Conventional and microwave-heated oxygen pulsing techniques on metal-doped activated carbons

Abstract

Conventional and microwave-heated oxygen pulsing techniques on metal-doped activated carbons to achieve a controlled meso/micropore structure were investigated. The gas pulsing experiments consisted of repeated cycles. Each cycle consists of an oxidising stage, under O2/Ar atmosphere and constant temperature, and a burn-off stage, under N2 atmosphere at variable temperature (heating and cooling). The porosity of the carbons was analysed by nitrogen adsorption at −196 °C. Two different activated carbons, Cu-doped BPL (BPL-Cu) and ASC, were used as raw materials. The commercial activated carbon ASC showed higher reactivity towards O2, due to the catalytic effect of the metals (mainly, Cu and Cr) that are on the carbon surface and their better dispersion. After several pulses, ASC underwent a moderate increase in the micropore volume and a significant increase in mesopore volume. BPL-Cu showed a higher increase in microporosity than mesoporosity, giving rise to a meso/micropore volume ratio lower than that of the original BPL-Cu. Oxygen pulsing technique was carried out in a conventional furnace and in a microwave oven. Conventional and microwave-heated oxygen pulsing on ASC yielded similar textural development. However, the time required under microwave heating was remarkably reduced respect to conventional heating (around 2.5 times less), which suggests that microwave-heated oxygen pulsing technique would be an interesting alternative to conventional activation.