Only supported catalysts are used, the silver being deposited on a poroussupport material in concentrations of 7 – 20 %. The support material is of critical importance [61]; currently, prefer ence is given to ultrapure (over 99 %) aluminum oxide [57828-03-2] fired at a high temperature that has a defined pore structure (pore diameter 0.5 – 50 mm) and low specific surface area (