Different dispersion behavior of glucose and sucrose on alumina and silica surfaces

Phenomena of spontaneous monolayer-dispersion have been found in many salt and oxide/support systems as well as in organic compound/support systems. In this paper, the dispersion behaviors of glucose and sucrose have been systematically compared using three types of alumina with different textures and one type of silica gel, as supports. The dispersion capacity of the saccharides was determined by XRD quantitative phase analysis and confirmed by DTA-TG and FT-IR results. The pore size distribution of carbon-covered alumina (CCA) derived from the saccharide/alumina composite was employed to evaluate the dispersion state of the saccharide precursor. It was found that both sucrose and glucose are dispersed on the alumina and silica surfaces as a monolayer when their loading is kept under the monolayer-dispersion capacity. However, at higher saccharide content, glucose and sucrose are dispersed differently. Just like other monolayer-dispersion systems, sucrose begins to form in the crystalline phase when its loading exceeds the monolayer-dispersion capacity. In contrast, glucose aggregates in an amorphous state in the pores of the supports until these pores are filled, and only then forms crystalline glucose.