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Zeolite Y was dealuminated in the solid-state at several degrees (5, 10, 15 and 20%) using (NH 4 ) 2 SiF 6 as dealumination agent. The materials were heated to 80, 100, 120, 140, 160, 180 and 200 °C to investigate the best temperature at which the samples retain their crystallinity and acidity. The solids obtained were characterized by XRD, FTIR, TG/DTG, XRF, 27 Al and 29 Si MAS NMR and N 2 physisorption. They were also subjected to pyridine adsorption and calorimetric experiments. Structural and textural results showed that lower temperatures (80 and 100 °C) and smaller degrees of dealumination (5 and 10%) maintained the zeolite crystallinity and increased its specific surface area, microporosity and mesoporosity. The study of the materials acidity indicated the presence of Bronsted acid sites with different strength, hydrogen bonding sites and Lewis sites originated from acid leaching. The calorimetric measurements showed higher enthalpy values for some of the dealuminated materials than for the parent zeolite. It also evidenced an increase for the number of acid sites between −160 and −140 kJ mol −1 and a reduction for the other sites, between −140 and −80 kJ mol −1 .

The dealumination of zeolites has been studied to tune acidity, resulting in enhanced catalytic efficiency. MOR, FER, and ZSM-5 were dealuminated to remove 5, 10, 15, or 20 mol% of Al with (NH4)2SiF6 (solid-state reaction at 80 °C). XRD, SEM, and FT-IR showed structural maintenance. Aluminum removal was confirmed by the total Si/Al ratio (XRF and AAS) and 27Al MAS NMR. The dealuminated samples were tested in the dehydration of different alcohols and compared to the protonic parent zeolites. Dealuminated MOR samples exhibited a decrease in coke formation (maximum decrease of 18.3%, 18.2%, and 6.1% for methanol, ethanol, and 1-propanol dehydration, respectively), and an increase in conversion values (maximum increase of 29.0%, 13.9%, and 6.2% for methanol, ethanol, and 1-propanol dehydration). H-FER/20% showed an improvement in methanol (19.9%) and ethanol (3.8%) conversions and a reduction of coke (decrease of 8.6% and 5.6%, respectively), corroborating the highest value of acid sites (0.73 mmol g−1). All catalysts showed 100% selectivity to each desired product. The mechanisms for all dehydrations were related to the presence of Bronsted acid sites. Methanol dehydration might involve the generation of methoxonion ion, and ethoxy groups might be formed for ethanol conversion. For ZSM-5, Lewis acid sites may also participate in the elimination mechanism. High reaction temperature (300 °C) favored intramolecular dehydration to ethylene, avoiding formation of diethyl ether and oligomers. Structural defects on H-ZSM-5/15% could facilitate the access of 1-propanol to active sites, leading to the best combination of TON (0.67), conversion (100%), and coke formation (0.35%).

In this work, activities of HUSY and Ce/HUSY zeolites were studied in transesterification cycles of soybean oil and ethanol to produce biodiesel. The characterization of the materials was performed by FT-IR, XRD, BET method and pyridine adsorption followed by thermal analyses. TG/DTG results indicated a decrease of acid sites for both samples after each reaction cycle. However, Ce/HUSY zeolite showed a superior stabilization of acidic sites after three catalytic cycles and intermediary activation procedures. Biodiesel production exhibited high conversion levels (>96%) for both zeolites in all transesterification cycles. Surface area and pore volume measurements evidenced that cerium incorporation reduced the number of acid sites by interacting with OH groups in the micropore and external area of the zeolitic surface. This interaction resulted in an acid and structural stability, which provided a better activity (99%) than HUSY (96%). The higher conversion values obtained by zeolites showed a final product with a different distribution when compared with the traditional transesterification process. The identification of free fatty acids, diethyl and glycerol ethers in the final products and the reduction of unsaturated compounds indicated that parallel reactions also occurred in the studied systems. Nonetheless, the biofuel produced showed high ester content and did not present changes in its calorific power.

Tese (doutorado)—Universidade de Brasília, Instituto de Química, 2014. A produção seletiva de olefinas a partir da desidratação de alcoóis foi alcançada utilizando uma zeólita Y desaluminizada no estado sólido, Y(80)5C. Resultados experimentais obtidos por CG-FID mostraram que uma quantidade reduzida (0,1 g) desse sólido foi capaz de gerar valores de seletividades superiores a 96% para produção de etileno com conversão média de 90% durante 5 dias de reação, mesmo mediante uma alta velocidade espacial de etanol de 14,2 h'1. A recuperação e a reativação da zeólita modificada reduziu o número de sítios ácidos do material de 1,1088 para 0,4850 mmol g1 e. apesar da menor acidez, a Y(80)5C manteve os valores de conversão do etanol PA acima de 86% e os de seletividade para etileno acima de 90%, convertendo quase 20% a mais que a zeólita HY no mesmo período. Estudos com soluções aquosas de etanol em distintas concentrações mostraram que a presença de água no álcool de partida não se comportou como um veneno para o catalisador desaluminizado durante o período reacional investigado. Ao contrário, elevou a 100% os valores de seletividade para a formação da olefina devido á menor proporção de álcool etílico que passava por minuto pela zeólita sem prejuízo nas taxas de conversão. O bioetanol, com 93% de pureza, também foi testado nesse trabalho, evidenciando um ligeiro decréscimo de seletividade por parte da zeólita Y(80)5C em relação á seletividade apresentada pela Y comercial, Y(pura)C, quando um curto tempo reacional, de até 25 h, é considerado. No entanto, a resistência do material desaluminizado foi consideravelmente superior à da Y(pura)C, conservando sua eficiência catalítica durante um longo tempo de reação. Novos materiais também foram investigados a partir da síntese dupla via molde biológico com o ácido 12- tungstofosfórico (HPW). Nesse caso, três diferentes cátions (Zr4*, Zn2’ e Ag') foram utilizados como substituintes dos prótons do heteropoliácido HPW, gerando tanto sólidos micrométricos como materiais nanoestruturados. Dessa forma, nanofibras foram obtidas por meio da modelagem dos sais de HPW com papel filtro ou celulose em pó. tendo sido detectadas por MEV e MET. Análises termogravimétricas evidenciaram uma alta estabilidade térmica e baixos valores de perda de água para esses sólidos. Os materiais com zircônia (ZrHPW) foram aqueles que apresentaram os maiores valores de conversão/seletividade para aplicação em catálise ácida, devido à facilidade dos íons zircônio de se hidrolisarem em meio aquoso, formando desde espécies monoméricas até polímeros e gerando sítios H*. Na esterificação do álcool benzílico com ácido acético, a molécula volumosa do álcool teve forte influência nas conversões alcançados, uma vez que efeitos estéricos podem ocorrer, sendo determinante a quantidade de sítios ácidos por unidade de área superficial do catalisador. Assim, os heteropolissais com maior quantidade de sítios ácidos fortes não foram aqueles que apresentaram as maiores conversões. Os catalisadores de ZrHPW também exibiram boas conversões na catálise oxidativa do álcool benzílico. Porém, os materiais de prata foram aqueles que apresentaram os melhores dados de seletividade para formação do benzaldeído (98%) em 2 h de reação. Nesse caso, a capacidade REDOX do centro metálico, em conjunto com ligações W-O, foi o fator determinante na reação de oxidação. The selective production of olefins from the dehydration of alcohols was achieved using the Y zeolite dealuminated in the solid-state, Y(80)5C. Experimental results obtained by GC-FID have shown that a reduced amount (0.1 g) of this solid was capable to generate selectivity values greater than 96% for ethylene with average conversion of 90% during 5 days reaction, even with a high ethanol space velocity of 14.2 If1. The recovery and the reactivation of the modified zeolite reduced the number of acid sites of the material from 1.1088 to 0.4850 mmol g 1 and, despite the lower acidity, the Y(80)5C kept the values of ethanol conversion over 86% and the selectivity to ethylene above 90%, converting almost 20% more than HY zeolite in the same period. Studies with aqueous ethanol solutions in different concentrations showed that the water in the reactant did not act as a poison in Y(80)5C catalyst during the investigated period of reaction. Instead, the presence of water elevated to 100% the selectivity values to olefin formation due to the smaller proportion of ethyl alcohol that passed through the zeolite per minute without decreasing the conversion rates. A sample of bioethanol, 93% purity, was also tested in this work, showing a slight decrease in selectivity for Y(80)5C compared with the selectivity presented by the commercial Y zeolite, Y(pure)C, when a short period of 25 h is considered. However, the resistance of the dealuminated material was considerably higher than the one showed by Y(pure)C, keeping its catalytic efficiency for a long reaction time. New materials were also investigated by the dual synthesis via biological template with the 12- tungstophosphoric acid (HPW). In this case, three different cations (Zr4*, Zn2* e Ag*) were used as proton substituents of the HPW heteropolyacid, resulting in either micrometric and nanometric materials. Therefore, nanofibers were obtained modeling the HPW salts with filter paper or powdered cellulose and they were detected by SEM and TEM. Thermogravimetric analysis showed a high thermal stability and low values of water loss for these solids. The zirconia materials (ZrHPW) presented the greater conversions/selectivity values for application in acid catalysis, since zirconium ions can be easily hydrolyzed in aqueous media, forming monomers and polymers and generating H* sites. In the esterification of benzyl alcohol with acetic acid, the bulky alcohol molecule had a strong influence on the achieved yields, since steric effects may occur, and the amount of acid sites per unit of catalyst surface area seems to be also decisive. Therefore, the solid heteropolyacids with higher amount of strong acid sites were not the ones that showed the highest conversions. ZrHPW catalysts also exhibited good yields in the oxidative catalysis of benzyl alcohol. However, the best selectivity data for benzaldehyde formation in 2 h of reaction was found employing silver materials. In this case, the REDOX capacity of the metal center, together with W-O bonds, was the key factor in the oxidation reaction.