Vast amount of shale gas and gas hydrates has been discovered, which will undoubtedly change the landscape of the chemical industry. In this context, methane is a feedstock of special interest for the production of key building blocks such as aromatic compounds. Processes that convert methane into chemicals are indirect oxidative (syngas), direct oxidative, and direct non-oxidative dehydrogenation. The syngas route with its low efficiency, high capital cost and CO2 emissions is the dominant industrial practice. One the other hand, the direct non-oxidative methane conversion is more environmentally friendly and economical. However, this route is very challenging due to thermodynamic and kinetic constraints. The activation of the strong C-H bond requires high temperature (750-1100°C) and an efficient catalyst, of which various metal-modified zeolites have been investigated.
With this work, we present gallium nitride – a semiconductor material that has not been used as a catalyst for a high temperature process – and explore its catalytic activity towards the direct methane conversion in a flow reactor. The GaN catalyst exhibits a much higher benzene selectivity than typical Mo-containing zeolites. Commercially available GaN material has a very low surface area of less than 10 m2 g-1, an increase in its surface area to more than 200 m2 g-1 result in a much higher methane conversion and benzene yield. This material an interesting catalyst worth for further investigation because to date all catalysts studied for C-H activation are metal oxides. III-nitride semiconductors are highly chemically stable due to the strongly ionic character of the atomic bonds. However, the interaction between CH4 and GaN and reaction mechanism are not known, but it is suggested that carbon from methane is attached to the lattice Ga+ cation, whereas one hydrogen atom of the methane molecule is adsorbed by the adjacent lattice N3- anion (alkyl adsorption model).