Catalytic conversion of methanol to hydrocarbons (MTH) provides an alternative route to the production of fuels and important industrial chemicals that are currently mainly produced from the refinery of petroleum. The ability to control the product distribution of MTH according to the demands of specific applications is of crucial importance, which relies on the thorough understanding of the reaction pathways and mechanisms. Despite the significant research efforts devoted to zeolite-catalyzed MTH, it remains a challenge to establish a firm correlation between the physicochemical properties of zeolites and their catalytic activity and selectivity. In this dissertation, we designed a series of experiments to gain fundamental understanding of how the structural and compositional parameters of zeolites influence their catalytic performances in MTH. We investigated different types of zeolites, covering large-pore Beta, medium-pore ZSM-5, and small-pore DDR zeolites, and tune their crystallite size/diffusion length, hierarchical (mesoporous) structure, and Si/Al ratio (density of acid sites) by controlled synthesis or post-synthesis treatments. The influence of mesoporosity of a zeolite catalyst on its catalytic performance for MTH, with zeolite Beta, was first investigated. The shorter diffusion length associated with the hierarchical structure results in a lower ethylene selectivity but higher selectivity towards C4-C7 aliphatics. Then we investigated the correlation between the Al content and the ethylene selectivity by ZSM-5 zeolites with similar crystal sizes but varied Si/Al ratios. We realized that ethylene selectivity is promoted with the increase of aluminum content in the framework. These two observations can be explained by the same mechanistic reason: the ethylene selectivity is associated with the propagation degree of the aromatics catalytic cycle and essentially determined by the number of the acid sites that methylbenzenes would encounter before they exit the zeolite crystallite. Last we explored how to maximize the propylene selectivity by tuning the physicochemical properties of DDR zeolites. Due to the confined pore space in DDR, the propagation of olefins-based catalytic cycle can be preferentially promoted in a tunable manner, which cannot be realized with zeolites having larger pores. Thus, the propylene selectivity increases with increasing the Si/Al ratio and decreasing the crystallite size.

Submitted by Kilvya Braga (kilvyabraga@hotmail.com) on 2018-04-24T14:36:49Z No. of bitstreams: 1 LUIZ ROBERTO ROCHA DE LUCENA - DISSERTAÇÃO (PPGEM) 2015.pdf: 2629611 bytes, checksum: 9d4b92496c709e6181c7746ee3d76d6d (MD5) / Made available in DSpace on 2018-04-24T14:36:49Z (GMT). No. of bitstreams: 1 LUIZ ROBERTO ROCHA DE LUCENA - DISSERTAÇÃO (PPGEM) 2015.pdf: 2629611 bytes, checksum: 9d4b92496c709e6181c7746ee3d76d6d (MD5) Previous issue date: 2015 / Este trabalho foi desenvolvido experimentalmente com o intuito de analisar o comportamento das emissões, da potência e do consumo do motor diesel, operando em “modo dual” com diesel/biodiesel e gás a uma taxa de substituição do diesel por gás natural da ordem de aproximadamente 85 %. Foram ensaiadas misturas de B20 a B80 com intervalos de 20%, além dos dois limites, inferior e superior (B5 e B100), do diesel comercial e do biodiesel puro respectivamente, onde foram realizados para cada condição de mistura, ensaios com rotação constante de 1800 RPM controlada eletronicamente e potências elétrica de 40, 60, 80, 100 e 120 kW, respectivamente. Todo o sistema foi monitorado por sensores de temperatura, pressão, vazão, velocidade e as emissões de NOx , NO, CO2, CO, O2, Excesso de Ar etc. foram registradas em um analisador de gases de combustão. Os dados dos ensaios foram adquiridos por meio de um sistema de aquisição de dados instalado em um PC e armazenados em mídia própria, para posterior tratamento e análise através de Tabelas e gráficos e comparação com o ensaio B5, denominado neste trabalho de padrão diesel, bem como confrontado com outros trabalhos. Ao término deste estudo podemos concluir a viabilidade do uso do gás natural em motores diesel operando no modo dual com vantagens econômicas e ambientais. / This work was developed experimentally in order to examine the performance of emissions, power and consumption of the diesel engine, operating in "dual mode" with diesel and natural gas at a fixed rate of replacement of diesel by natural gas of approximately 85%. Mixtures from B20 to B80 were tested with intervals of 20%, plus the two limits, upper and lower (B5 and B100) of commercial diesel and biodiesel respectively, which were performed for each mixture condition with constant test speed of 1,800 RPM, electronically controlled, and electric powers at 40, 60, 80, 100, and 120 kW respectively. The entire system was monitored by temperature and pressure sensors and test data were acquired by means of a data system installed on a PC and stored in adequate media, for further processing and analysis in tables and graphs and comparison with B5 test, which is called standard diesel and confronted with other studies. At the end of this research we can perceive the viability of the use of natural gas in diesel engines in dual mode with a range of economic and environmental advantages.