In situ surface dynamics in heterogeneous catalysis

During the former half of the last century the mechanism of heterogeneous catalysis had been studied, keeping the catalyst in a black box, and on the basis of the information outside of the black box, it was discussed just from mere conjectures. The author initiated a method to study directly the behavior of the working catalyst surface, looking into the inside of the black box by measuring adsorption on the working catalyst surface. In the same period many varieties of recent physical tools to study the solid surfaces have been developed and were applied to study the in situ dynamics of working catalyst surface. However, even if some chemisorbed species were observed on the working catalyst surface, it does not follow that they are reaction intermediates. A new dynamic approach to identify the dynamic behavior of each of the chemisorbed species under the reaction conditions, had been proposed by the author by use of “isotope jump method”, in which labeled species are replaced during the course of reaction to study the behavior of each of the adsorbed species under the reaction conditions. By using such new techniques we could not only identify the reaction path and the rate-determining step, but also new phenomena which are called “adsorption assisted processes” were discovered, It is, accordingly, hoped that by means of new nanotechnologies recently developed to study the behavior of single molecules on solid surfaces the nature of heterogeneous catalysis should make a remarkable advances on the basis of this in situ dynamic methods. In this review article emphasis has been put in the fundamental methods of dynamic approaches.     

In situ ultrasonic diagnostic of zeolite X crystallization with novel (hierarchical) morphology from coal fly ash

In this paper the applicability of an in situ ultrasonic diagnostic technique in understanding the formation process of zeolite X with a novel morphology was demonstrated. The complexity of the starting fly ash feedstock demands independent studies of the formation process for each type of zeolite since it is not known whether the crystallization mechanism will always follow the expected reaction pathway. The hierarchical zeolite X was noted to follow a solution phase-mediated crystallization mechanism which differs from earlier studies of the zeolite A formation process from unaged, clear solution extracted from fused fly ash. The use of the in situ ultrasonic monitoring system provided sufficient data points which enabled closer estimation of the time of transition from the nucleation to the crystal growth step. In order to evaluate the effect of temperature on the resulting in situ attenuation signal, synthesis at three higher temperatures (80, 90 and 94 °C) was investigated. It was shown, by the shift of the US-attenuation signal, that faster crystallization occurred when higher temperatures were applied. The novel hierarchical zeolite X was comprised of intergrown disc-like platelets. It was further observed that there was preferential growth of the disc-shaped platelets of zeolite X crystals in one dimension as the synthesis temperature was increased, allowing tailoring of the hierarchical morphology.     

In situ observation of carbon nanotube yarn during voltage application

Carbon nanotube (CNT) yarns are fabricated by drawing (combined with spinning) from CNT forests and grown on a substrate. Three types of phenomena occur in these CNT yarns with increasing amounts of current: yarn rotation, catalyst evaporation, and breakage of the yarn. These phenomena result from the resistive heating occurring during the current flow, and have been observed in situ under vacuum by transmission electron microscopy. If these CNT yarns are applied to electronic circuits, the rotation and breakage may lead to circuit failure. However, catalyst evaporation is a useful method for purifying CNT yarns without additional treatments prior to yarn fabrication.     

In situ ellipsometric study of electrodeposition of manganese films on copper

Electrodeposition of manganese film on copper substrate in a chloride-based solution was investigated by cyclic voltammetry (CV) in combination with in situ spectroscopic ellipsometry (SE). The SE results at different polarization potentials show that the hydrogen evolution has no influence on the SE measurement. The CV results, confirmed by SE data, indicate the starting reduction and oxidation potentials of manganese. The potential for electrodeposition of manganese film with the maximum thickness was determined based on the SE measurements. The SE results show that the manganese film is relatively loose, which is consistent with the observation by scanning electron microscopy (SEM). The growth kinetics of manganese electrodeposition was proposed according to the SE measurements.     

Au nanoparticles in PMMA matrix: In situ synthesis and the effect of Au nanoparticles on PMMA conductivity

Thin PMMA films with and without gold nanoparticles were subjected to ±10 V d.c. and a.c. (square wave) excitations in various frequencies while recording their XPS spectra, and the resulting differences due to charging were examined. Both pure PMMA films and films containing gold nanoparticles showed charging shifts, but those of pure PMMA were more extensive than of PMMA containing gold nanoparticles, suggesting enhanced conductivity, induced by the incorporated gold nanoparticles. Non-charging behavior for these films was also observed with the increase of gold nanoparticle concentration. Gold nanoparticles were in situ synthesized and photo-patterned within the polymer films by UV irradiation.     

In situ determination of radon in surface water bodies by means of a hydrophobic membrane tubing

The naturally occurring radioisotope 222-radon is increasingly recognized as a powerful environmental tracer in hydrology. Several studies proved its applicability for the investigation of groundwater migration processes or of interactions between surface waters and groundwater. While the determination of radon-in-water concentrations is generally done in the laboratory by means of liquid scintillation counting, radon-in-water concentrations can also be measured right away in the field by stripping radon from a water sample into a gas volume and measuring the respective radon-in-gas concentration using a portable radon-in-gas monitor. However, one of the major obstacles of such on-site determination is the potential loss of radon during water sampling and sample handling. A much more promising way of representative radon on-site detection is in situ extraction of radon directly from the water body of concern without any water sampling involved. This approach is in particular advantageous if large water bodies with low radon concentrations, such as lakes or rivers, are subject of investigation. The paper discusses results of laboratory and field experiments in which a newly developed portable “radon extraction module” was used. The module works on the principle of liquid–gas membrane extraction and mainly consists of a coiled-up hydrophobic membrane tubing, which shows a very high permeability with regard to radon. All experimental set-ups and experimental results discussed in the paper are supported by theoretical considerations.     

Facile fabrication of novel cyclomatrix-type polyphosphazene nanotubes with active hydroxyl groups via an in situ template approach

Novel polyphosphazene nanotubes with active hydroxyl groups were fabricated via an in situ template approach under ultrasonic irradiation. SEM and TEM results indicated that the nanotubes were uniform with length of several micrometers, inner diameter of ca. 20 nm and outer diameter of 60-80 nm. FTIR spectra revealed that the content of the hydroxyl groups on the nanotube surface was dependent on the feed ratio of hexachlorocyclotriphosphazene (HCCP) to 4,4′-sulfonyldiphenol. The successful esterification of polymer nanotubes with benzoxy chloride demonstrated the high reactivity of the hydroxyl groups. The method employed here might provide a simple and effective way to prepare functional nanotubes used for biological applications.     

Reaction/crystallization kinetics studied via in situ XRD: experimental conditions versus methods of kinetic analysis

ABSTRACT

Theoretically simulated kinetic data were used to evaluate the errors associated with the common issue of evaluating the in situ non-isothermal X-ray diffraction data, where the complex multi-step temperature program (alternating the non-isothermal heating steps with isothermal steps during which the diffraction patterns are collected) is for the purposes of evaluation replaced by a simple non-isothermal heating performed at the reduced/effective heating rate. The kinetic analysis has shown that, in general, best results are provided by the non-linear optimisation methods simultaneously evaluating the data-curves obtained for all the different heating rates. For the nucleation growth (KMJMA) kinetics the distortive influence of the temperature program parameters increases as follows: heating rate during non-isothermal segments?<?duration of the isothermal segment?<?temperature interval between the isothermal segments. The non-optimisation methods of kinetic analysis (integral isoconversional methods for evaluation of activation energy E and master plots for determining the appropriate kinetic model) were found to perform inaccurately, with large degree of randomness based on the selection of starting temperature, and are not recommended for evaluation of the in situ XRD data – the only exception seem to be the differential isoconversional methods that provided accurate E values. Generalisation of the present conclusions for all KMJMA processes is suggested and discussed.     

In situ measurements of surface impedance and absorption coefficients of porous materials using two microphones and ambient noise

An in situ measurement method is proposed for obtaining the normal surface impedance and absorption coefficient of porous materials using two microphones located close to the material without a specific sound source such as a loudspeaker. Ambient environmental noise that does not excite distinct modes in the sound field is employed as the sound source. Measurements of the normal surface impedance of glass wool and rockwool have been made using this method in various sound fields. The repeatability and wide applicability of the method are demonstrated by comparing results of measurements in one room with different noise conditions and in three other environments (corridor, cafeteria and terrace). The assumed diffuse nature of the sound field on the material is validated by using absorption characteristics obtained experimentally at oblique incidence. This method allows simple and efficient in situ measurements of absorption characteristics of materials in a diffuse field.     

In situ characterization of localized corrosion of stainless steel by scanning electrochemical microscope

Scanning electrochemical microscopy (SECM) area scan measurements have been performed to investigate the localized corrosion of type 304 stainless steel in neutral chloride solution. Variations in the Faradaic current measured at selected tip potential values can be related to changes in the local concentration and electrochemical activities of electroactive species involved in corrosion reactions occurring at the substrate as a function of immersion times of the substrate and polarized currents or potentials applied on the substrate. To further verify the results acquired from cyclic voltammetric experiments, SECM measurements were employed to in situ study the compositions and electrochemical activity distribution profile of the pitting corrosion products of stainless steel. It has been demonstrated that the combination of feedback current mode with generation-collection (G-C) mode of SECM is suitable to elucidate the possible reaction mechanisms and paths involved in the localize corrosion of stainless steel in neutral chloride solution.     

Transition from layer-by-layer to rapid roughening in the growth of DIP on SiO2

Combining atomic force microscopy (AFM) and in situ grazing incidence X-ray diffraction (GIXD) we study the morphology and in-plane structure of diindenoperylene (DIP) on SiO₂ in the early stages of the growth. We unravel noticeable strain relaxation phenomena in the in-plane structure during the growth of the first layers, concomitant with a transition from layer-by-layer growth to rapid roughening at a certain critical thickness of about five monolayers.     

Preparation of poly(3-hexylthiophene)/graphene nanocomposite via in situ reduction of modified graphite oxide sheets

Poly(3-hexylthiophene) (P3HT)/graphene nanocomposites were facilely prepared via an in situ reduction of modified graphite oxide (mGO) in the presence of P3HT. The chemical and aggregated structures of the P3HT/mGO nanocomposites were successfully characterized by means of atomic force microscope (AFM), transmission electron microscope (TEM), photoluminescence (PL), Raman spectra, X-ray photoelectron spectroscopy (XPS) and UV-vis measurements. Coated by P3HT, reduced modified graphite oxide (re-mGO) could significantly improve their processing problem in common organic solvent. It was shown that P3HT chains were attached to re-mGO sheets closely and there existed the pi-pi interaction between P3HT and re-mGO. The P3HT/mGO nanocomposites exhibited good dispersion in chloroform and show high storage stability (>20 days). This finding provides an efficient method for fabricating a light energy conversion materials with new optical and electrical properties, combining excellent mechanics, heat-stabilization properties of graphene and excellent optical, electrical, processing and film forming properties of soluble polythiophene materials.     

In situ QCM and TM-AFM investigations of the early stages of degradation of silver and copper surfaces

The early stages of atmospheric corrosion of pure copper and pure silver specimens were investigated performing in situ tapping mode atomic force microscopy (TM-AFM), in situ quartz crystal microbalance (QCM) and X-ray photoelectron spectroscopy (XPS). The information obtained by TM-AFM is the change of the topography of the sample surfaces with emphasis on the shape and lateral distribution of the corrosion products grown within the first hours of weathering. The simultaneously performed in situ QCM measurements are indicating the mass changes due to possibly occurring corrosive processes on the surface during weathering and are therefore a valuable tool for the determination of corrosion rates. Investigations were carried out in synthetic air at different levels of relative humidity (RH) with and without addition of 250 ppb SO₂ as acidifying agent. On a polished copper surface the growth of corrosion products could be observed by TM-AFM analysis at 60% RH without any addition of acidifying gases [M. Wadsak, M. Schreiner, T. Aastrup, C. Leygraf, Surf. Sci. 454-456 (2000) 246-250]. On a weathered copper surface the addition of SO₂ to the moist air stream leads to the formation of additional features as already described in the literature [M. Wadsak, M. Schreiner, T. Aastrup, C. Leygraf, Surf. Sci. 454-456 (2000) 246-250; Ch. Kleber, J. Weissenrieder, M. Schreiner, C. Leygraf, Appl. Surf. Sci. 193 (2002) 245-253]. Exposing a silver specimen to humidity leads to the degradation of the surface structure as well as to a formation of corrosion products, which could be detected by in situ QCM measurements. After addition of 250 ppb SO₂ to the moist gas stream an increase of the formed feature's volume on the silver surface could be observed by TM-AFM measurements. The results obtained additionally from the in situ QCM measurements confirm the influence of SO₂ due to a further increase of the mass of the formed corrosion layer (and therefore an increase of the calculated corrosion rates) compared to the data obtained from the experiment carried out in humidity only.     

CO吸附和加氢反应过程的原位高压MAS NMR研究

应用原位变温高压MAS核磁共振技术,对比研究了CO在不同Rh基催化剂上的吸附和加氢反应过程. ²⁹Si MAS NMR研究结果表明：Rh基催化剂中加入金属助剂后,载体Silicate-1上的表面硅羟基减少,助剂金属与硅羟基作用锚锭在载体表面.¹³C MAS NMR研究结果表明：当引入CO/H2混合气后,在Rh/Silicate-1催化剂上只能观测到气相CO、线式吸附CO和孪式吸附CO的快速交换信号;而在Rh-Mn/Silicate-1和Rh-Mn-Li/Silicate-1催化剂上,还观测到了倾斜式吸附的CO共振信号,表明助剂Mn或Mn-Li的加入促进了CO的吸附. 随着反应温度升高,CO/H₂在Rh/Silicate-1催化剂上转化生成CO_²,进一步升高温度会有CH₄生成;而CO/H₂在RhMnLi/Silicate-1催化剂上反应活性更高,在较低的温度下就会转化生成CO₂,但未观测到甲烷的生成. ¹H MAS NMR 谱显示,反应后载体Silicate-1上硅羟基的量会减少,表明CO与载体部分表面硅羟基反应生成了CO₂.     

液氨中原位制备Si3N4-TiN纳米复合材料及表征

"提出了一种合成氮化钛/氮化硅(TiN/Si3N4)纳米复合材料的新方法．采用TiCl4和SiCl4作为原料,金属钠作为还原剂,以液氨为介质．在-45 ℃左右同时还原四氯化钛和四氯化硅,通过原位共沉淀获得TiN/Si3N4的纳米复合粉体．X射线衍射表明产物为非晶结构,副产物为氯化钠．产物粉末加热到1600 ℃晶化为TiN和ˉ-Si3N4．由于TiN的存在,混合粉末中的氮化硅晶化温度高于纯氮化硅的晶化温度．透射电镜照片显示粉末平均粒径在10~40 nm,扫描电镜照片表明钛、硅元素彼此均匀分布．在1500~1     

In situ preparation of hydrophobic CaCO3 in the presence of sodium oleate

Hydrophobic CaCO₃ particles were directly prepared via carbonation of Ca(OH)₂ slurry in the presence of sodium oleate at room temperature. Sodium oleate was used to modify the surface property of CaCO₃ particles. The measurement of relative contact angle and active ratio indicated that CaCO₃ samples were hydrophobic. DTG, FT-IR and TEM analysis of the obtained product indicated that the hydrophobic property was attributed to the deposition of calcium oleate, produced in the reaction mixture, onto the surface of calcium carbonate particles. They were covered on the CaCO₃ crystals surface and modified their surface property; at the same time they own CC bonds and could be polymerized or copolymerized later to give a polymeric monolayer.     

Structure and Properties of a cis-1,4-Polybutadiene/Organic Montmorillonite Nanocomposite Prepared via In Situ Polymerization

Cis-1,4-polybutadiene (cis-1,4-PB) is one of the most important synthetic rubbers, having superior performances such as wear resistance, cold resistance and high elasticity. However, its mechanical properties, including low tensile strength, tear resistance and thermal stability, limit its application in comparison to natural rubber and butadiene-styrene rubber that have excellent overall performances. Thus, the reinforcing of cis-1,4-PB is a necessity. The dispersion of clay in rubbers on the nanoscale can improve the mechanical, gas permeability and thermal properties of the resulting composites. In this paper, organic montmorillonite (OMMT) clay was dispersed into the cis-1,4-PB matrix via an in-situ polymerization method and the chemical structure, phase morphology, mechanical properties and thermal stability of the composite were investigated. The properties of the composite were analyzed by such techniques as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and thermal gravimetric analysis (TGA). In the in-situ polymerization, a Ni-based catalyst system with the presence of OMMT showed high efficiency and 1,4-selectivity for the polymerization of butadiene. The OMMT could be dispersed in the polymeric matrix on the nanoscale during the polymerization. The interfusion of OMMT had little influence on the thermal stability and the chemical micro-structure of the cis-1,4-PB when the content of cis-1,4 units was more than 95%. The loss tangent of the composite was higher than that of cis-1,4-PB from ?110 to ?55°C, the temperature range examined, and the mechanical properties of the cis-1,4-PB/OMMT nanocomposite (NC) were improved upon the addition of OMMT.     

In situ hot-stage transmission electron microscopy of Pb(Zr0.52Ti0.48)O3

The domain structure of Pb(Zr_0.52Ti_0.48)O₃ before and after hot-stage experiment has been studied. The influence of maximum temperature, heating and cooling rate on the domain configuration of Pb(Zr_{1? x} , Ti _x )O₃ with x = 0.40, 0.45, 0.48 and 0.55 was analysed. A reliable basis for further hot-stage experiments of Pb(Zr_1?x, Ti_x)O₃ has been established. The investigations revealed a temperature dependent appearance and disappearance of nano- and microdomains. The appearance of microdomains in the nano scale range during cooling, denoted as domain miniaturisation, and the time dependent recovering of the former domain structure, revealed that under specific experimental conditions the domain configuration is reversible.     

In situ synthesis and photophysical properties of the Eu(TTA)3Dipy complex in vinyltriethoxysilane-derived gel glass

The complex of Eu(TTA)₃Dipy was in situ synthesized in vinyltriethoxysilane-derived sol-gel glass (organically modified silicate, ORMOSIL) during heat treatment to obtain homogeneous transparent monolith by using thenoyltrifluoroacetone (TTA) as ligand and 2,2′-dipyridyl (Dipy) as synergic agent. The ORMOSIL doped with the Eu(TTA)₃Dipy complex exhibits enhanced red light emission (∼614 nm) under UV excitation. The steady-state PL spectra at various temperatures and time-resolved luminescence spectra of the Eu(TTA)₃Dipy complex in situ synthesized in the ORMOSIL and the complex polycrystalline powder dissolved in ethanol solution were measured. The photophysical properties responsible for the electronic transitions and excitation energy migration of the complex in ORMOSIL were discussed in this paper by comparison to that in ethanol.     

In situ DRIFTS研究NO在Cu-ZSM-5上的表面吸附及选择性催化还原

Cu-ZSM-5分子筛催化剂选择性催化还原NO具有较好的低温活性,在613 K时NO还原成N2的转化率达70.6%。原位漫反射红外光谱(In situ DRIFTS)是研究催化剂表面吸附物种及催化机理的重要方法,应用该方法在298～773 K范围原位考察了以C₃H₆为还原剂及富O₂ 条件下,NO在Cu-ZSM-5催化剂上的表面吸附及选择性催化还原。认为NO在Cu-ZSM-5催化剂上还原为N₂的过程中,NO以一系列NO_x吸附态形式与丙稀的活化物种(C_xH_y或C_xH_iyO_z)反应,生成有机中间体,再进一步反应,最终生成N₂。有机中间体存在一个明显的从有机胺物种到腈(或—CN)再到有机氮氧物种(R—NO₂或R—ONO)的过程,催化剂表面形成有机中间物种是关键步骤,Cu的作用是促进NO_x形成,O₂ 的作用是促进C₃H₆活化,并且是有效产生有机-氮氧化物不可缺少的条件。