MgO纳米晶负载镍催化剂用于甲烷蒸汽重整反应(英文)

Nanocrystalline MgO with a relatively high surface area and mesoporous structure was synthesized by a surfactant assisted precipitation method for use as the support of nickel catalysts for steam reforming of methane. The samples were characterized by X‐ray diffraction, N2 adsorption, temperature‐programmed reduction, temperature‐programmed oxidation, scanning electron microscopy, and transmission electron microscopy. The catalysts showed high catalytic activity and good stability in the steam reforming of methane. Increasing the nickel loading up to 10 wt% gave increased activity. Catalysts with higher nickel loadings showed more deposited carbon after reaction. The excellent anti‐coking performance of the catalysts was attributed to the formation of a nickel‐magnesia solid solution, basicity of the support surface, and nickel‐support interaction.     

Electrochemical Oxidation of Catechols in the Presence of Triethyl Phosphite

The mechanism of electrochemical oxidation of catechol and some of its derivatives have been studied in the presence of triethyl phosphite as a nucleophile in aqueous solution. Voltammetric studies indicate that the quinones derived from catechol, and its derivatives, participate in Michael addition reaction with triethyl phosphite. The reaction mechanism consists of electron transfer followed by a chemical reaction which is named as an EC mechanism. The homogeneous rate constants (k_obs) were estimated by comparing the experimental cyclic voltammograms with the digitally simulated voltammograms based on EC mechanism. Also the effects of nucleophile concentration and substituted group of catechols on voltammetric behavior and the rate constants of chemical reactions were examined.     

Hot-Electron Photodynamics in Silver-Containing BEA-Type Nanozeolite Studied by Femtosecond Transient Absorption Spectroscopy

Silver cations were introduced in nanosized BEA-type zeolite containing organic template by ion-exchange followed by chemical reduction towards preparation of photoactive materials (Ag⁰-BEA). The stabilization of highly dispersed Ag⁰ nanoparticles with a size of 1–2 nm in the BEA zeolite was revealed. The transient optical response of the Ag-BEA samples upon photoexcitation at 400 nm was studied by femtosecond absorption. The photodynamic of the hot electrons was found to depend on the sample preparation. The lifetime of the hot electrons in the Ag−BEA samples containing small Ag nanoparticles (1–2 nm) is significantly shortened in comparison to bear Ag nanoparticles with a size of 10 nm. While for the larger Ag nanoparticles, the energy absorbed in the conduction band is decaying by electron-phonon coupling into the metal lattice, the high surface-to-volume ratio of the small Ag nanoparticles favors the dissipation of the energy of the hot electrons from the metal nanoparticles (Ag⁰) towards the zeolitic micro-environment. This finding is encouraging for further applications of Ag-containing zeolites in photocatalysis and plasmonic chemistry.     

Effect of Ni loadings on the activity and coke formation of MgO-modified Ni/Al_2O_3 nanocatalyst in dry reforming of methane

MgO-modified Ni/Al2O3 catalysts with different Ni loadings were prepared and employed in dry reforming of methane （DRM）. The effect of Ni loadings on the activity and coke formation of Ni/MgO-A1203 catalysts were investigated. The synthesized catalysts were characterized by XRD, N2 adsorption-desorption, SEM, TPO and TPR techniques. The obtained results showed that increasing nickel loading decreased the BET surface area and increased the catalytic activity and amount of deposited carbon. In addition, the effect of gas hourly space velocity （GHSV） and feed ratio were studied.     

Application of a Bayesian algorithm for the Statistical Energy model updating of a railway coach

The classical statistical energy analysis (SEA) theory is a common approach for vibroacoustic analysis of coupled complex structures, being efficient to predict high-frequency noise and vibration of engineering systems. There are however some limitations in applying the conventional SEA. The presence of possible strong coupling between subsystems and the lack of diffuseness result in a significant uncertainty. This is the main motivation for the present study, where a procedure to update SEA models is proposed. The proposed procedure is the combination of the classical SEA method and a Bayesian technique. Due to reasons such as finding a limited number of important parameters, using a limited search range, avoiding matrix inversion and taking the effect of noise into account, the proposed strategy can be considered as a proper alternative to the experimental SEA approach. To investigate the performance of the proposed strategy, the SEA model updating of a railway passenger coach is carried out. First, a sensitivity analysis is carried out to select the most sensitive parameters of the SEA model. For the selected parameters of the model, prior probability density functions are then taken into account based on published data on comparison between experimental and theoretical results, so that the variance of the theory is estimated. The Monte Carlo Metropolis Hastings algorithm is employed to estimate the modified values of the parameters. It is shown that the algorithm can be efficiently used to update the SEA models with a high number of unknown parameters.     

Molecularly imprinted polymer based potentiometric sensor for the determination of hydroxyzine in tablets and biological fluids

Molecular imprinting is a useful technique for the preparation of functional materials with molecular recognition properties. In this work, a biomimetic potentiometric sensor, based on a non-covalent imprinted polymer, was fabricated for the recognition and determination of hydroxyzine in tablets and biological fluids. The molecularly imprinted polymer (MIP) was synthesized by precipitation polymerization, using hydroxyzine dihydrochloride as a template molecule, methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylat (EGDMA) as a cross-linking agent. The sensor showed a high selectivity and a sensitive response to the template in aqueous system. The MIP-modified electrode exhibited a Nernstian response (29.4 ± 1.0 mV decade⁻¹) in a wide concentration range of 1.0 × 10⁻⁶ to 1.0 × 10⁻¹ M with a lower detection limit of 7.0 × 10⁻⁷ M. The electrode demonstrated a response time of ∼15 s, a high performance and a satisfactory long-term stability (more than 5 months). The method has the requisite accuracy, sensitivity and precision to assay hydroxyzine in tablets and biological fluids.     

Relationship between Activation Energy of Thermolysis and Friction Sensitivity of Cyclic and Acyclic Nitramines

The knowledge of sensitiveness of an energetic compound to friction stimuli is important to ensure the safety of people and protection of property during shipment. The information on sensitivity to friction is considered very valuable for nitramines, which show relatively higher sensitivity with respect to the other classes of secondary explosives. This study presents a novel general simple model for prediction of the relationship between friction sensitivity and activation energy of thermolysis of cyclic and acyclic nitramines on the basis of their molecular structures. This methodology assumes that friction sensitivity of an energetic compound with general formula C_aH_bN_cO_d can be expressed as a function of activation energy of thermolysis and the contribution of specific molecular structural parameters. For 21 nitramines with different molecular structures, the new correlation has the root mean square and the average standard deviations of 14.2 and 17.8 N, respectively, as compared to experimental values. The proposed new method is also tested for further 8 nitramines containing complex molecular structures, which gives good predictions.     

Radiolytic Approach for Efficient,Selective and Catalyst-free CO2 Conversion at Room Temperature

The present study proposes a new approach for direct CO₂ conversion using primary radicals from water irradiation. In order to ensure reduction of CO₂ into CO₂^−. by all the primary radiation-induced water radicals, we use formate ions to scavenge simultaneously the parent oxidizing radicals H^. and OH^. producing the same transient CO₂^−. radicals. Conditions are optimized to obtain the highest conversion yield of CO₂. The goal is achieved under mild conditions of room temperature, neutral pH and 1 atm of CO₂ pressure. All the available radicals are exploited for selectively converting CO₂ into oxalate that is accompanied by H₂ evolution. The mechanism presented accounts for the results and also sheds light on the data in the literature. The radiolytic approach is a mild and scalable route of direct CO₂ capture at the source in industry and the products, oxalate salt and H₂, can be easily separated.     

Steam reforming for syngas production over Ni and Ni-promoted catalysts

In this article, nanocrystalline γ-alumina with high surface area (309 m² g^?1) and mesoporous structure with an average pore size of 4.3 nm was synthesized and employed as a carrier for the synthesis of Ni catalysts in steam reforming of methane. The results revealed that the metal–support interaction decreased by increasing the nickel loading and led to the movement of the T_max of reduction temperature to lower temperatures. The results demonstrated that the synthesized catalysts exhibited high CH₄ conversion and stability and increasing the nickel loading up to 10 wt% improved the CH₄ conversion. The results revealed that the incorporation of MgO in nickel catalyst improved the resistance of the catalyst against carbon deposition and also enhanced the catalytic activity and the 10%Ni–5%MgO–Al₂O₃ catalyst exhibited high stability during 60 h. The high stability of the promoted catalyst was related to the high basicity of the catalyst.

     

Identification of potential antioxidant compounds in the essential oil of thyme by gas chromatography with mass spectrometry and multivariate calibration techniques

Thyme species are used in traditional medicine throughout the world and are known for their antiseptic, antispasmodic, and antitussive properties. Also, antioxidant activity is one of the interesting properties of thyme essential oil. In this research, we aim to identify peaks potentially responsible for the antioxidant activity of thyme oil from chromatographic fingerprints. Therefore, the chemical compositions of hydrodistilled essential oil of thyme species from different regions were analyzed by gas chromatography with mass spectrometry and antioxidant activities of essential oils were measured by a 1,1‐diphenyl‐2‐picrylhydrazyl radical scavenging test. Several linear multivariate calibration techniques with different preprocessing methods were applied to the chromatograms of thyme essential oils to indicate the peaks responsible for the antioxidant activity. These techniques were applied on data both before and after alignment of chromatograms with correlation optimized warping. In this study, orthogonal projection to latent structures model was found to be a good technique to indicate the potential antioxidant active compounds in the thyme oil due to its simplicity and repeatability.