The Effect of Different Polyol Precursors on Disordered Spinel ZnAl<sub>2</sub>O<sub>4</sub> Structure Prepared by the Polymeric Citrate Complex Method and the Corresponding Catalytic Behavior in the Glycerolysis of Urea
Nhiem Pham-Ngoc, Huy Nguyen‐Phu, Youngil Lee, Eun Woo Shin
Abstract
ZnAl 2 O 4 is a cubic close‐packed oxide with tetrahedral and octahedral sites in the lattice structure. The catalytic activity of ZnAl 2 O 4 is strongly connected with the surface properties caused by the partially inverse spinel ZnAl 2 O 4 structure. In this research, ZnAl 2 O 4 catalysts are prepared for the glycerolysis of urea via the polymeric citrate complex method using polymeric templates made of citric acid with a different polyol precursor. Depending on the polyol precursor, the partial inversion parameters representing the disordered bulk ZnAl 2 O 4 structure are controlled, which results in different surface AlO 4 /AlO 6 ratios and surface acidity. The specific surface areas of the prepared ZnAl 2 O 4 catalysts are proportional to the molecular weight of the polyol precursor. The s–ZnAl 2 O 4 (polyol precursor = sorbitol) prepared via two pathways from citrate complex and polymeric citrate complex shows the highest inversion parameter and surface acidity, leading to the highest glycerol carbonate (GC) yield and glycerol conversion in the glycerolysis of urea. A relationship between the GC yield and the surface properties, such as the acidity and inversion parameters, is established.