A simple semi sol-gel method for preparation of alumina monoliths with hierarchical pore structures

A simple semi sol-gel method for preparation of stable alumina monoliths is presented. The approach is based on chemical binding of boehmite by hydrolysis products of aluminium nitrate. The crystalline phase of the monoliths depends on the calcination temperature, and the size and shape of the alumina crystallites were determined by transmission electron microscopy and modelling of X-ray diffraction patterns. The monoliths have bimodal pore size distributions with mesopores ranging from 3 to 20 nm and macropores ranging from 10 to 40 μm. Incipient wetness impregnation resulted in gold particles, ranging from 4 to 20 nm, supported on the monoliths. The size of the gold particles depended largely on the crystalline phase of the support, but also on the amount of gold precursor. The catalytic activity of the functionalised materials in liquid-phase oxidation of glucose was higher in continuously stirred batch reactor tests compared to continuous flow fix bed tests. In both cases the activity was improved as the size of gold particles decreased.