Remarkable Enhancement in the Dispersion and Low-Temperature Activity of Catalysts Prepared via Novel Plasma Reduction-Calcination Method

A novel plasma reduction and calcination (PR&C) method has been recently developed. Upon the experimental investigations on methane conversions, including partial oxidation, methane combustion, NO reduction by methane and CO₂ reforming, the catalysts prepared by this PR&C method exhibit a remarkable enhancement in the dispersion, low-temperature activity and stability. A plasma-enhanced acidity has also been addressed, which would play an important role in the improved dispersion. The PR&C method is leading to a better preparation of supported catalysts, esp., those for methane conversion.     

Low-temperature synthesis of nanocrystalline β-dicalcium silicate with high specific surface area

β-Dicalcium silicate (β-Ca₂SiO₄) was synthesized for the first time by a simple solution combustion method using citric acid as fuel. The influence of calcination temperature on the average crystallite size, specific surface area and morphology of the powders were investigated by X-ray diffraction technique (XRD), scanning electron microscopy (SEM) and N₂ adsorption measurements (BET). The results showed that the increase of calcination temperature from 650°C to 1100°C resulted in larger crystallite size and lower specific surface area of β-Ca₂SiO₄. The highest specific surface area could reach as high as 26.7 m²/g when the as-burnt powders were calcined at 650°C.     

焙烧温度对甲醇水蒸气重整制氢Ce/Cu/Zn-Al水滑石衍生催化剂的影响

采用原位合成法在γ-Al_2O_3载体表面上合成了Zn-Al水滑石,再采用顺序浸渍法制备了一系列Ce/Cu/Zn-Al催化剂,并采用XRD、BET、H_2-TPR和XPS等手段对催化剂进行了表征,考察了焙烧温度对Ce/Cu/Zn-Al催化剂表面结构及其催化甲醇水蒸气重整制氢性能的影响。结果表明,焙烧温度主要影响了催化剂的Cu比表面积、表面氧空穴含量和Cu-Ce间相互作用。当焙烧温度为500℃时,催化剂Cu的比表面积较大,表面氧空穴含量较多,Cu-Ce间相互作用较强,因此,催化甲醇水蒸气重整制氢活性较好。当焙烧温度升高到700℃时,Cu物种主要以稳定的CuAl_2O_4尖晶石形式存在,不利于甲醇水蒸气重整制氢反应的进行,因此,催化活性较差。     

焙烧温度对MgAlOx复合氧化物催化甲醛和乙醛合成正丙醛反应性能的影响

采用共沉淀法制备了镁铝水滑石前驱体,通过在不同温度下焙烧得到系列MgAlO_x复合氧化物催化剂,采用XRD、TG、N₂吸附-脱附、NH₃-TPD和CO₂-TPD等技术对催化剂的物理和化学性质进行了表征,采用甲醛和乙醛缩合反应对催化剂反应性能进行了评价。结果表明,随着焙烧温度的提高,乙醛转化率以及正丙醛时空收率先增加后减少,C-550催化剂最大,分别达到39.22%和103.86 g/（kg·h）,这与催化剂中强碱和强碱数目变化趋势一致。此外,提高催化剂中强碱和强碱数目还会促进副产物甲醇和CO₂的生成。     

Characterization of Thermally Stable Brønsted Acid Sites on Alumina‐Supported Niobium Oxide after Calcination at High Temperatures

Thermally stable Brønsted acid sites were generated on alumina‐supported niobium oxide (Nb₂O₅/Al₂O₃) by calcination at high temperatures, such as 1123 K. The results of structural characterization by using Fourier‐transform infrared (FTIR) spectroscopy, TEM, scanning transmission electron microscopy (STEM), and energy‐dispersive X‐ray (EDX) analysis indicated that the Nb₂O₅ monolayer domains were highly dispersed over alumina at low Nb₂O₅ loadings, such as 5 wt %, and no Brønsted acid sites were presents. The coverage of Nb₂O₅ monolayer domains over Al₂O₃ increased with increasing Nb₂O₅ loading and almost‐full coverage was obtained at a loading of 16 wt %. A sharp increase in the number of hydroxy groups, which acted as Brønsted acid sites, was observed at this loading level. The relationship between the acidic properties and the structure of the material suggested that the bridging hydroxy groups (Nb? O(H)? Nb), which were formed at the boundaries between the domains of the Nb₂O₅ monolayer, acted as thermally stable Brønsted acid sites.     

焙烧气氛对Ru/Al2O3催化剂上甲烷部分氧化制合成气反应性能的影响

采用气相色谱、质谱和原位时间分辨红外光谱等技术对空气和Ar气氛中焙烧的Ru/Al2O3催化剂样品上甲烷部分氧化(POM)制合成气反应进行了跟踪,并采用化学吸附、X射线衍射、拉曼光谱和H2-程序升温还原等技术对催化剂进行了表征.结果表明,在Ru/Al2O3-Air上POM反应出现振荡现象,而在Ru/Al2O3-Ar上则可...     

载体焙烧温度对Ru/MgAl2O4催化剂液相苯部分加氢性能的影响

采用水热合成法制备了镁铝尖晶石(MgAl2O4)材料,制备了其负载的Ru催化剂,研究了MgAl2O4焙烧温度对Ru/MgAl2O4催化剂上液相苯部分加氢催化性能的影响.采用X射线粉末衍射、27A1固体核磁共振、傅里叶变换红外光谱、H2-程序升温还原、H2-程序升温脱附、N2物理吸附、透射电子显微镜和X射线光电子能谱等手...     

煅烧时间对正极材料LiNi0.80Co0.15Al0.05O2浓度梯度结构及电化学性能的影响

将铝溶液按3种不同的流速连续注入,联合共沉淀结晶控制法合成了具有核壳结构的Ni_0.80Co_0.15Al_0.05(OH)₂前驱体,即内核为均相组成的Ni_0.88Co_0.12(OH)₂,外壳为Ni、Co和Al含量呈连续变化的Ni_0.72Co_0.18Al_0.10(OH)₂。将该前驱体与LiOH·H₂O混合均匀,在700℃的氧气气流下进行煅烧,通过控制煅烧时间使材料中Ni、Co和Al扩散形成含量呈连续梯度变化的且具有类球形形貌的LiNi_0.80Co_0.15Al_0.05O₂正极材料。梯度结构中Ni、Co和Al的分布情况直接影响材料的电化学性能和结构稳定性。当煅烧时间为12 h时,从颗粒的核心到表面,Ni含量(原子分数)由0.855下降至0.732,Al含量由0.003增加至0.115,Co含量维持在0.142~0.163之间,而表面组成为LiNi_0.732Co_0.153Al_0.115O₂。此时材料具有良好完整的层状结构且Li⁺/Ni²⁺混排程度最低,在0.2C下的放电比容量为201.3 mAh·g^-1,略低于均相LiNi_0.80Co_0.15Al_0.05O₂的放电比容量(205.8 mAh·g^-1);以0.2C充电、1C放电循环200周后,其容量保留率为71.6%,优于均相组成的材料(54.6%)。这是因为镍含量低而铝、钴含量高(相对于均相材料)的外层可以有效抑制充放电循环过程中引起颗粒体积的各向异性变化,减少电极极化,从而减缓极片表面裂纹的生成和扩展,降低电池的电荷传递阻抗,从而提高循环稳定性和结构稳定性。该材料合成过程中只有在铝溶液流速切换时使pH值发生小幅度的波动,但很快恢复到稳定,可以保证前驱体具有良好的结晶性,使核壳结构易设计、控制;而后通过调控煅烧时间合成LiNi_0.80Co_0.15Al_0.05O₂,有利于进一步地精准设计材料的浓度梯度结构。