乙醇羰化非均相催化剂的研究进展

介绍了乙醇羰化制丙酸及丙酸乙酯的非均相催化过程,综述了非均相催化反应过程中的活性组分、催化助剂、载体的选择及其对催化过程的影响。介绍了活性组分分类(络合物、金属氯化物、贵金属和非贵金属),同时介绍了助剂的使用情况和活性炭载体的应用。论述了以往研究的成果和不足,提出了今后的发展方向。     

Structural development of natural rubber during uniaxial stretching by in situ wide angle X-ray diffraction using a synchrotron radiation

Structural development of natural rubber during uniaxial stretching was examined by an in situ wide angle X-ray diffraction measurement using a synchrotron. During stretching, the amorphous part showed little change, i.e. an amorphous halo remained clear even at 500% strain. The fraction of induced crystals was very small, though a clear crystalline pattern was observed at 400% strain. Some polymer chains were oriented and crystallized, but most of the chains were not oriented at all in spite of large deformations of the specimen. Only a small amount of polymer chains contributes to the stress and hysteresis loss during elongation.     

低温等离子体协同催化处理VOC技术中填充材料的研究进展

低温等离子体协同催化净化挥发性有机物(VOC)的方法是一种新型高效的有毒、有害气体处理技术。目前,该技术的完善和改进的主要途径归结于在等离子体反应区填充催化材料上。作者对该技术国内外研究现状进行了综述性评价,对等离子体反应器填充材料进行了分类,对填充材料的性能在等离子体作用前后的变化进行了讨论,在此基础上探讨了低温等离子体-催化协同净化气体技术的发展趋势。     

Use of stirred batch reactors for the assessment of adsorption constants in porous solid catalysts with simultaneous diffusion and reaction. Theoretical analysis

A simple, pseudo-equilibrium model was derived for a catalytic system with a first order chemical reaction and simultaneous diffusive and adsorptive processes, in order to assess the corresponding kinetics and Henry law's-type adsorption parameters. Solutions from this model were compared to exact solutions from a more detailed, general model. It was shown that under most of the experimental conditions used in stirred batch reactors and the usual model considerations, it is only possible to assess apparent adsorption parameters. Also, we observed that a stable relationship between the concentrations in the gas and solid phases is reached. The error produced in assuming that the apparent adsorption constant is the real one was calculated to be very important. The value of the apparent adsorption constant depends on various system properties and experimental conditions, such as the Thiele modulus, the amount of catalyst and the contact time. The ratio between the apparent and real adsorption constants was shown to be the transient effectiveness factor at any moment. This ratio reaches a maximum value for the pseudo-equilibrium state, that is always larger than the steady-state effectiveness factor, becoming closer as long as the system's adsorption capacity decreases. The analysis determines the operative conditions to reduce the parametric correlation. Also a criterion for the applicability of usual approximations in the assessment of kinetics and equilibrium adsorption parameters in porous solid catalysts by means of pulse injection methods is established.     

In situ FTIR experimental results in the silylation of low-k films with hexamethyldisilazane dissolved in supercritical carbon dioxide

In situ Fourier Transform Infrared Spectroscopy measurements were performed using an innovative equipment to study the surface modification reaction between a functionalized porous MSQ-film and hexamethyldisilazane (HMDS) dissolved in CO₂ at supercritical conditions (scCO₂). scCO₂ was used in the heterogeneous reaction due to enhancing properties, ideal for porous materials. Different infrared signatures, from the gas and solid phases, were observed and identified, implying gas–gas and solid–gas phase reactions. Among the different component signatures observed in the gas phase, carbonic acid was observed as a possible silylating gas phase nucleophilic component, while in the solid phase the predominant reaction mechanism proceeded by forming SiOSi bonds and Trimethylaminosilane (as gas phase product).     

An in situ study on the coalescence of monolayer-protected Au-Ag nanoparticle deposits upon heating

The structural evolution of thiolate-protected nanoparticles of gold, silver, and their alloys with various Au/Ag ratios (3:1, 1:1, and 1:3) upon heating was investigated by means of in situ synchrotron radiation X-ray diffraction. The relationships between the coalescence and composition of nanoparticles, as well as the surfactant reactions, were clarified. Experimental results show that there existed a critical temperature ranging from 120°C to 164°C, above which the tiny broad X-ray diffraction peaks became sharp and strong due to particle coalescence. The coalescence temperatures for alloy nanoparticle deposits were clearly lower than those for pure metals, which can be ascribed to the rivalry between the thermodynamic effect due to alloying and the interactions between surface-assembled layers and the surface atoms of the nanoparticles. The strong affinity of thiolates to Ag and thus complex interactions give rise to a greater energy barrier for the coalescence of nanoparticles into the bulk and subsequent high coalescence temperature. The influences of particle coalescence on the optical and electrical properties of the nanoparticle deposits were also explored.     

Advances on the development of novel heterogeneous catalysts for transesterification of triglycerides in biodiesel

This paper describes experimental work done towards the search for more profitable and sustainable alternatives regarding biodiesel production, using heterogeneous catalysts instead of the conventional homogenous alkaline catalysts, such as NaOH, KOH or sodium methoxide, for the methanolysis reaction. This experimental work is a first stage on the development and optimization of new solid catalysts, able to produce biodiesel from vegetable oils. The heterogeneous catalytic process has many differences from the currently used in industry homogeneous process. The main advantage is that, it requires lower investment costs, since no need for separation steps of methanol/catalyst, biodiesel/catalyst and glycerine/catalyst. This work resulted in the selection of CaO and CaO modified with Li catalysts, which showed very good catalytic performances with high activity and stability. In fact FAME yields higher than 92% were observed in two consecutive reaction batches without expensive intermediate reactivation procedures. Therefore, those catalysts appear to be suitable for biodiesel production.     

In situ observation of the capillary infiltration of molten silicon in a SiC/SiC composite by X-ray radiography

Capillary infiltration is an innovative fabrication method for metal and ceramic-matrix composites. SiC/SiC composites can be infiltrated by molten silicon to decrease residual porosity. Physical and chemical mechanisms involved during Liquid Silicon Infiltration (LSI) are complex to analyse. An in situ observation setup for capillary infiltration of molten silicon has been designed for synchrotron observations. The setup reproduces the extreme high temperature and high vacuum conditions used in the LSI process. It is also designed for X-ray observations in synchrotron beamlines and tomography stages. Sets of 2D X-ray absorption radiographs were acquired at high frequency during the LSI process. The study outlines the capillary infiltration mechanisms of molten silicon inside SiC/SiC composites. It proves that full saturation of the composite is not directly achieved after the rise of molten silicon. It is a two step mechanism. First, the infiltration occurs inside the intra granular porosity of the SiC powder matrix. Then, larger scale porosities such as cracks are filled. These phenomena have been discussed previously in the literature but never observed in situ.     

NO reduction with NH3 over chromia–vanadia catalysts supported on TiO2: an in situ Raman spectroscopic study

In situ Raman spectroscopy was used for studying the ternary 2% CrO₃–6% V₂O₅/TiO₂ catalyst, for which a synergistic effect between vanadia and chromia leads to enhanced catalytic performance for the selective catalytic reduction (SCR) of NO with NH₃. The structural properties of this catalyst were studied under NH₃/NO/O₂/N₂/SO₂/H₂O atmospheres at temperatures up to 400 °C and major structural interactions between the surface chromia and vanadia species are observed. The effects of oxygen, ammonia, water vapor and sulfur dioxide presence on the in situ Raman spectra are presented and discussed.     

In situ adaptive tabulation for the CFD simulation of heterogeneous reactors based on operator‐splitting algorithm

In situ Adaptive Tabulation algorithm is applied to efficiently solve the chemical substep in the context of the simulation of heterogeneous reactors. A numerical strategy—specifically conceived for unsteady simulation of catalytic devices—has been developed and interfaced, in the context of the operator splitting technique, with the solution of the chemical substep, which requires 70–90% of the total computational time. The algorithm performances have been illustrated by considering a single channel of a honeycomb reactor operating the catalytic partial oxidation of methane and a methane steam reforming packed bed reactor. The application of in situ adaptive tabulation resulted in a speed‐up of the chemical substep up to ～500 times with an overall speed‐up of ～5–15 times for the whole simulation. Such reduction of the computation effort is key to make affordable fundamental computational fluid dynamics simulations of chemical reactors at a level of complexity relevant to technological applications. © 2016 American Institute of Chemical Engineers AIChE J, 63: 95–104, 2017     

The beneficial role of use of ultrasound in heterogeneous Fenton-like system over supported copper catalysts for degradation of p-chlorophenol

A heterogeneous sono-catalytic system with addition of hydrogen peroxide (US_H2O2+Cat.) was employed for the degradation of 200 ppm of p-chlorophenol (4-CP) at 25 °C and 100 W of ultrasound power. One thousand and six hundred parts per million of initial hydrogen peroxide (H₂O₂) concentration and 1 g/L of catalyst loading over three heterogeneous copper catalysts, CuO, Cu/Al₂O₃ (Cu/Al) and CuO·ZnO/Al₂O₃ (Cu/Zn) was used. The benefits of ultrasound in a heterogeneous catalytic system were evaluated. A considerable synergistic effect of the US_H2O2+Cat. system was only achieved with supported catalysts (Cu/Al and Cu/Zn) possibly due to good dispersion of catalysts as a result of catalyst size reduction during ultrasound irradiation. Moreover, between the two supported copper catalysts, the Cu/Al provided promising catalytic performance by giving higher 4-CP and TOC removal accompanied with efficient H₂O₂ consumption. Experiments with a homogeneous copper catalyst revealed that use of ultrasound in a homogeneous system shows an adverse effect on decomposition of 4-CP.     

Structure–reactivity relationships in VOx/TiO2 catalysts for the oxyhydrative scission of 1-butene and n-butane to acetic acid as examined by in situ-spectroscopic methods and catalytic tests

Different VO_x/TiO₂ catalyst have been catalytically tested and studied by in situ-spectroscopic methods (FT-IR, UV/vis, EPR) in the oxyhydrative scission (OHS) of 1-butene and n-butane to acetic acid (AcOH). While 1-butene OHS follows the sequence butene → butoxide → ketone → AcOH/acetate with a multitude of side products also formed, n-butane OHS leads to AcOH, CO_x and H₂O only. Water vapour in the feed improves AcOH selectivity by blocking adsorption sites for acetate. The admixture of Sb₂O₃ was found to improve AcOH selectivity which is due to deeper V reduction under steady state conditions and lowering of surface acidity. VO_x/TiO₂ catalysts with sulfate-containing anatase are the most effective ones. Covalently bonded sulfate at the catalyst surface causes specific bonding of VO_x, stabilizes active V species and ensures their high dispersity.     

Mechanistic study of partial oxidation of methane to synthesis gas over supported rhodium and ruthenium catalysts using in situ time-resolved FTIR spectroscopy

In situ time-resolved FTIR spectroscopy was used to study the reaction mechanism of partial oxidation of methane to synthesis gas and the interaction of CH₄/O₂/He (2/1/45) gas mixture with adsorbed CO species over SiO₂ and γ-Al₂O₃ supported Rh and Ru catalysts at 500–600°C. It was found that CO is the primary product for the reaction of CH₄/O₂/He (2/1/45) gas mixture over H₂ reduced and working state Rh/SiO₂ catalyst. Direct oxidation of methane is the main pathway of synthesis gas formation over Rh/SiO₂ catalyst. CO₂ is the primary product for the reaction of CH₄/O₂/He (2/1/45) gas mixture over Ru/γ-Al₂O₃ and Ru/SiO₂ catalysts. The dominant reaction pathway of CO formation over Ru/γ-Al₂O₃ and Ru/SiO₂ catalysts is via the reforming reactions of CH₄ with CO₂ and H₂O. The effect of space velocity on the partial oxidation of methane over SiO₂ and γ-Al₂O₃ supported Rh and Ru catalysts is consistent with the above mechanisms. It is also found that consecutive oxidation of surface CO species is an important pathway of CO₂ formation during the partial oxidation of methane to synthesis gas over Rh/SiO₂ and Ru/γ-Al₂O₃ catalysts.     

A novel spectroelectrochemical cell for in situ surface X-ray scattering measurements of single crystal disk electrodes

A newly designed spectroelectrochemical cell was constructed for surface X-ray scattering (SXS) to study single crystal electrodes. Electrochemical characteristics of a specific face of a single crystal electrode can be investigated in the meniscus mode, and SXS measurement can be easily carried out using the spectroelectrochemical cell. The usefulness of the present cell was demonstrated by studying the electrochemical deposition of thin Pd layers on Au(111) and Au(100) that require precise amounts of Pd deposits.     

A preliminary CFD study of the gas-solid flow fields in multizone circulating polymerization reactors

A Eulerian-Eulerian model incorporating the kinetic theory of granular flow is adopted to describe the gas-solid two-phase flows in a multizone circulating propylene polymerization reactor. Corresponding simulations are carried out in a commercial computational fluid dynamics (CFD) code Fluent. First, the model is validated by comparing simulation results with the experimental data. Entire fields in the reactor composed of a riser and a downer are also obtained numerically. Furthermore, the model is used to distinguish the flow behaviors in the riser and the downer. The effects of riser-outlet configuration and operation gas velocity on the flow behaviors in the reactor are also investigated numerically. The simulated results show that the flow behaviors in the riser of MZCR are different from those in the downer of MZCR. In addition, the simulation results also show that both the exit configuration of the riser and the operation gas velocity can significantly affect the flow behaviors in the MZCR.     

Dynamic behavior of supported vanadia catalysts in the selective oxidation of ethane: In situ Raman, UV–Vis DRS and reactivity studies

The coordination and oxidation states of surface vanadia species on different oxide supports were studied by in situ UV–Vis DRS and in situ Raman spectroscopy. Surface vanadia species remain essentially oxidized during the steady-state ethane oxidation reaction. Polymeric surface vanadia species are more reducible than isolated ones, but this has only a minor effect on the ethane oxidation reactions. It appears that only one surface V site is involved in the rate-determining step for ethane oxidation. The reducibility of supported vanadium oxide species corresponds with the TOF values, but not with the average oxidation state under steady-state reaction. Ceria- and niobia-supported vanadia catalysts do not follow this trend due to solid-state reaction between the surface vanadia species and the oxide support that decreases the number of exposed vanadia sites. This solid-state reaction does not appear to affect the nature of the active site, which is associated with the V–O–Support bond rather than with the terminal V=O bond.     

Combined EXAFS and XRD for the in situ structural elucidation of solid catalysts under operating conditions

Two distinct kinds of experimental arrangement permit X-ray absorption and X-ray diffraction data to be recorded in a combined manner under in situ conditions. Results are shown for the conversion of a copper-zinc hydroxycarbonate precursor to a live water-gas shift catalyst and for a zinc oxide and a zeolite model catalyst heated to ca. 1000 ° C. The short-range and long-range structural changes accompanying the conversion of the zeolite into cordierite are charted at high temperature. EXAFS and XANES data can be recordable both in fluorescence or transmission mode with one of the arrangements, which also permits successive measurements (around more than one absorption edge) within a short space of time.     

非均相催化臭氧化水中药物与个人护理品研究进展

药物和个人护理用品（PPCPs）是一类新兴的有机污染物，与常见的污染物相比，在水环境中浓度很低但化学结构复杂，种类多，性质差异大，具有毒性，常规处理技术很难完全去除。非均相催化臭氧化技术的固相催化剂可回收重复利用，二次污染少，目前此处理技术在PPCPs领域的研究已经非常广泛。文章详细描述了非均相催化臭氧化技术降解PPCPs时常遵循的表面反应机理、自由基反应机理、协同反应机理，进一步阐释了自由基反应机理中的4种途径，简要介绍了催化剂等因素对PPCPs降解的影响，归纳总结了非均相催化臭氧化在PPCPs治理领域的应用进展，提出了现今非均相催化臭氧化技术存在的问题，最后展望了非均相催化臭氧化技术的未来研究方向及应用前景。     

The use of temperature-programmed and dynamic/transient methods in catalysis: characterization of ceria-based, model three-way catalysts

Temperature-programmed (TP) methods have been increasingly used in recent years for the characterization of catalytic materials under conditions similar to those encountered in commercial applications. A large variety of complementary TP techniques can be used with minimum variation of experimental conditions, thus allowing great characterization potential in a single apparatus. Modern analytical and numerical tools allow accurate analysis and modeling of TP profiles, to obtain kinetic and other reaction parameters. Here, we will briefly review the experimental TP methods used for the characterization of the reduction features and the dynamic behavior of oxygen-storage/redox components of auto exhaust catalysts, based mainly on CeO₂ and ceria-zirconia.