الفهرس 
INTRODUCTION AND LITERATURE SURVEYOnly 14 pages are availabe for public view
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Abstract
This work introduced a green technology toward green hydrogen production without any Cox evolutions which can be utilized in both of energy sector and industrial applications without any further treatments. Moreover, it commenced an effective ecological and economical management scenario of plastic wastes to smart nano materials such as CNTs, CNFs, CNOs and graphitic layers which are emerged in various practical and industrial applications. Therefore, our thesis could solve multiple challenges suchlike plastic waste accumulations with their hazard impacts and clean alternative energy carrier as well as extraordinary CNMs production with their versatile applications without any harmful side effects. So, both of material reserve and energy conversion would be achieved from no resource (LDPE waste).
Via continuously two stage processes, thermal decomposition of LDPE waste was achieved in the first furnace to three parts (no condensable gases, liquid and solid) then the resultant gases were passed through the vertical condenser for continuous condensation during the reaction. Hence, the resultant non-condensable gases C1-5 were catalytically decomposed in the second furnace to yield clean hydrogen and to deposit carbon nanomaterials. Continuously, the final resultant gases were evaluated and detected via online gas chromatography to detect the resultant hydrogen concentration and other gases (not decomposed). After reaction termination, the as-deposited CNMs were investigated via XRD, Raman, TGA and TEM analyses to indicate their nature, quality structure and morphology. So, the mission and strategy of this thesis rely on proper design of catalyst with highly catalytic activity and stability during the reaction period without any inhibition to be able to decompose whole the resultant gases from the first furnace to hydrogen and CNTs.
Originally, catalytic activity and durability of both of Co/MgO and CoMo/MgO were investigated. Molybdenum not only improved the distribution of active cobalt nano particles through forming mixed oxide species and its structural dispersant function but also facilitated the catalyst reducibility. Additionally, molybdenum increased the overall catalytic activity and stability toward higher concentration of hydrogen outputs during all the reaction period. It managed and adjusted the reaction steps rates to deposit well organized and regular crystalline and graphitized tubular CNTs. This behavior of CNMs growth not only prevented the formation of harmful deactivated carbon forms but also enhanced the catalyst active as the CNT with closed or opened tips could function as good supports for active metallic cobalt nano particles.
Consequently, hydrogen yield, deposited CNMs structures, crystallinity, quality as well quantity were managed with support composition of the applied CoMo catalysts over bare Al2O3, MgO and Al-Mg matrices from LDPE waste as feedstock, separately. Textural properties of the investigated supports and their structural composition indicated limit interactions between Al2O3 and MgO in their matrixes. Both of Al2O3 and MgO features governed their CoMo fresh catalysts compositions and CoMo catalysts supported over their binary oxides. Fresh catalysts characterizations suchlike FTIR, XRD, Raman and TPR confirm a preferential affinity of MgO toward active species (Co and Mo) and release more accessible interacting species than with Al2O3. Although there was no complete confirmation for Al-Mg interactions, the possibility of MgAl2O4 existence in catalysts with Al-Mg matrixes might support their easier reducibility. Accordingly, catalytic efficiency of CoMo with bare MgO and bare Al2O3 were better than catalysts with their binary oxides suchlike Al75–Mg25 and Al50–Mg50. Synergist structural influence of both Al2O3 and MgO hinders good distributions of active species resulting in less active segregated Co3O4 and bulk CoMoOx as well inactive CoAl2O4 phases. This agglomeration behavior confirmed that weak metal support interaction via structural barrier action as well disrupting of molybdenum dispersing function especially in CoMo/Al75-Mg25 and CoMo/Al50-Mg50. In addition, CoMo/Al25-Mg75 generated the maximum hydrogen concentration regard to other CoMo catalysts supported over Al-Mg binary oxides. Thereby, it was concluded that increasing MgO content release more accessible active sites and enhance their catalysts activity. According to the deposited CNMs morphologies, Catalysts with bare MgO or with little amount of Al2O3 promote deposition of tubular CNMs structures with ordered graphene walls where CoMo catalysts with bare Al2O3 or with higher content of it, CoMo/Al2O3, CoMo/Al75–Mg25 and CoMo/Al50–Mg50, triggered randomly graphitic layers depositions with poor organization called turbostratic materials as well variety of CNMs shapes like CNOs, B-CNTs and extremely dense graphitic flakes. Briefly, combination of these CNMs confirmed their low graphitization and quality. Additionally, these CNMs configurations might be the reason of catalytic deactivation trend. Contrary, homogeneity in MWNTS over CoMo/Al25-Mg75 ensures higher quality and purity of them. Hence, these well graphitized tubular CNMs haven’t any negative action on the catalytic activity toward hydrogen production.
Therefore, a group of Co-Mo/MgO catalysts with different bimetallic Co-Mo contents were prepared and examined for converting real LDPE waste into clean H2 and valuable CNMs under non-oxidative condition. The impact of total bimetallic Co-Mo contents on the activity and stability as well as the nature and morphology of deposited carbon was studied. The analyses of fresh catalysts revealed that the presence of various individual and mixed oxide species with different levels of interaction with MgO support depending on the metal contents. Catalysts with low Co-Mo loadings were composed mainly of CoMoOx, MgMoOx, and MgCoOx species with the presence of little quantities of non-interacting cobalt oxide particles as shown from XRD, TPR and Raman results. Meanwhile, the non-interacted Co3O4 appeared extensively on the surface of high loaded catalysts (50 and 60 wt% of Co-Mo) accompanied by many mixed oxides species. The catalytic activity and stability in terms of H2 yield as well as the nature of deposited carbon were found to strongly depend on the Co-Mo content. Both 30% and 40%CoMo/MgO catalysts exhibited the highest activity within most of the reaction periods due to the presence of suitable metallic cobalt particle size, appropriate MSI, and good metal dispersion. The H2 yield over these catalysts reached as high as a value of " ~ " 90% after running 240 minutes without any deactivation. XRD and Raman studies of spent catalysts showed that all catalysts have a good efficiency to grow highly graphitized and crystalline CNMs. Furthermore, TEM images revealed that CNMs with diverse morphologies were obtained on the catalyst surface according to the Co-Mo loadings. CNTs with narrow and uniform diameters were grown over 10-30%CoMo/MgO catalysts, while large diameter CNFs were obtained over the high loaded catalysts.