The influence of pretreatment and doping of Fe, Co and Ni on Mo/HZSM-5 catalysts in methane dehydroaromatization
| dc.contributor.committeeChair | Khatib, Sheima J. | |
| dc.contributor.committeeMember | Khare, Rajesh | |
| dc.contributor.committeeMember | Gill, Harvinder | |
| dc.contributor.committeeMember | Korzeniewski, Carol | |
| dc.creator | Sridhar, Apoorva | |
| dc.creator.orcid | 0000-0003-0069-069X | |
| dc.date.accessioned | 2020-07-08T15:04:46Z | |
| dc.date.available | 2020-07-08T15:04:46Z | |
| dc.date.created | 2019-08 | |
| dc.date.issued | 2019-08 | |
| dc.date.submitted | August 2019 | |
| dc.date.updated | 2020-07-08T15:04:47Z | |
| dc.description.abstract | With abundant methane resources available in natural gas, shale gas, and methane hydrates, methane has found its importance as potential alternative chemical feedstock in the manufacturing industry. Methane conversion into higher hydrocarbons has been extensively studied by researchers all over the world for the past few decades. Although the indirect route is operated at an industrial scale today, wherein methane is converted into syngas, which is then consequently converted into other chemicals, the cost and energy consumption is very high. Direct conversion involves converting methane directly into other useful products, with the advantage that the process is simplified to one step, thus lowering processing costs. However, this process is currently at the laboratory stage of development. Continuous efforts are being made to develop new pathways to utilize the natural gas efficiently. One of such pathways is the conversion of methane to benzene, also called methane aromatization reaction, and transition metals supported on ZSM-5 are known to be active for this reaction. But the use of these catalysts at an industrial level is hindered by their fast deactivation. The main objective of this study is to improve the reactivity and stability of the methane dehydroaromatization catalyst, Mo/ZSM-5, which is a widely used catalyst for this reaction. To improve the catalytic performance, the effects of transition-metal additives X, (X= Fe, Co, Ni) along with the influence of the type of pretreatment on Mo/HZSM-5 catalysts was investigated. In this study, X with a loading of 0.2 wt%, 0.6 wt% and 1 wt% were added on to 6 wt% Mo/ZSM-5 and tested under two different pretreatment conditions, namely, reduction in H2/CH4 followed by carburization in CH4 (ex-situ carbide formation) and He pretreatment (in-situ carbide formation). Pretreatments are known to influence the catalytic performance. H2/CH4 followed by carburization was chosen as the pretreatment in view of the idea that carburizing the catalysts first can prevent migration of the Mo oxide species from blocking the pores by forming Mo carbides which are less mobile, unlike the case in He pretreatment. Reactive studies of these two family of catalysts were carried out to compare their performance. The results indicated that precarburized catalysts resulted in better benzene yield and stability compared to He pretreated samples, but addition of an optimum amount of Fe, Co, Ni loading at 0.2, 0.6, 0.2 wt% respectively, improved the benzene yield as well as the catalytic stability further. The fresh and spent catalysts were characterized by XRD, TPO, TPR, TGA, XPS and SEM. The results suggest that catalytic enhancement in precarburized Mo-Fe, Mo-Co and Mo-Ni samples is due to a combination of effects: migration of Mo species at high temperature is prevented, the activity of the Mo carbide sites is modified and growth of reactive carbon deposits that reduce deactivation of the catalyst is favored. | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.uri | https://hdl.handle.net/2346/86119 | |
| dc.language.iso | eng | |
| dc.rights.availability | Restricted to TTU only. For access, please log in at the top of this page using your eRaider credentials. | |
| dc.subject | Methane dehydroaromatization | |
| dc.subject | Catalytic activity | |
| dc.subject | Pretreatment | |
| dc.subject | Iron (Fe) | |
| dc.subject | Cobalt (Co) | |
| dc.subject | Nickel (Ni) | |
| dc.subject | Iron (Fe), Cobalt (Co) and Nickel (Ni) additive | |
| dc.subject | Mo/ZSM-5 | |
| dc.title | The influence of pretreatment and doping of Fe, Co and Ni on Mo/HZSM-5 catalysts in methane dehydroaromatization | |
| dc.type | Thesis | |
| dc.type.material | text | |
| thesis.degree.department | Chemical Engineering | |
| thesis.degree.discipline | Chemical Engineering | |
| thesis.degree.grantor | Texas Tech University | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy |