Catalytic properties of graphene oxide in the oxidation of methanol with air to formaldehyde

Abstract

The catalytic activity of graphene oxide (GO) and thermally reduced graphene oxide (rGO) towards selective oxidation of methanol to formaldehyde by air was studied. These catalysts were characterized using (FTIR) spectroscopy and atomic force microscopy (AFM), and energy-dispersive X-ray spectroscopy (EDX). It was found that GO prepared by Hammer method, when treated with high temperatures in an oxygen-poor atmosphere, is subjected to partial reduction, which was demonstrated by dropping the percentage of surface oxygen atoms to half their initial quantity and completely exfoliation of the graphene sheets from each other to form rGO. No appreciable catalytic activity was found for GO in the liquid or gas phase of methanol oxidation, while a good catalytic activity appeared for the thermally reduced graphene oxide rGO represented by the degree of methanol conversion of 3.1 mol% and selectivity towards the formaldehyde product amounting to 100 mol% in a micro plug flow reactor with a weight space velocity of 22 mgMeOH/gGO/min and a temperature of 350 ^oC, without declining activity for 33 hours of continuous oxidation. It has also been proven that heat treatment at 430 ^oC is sufficient to form the necessary active centers for selective oxidation, which remain stable up to 600 ^oC. The carbon then begins to oxidize, and vanishes completely at 700 ^oC.