并将其用于催化对硝基苯酚(p-NIP)的加氢反应。实验系统研究了碱基分子(如腺嘌呤A、鸟嘌呤G、胸腺嘧啶T、胞嘧啶C)及对应的核苷分子对Pt纳米晶构型和催化加氢活性的调控规律。研究发现,碱基分子和核苷分子对于Pt纳米晶的形貌以及尺寸具有明显的调控作用,通过不同结构生物分子的精密调控,实验制备得到了形貌和尺寸各异的Pt纳米晶。同时,所得Pt纳米晶在p-NIP的加氢反应中表现出了精密可调的催化性能。鸟嘌呤核苷、腺嘌呤核苷、β-胸腺嘧啶核苷调控制备的Pt纳米催化剂的TOFave均可达到无调控剂制备得到的催化剂的两倍以上,其中腺嘌呤核苷调控制备得到的Pt催化剂性能最好。     

PtSn-丝光沸石催化剂的制备及其肉桂醛加氢性能的研究

利用微乳液法制备了一系列Fe和Sn改性的Pt基催化剂,并将其应用于肉桂醛选择性加氢反应中。通过XRD、TEM、FT-IR、BET、XPS等对催化剂的结构和性质进行表征。结果表明,丝光沸石分子筛可以较好地分散活性组分,双组分负载的催化材料仍保持较好的介孔结构,适量Sn组分的加入提高了Pt物种的分散度,并使Pt物种处于富电子状态。在3.0MPa、80℃条件下,Pt-1Sn-2/H-丝光沸石催化剂的最优催化性能为:肉桂醛转化率为74.0%,肉桂醇选择性为77.0%。催化剂的重复循环反应测试结果表明,催化剂活性组分基本没有流失,催化剂稳定性较好。     

过渡金属改性的Pt/n-Al_2O_3在肉桂醛加氢反应中的催化性能

用NaBH4作还原剂,制备了中性氧化铝(n-Al2O3)负载的Pt-M(M=Fe,Co,Ni,Cu,Mn,Sn)双金属催化剂。考察了过渡金属及反应条件对Pt-M/n-Al2O3催化肉桂醛加氢制肉桂醇的影响。结果表明,Fe改性的Pt/n-Al2O3对催化肉桂醛加氢制肉桂醇具有较好的催化性能,当Pt-Fe/n-Al2O3(中性)催化剂中Pt、Fe的含量均为0.3%时,在70℃,2 MPa氢气条件下反应1.5 h,肉桂醛的转化率为100%,肉桂醇选择性高达84.8%。     

碱处理法制备Pt/ZSM-5催化剂用于肉桂醛选择加氢反应

负载型催化剂中贵金属的负载方法常常会影响催化剂的结构以及催化反应性能。本研究采用碱处理法制备了ZSM-5负载Pt纳米粒子催化剂，并用透射电镜(TEM)、X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、N₂物理吸脱附、氨气程序升温脱附(NH₃-TPD)等方法对催化剂物理化学性质进行了表征，同时将肉桂醛选择加氢反应作为模型反应，考察了合成催化剂的催化性能。结果表明：对比传统浸渍法制备的Pt/ZSM-5催化剂，用碱处理制备的催化剂能够显著地提高肉桂醛的转化率，其转化频率(TOF)值明显高于传统方法制备的催化剂，并且通过改变压力和反应温度可以进一步提高其催化活性。表征结果发现：碱处理法制备的Pt/ZSM-5催化剂具有更小粒径的Pt纳米粒子和更多的表面酸性位，有利于肉桂醛在催化剂表面的吸附和活化，使其具有更高的催化活性。     

纳米金催化剂的制备及其对肉桂醛选择性加氢的催化性能

以多壁碳纳米管和椰壳活性炭为载体,分别采用溶胶固载法和等体积浸渍法制备负载型纳米金催化剂。采用N_2吸附-脱附、XRD、TEM和XPS等对碳载体和纳米金催化剂样品进行表征,并研究纳米金催化剂在肉桂醛选择性加氢反应中的催化性能。结果表明,HNO_3-H_2SO_4预处理可以增加碳载体表面的含氧基团和含氮基团,在肉桂醛加氢反应中,溶胶固载法得到的更小尺寸的纳米金催化剂对C=C双键加氢选择性高,等体积浸渍法制备的纳米金催化剂对C=O双键加氢选择性高,椰壳活性炭为载体催化剂的C=C加氢催化活性优于多壁碳纳米管。     

肉桂醛选择性加氢Co-Fe/硅藻土催化剂稳定性考察

通过肉桂醛在高压微反固定床上24 h的催化加氢反应,考察了肉桂醛选择加氢的催化剂Co-Fe/硅藻土稳定性。结果表明,肉桂醛选择加氢催化剂Co-Fe/硅藻土在反应初期存在反应的诱导期,诱导期后,肉桂醛转化率70%,肉桂醇选择性80%,肉桂醇收率可达60%以上,且催化性能趋于平稳,表现出良好的催化性能和稳定性。利用XRD、SEM、TG-DSC对反应前后催化剂结构进行表征,发现催化剂经24 h反应,结构不变,表面颗粒分布更细化,无积炭迹象。     

负载Pt-B非晶态催化剂的氯代硝基苯加氢性能

分别以纳米碳管（CNTs）、SiO₂、γ-Al₂O₃和活性炭(AC)为载体,贵金属铂(Pt)为活性组分,用浸渍－化学还原法制备了负载型Pt-B非晶态催化剂,并以邻氯硝基苯的氢化为探针反应考察其催化性能。结果表明,Pt-B/CNTs催化剂具有较好的抑制脱卤的效果,分别较其他三种载体所得脱卤率降低了5.5倍、12.1倍和14.75倍。在SAED和TEM表征的基础上,从电子效应、催化剂粒子大小及载体的结构等方面解释了产生上述差别的原因。     

Reducibility of Platinum Supported on Nanostructured Carbons

The nanostructure of graphite like carbon, i.e. carbon nanofibers (CNF), carbon nanotubes (CNT) and carbon nanoplatelets (CNP), displayed a significant influence on the reducibility of platinum deposited on these carbons. The onset temperature for reduction increased from 461 K for Pt/CNF to 466 K for Pt/CNP and 487 K for Pt/CNT. The retarded reduction for Pt/CNT was related to the higher amount of acidic oxygen surface groups on this support resulting in a strong stabilization of the cationic platinum species. A higher reduction temperature for that sample increased the amount of metallic platinum, however the platinum particle size was larger (2–11 nm) compared to that of Pt/CNF and Pt/CNP (both 1–3 nm). The orientation of the graphene sheets had a significant influence on the selectivity for cinnamaldehyde hydrogenation: Pt/CNP resulted in a higher selectivity towards cinnamyl alcohol compared to Pt/CNF.     

Ultrasonic synthesis of highly dispersed Pt nanoparticles supported on MWCNTs and their electrocatalytic activity towards methanol oxidation

A new method of synthesis of highly dispersed Pt nanoparticles with large catalytic surface area on multi-walled carbon nanotubes (MWCNTs) under high-intensity ultrasonic field was developed. The method, with low processing temperature at 25 °C, took only about 5 min. The surface characterization of MWCNTs was carried out by fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy methods. The electrochemical surface area and pore volume of MWCNTs were also examined. The result showed that functional groups of the MWCNTs which favored the high loading and high dispersion of particles and electrochemical surface area of MWCNTs were reinforced in the case of high-intensity ultrasonic field. The Pt/MWCNT catalysts were characterized by energy dispersion X-ray spectra analysis (EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurements. The prepared Pt nanoparticles were uniformly dispersed on the MWCNT surface. The mean size of Pt particles was 3.4 ± 0.2 nm. The electrocatalytic properties of Pt/MWCNT composites and kinetic characterization for methanol electro-oxidation were investigated by cyclic voltammetry. The Pt/MWCNT catalysts prepared for 5 min in ultrasonic field present excellent electrochemical activities. The schematic of the reaction was also introduced.     

EMI shielding effectiveness of carbon based nanostructured polymeric materials: A comparative study

The microstructure, electromagnetic interference (EMI) shielding effectiveness (SE), DC electrical conductivity, AC electrical conductivity and complex permittivity of nanostructured polymeric materials filled with three different carbon nanofillers of different structures and intrinsic electrical properties were investigated. The nanofillers were multiwall carbon nanotubes (MWCNT), carbon nanofibers (CNF) and high structure carbon black (HS-CB) nanoparticles and the polymer was acrylonitrile-butadiene-styrene (ABS). In addition, the EMI SE mechanisms and the relation between the AC electrical conductivity in the X-band frequency range and the DC electrical conductivity were studied. The nanocomposites were fabricated by solution mixing and characterized by uniform dispersion of the nanofillers within the polymer matrix. It was found that, at the same nanofiller loading, the EMI SE, permittivity and electrical conductivity of the nanocomposites decreased in the following order: MWCNT > CNF > CB. MWCNT based nanocomposites exhibited the lowest electrical percolation threshold and the highest EMI SE owning to the higher aspect ratio and electrical conductivity of MWCNT compared to CNF and HS-CB. The AC conductivity in the X-band frequency range was found to be independent of frequency.     

Highly Durable Platinum based Cathode Electrocatalysts for PEMFC Application using Oxygen and Nitrogen Functional Groups Attached Nanocarbon Supports

The combined effect of oxygen and nitrogen functional groups on highly crystalline carbon supports like multiwalled carbon nanotubes (MWCNT) and MWCNT‐few layer graphene hybrid structures (MWCNT+FLG) have been investigated towards oxygen reduction reaction (ORR) performance and carbon corrosion durability in polymer electrolyte membrane fuel cell (PEMFC) applications. The pristine carbon supports were modified with oxygen and nitrogen functionalities by treating with concentrated mineral acids and subsequent nitrogen plasma treatment assisted with R.F. magnetron sputtering. Pt nanoparticles were dispersed over these chemically modified carbon supports by polyol reduction method. The physicochemical properties of as synthesized electrocatalysts were studied by different techniques such as XRD, TEM, FTIR, Raman and XPS. Electrochemical properties were investigated by cyclic voltammetry and linear sweep voltammetry in 0.1M HClO₄ medium. Compared to commercial Pt/C catalysts, durability show ∼30 % enhancement for the as prepared electrocatalysts due to the presence of large amount of pyrrolic nitrogen and highly oriented graphitic nature of the catalyst supports. The ORR performance were comparable with Pt/C (TEC10E30E) in terms of MSA, 259, 270, 252 A g⁻¹ for Pt/C, Pt/N‐f‐MWCNT, Pt/N‐f‐(MWCNT+FLG) respectively.     

Synthesis and activity of the Pt catalyst supported on CNT

Carbon nanotubes (CNT) were obtained by the decomposition of methane on a Ni catalyst supported on Al₂O₃. After the removal of the catalyst materials from CNT, a CNT-supported Pt catalyst was prepared, and this catalyst was characterized by XRD, XPS, and TEM. Activity of the CNT-supported Pt catalyst for hydrogenation of carbon–carbon double bonds at room temperature under the atmospheric pressure of hydrogen was examined. The CNT-supported Pt catalyst showed higher activity than the commercial Pt catalysts supported on activated carbon.     

Palladium on carbon nanofibers grown on metallic filters as novel structured catalyst

A novel composite material based on carbon nanofibers (CNF) grown on sintered metal fibers (SMF_Inconel) filter was investigated for its favorable properties as catalytic support. The CNF were formed directly over the SMF_Inconel by thermal (650 °C) chemical vapor deposition of ethane–hydrogen mixture. The CNF/SMF_Inconel composite consists of metal fibers entangled by CNF network of microns thickness and strongly anchored to the metal surface. The properties of the CNF/SMF_Inconel were controlled by the synthesis conditions. The CNF coating reduced the filter porosity and decreased the material permeability, but the pressure drop during the gas passage through the reactor remained low for CNF fraction <10%. Palladium was deposited on CNF previously activated by boiling in hydrogen peroxide. The activity and selectivity of Pd°/CNF/SMF_Inconel catalysts were tested in the selective hydrogenation of acetylene and compared with Pd supported on activated carbon fibers (Pd°/ACF). The TOF was one order of magnitude higher for Pd°/CNF/SMF_Inconel as compared to Pd°/ACF. This effect was attributed to a strong metal-support interaction of Pd°-nanoparticles with the graphitized CNF. The reaction was found to be structure sensitive leading to a decrease of TOF for the Pd°-particles <3 nm.     

Nanomechanical characterization of chemical interaction between gold nanoparticles and chemical functional groups

Core/shell nanostructured carbon materials with carbon nanofiber (CNF) as the core and a nitrogen (N)-doped graphitic layer as the shell were synthesized by pyrolysis of CNF/polyaniline (CNF/PANI) composites prepared by in situ polymerization of aniline on CNFs. High-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared and Raman analyses indicated that the PANI shell was carbonized at 900°C. Platinum (Pt) nanoparticles were reduced by formic acid with catalyst supports. Compared to the untreated CNF/PANI composites, the carbonized composites were proven to be better supporting materials for the Pt nanocatalysts and showed superior performance as catalyst supports for methanol electrochemical oxidation. The current density of methanol oxidation on the catalyst with the core/shell nanostructured carbon materials is approximately seven times of that on the catalyst with CNF/PANI support. TEM tomography revealed that some Pt nanoparticles were embedded in the PANI shells of the CNF/PANI composites, which might decrease the electrocatalyst activity. TEM-energy dispersive spectroscopy mapping confirmed that the Pt nanoparticles in the inner tube of N-doped hollow CNFs could be accessed by the Nafion ionomer electrolyte, contributing to the catalytic oxidation of methanol.     

炭载体对Pt-C复合物非碱性条件下催化甘油氧化性能的影响

采用等量浸渍法制备了具有相似平均粒径的活性炭（AC）和碳纳米管（CNTs）负载的Pt催化剂,并比较研究了非碱性条件下两种催化剂催化甘油氧化反应的性能。结果表明,炭载体对Pt-C复合物催化甘油氧化反应的活性、选择性和稳定性有重要影响。相对于Pt/CNTs催化剂,Pt/AC催化剂中Pt 4f结合能较低,导致其表面氧的覆盖度相对较高,因而抑制了甘油的吸附,降低了甘油氧化反应的初始活性;Pt/AC催化剂会促进甘油醛进一步氧化成甘油酸以及C₃产物的氧化断键;Pt/AC催化剂失活的主要原因是氧中毒和中间产物的吸附,而Pt/CNTs催化剂的失活主要是由于甘油酸的吸附堵塞Pt表面的活性位造成的。