Multiple transient response methods to identify mechanisms of heterogeneous catalytic reactions

Identification of mechanisms of heterogeneous catalytic reactions is challenging because there are few effective in-situ techniques with which to determine reactive intermediates on surfaces. An effective multiple transient technique consisting of a combination of a broadened pulse with step changes and a sharp isotopic pulse was developed in our group. This technique provides much richer dynamic information than is obtainable from experiments with individual pulses or step changes in reactant concentration. In this Account, we illustrate the method by its application to high-temperature heterogeneous catalytic reactions.     

Polarizing Nuclear Spins Via Photo-Excited Triplet States

In this paper we discuss two methods to achieve high nuclear polarizations at room temperature using pulsed EPR techniques and triplet spins which are optically excited by a laser pulse. The results of our experiments, which are performed on a single crystal of napthalene doped with pentacene, show that an unusually high proton spin polarization can be achieved and that the transfer occurs in a time determined by the dipolar interaction between the electron spins of the pentacene guests and the proton spins on the surrounding napthalene molecules.     

Refining the Dynamic Network of T2SS Endopilus Tip Heterocomplex Combining cw-EPR and Nitroxide–GdIII Distance Measurements

The type 2 secretion system (T2SS) is a bacterial nanomachine composed of an inner membrane assembly platform, an outer membrane pore and a dynamic endopilus. T2SS endopili are organized into a homo-multimeric body formed by the major pilin capped by a heterocomplex of four minor pilins. The first model of the T2SS endopilus was recently released, even if structural dynamics insights are still required to decipher the role of each protein in the full tetrameric complex. Here, we applied continuous-wave and pulse EPR spectroscopy using nitroxide-gadolinium orthogonal labelling strategies to investigate the hetero-oligomeric assembly of the minor pilins. Overall, our data are in line with the endopilus model even if they evidenced conformational flexibility and alternative orientations at local scale of specific regions of minor pilins. The integration of different labelling strategies and EPR experiments demonstrates the pertinence of this approach to investigate protein–protein interactions in such multiprotein heterocomplexes.     

氯化钠存在下微波辐射高稠原油脱水研究

采用SH9402微波反应系统对含水质量分数50%的大庆稠油进行了微波辐射脱水研究。考察了微波辐射时间、压力、功率以及氯化钠对原油脱水率的影响。在微波辐射时间4 min,压力0.2MPa,功率350 W,氯化钠质量分数为3%的条件下,脱水率达到了96.67%。该方法改善了工艺条件,拓宽了微波辐射原油脱水的应用范围。     

Main Source of Microwave Loss in Transition‐Metal‐Doped Ba(Zn1/3Ta2/3)O3 and Ba(Zn1/3Nb2/3)O3 at Cryogenic Temperatures

Microwave resonator measurements were performed on high‐performance microwave ceramics Ba(Zn_1/3Ta_2/3)O₃ (BZT) and Ba(Zn_1/3Nb_2/3)O₃ (BZN) containing additives commonly used by commercial manufacturers (i.e., Co, Mn, and Ni). We find that the loss tangent, even in ambient magnetic fields, is dominated by electron paramagnetic resonance (EPR) absorption by exchange‐coupled 3d electrons in transition metal clusters at cryogenic temperatures. The large orbital angular momentum in Co²⁺ and Ni²⁺ ions of L = 3 causes strong anisotropic‐broadened dipolar interactions that extend EPR losses to zero applied field. This effect is greatest in BZN with Co concentrations greater than 0.5 mol%, dominating the losses at liquid nitrogen temperatures (77 K) and below. In samples containing Mn²⁺ ions with L = 0, the dipolar interactions and associated EPR losses in ambient fields are smaller. We show the magnetic‐field‐dependent changes in the EPR losses (i.e., tan δ) and magnetic reactive response (i.e., μ_r) are from the same mechanism, as they follow the Kramers–Kronig relation. Finally, we note that these materials can make ultra‐high Q passive microwave devices with externally controlled transfer functions, as the quality factor (Q) of the composition Ba(Co_1/15Zn_4/15Nb_2/3)O₃ at 77 K can be tuned from 1 100 to 12 000 at 10 GHz by applying practical magnetic fields.     

Microwave-promoted burning of Portland cement clinker

A new method of burning Portland cement clinker is studied. The microwave sintering is adopted after the raw meal is heated to certain temperature in an electric furnace. The experimental results show that after the raw meal is heated at a low electric heating temperature (1000-1200 °C) and then further sintered with microwave for 1 to 2 min, Portland cement clinkers can be formed. The f-CaO contents of the clinkers are 1-2%. It has also been found that the higher the temperature of the samples put into the microwave cavity, the shorter the time needed for microwave burning. When the temperature is up to 1300 °C, the sample needs to be heated by microwave for only 40 s, and the f-CaO content decreases to 0.65%. It has been proved by the experiments that (1) the new burning technique can greatly increase the forming speed of Portland cement clinkers, (2) Fe₂O₃ can enhance the microwave clinkering. XRD patterns of the clinkers show that their mineral compositions and the characteristic XRD peaks are similar to those of clinkers by conventional burning method.     

乙丙橡胶中试装置进料单元优化控制研究

乙丙橡胶中试装置是吉林石化公司研究院开展中试实验和开发新牌号乙丙橡胶的实验基地。通过对中试装置进料单元改造及优化控制,进料单元乙烯、丙烯、氢气、催化剂等原料的流量和进料比例更加精确、稳定、可控,使中试实验和开发新牌号乙丙橡胶的相对分子质量稳定且门尼粘度值更接近设计要求,胶液性能达到预期效果。     

微波加热在钛带冷轧酸洗中的应用

阐述了传统加热方式在钛带冷轧酸洗中的应用及其存在的问题,并分析了微波加热酸洗液的原理和技术特点,利用一种新型的微波加热设备,提出一种利用微波加热钛带冷轧酸洗液的新技术,通过中试实验证明新技术是有效合理的。并展望了微波加热技术在钢铁及有色金属行业冷轧酸洗工艺加热中的应用前景。     

Specific Features of Sheet Acceleration under Conditions of Magnetic Pulse Welding

Magnetic pulse welding differs from explosive welding only by sources of energy for sheet acceleration: magnetic field energy is used instead of explosion energy. Magnetic field interaction with the sheet has some specific features associated with the value of energy stored in the battery, the rate of heating to the melting point, and the possibility of sheet buckling, which impose constraints on using magnetic pulse welding. These constraints are associated with geometric parameters of the welded sheets and the gaps between them; the critical values of these parameters are obtained in the present study. A capacitor battery is used in the experiments for sheet acceleration. A new pioneering scheme of magnetic pulse welding of more than two sheets is developed.     

COMBINED SUPERHEATED STEAM AND MICROWAVE DRYING OF SINTERED GLASS BEADS: DRYING RATE CURVES

A new drying method of combined superheated steam and microwave drying is being proposed. The drying rates of sintered glass beads in combined superheated steam and microwave drying are experimentally and theoretically investigated. Drying experiments have been carried out in a waveguide where a standing wave is formed to uniformly heat a small sample. Concerning drying rate curves in combined superheated steam and microwave drying, a distinct constant rate period has been observed. For the falling rate period, high drying rates have been observed. For both periods, the drying rates in combined superheated steam and microwave drying are higher than those in superheated steam alone. Also, in comparison with the results of combined nitrogen and microwave drying, the normalized drying rates in combined superheated steam and microwave drying are higher than those at less than the critical moisture content in combined nitrogen and microwave drying. Moreover, theoretical drying rates for the falling rate period (predicted by a modified receding evaporation front model) in combined superheated steam and microwave drying, are in good agreement with the observed drying rates. The combined superheated steam and microwave drying method can attain higher drying rates under mild external conditions.     

放射性废树脂微波桶内干燥控制方式研究

用微波作为热源,在桶内干燥核电厂产生的废树脂。通过对脉冲式和旋转式两种控制方式在12L规模和200L规模台架中的实验研究可知,两种控制方式均可有效的改善树脂干燥的均匀性问题,但从试验安全和设备设计角度出发建议下一步以脉冲式控制为台架装置设计基础。     

Design and analysis of the commercialized drier processing using a combined unsymmetrical double-feed microwave and vacuum system (case study: tea leaves)

Combined microwave (MW) and vacuum drying of biomaterials has a promising potential for high-quality dehydrated products. A better knowledge of the drying kinetics of biomaterial products could improve the design and operation of efficient dehydration systems. The experiments were carried out on commercialized biomaterials drier using a combined unsymmetrical double-feed microwave and vacuum system. Three kilograms of tea leaves were applied with the microwave power of 800 (single-feed magnetron) and 1600 W (unsymmetrical double-feed magnetrons) operating at 2450 MHz frequency. Rotation rates of the rotary drum were held constant at 10 rpm. Vacuum pressure was controlled at the constant pressure of 385 Torr and 535 Torr, respectively. In this study, the system can be operated either in continuous or pulse mode in each experiments. Experiments show that in the case of high power level and continuous operating mode causes greater damage to the structure of tea leaves sample. Microwave drying with pulse operating mode at 385 Torr ensured the shortest drying time and the best overall quality of dried tea leaves, and thus was chosen as the most appropriate technique for tea leaves drying.     

Experimental Evidence for the Anisotropic Nature of the Transient EPR Spectrum from Photosystem I Observed in Cyanobacteria

Early transient EPR spectra at room temperature, with high spectral (K-band, 24 GHz) and time (50 ns) resolution, are presented for whole cells of deuterated cyanobacteria (Synechococcus lividus). A full range, between high and low microwave power, is covered. The true low-power spectrum of the charge-separated state in Photosystem I prior to electron transfer to the iron-sulfur center acceptors could be established. The anisotropic nature of the signal has been confirmed with the observation of transient nutations at high microwave power, which indicate possible motional effects or spin dynamics.     

Drying activity of oxovanadium(IV) 2-ethylhexanoate in solvent-borne alkyd paints

Oxovanadium(IV) 2-ethylhexanoate was established as a new primary drier for alkyd-based paints. A series of experiments has demonstrated an excellent drying activity toward solvent-borne alkyd resins of different oil length at considerably lower metal concentration than optimal for commercial cobalt(II) 2-ethylhexanoate. The behavior in real paint was simulated on formulations bearing inhibitor of autooxidation. The detailed studies of the drying process have shown that the relatively slow initial step of autooxidation reaction, when compared with cobalt compounds, is compensated for by the absence of the induction times. Furthermore, the active oxovanadium(IV) species are not consumed during the drying processes as evidenced by EPR spectroscopic measurements.     

Organic/inorganic electrodes (ORINELs) with continuous phase components

A new class of composite materials for electrodes is introduced; their characteristic feature is the connectivity of the components. Composites comprising hydrated iridium oxide and polyaniline are characterized by impedance spectroscopy and current pulse experiments.     

Initiation of reaction in the vicinity of a single particle heated by microwave radiation

A model of initiation of the decomposition of liquid hydrocarbon in the vicinity of a single particle heated by microwave radiation is proposed. An analytical dependence of the critical particle size on the power density, the pulse duration of the microwave generator, and the ratios of the heat capacities and densities of the particles and reactant is obtained numerically.     

Morphology evolution during cooling of quiescent immiscible polymer blends: matrix crystallization effect on the dispersed phase coalescence

The influence of the matrix crystallization on the coalescence of the dispersed phase particles, in quiescent immiscible polymer blends, is a topic that is scientifically addressed scarcely. The coarsening of the phase structure that is induced by the matrix crystallizing domains was studied using the well-established system comprising a polypropylene and an ethylene–propylene rubber (PP/EPR blends). This subject is of great importance as the effectiveness in the toughening of PP is directly determined by the EPR particle size. Cooling experiments were commenced for resolving the correlation among the imposed cooling conditions, the formed matrix crystalline morphology, and the coalescence of the dispersed phase particles. A confirmation of the profound effect of the PP crystallization on the coalescence of EPR particles was undoubtedly obtained. The contribution of the crystallization to the coalescence of the dispersed phase particles is largest at a finite rate of cooling. A thorough discussion regarding the observed effects, encompassing a potential rejection or an engulfing of the dispersed phase particles by the growing crystallites, was undertaken.     

Application of nonlinear wave propagation theory to adsorption kinetic measurements on supported catalysts

A new technique has been developed which can be used to determined the coverage-dependent heat of adsorption on supported catalysts from pulse experiments using a packed-bed adsorption column. This development is based on the theory of nonlinear wave propagation applied to a transient adsorption system. The unique feature of this technique is that the coverage-dependent heat of adsorption can be determined solely from the measurement of the column-average propagation speed of the adsorbate pulse, without any knowledge on the details of the pulse shape.     

Radicals,radical pairs and triplet states in photosynthesis

The investigation of radical ions, radical pairs, and triplet states that occur in the primary processes of photosynthesis by various EPR techniques is described. The determination of the valence electron spin density distribution by ENDOR/TRIPLE spectroscopy is demonstrated for the primary electron donor. In combination with site-directed mutagenesis, these studies show that the spin distribution in the chlorophyll donor is strongly affected by the protein environment, and a link is established with the donor's oxidation potential and function in the electron transfer process. Similarities and differences between electron donors in anoxygenic (bacterial) and oxygenic photosynthesis are briefly discussed. Application of transient and pulse EPR techniques give information also on short-lived intermediates, such as radical pairs and triplet states, and allow the determination of distances and relative orientations of these species. The extension to time-resolved pulse ENDOR spectroscopy opens the possibility to resolve the electron-nuclear hyperfine structure of these reaction intermediates, even on a very short time scale.     

Experimental methods in chemical engineering: Electron paramagnetic resonance spectroscopy-EPR/ESR

Electron paramagnetic resonance (EPR) spectroscopy, also known as electron spin resonance spectroscopy (ESR), utilizes absorption of microwave radiation by unpaired electrons in a magnetic field. The interaction between the unpaired electron(s) and nearby magnetic nuclei helps identify paramagnetic species and can provide information about the motion of the molecule and the local polarity, pH, viscosity, concentration, and accessibility to other paramagnetic species. This mini-review discusses the fundamental underpinnings of EPR needed to correctly interpret EPR spectra. We describe various types of EPR spectra encountered by chemical engineers, and use application examples drawn from the chemical engineering literature to illustrate the information available from the technique. Few chemical engineering departments or even chemistry departments have EPR instruments, which contributes to the significant barrier that prevents this being adopted as a routine measurement technique. However, in 2016 and 2017, Web of Science indexed 7000 articles that applied EPR spectroscopy. A bibliometric map categorized the keywords in four categories based on co-occurrences: magnetic properties, films, and luminescence; crystal structure, complexes, and ligands; nanoparticles, oxidation, and degradation; and, systems, radicals, and H₂ O₂ .