Influence of ammonium salt formation on the activity and selectivity of the 12-molybdophosphate heteropolyacid catalyst prepared by solid–solid interaction in the ammoxidation of 2-methylpyrazine

The ammonium salt of 12-molybdophosphoric acid has been prepared by the solid-state interaction of the ammonium salts of molybdenum and phosphorus. The catalysts obtained by pretreatment of the precursor at various temperatures, have been characterized by nitrogen adsorption, X-ray diffraction (XRD), Fourier-transformed infrared (FTIR) spectroscopy and temperature-programmed decomposition (TPD) of the catalysts. Ammoxidation of 2-methylpyrazine has been carried out on these catalysts. The amount of ammonium salt present in the catalyst has been correlated with the activity and selectivity of the catalysts.     

Spin–spin exchange in vanadium-containing catalysts studied by in situ-EPR: a sensitive monitor for disorder-related activity

In unsupported V-containing catalysts, V⁴⁺ sites are frequently present in amorphous oxidic clusters and/or crystalline paramagnetic bulk phases in which they are coupled by effective spin–spin exchange interactions. This work presents two EPR procedures for evaluating these interactions and relating their strength to the degree of disorder and catalytic performance, namely (1) evaluating permanent structural disorder by calculating exchange energies and integrals and (2) monitoring transient electronic disorder caused by catalyst–reactant interaction in working catalysts using the ratio of the fourth and the square of the second moment of the EPR signal. Selected application examples comprise VPO catalysts such as (i) (VO)₂P₂O₇, in which a certain degree of structural disorder revealed to be essential for high catalytic performance in the selective oxidation of n-butane to maleic anhydride, (ii) (NH₄)₂(VO)₃(P₂O₇)₂ in which transient perturbation of spin–spin exchange sensitively reflects the strength of reactant adsorption during ammoxidation of toluene and (iii) (NH₄)₂VOP₂O₇ in which an amorphous VO²⁺-containing phase could be identified as active component besides inactive crystalline phases. Based on operando-EPR measurements, reasons for activity differences in MoVTeNb oxide catalysts could be suggested.     

Nitrogen‐Doped Carbon Materials Prepared by Ammoxidation as Solid Base Catalysts for Knoevenagel Condensation and Transesterification Reactions

Nitrogen‐doped carbon materials were prepared by ammoxidation of commercial carbon sources (carbon black and activated carbon) and applied as base catalysts for Knoevenagel and transesterification reactions. It was shown that these carbon materials were active and the activities were different depending on the ammoxidation conditions (temperature and ammonia concentration in air) and carbon sources used. The bulk, textural, and surface properties of the nitrogen‐doped carbon materials were examined by several methods to clarify possible factors determining their final catalytic activities. The activated carbon‐derived catalysts were more active than the carbon black‐derived ones. The surface area and porosity were not responsible for this difference between the two carbon sources but the difference in the reactivity with oxygen was important. The reactivity of carbon sources with oxygen should influence the doping of nitrogen onto their surfaces by ammoxidation with ammonia and air and the resulting activities as base catalysts. The catalytic activity increases with the amount of nitrogen doped and, therefore, the nitrogen doped should be responsible for the catalytic activities. In addition, the activities are maximal at a ratio of nitrogen to oxygen of around 1, suggesting the importance of cooperative functions of nitrogen and oxygen on the surface of carbons.     

SANC-08丙烯腈合成催化剂的开发

实验室开发出新型SANC-08丙烯腈合成催化剂,在反应温度440 ℃、反应压力0.084 MPa、催化剂负荷0.06 h^-1、n(空气)∶n(丙烯)=9.5和n(氨气)∶n(丙烯)=1.25反应条件下,丙烯转化率97%以上,丙烯腈选择性82%以上,丙烯腈收率大于80%,氨转化率94%以上。流化床反应器稳定性试验结果表明, 2 177 h时,丙烯腈收率78.9%,丙烯转化率94.6%,丙烯腈选择性83.3%。     

反应条件对SANC-08丙烯腈催化剂活性的影响

通过对反应工艺条件的研究,得出了SANC-08催化剂实验室的最佳工艺条件：反应温度（425～445） ℃,压力（0.082～0.14） MPa,n(空气)∶n(丙烯)=9.0～10.0、n(氨气)∶n(丙烯)=1.15～1.30、空速（0.060～0.090） h^-1。催化剂在较宽的工艺条件范围,具有丙烯腈收率高、氨转化率高、丙烯选择性好、反应温度低且可在低n(空气)∶n(丙烯)和高空速下运行等特点。     

Genesis of site isolation and phase cooperation in selective oxidation catalysis

Two of the important principles governing selective oxidation catalysis are site isolation and phase cooperation. They are discussed here in light of their inception, development, historic perspective and current acceptance in the field of selective oxidation and ammoxidation catalysis.     

Fe~(3+)的还原对丙烯腈催化剂活性的影响

针对某企业丙烯睛装置催化剂活性下降的问题,通过XRD、IR和化学分析等研究,发现丙烯腈催化剂的重要组成元素Fe~(3+)在使用过程中被过度还原及催化剂结构变化是造成催化剂性能下降的主要原因。应用催化剂器外再生技术再生后,丙烯腈收率显著提高。实验室评价结果表明,丙烯腈收率由再生前的76.11%提高到81.62%,提高了约5个百分点;通过部分再生剂置换工业装置反应器床层催化剂,丙烯腈收率由部分再生剂置换前的75.01%提高到78.82%,提高了3.81个百分点,取得了很好的技术效果。     

Strategies for the selective catalytic oxidation of alkanes

An overview is provided of the state of technology for the upgrading of alkane feedstocks to chemical intermediates. This is a technology survey based largely on the information from recent patent literature. Examples are described for options for commercial application of oxidation catalysis for converting alkanes to commodity chemicals. These examples are used to illustrate points about economic incentives and technical hurdles across several prospective alkane conversion processes.     

Rutile-type metal (Cr, V) niobates as catalysts for propane ammoxidation to nitriles: In situ characterization and operando reactivity

Rutile-type Cr/Nb and V/Nb mixed oxides were prepared by co-precipitation from ethanolic solutions, and calcination at 700 °C. The development of the rutile structure during the thermal treatment of the precursor was investigated by in situ TP–Raman spectroscopy. It was found that graphite-like carbon deposits build-up during calcinations in inert. Their decomposition provides the reducing agent that leads to the formation of rutile VNbO₄ at relatively mild conditions. Rutile Cr and V niobates were tested as catalysts for the ammoxidation of propane, under both hydrocarbon-rich and hydrocarbon-lean conditions. Catalysts were active but non-selective to acrylonitrile. The catalyst modifications occurring during reaction were followed by operando Raman–GC methodology. VNbO₄ transforms into a catalyst active and selective for acetonitrile under leaner hydrocarbon feed.     

焙烧气氛对丙烷氨氧化Mo-V-Te-Nb-O催化剂性能的影响

采用不同气氛焙烧共沉淀方法制备MoV0.31Te0.23Nb0.24氧化物催化剂,考察焙烧气氛对该催化剂结构及其催化丙烷氨氧化反应性能的影响,并采用X-射线粉末衍射(XRD)、拉曼光谱(Raman)和X射线光电子能谱(XPS)等手段对所制备的催化剂进行表征。结果表明:采用惰性的氮气气氛焙烧的MoV0.31Te0.23Nb0.24氧化物催化剂具有良好的丙烷氨氧化反应性能。在氮气气氛下焙烧的催化剂,构成催化剂的各种元素在焙烧过程中形成了价态分布合理的活性相M1和M2,用于催化丙烷氨氧化反应,丙烷转化率可达58.7%,丙烯腈收率为35.0%;在空气和氧气气氛下焙烧的催化剂,其组成中各元素以高价态的单一氧化物形式存在,不利于丙烷选择性氧化生成丙烯腈。