小中大(7) Neutron Scattering and Attenuation
可提供信息: measure coke content and C/H ratio.
优点:This technique has the advantage that the coke content and thereforethe coke profile along the catalyst bed, can be measured in-situ.
(8) Nuclear Magnetic Resonance (NMR)
提供信息:
(a) The NMR technique is a powerful technique to investigate the nature of carbonaceous deposits;
(b) detect bindings between aromatic rings, alkyl fragments, and even tertiary carbenium ion-like species.
缺点: The information provided by NMR is not quantitative.
(9) Auger Electron Spectroscopy (AES)
Augerelectron spectroscopy (AES) was used in combination with secondary ionmass spectrometry (SIMS) to distinguish between four types ofcarbonaceous deposits, on metal foils (rhodium, iridium and platinum).The foils were coked by exposing to ethylene at low pressure. Augerspectroscopy can distinguish between molecular or carbidic on the onehand, and graphitic or amorphous carbon on the other.
(10) X-Ray diffraction (XRD)
Cokestructure can be characterized by X-Ray diffraction analysis. Thistechnique makes it possible to determine if there is coke withcrystalline structure on the catalyst.
缺点: the sensitivity of this type of determination is rather low，being it difficult to determine the fraction and/or amount of coke in the crystalline form.
(11) Secondary Ion Mass Spectrometry (SIMS)
SIMSis among the few surface sensitive techniques which are capable ofdetecting hydrogen content of the deposits. It has been used incombination with AES to analyse coke on metal foils.
缺点: However, it was not possible to obtain the real H/C ratio of the carbon deposit.
(12) Sorption Capacity: Surface Area and Pore Volume
原理:Adsorption measurements allow the determination of coke location. Whenthe volume occupied by coke is much smaller than the volumeinaccessible to adsorbates, it means that there is a pore blockage.
缺点:However, in many cases the adsorption study is carried out at adifferent temperature than the reaction, and therefore diffusivitycould be quite different. Another aspect that should be taken intoaccount is that if the pretreatment for adsorption measurement requirestemperatures higher than the reaction temperature, an importantfraction of carbonaceous deposits could be stripped off the catalystand, therefore, the pore volume measured in this way will be higherthan the actual volume under reaction conditions.
(13) X-Ray Photo-electron Spectroscopy (XPS)
(14) Ultra Violet-Visible Spectroscopy (UV-VIS)
TheUV-VIS spectroscopy can be used to determine the chemical identity ofthe coke componentes. UV-VIS, unlike NMR and IR, can easily detectalkyl and alkenyl carbenium ions, essentially due to its much highersensitivity 55. This is usually carried out under vaccum, andtherefore, the more volatile compounds could be lost under theseconditions.
(15) Electron Paramagnetic Resonance (EPR)
TheEPR (or ESR) technique allows the study of the radicals that accompanythe coke formation, and thus estimate roughly the amount of coke andobtain information regarding its nature.
One of the advantages of this technique, is that it can be used both under static or under on-stream conditions.
(16) Coke Formation Rate
Theamount of coke that is being deposited on a catalyst has beentraditionally followed with conventional microbalances. However, due tothe inherent limitations of this equipment, in which it is almostimpossible to avoid feed by-pass effect and diffusional effects, thistechnique has not been very useful to determine coking kinetics as afunction of feed composition. A recycle electrobalance reactor has beendesigned to avoid this undesirable effect.
(17) 其他
特殊表征手段, 只针对某些特殊催化剂、反应有效.
Someof the techniques limited to single crystals or polycrystalline foils,such as low energy electron diffraction (LEED), He scattering, coreelectron energy loss spectroscopy (CEELS), and metastable deactivationspectroscopy (MDS).
而通常情况下，催化剂若积炭后在烧炭过程中都会伴随重量的变化, 鉴于热分析特别是热重法可以原位定量检测, 所以采用热分析技术来研究催化剂的积炭行为不仅可行而且也十分方便.
