Pérez-Ramírez Javier, Gallardo-Llamas Amalia
Laboratory for Heterogeneous Catalysis, Catalan Institution for Research and Advanced Studies (ICREA) and Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, E-43007 Tarragona, Spain.
J Phys Chem B. 2005 Nov 3;109(43):20529-38. doi: 10.1021/jp054447b.
The N(2)O-mediated oxidative dehydrogenation of propane (ODHP) to propylene has been investigated in the temperature range of 673-773 K over steam-activated FeMFI zeolites with different framework compositions (Si-Al, Si-Ga, Si-Ge, and pure Si). The catalysts, which were characterized by ICP-OES, XRD, SEM, N(2) adsorption, NH(3)-TPD, and FTIR of pyridine adsorbed, HRTEM, and UV/vis, have a very similar iron content (0.6-0.7 wt %). A tapered element oscillating microbalance (TEOM) coupled to on-line analysis of products has been applied to simultaneously monitor activity and mass changes during the ODHP reaction. FeAlMFI and FeGaMFI zeolites display higher propylene yields (up to 25%) and a much slower deactivation due to coking than do FeGeMFI and FeMFI zeolites. The higher density and strength of acid sites in the former samples did not induce a faster catalyst deactivation. In general, catalyst deactivation was accelerated upon decreasing the reaction temperature. The total amount of coke formed in the samples during 400 min on stream ranged from 6 to 23 wt %, increasing linearly with the amount of propylene produced. The distinct performance of both groups of zeolites is likely related to the different iron speciation, which is influenced by the composition of the framework. The smaller primary crystallites of FeAlMFI and FeGaMFI, as well as the presence of mesopores in these samples, which are created by dislodgement of aluminum and gallium to extraframework positions, appear to be also beneficial for higher catalyst effectiveness and a reduced deactivation.
在673 - 773 K温度范围内，研究了N₂O介导的丙烷氧化脱氢（ODHP）制丙烯反应，所用催化剂为具有不同骨架组成（Si - Al、Si - Ga、Si - Ge和纯Si）的经蒸汽活化的FeMFI沸石。通过ICP - OES、XRD、SEM、N₂吸附、NH₃ - TPD、吡啶吸附的FTIR、HRTEM和UV/vis对催化剂进行表征，发现它们的铁含量非常相似（0.6 - 0.7 wt%）。采用与产物在线分析耦合的锥形元件振荡微天平（TEOM）来同时监测ODHP反应过程中的活性和质量变化。与FeGeMFI和FeMFI沸石相比，FeAlMFI和FeGaMFI沸石显示出更高的丙烯产率（高达25%），并且由于结焦导致的失活要慢得多。前一组样品中较高的酸位密度和强度并未导致催化剂失活更快。一般来说，降低反应温度会加速催化剂失活。样品在400分钟的反应过程中形成的焦炭总量在6至23 wt%之间，随丙烯生成量线性增加。两组沸石的不同性能可能与不同的铁形态有关，而铁形态受骨架组成的影响。FeAlMFI和FeGaMFI较小的初级晶粒，以及这些样品中由铝和镓迁移到骨架外位置而产生的介孔，似乎也有利于提高催化剂效率和减少失活。
