Study on the mechanism of NH3-selective catalytic reduction over CuCexZr1--<?Pub Caret?>x/TiO2

Copper--cerium--zirconium catalysts loaded on TiO₂ prepared by a wet impregnation method were investigated for NH₃-selective catalytic reduction (SCR) of NO_x. The reaction mechanism was proposed on the basis of results from in situ diffuse reflectance infrared transform spectroscopy (DRIFT). When NH₃ is introduced, ammonia bonded to Lewis acid sites is more stable over CuCe_0.25Zr_0.75/TiO₂ at high temperature, while Br?nsted acid sites are more important than Lewis acid sites at low temperature. For the NH₃+NO+O₂ co-adsorption, NH₃ species occupy most of activity sites on CuCe_0.25Zr_0.75/TiO₂ catalyst, and mainly exist in the forms of NH₄⁺ (at low temperature) and NH₃ coordinated (at high temperature), playing a crucial role in the NH₃-SCR process. Two different reaction routes, the L-H mechanism at low temperature (<200°C) and the E-R mechanism at high temperature (>200°C), are presented for the SCR reaction over CuCe_0.25Zr_0.75/TiO₂ catalyst.     

The Auxin-like Activity of Humic Substances is Related to Membrane Interactions in Carrot Cell Cultures

A detailed characterization of two humic fractions was performed: One with low relative molecular mass (LMr < 3,500 Da) and one with high relative molecular mass (HMr > 3,500 Da). Distinct ¹H NMR spectroscopic patterns were observed for the two fractions. HMr showed an aromatic proton region, an intense and broad region (3.0–5.0 ppm) attributed to sugar-like and polyether components, and an intense doublet at 1.33 ppm (identified as protons of the β-CH₃ in lactate). In contrast, LMr did not show resonances due to aromatic protons and was characterized by a broad unresolved region, assigned to sugar-like components. The ¹³C NMR spectra showed that the LMr humic fraction was richer in carboxylic and aliphatic C groups compared to HMr fraction. These substances were fluorescein-labeled [fluorescein isothiocyanate (FITC)], and their interaction with carrot cells in culture was monitored for 10 d, and compared to FITC–indole-3-acetic acid (IAA) to clarify their mechanisms of biological activity. After different incubation times, fluorescein staining of carrot cells and decrease of fluorescein concentration in the culture medium were evaluated. Fluorescent membrane staining was only present in IAA and the LMr humic fraction treated cell cultures. A consequential decrease of fluorescein concentration in the culture media was also observed. Pretreatment of carrot cells with unconjugated IAA or LMr humic fraction markedly reduced fluorescein staining of both FITC–IAA and FITC–LMr humic fraction. Blocking tests gave indirect evidence of possible binding of the LMr humic fraction to IAA cell membrane receptors. These results indicate that the two humic fractions behave differently. Only LMr humic fraction, like IAA, interacts with cellular membranes in carrot cell cultures.     

泥质烃源岩中蒙皂石与有机质的水桥结合作用——来自原位漫反射红外光谱的证据

对济阳坳陷东营凹陷古近系渐新统沙河街组粘土矿物含量较高的烃源岩粉碎后,提取粒径小于2 μm的粘土组分,运用原位漫反射红外光谱技术研究有机质与蒙皂石结合作用机制。当升温至250℃以上时,谱图显示水与羧基振动峰位置发生同步性对应变化,在400℃附近两峰同时消失。将每50℃间水和羧基振动峰面积的差值量作对比发现,在250℃以上温度段面积损失量具有明显的相关性。X-射线衍射结果显示,蒙皂石层间由于物质柱撑作用,d001衍射峰直到450℃才收缩至10 nm,表明含羧基有机分子主要通过氢键与蒙皂石层间水合阳离子相互作用,层间水分子作为“桥梁”将有机质和蒙皂石联结起来。由于“水桥”的联结作用,“水桥”水分子的脱附温度和所联结羧酸分子的分解温度均明显升高,在较高温度下水桥断裂,二者才从蒙皂石层间一同排出。泥质烃源岩中有机质-粘土相互作用机制——水桥机理及其排水滞后性特征,对源岩的生烃、排烃和油气的初次运移具有十分重要的影响。     

Optical characterization of boron carbide powders synthesized with varying B-to-C ratios

Boron carbide powders were synthesized from elemental powders and studied using X-ray diffraction (XRD) and UV–visible diffuse reflectance, Raman, and diffuse reflectance IR spectroscopies. Following reaction at 1400°C for 6 h, synthesized powders exhibited possible faulting as suggested by XRD patterns. B₃C, B_4.3C, and B₅C powders contained graphitic carbon whereas the boron carbides with higher B/C ratios contained no residual carbon, suggesting that the carbon rich phase boundary is likely temperature dependent. Analysis by Raman and IR spectroscopy suggested that Raman spectra are influenced by excitation frequency due to resonance. We suggest that measurement of boron carbides with resonant Raman lifts the selection rules to allow measurement of Raman silent modes that are present in the IR spectra. Optical reflectance of the boron carbide powders revealed that the B/C ratio governed the indirect and direct optical band gaps of the faulted powders. B₃C and B_4.3C powders were light gray in spite of the presence of the carbon, whereas B₅C, B_6.5C, B₁₀C, and B₁₂C were gray, green, brown, and dark brown, respectively. Increasing carbon content increased the optical indirect band gap from 1.3 eV for B₁₂C to 3.2 eV for B₃C, causing the observed color changes.