The reactor was pressurized with oxygen up to the selected initial pressure (corresponding to a higher pressure once the reactor was heated). The autoclave was positioned in the aluminium block on the heating plate, and the heating and magnetic stirring (500 rpm) were turned on. The heating was regulated from the heating plate. As the reactor temperature increased, the pressure increased, too. The time zero was defined as the point at which the system reached an internal temperature of 20 °C lower than the desired reaction temperature (due to the long time required to reach the desired temperature). After the desired time, the heating and the magnetic stirring were turned off, and the reactor was removed from the aluminium jacket.