Rusiene M. de Almeida

TiO2 with a high sulfate content—thermogravimetric analysis, determination of acid sites by infrared spectroscopy and catalytic activity

Sulfated metal oxides have a very high acidity, being considered by some as superacids, although it is still a controversial matter. There has been considerable investigation into sulfated ZrO2 in recent years, but sulfated TiO2 has been relatively neglected. There is evidence that the Bronsted acid sites would be responsible for the high levels of acidity and catalytic activity in sulfated ZrO2, since these sites would be present in samples with higher sulfate content. In order to verify whether for sulfated TiO2, a high level of acidity also occurs in samples with a higher sulfate content, samples were prepared with elevated levels of sulfate. Characterization was carried out through thermogravimetric analysis, determination of acid sites by infrared spectroscopy, through adsorption of pyridine and measurement of the catalytic activity in the isomerization reaction of n-hexane. It was verified that samples with elevated sulfate content were actually those which had Bronsted acid sites and a higher catalytic activity in the isomerization reation of n-hexane. It was also verified that the sulfate loss in the thermogravimetric analysis occurred at different temperatures, depending on the sulfate content of the sample.

Microwave hydrothermal synthesis, characterisation, and catalytic performance of Zn1-xMnxO in cellulose conversion

Wurtzite-type Zn1−xMnxO (x = 0, 0.03, 0.05, 0.07) nanostructures were successfully synthesised using a simple microwave-assisted hydrothermal route and their catalytic properties were investigated in the cellulose conversion. The morphology of the nanocatalysts is dopant-dependent. Pure ZnO presented multi-plate morphology with a flower-like shape of nanometric sizes, while the Zn0.97Mn0.03O sample is formed by nanoplates with the presence of spherical nanoparticles; the Zn0.95Mn0.05O and Zn0.93Mn0.07O samples are mainly formed by nanorods with the presence of a small quantity of spherical nanoparticles. The catalyst without Mn did not show any catalytic activity in the cellulose conversion. The Mn doping promoted an increase in the density of weak acid sites which, according to the catalytic results, favoured promotion of the reaction.