Julio L. de Macedo

Acidity measurements of zeolite Y by adsorption of several probes

Acid strength distribution measurements of zeolite Y by a combined analysis of calorimetric and adsorption data, Cal-ad, for the reaction of zeolite Y with pyridine, 2,6-lutidine, 2,6-di-tert-butylpyridine, quinoline, tetrahydrothiophene and benzonitrile show the presence of three families of acid sites. The strongest sites (heats above −29 kcal mol−1) contain a significant number of Bronsted sites (n = 0.1 mmol g−1), which are located inside the large cages. The sites of intermediary strength (heats around −17 kcal mol−1) are of Lewis and Bronsted types and the weaker sites (heats below −10 kcal mol−1) contain significant hydrogen bonding. The strength of these sites is probably due to mutual interaction between Lewis and Bronsted sites. The accessibility on zeolite and the size of the probe molecules play fundamental role on the determination of acid site distribution. Application of the electrostatic–covalent model (ECW) to this acid provides quantitative parameters for determination of donor-acceptor contributions based on electrostatic (EA) and covalent (CA) intrinsic characters to each chemical bonding. The results demonstrate that zeolite Y has a stronger covalent character with EA = 5.25, CA = 6.89 (CA/EA = 1.31) consistent with softness properties suggested in the literature.

Liquid phase calorimetry and adsorption analyses of zeolite beta acidity

Zeolite beta acidity, activated at 550 °C, was characterized by calorimetric and adsorption studies of pyridine in cyclohexane (Cal–Ad). Two different acid sites were found: n1 = 0.1612 mmol g−1 with ΔH1 = −83.6 kJ mol−1; and n2 = 0.3820 mmol g−1 with ΔH2 = −62.8 kJ mol−1. Step calcinations followed by FTIR indicated n1 as Lewis sites and n2 as weak Bronsted sites. When activated at 450 °C, zeolite beta showed three different sites: n1 = 0.0467 mmol g−1 with ΔH1 = −227.3 kJ mol−1; n2 = 0.1163 mmol g−1 with ΔH2 = −93.3 kJ mol−1; and n3 = 0.3322 mmol g−1 with ΔH3 = −80.4 kJ mol−1. Sites n1 and n2 were assigned as Bronsted centers, while n3 as a combination of Bronsted and Lewis sites. These results suggest that the zeolite beta strongest Bronsted sites are converted to Lewis sites at 550 °C. These Lewis sites are not only related to extra-framework Al species, but also to aluminium atoms partially bonded to the zeolite framework, as evidenced by infrared bands at 3777 and 875 cm−1. FTIR and thermogravimetric analyses of gas phase adsorbed pyridine were also used to investigate the materials acidity and a good agreement was found with Cal–Ad data. The results showed that the Cal–Ad method offers a more detailed description of the zeolite surface acidity by providing thermodynamic parameters not easily obtained by other techniques. A linear relationship between enthalpy and entropy values for several zeolites (ZSM-5, TS-1, MOR, Y and BEA) is also reported.

Effect of cerium loading on structure and morphology of modified Ce-USY zeolites

Este trabalho descreve detalhadamente o efeito da quantidade de cerio na estrutura e morfologia da zeolita NH4USY. Ce-USY (2-25% m/m de CeO2) foi obtido por impregnacao umida de CeCl3 seguida de calcinacao a 550oC por 8 h. Em quantidades baixas (2-10%), foi observado que as especies de cerio encontram-se nas posicoes de troca ionica na rede, enquanto em maiores teores (15-25%) pequenos agregados formaram-se na superficie da HUSY. Difratometria de raios X (XRD) mostrou apenas reflexoes relacionadas a HUSY, confirmando a alta dispersao das especies de cerio, porem as analises por espectroscopia Raman com transformada de Fourier (FT-Raman) detectaram CeOx para os materiais acima de 10%. A reacao do CeCl3 com NH4USY produziu NH4Cl, o qual se decompoe em HCl, ocasionando a desaluminizacao da rede. Os materiais apresentaram um aumento da razao Lewis/Bronsted com o aumento da quantidade de cerio, devido a interacao do excesso de cerio com os grupos OH da USY e consequente formacao de especies CeOx.

Produção de biodiesel via transesterificação etílica com zeólitas básicas

Soybean oil transesterification with ethanol was carried out in a batch reactor using USY zeolites modified with barium and strontium (15 wt.%) as catalysts. A series of three catalytic cycles were performed for each zeolite without any loss of activity. The biodiesel product was analyzed by HPLC and FT-Raman, and the catalysts by pyridine and CO2 adsorption. Ba/USY provided higher conversions (> 97%) than Sr/USY (< 75%). The increased catalytic activity of Ba/USY was attributed to two different effects: a larger number of basic sites; and a lower interaction between barium species and HUSY BrOnsted sites.

Acidity and Characterization of 12-Tungstophosphoric Acid Supported on Silica-Alumina

This work deals with preparation and characterization of H3PW12O40 (H3PW) supported on silica-alumina. Impregnation of H3PW (15, 20, 30 and 40 wt.%) on commercial silica-alumina support in acidic aqueous solution is effective for preparing this catalyst keeping its Keggin structure, according to different methods of characterization. The catalysts were tested in a model reaction of acetic acid with ethanol and 30 wt.% H3PW/SiO2-Al2O3 had the highest activity under the conditions: catalyst calcination at 300 oC, temperature of 100 oC, acetic acid:ethanol molar ratio of 2:1 and catalyst:acetic acid mass ratio of 10 wt.%. The reaction yield was 79 and 100% selectivity for ethyl acetate over three reutilizations, for reaction time of 2 h. The calculated total acid site distribution was 0.299 mmol g-1 (97% of the theoretical probed by pyridine), and most of these (0.236 mmol g-1) were Bronsted weak-medium strength (pyridine desorption between 300 and 500 oC).

Heteropolyacid-Containing Ionic Liquid-Catalyzed Multicomponent Synthesis of Bridgehead Nitrogen Heterocycles: Mechanisms and Mitochondrial Staining

The current manuscript describes the use of a heteropolyacid-containing task-specific ionic liquid, supported in imidazolium-based ionic liquids, as the catalyst for an efficient multicomponent synthesis of hexahydroimidazo[1,2-α]pyridine derivatives. The reactions conditions were fully optimized, and the bridgehead nitrogen heterocycle derivatives could be obtained in just 1 h exclusively as a single isomer ( trans). Single crystal X-ray analysis confirmed the trans derivative as the only isomer. The mechanism of the reaction was investigated by ESI(+)-MS(/MS), and the use of the elegant charge-tag strategy allowed a catalytic cycle to be proposed for the current transformation and revealed the possibility of at least two reaction pathways. One derivative bearing a coumarin scaffold was synthesized, and its fluorescent properties allowed it to be tested as a probe for live-cell imaging experiments with a preference for mitochondria.

Evaluation of Brasilia wastewater sludge as a biomass resource for the production of energy by gasification simulation

Abstract This work evaluated the sludge potential of the Wastewater Treatment Plant (ETA) in the city of Brasília to be used as a fuel by gasification. It is known that ETA sludge is a significant environmental liability, since current legislation restricts its final disposal. For this, the chemical characterisation of ETA sludge was performed by immediate and elemental analysis. No traces of heavy metals were observed, and the moisture (ω) and ash contents were 31.17 and 51.77%, respectively, different from those already reported in the literature because the composition depends on the water treatment technology employed. The gasification process was numerically simulated; once dry, it constitutes a residue with an energy content (HHV) of 22.4498 MJ kg−1, comparable with other types of biomass currently used for large-scale energy generation by thermochemical processes (e.g. agricultural residues, wood and sugar cane bagasse). For the numerical simulation with an equivalence ratio (Φ) near 3, higher concentrations of CO and H2 can only be achieved with ω lower than 15%. The results showed that gasification can be an attractive option for the disposal and use of a renewable waste resource, such as ETA sludge, in an environmentally safe way, and it is allowed by local legislation.

ESTUDO PROSPECTIVO SOBRE PROCESSO DE EXTRAÇÃO DE MATERIAL GRAXO DE RESÍDUOS AGROINDUSTRIAIS COM PRODUÇÃO SIMULTÂNEA DE BIODIESEL

O biodiesel e um biocombustivel importante para a matriz energetica nacional e produzido de diferentes fontes oleaginosas, desempenhando papel importante na producao final do biocombustivel. Diante de sua cadeia produtiva e da importância de metodos mais sustentaveis, realizou-se um estudo prospectivo sobre o processo simultâneo de producao de biodiesel visando a condensacao das etapas de producao via simultaneidade de extracao e respectiva conversao a partir de residuos agroindustriais oleaginosos. Alem disso, tem-se como objeto de estudo a utilizacao de catalise heterogenea ao sistema, agregando facilidades na separacao do produto e do meio catalitico. Neste nicho de pesquisa e desenvolvimento de metodos alternativos para o setor do biodiesel encontram-se poucas patentes e artigos, sendo em sua maioria evidenciados processos em escala laboratorial. Sendo assim, tal tecnologia merece atencao, investimento e desenvolvimento para seu escalonamento, tendo em vista agregar diversos beneficios ao setor, desde a materia-prima ate o processo e distribuicao.

Effect of Acidity, Structure, and Stability of Supported 12-Tungstophosphoric Acid on Catalytic Reactions

Polyoxometalates are large metal–oxygen nanostructured compounds that can be modified at the molecular level. Catalysts based on 12-tungstophosphoric acid (H3PW12O40) supported on different carries such as silica, silica–alumina, zirconia, and mesoporous MCM-41 have been successfully prepared and characterized by several physicochemical techniques (e.g., FTIR, FT-Raman, 31P MAS-NMR, calorimetry, thermal analysis, TPD of pyridine). The materials were tested in different reactions: transalkylation of benzene with aromatics, esterification of acetic acid and ethanol, esterification of oleic acid with ethanol, and cyclization of (+)-citronellal. The results, coupled with other applications of heteropoly acids in the literature, illustrate the potential for these catalysts to be used in greener processes, i.e., a more effective, selective, economical, and environmentally benign technique. The effects of support interaction, loading of H3PW12O40, calcination temperature and stability, leaching, and acidity were addressed for all studied catalysts. These data were correlated to the conversion and/or selectivity of the main product and were used for recovery of the catalysts. Moreover, it was clear that the strength of interaction of the heteropoly acid with the surface support as well as the acidity define the capacity of utilization of these catalysts. Effective ways to recovery the initial activity is still a challenge to take full advantage of these materials.