Selective oxidation of methane by using aqueous hydrogen peroxide solution as oxidant was investigated. Colloidal nanosized Cu-Fe-silicalite-1 was prepared and a micro reactor was used to intensify mass transport. It was found that the oxygenate productivity could be enhanced nearly three orders of magnitude while simultaneously ensuring high turn-over-frequencies of some 100h(-1). However, the main product in liquid phase was not methanol, but formic acid. At optimized reaction conditions, a selectivity to formic acid of 96.7% at a methane conversion of 10.3% could be achieved.