Identification of the role of surface acidity in the deactivation of TiO2 in the selective photo-oxidation of cyclohexane

Anatase-structured Ti_1−xZr_xO₂ materials with x = 0.00, 0.01 and 0.06, were prepared by a reverse microemulsion method, characterized, and tested as catalysts for the selective photo-oxidation of cyclohexane to cyclohexanone. In situ ATR-FTIR spectroscopy was used to evaluate the reaction. Zr incorporation into the anatase lattice enhances the surface acidity of TiO₂ without causing any significant structural or electronic modification. As expected, also the stability of surface adsorbed water, i.e. the hydrophilicity, was enhanced. The increase in the Brønsted acidity, together with the higher hydrophilicity, is shown to be detrimental for performance (selectivity and stability) in the selective photo-oxidation of cyclohexane. Apparently potential intrinsic catalytic advantages of having higher acidity are outweighed by (i) the enhanced number of water born OH radicals, inducing non-selective reactions, and (ii) enhanced hydrophilicity leading to slow desorption and consecutive oxidation of cyclohexanone.     

Novel Mo/Ga/H-ZSM-5 catalyst in environmentally important reductive transformation of N2O in presence of CH4

Direct decomposition of N₂O and the reduction of N₂O with CH₄ over Ga/H-ZSM-5 and Mo/Ga/H-ZSM-5 (Si/Al = 40) catalysts in a plug flow reactor under steady-state conditions as well as by temperature programmed surface reaction (TPSR) have been investigated. Ga ions were ion-exchanged from liquid phase while Mo was deposited onto the Ga/H-ZSM-5 sample using incipient wetness technique. The catalysts were characterized by means of XRF, XPS, TPR, CO chemisorption, TEM and EDS. The N₂O forms redox centers in the Mo/Ga/H-ZSM-5 catalysts at elevated temperatures, which are extremely active in the reaction with CH₄ already at around 373 K. Addition of Mo to the Ga/H-ZSM-5 decreased the T₅₀ temperature in the N₂O decomposition and reduction of N₂O with CH₄ from 819 to 787 K and from 755 to 646 K, respectively. The oxidation/reduction of the Mo/Ga/H-ZSM-5 sample is more favoured in the interaction with N₂O/CH₄ as compared to that using O₂/H₂ and the mechanism of the redox reactions might also be different. The reduction of N₂O with CH₄ cannot be described with the Mars–van Krevelen redox mechanism, but by the participation of CH₄ via MoGa–OCH₃ species in a complex oxygen transfer mechanism is proposed at which N₂O does not directly reoxidise the reduced active centers.     

V–Mg–O catalysts for oxidative dehydrogenation of alkylpyridines and alkylthiophenes

Vanadium appears to be the element that is most frequent (along with molybdenum) used in the catalyst formulations for oxidative dehydrogenation (ODH) of hydrocarbons and alcohols. In the present work the employment of ODH reaction in the presence of air has been extended for the preparation of vinyl substituted pyridines and thiophenes using vanadium (and for comparison molybdenum) oxide catalysts.The efficiency of vanadium–magnesium oxide catalysts in the production of vinylpyridines and vinylthiophenes has been evaluated. A strong dependence of the yield and selectivity of the latter upon the vanadium (molybdenum) oxide loading and the conditions of heat treatment were observed. In optimized reaction conditions V–Mg–O catalysts at the temperature approximate 450 °C ensured the formation of vinylpyridines and vinylthiophenes with the yield of 40–60% at the selectivity of 90%. In prolonged runs no visible changes in the performance of the catalyst were observed. DTA–DTG, XRD, IR ESR, NMR methods have been used detecting the formation of species of V–Mg–O catalysts that appear to be responsible for the catalyst efficiency in the reactions under consideration.     

Ca1-x（Li1/2Sm1/2）xTiO3体系微波介质陶瓷的低温烧结研究

采用传统陶瓷制备工艺,制备了添加10 wt%NCB(Na2O-CaO-B3O3)复合氧化物的Ca1-x(Li1/2Sm1/2)xTiO3(x=0.700～0.875)(CLST-x)体系陶瓷,研究了添加NCB后CLST-x体系的晶相组成、显微结构、烧结性能及微波介电性能与组成关系.研究结果表明,添加复合氧化物NCB后,CLST-x体系各组成主晶相仍呈斜方钙钛矿结构,没有其它杂相.添加10wt%NCB后,CLST-x体系陶瓷均可在950℃下烧结致密,在此温度下材料具有较佳的微波介电性能,其中CLST-0.875陶瓷在950℃保温5 h烧结后具有良好的微波介电性能:εr=63.6,Qf=1591 GHz,τ f=0 ppm/℃,可满足高介多层微波器件的设计要求.     

ClO2催化氧化含酚废水的实验研究

采用浸渍法制备Fe/γ-Al₂O₃催化剂,用于ClO₂催化氧化处理含酚废水,研究废水初始pH、ClO₂用量、催化剂加入量、反应温度和催化剂重复使用等因素对含酚废水总有机碳(TOC)去除率的影响。结果表明,在pH为7、V(ClO₂)∶V(酚溶液)=0.20、Fe/γ-Al₂O₃催化剂加入量20 g·L^-1和反应温度20 ℃条件下,Fe/γ-Al₂O₃催化剂能连续使用7次,保持稳定的催化活性,对含酚废水的TOC去除率为58.83%。     

化学合成制药综合废水的处理

本文介绍了化学合成制药废水的处理工艺、原理和运行效果,该工艺处理后的污水完全达到国家规定的污水排放标准。     

过氧化氢处理含染料废水研究新进展

简要介绍近来利用过氧化氢处理含染料废水的各种方法研究进展,染料包括直接染料、酸性染料、活性染料、媒介染料等,其中多含偶氮键。处理方法包括Fenton法、UV／Fenton法、UV／H2O2法、超声波／H2O2法、O3／H2O2法等。大多均以脱色率和TOC去除率来评价处理效果。实验结果表明,各种方法的处理效果均较显著,但均是以模拟染料废水进行的实验室研究,有待生产应用和检验。有些研究涉及染料降解脱色反应动力学方面,均确定过程为一级或假一级反应,有些研究给出动力学方程式和反应速率常数。     

掺杂W~(6+)的Zr(WV)_xO_y质复相陶瓷的制备及特性研究

以WO3、V2O5及ZrO2粉末为原料,用氧化物煅烧法制备了掺杂W6+的Zr(WV)xOy质复相陶瓷。结果表明,复相陶瓷纯度高,杂质含量少;采取W元素和V元素的不同配比的两种配方分别实现了W元素的少量掺杂和以W元素为主、ZrV2O7为辅的良好复合;复相陶瓷在室温到100℃呈现正热膨胀特性,继续升高温度到420℃,材料表现出负热膨胀特性。但平均线膨胀系数与纯ZrV2O7的线膨胀系数相比有明显的增大。     

仿滑石瓷釉的研制——用于低温釉中彩装饰

根据仿滑石质瓷的特点,本试验探讨了不同熔剂和熔剂比例、工艺条件和烧成制度等因素对釉面效果的影响.最终研制出一种适应滑石瓷在900～1 200 ℃适合釉中彩装饰的Li2O-BaO-SrO-CaO-B2O3-SiO2系统低温熔块釉.     

TiN改性Al2O3纳米复相陶瓷的研究进展

Al2O3陶瓷具有高硬度、耐高温、耐腐蚀和耐磨损等优点．是应用最广泛的陶瓷之一．但脆性大．难以加工．严重限制了它的应用范围。主要介绍了TiN改性Al2O3纳米陶瓷的研究进展．与SiC、ZrO2改性Al2O3纳米陶瓷相比,TiN—Al2O3纳米复相陶瓷不仅力学性能优异,而且具有导电能力,可用于电火花加工．扩大了Al2O3陶瓷的应用范围。最后对Al2O3纳米复相陶瓷的发展前景作了展望。