2 research outputs found
Desenvolvimento de argilas montmorilonitas modificadas para aplicação em catálise
Dissertação (mestrado)—Universidade de BrasÃlia, Instituto de QuÃmica, 2012.As argilas montmorilonita e bentonita (Aldrich e Nacalai Tesque, respectivamente) foram impregnadas com sete ácidos de Lewis/surfactantes
combinados (cério, cobalto, cobre, cromo, gadolÃnio, lantânio e samário),
usando duas técnicas diferentes: troca iônica e impregnação incipiente. Vale
destacar que a troca iônica foi utilizada para verificar se seria melhor sintetizar
o complexo na intercamada das argilas ou inseri-lo previamente preparado.
Esse procedimento foi realizado somente para a sÃntese das argilas com o
complexo de cobre, para fins de teste. Já a impregnação incipiente foi usada
para preparar as argilas modificadas com três concentrações dos complexos
(1, 2,5 e 5% m/m). Os sólidos obtidos foram caracterizados pelas técnicas de
FTIR, DRX, análise elementar (CHN e FRX/EDX) e TG/DTG/DTA. Os
resultados de FTIR dos complexos puros mostraram bandas correspondentes
aos modos de vibração dos grupos alquilas e do grupo aniônico (OSO3). Após
a sÃntese das argilas modificadas, as bandas dos grupos alquilas se mostraram
presentes, porém as do grupo aniônico foram encobertas pelas bandas das
argilas. Os resultados de análise elementar dos complexos puros
demonstraram que as quantidades teóricas e experimentais dos elementos se
aproximaram bastante, confirmando a formação dos complexos. Da mesma
forma, os resultados de análise elementar feitos para as argilas modificadas mostraram a concentração efetiva dos complexos nos materiais preparados. As
análises de DRX mostraram que os complexos puros apresentam estrutura
lamelar. Para o catalisador sintetizado na bentonita por troca iônica, foi possÃvel
a observação dos picos do dodecilsulfato de cobre, mostrando que parte do complexo se encontra na superfÃcie externa. Os catalisadores sintetizados na
montmorilonita pela técnica de impregnação incipiente mostraram um aumento na intercamada de acordo com a maior porcentagem de complexo. O mesmo
foi observado para os complexos de cobalto, cromo e cobre na bentonita. As atividades catalÃticas dos materiais foram testadas em até três reações:
esterificação do ácido acético e do ácido oleico e transesterificação do óleo de
soja. Os resultados mostraram que as atividades dependem dos centros ativos
metálicos e da acessibilidade do sÃtio ativo na lamela das argilas. ______________________________________________________________________________ ABSTRACTMontmorillonite (Aldrich) and bentonite (Nacalai Tesque) clays were impregnated with seven different Lewis Acid-Surfactant Combined (LASC’s) (cerium, cobalt, copper, chrome, gadolinium, lanthanum and samarium), using
two methods: ionic exchange and wetness impregnation. It is worth mentioning
that the ionic exchange was used to verify whether it was better to synthesize
the complex inside the clay’s layer or to insert it already prepared. This
procedure was realized only for the copper complex. On the other hand, the
wetness impregnation was used to prepared the modified clays with the seven
complexes in three concentrations (1, 2,5 and 5% w/w). The obtained solids
were characterized by FTIR, XRD, elementary analysis (CHN and FRX/EDX)
and TG/DTG/DTA. The results of FTIR of the complexes showed bands that
correspond to the vibration mode of the anionic (OSO3) and alquil groups. After
modifying the clays with the complexes, the same alquil bands were present on
the FTIR spectra, although the anionic bands were covered by the clay bands.
The results of the elementary analysis of the pure complexes demonstrated that
the content of the elements were consisted with the expected theoretical values.
Likewise, the results of the elementary analysis obtained for the modified clays
showed the real concentration of the complexes on the prepared materials. The
XRD patterns of the pure complexes were characteristic of lamellar
arrangements, while the diffractograms of the copper, chrome and samarium
complexes presented some other peaks that differ from those on the pattern. It
was possible to observe, for the catalyst synthesized inside the bentonite clay
using ionic exchange, peaks that can be assigned to the copper dodecylsulfate.
This proves that part of the complex was located on the external surface. The
catalysts synthesized in the montmorillonite clay by incipient wetness impregnation technique showed an increase in the interlayer according to the highest percentage of compound. The same result was observed for cobalt,
chrome and copper in the bentonite clay. The catalytic activities of the prepared
materials were tested in up to three reactions: esterification of acetic and oleic acid and transesterification of the soybean oil. The results showed that the activities depend on the active metal centers and the accessibility of the active site of the clay
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 Brønsted weak-medium strength (pyridine desorption between 300 and 500 ºC)