焙烧温度及焙烧时间对异丁烯部分氧化合成甲基丙烯醛催化剂性能的影响

采用沉淀法制备了Mo-Bi-Co-Fe-Cs复合氧化物催化剂, 并用于异丁烯部分氧化制备甲基丙烯醛反应, 结合H_2-TPR、 XRD、 BET和TEM表征, 考察了焙烧温度以及焙烧时间对催化剂物理化学性质及催化性能的影响.研究结果表明, 随焙烧温度升高, 催化剂物相结构没有明显的改变, 而催化剂颗粒则逐渐增大, 氧化能力降低, 且组分之间的协同作用减弱;当焙烧温度提高到540 ℃时, 催化剂局部颗粒已出现烧结. 催化剂活性随焙烧温度提高逐渐下降, 而甲基丙烯醛选择性则在焙烧温度为520 ℃时达到最大值, 焙烧温度对催化剂性能的影响可能因催化剂表面活性位密度不同所致.合适的焙烧温度为520 ℃, 焙烧时间为5 h, 此时异丁烯转化率为98.4%时, MAL选择性可达到87.2%, 具有较好的反应效果.     

预处理条件对用于CO_2加氢的超细CuO－ZnO－SiO_2催化剂性能的影响

采用ＸＲＤ、ＢＥＴ、ＴＰＲ手段，研究了焙烧和还原温度对超细ＣｕＯ－ＺｎＯ－ＳｉＯ２催化剂的性质及其ＣＯ２加氢反应催化活性的影响．胶体在５７３－７７３Ｋ范围内焙烧生成ＣｕＯ、Ｃｕ２Ｏ、ＺｎＯ晶相，随着焙烧温度继续升高，ＣｕＯ和ＺｎＯ晶粒逐渐变大，但催化剂的比表面积和孔容变化很小．在９７３Ｋ焙烧后出现Ｚｎ２ＳｉＯ４晶相，使催化剂比表积和孔容变小，导致催化剂活性降低．焙烧温度对催化剂活性的影响大于对ＣＯ２加氢产物分布的影响．在５４８－６４８Ｋ范围内，催化剂还原温度对其催化活性影响不大．７０３Ｋ高温还原后，可能由于Ｃｕ０晶粒的出现，使得催化剂的活性下降．ＴＰＲ研究结果进一步表明，焙烧温度影响ＣｕＯ同ＺｎＯ、ＳｉＯ２之间的相互作用和催化剂的还原行为．     

Rod-shaped porous alumina-supported Cr2O3 catalyst with low acidity for propane dehydrogenation

Direct catalytic propane dehydrogenation (PDH) to obtain propylene is a more economical and environmentally friendly route for propylene production. In particular, alumina-supported Cr₂O₃ catalysts can have better potential applications if the acidic properties could be tuned. Herein, a series of rod-shaped porous alumina were prepared through a hydrothermal route, followed by calcination. It was found that the acidity of the synthesized alumina was generally lower than that of the commercial alumina and could be adjusted well by varying the calcination temperature. Such alumina materials were used as supports for active Cr₂O₃, and the obtained catalysts could enhance the resistance to coke formation associated with similar activity in PDH reaction compared to the commercial alumina. The amount of coke deposited on a self-made catalyst (Cr-Al-800) was 3.6%, which was much lower than that deposited on the reference catalyst (15.7%). The lower acidity of the catalyst inhibited the side reactions and coke formation during the PDH process, which was beneficial for its high activity and superior anti-coking properties.     

Co-K-Mo/γ-Al2O3催化剂的合成低碳醇性能及其结构研究

氧化态Ｋ－ＭｏＯ３／γ－Ａｌ２Ｏ３催化剂中添加Ｃｏ（ＮＯ３）２后在空气中四个不同温度下焙烧再硫化,制得Ｃｏ－Ｋ－ＭｏＯ３／γＡｌ２Ｏ３催化剂,对其ＣＯ加氢合成低碳醇的催化反应性能进行了评价,运用ＸＲＤ,ＬＲＳ及ＥＸＡＦＳ等手段对催化剂及其氧化态前躯体的结构进行了表征,活性测试结果表明加Ｃｏ后于５００－６５０℃焙烧制得的催化剂活性较高,且使Ｃ２＋醇比例增加,结构分析结果显示加Ｃｏ后３５０℃焙烧时,Ｃ     

Thermochemical decomposition of cobalt doped ammonium paratungstate precursor

The calcination is one of the important steps in the preparation of nanostructured WC and WC–Co powders from chemically co-precipitated W–Co precursors. In the present paper, the processing of the precursor prepared by co-precipitation from cobalt(II) hydroxide and ammonium paratungstate is reported. The precursor was calcined at different temperatures under various atmospheres. The resulting powders were investigated using scanning electron microscopy, X-ray diffraction, thermogravimetric analysis (TGA), differential TGA, BET, and mass spectrographic analysis techniques. The results showed that the precursor decomposes differently by calcination under different atmospheres, i.e. nitrogen, air, and helium–5% oxygen. Different decomposition behaviour was observed when the calcination was carried out at medium temperature in flowing and non-flowing air. Nanostructured powders with particle size of around 90 nm can be obtained after calcination. The precursor decomposes into CoWO₄ and WO₃ oxides at 520 °C in air after a weight loss of 10.3%.     

锂锌铁氧体微纳米纤维的电纺制备及吸波性能

采用静电纺丝技术结合后续热处理制备了尖晶石型Li_0.35Zn_0.3Fe_2.35O₄微纳米纤维. 利用差示扫描量热(DSC)-热重分析(TGA)、 傅里叶变换红外光谱(FTIR)、 X射线衍射(XRD)和场发射扫描电子显微镜(FESEM)等手段研究了煅烧温度(700, 800, 900, 1000 ℃)对产物物相和形貌的影响; 利用矢量网络分析仪分析了纤维状产物的吸波性能. 研究结果表明, Li_0.35Zn_0.3Fe_2.35O₄在700 ℃及以上温度煅烧后可生成单一尖晶石结构. 随着煅烧温度的升高, 产物依次呈现出微纳米纤维状、 三维网络状、 竹节状和颗粒状的微观形貌. 随着匹配厚度增加, 微纳米纤维状Li_0.35Zn_0.3Fe_2.35O₄的最低反射率向低频移动, 在8 GHz以下的最佳匹配厚度为6 mm, 在此厚度下吸波性能优良, 最低反射率为-26 dB, 对应的吸收频率为5.0 GHz, 低于-10 dB的吸收频带为4.0~8.0 GHz, 带宽为4 GHz.     

Effect of Calcination Temperature on Catalytic Activity and Textual Property of Cu/HMOR Catalysts in Dimethyl Ether Carbonylation Reaction

The effect of calcination temperature on the catalytic activity for the dimethyl ether (DME) carbonylation into methyl acetate (MA) was investigated over mordenite supported copper (Cu/HMOR) prepared by ion-exchange process. The results showed that the catalytic activ-ity was obviously affected by the calcination temperature. The maximal DME conversion of 97.2% and the MA selectivity of 97.9% were obtained over the Cu/HMOR calcined at 430 oC under conditions of 210 oC, 1.5 MPa, and GSHV of 4883 h^-1. The obtained Cu/HMOR catalysts were characterized by powder X-ray diffraction, N₂ absorption, NH₃ temperature program desorption, CO temperature program desorption, and Raman techniques. Proper calcination temperature was effective to promote copper ions migration and diffusion, and led the support HMOR to possess more acid activity sites, which exhibited the complete decomposing of copper nitrate, large surface area and optimum micropore structure, more amount of CO adsorption site and proper amount of weak acid centers.     

Effect of Calcination Temperature on Surface Oxygen Vacancies and Catalytic Performance Towards CO Oxidation of Co3O4 Nanoparticles Supported on SiO2

Co₃O₄/SiO₂ catalysts for CO oxidation were prepared by conventional incipient wetness impregnation followed by calcination at various temperatures. Their structures were char-acterized with X-ray diffraction (XRD), laser Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and X-ray absorption fine structure (XAFS) spectroscopy. Both XRD and Raman spectroscopy only detect the ex-istence of Co₃O₄ crystallites in all catalysts. However, XPS results indicate that excess Co²⁺ ions are present on the surface of Co₃O₄ in Co₃O₄(200)/SiO₂ as compared with bulk Co₃O₄. Meanwhile, TPR results suggest the presence of surface oxygen vacancies on Co₃O₄ in Co₃O₄(200)/SiO₂, and XAFS results demonstrate that Co₃O₄ in Co₃O₄(200)/SiO₂ con-tains excess Co²⁺. Increasing calcination temperature results in oxidation of excess Co²⁺ and the decrease of the concentration of surface oxygen vacancies, consequently the for-mation of stoichiometric Co₃O₄ on supported catalysts. Among all Co₃O₄/SiO₂ catalysts,Co₃O₄(200)/SiO₂ exhibits the best catalytic performance towards CO oxidation, demon-strating that excess Co²⁺ and surface oxygen vacancies can enhance the catalytic activity of Co₃O₄ towards CO oxidation. These results nicely demonstrate the effect of calcination temperature on the structure and catalytic performance towards CO oxidation of silica-supported Co₃O₄ catalysts and highlight the important role of surface oxygen vacancies on Co₃O₄.     

Low-temperature CO gas sensors based on Au/SnO2 thick film

A study on the low-temperature CO gas sensors based on Au/SnO₂ thick film was reported. Au/SnO₂ powders were prepared by a deposition-precipitation method. Thick films were fabricated from Au/SnO₂ powders. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) analyses were carried out for investigation of morphology and crystalline structure. Au/SnO₂ thick film sensors exhibited high sensitivity to CO gas at relatively low operating temperature (83-210 °C). We also reported the effect of the calcination temperature of Au/SnO₂ on the CO gas sensing behavior. The optimal calcination temperature of Au/SnO₂ was 300 °C.     

Role of calcination on geopolymerization of lateritic clay by alkali treatment

In the present study, the role of calcination of a low iron lateritic clay sample was investigated to synthesize the geopolymer. The analyses like X-ray fluorescence (XRF) spectroscopy for chemical composition, X-ray diffractometry (XRD) for mineral composition, and Fourier transform infrared (FT-IR) spectroscopy & scanning electron microscopy (SEM) for structural changes upon calcination at 500, 700 and, 900 °C were used to assess the suitability of selected lateritic clay sample for geopolymer. The drop in electrical conductivity and greater consumption of calcium hydroxide by CS-900 confirmed its potential reactivity than CS-700, CS-500, and CS-Control. The quality of geopolymer derived from un-calcined and calcined lateritic clay samples by alkali activation was evaluated by comparing results of compressive strength, water absorption test, and stability in the aggressive environment of chloride, FT-IR, XRD, and SEM analyses. The experimental results reveal that the quality of geopolymer enhances as the calcination temperature of the lateritic clay sample increases, However, calcination of the lateritic clay sample at 900 °C gives significant results and yield good quality geopolymer with 24.8 MPa of compressive strength, 7.07% of water absorption and 2.22% loss in mass in an aggressive environment.