Syngas production by CO2 reforming of CH4 under microwave heating – Challenges and opportunities

The main industrial process used to produce synthesis gas (H2 + CO) and its resulting byproducts is the steam reforming of natural gas. Methane reforming with carbon dioxide, or dry reforming, is a promising alternative that may lead to the reduction of CO2 emissions and the production of a syngas with a lower ratio of H2/CO. The main obstacle to the industrial implementation of CH4 reforming with CO2 is that there are no commercial catalysts that can operate without undergoing deactivation due to carbon deposition. Consequently, new catalysts are being developed and changes are being introduced in the process in order to achieve high and steady conversions. The microwave-assisted CO2 reforming of CH4 over carbon-based catalysts combines the catalytic and dielectric properties of carbonaceous materials with the advantages of microwave heating, which favours catalytic heterogeneous reactions due to, among other reasons, the generation of hot spots or microplasmas. Under certain operating conditions, the microwave-assisted dry reforming reaction can be considered as a combination of CH4 decomposition and CO2 gasification of carbon deposits, leading to the continuous regeneration of active centres. The most appropriate operating conditions to achieve high conversions for a long period of time are temperatures ranging between 700 and 800oC and the presence of high proportions of CO2 in the feed (at least 50%). The use of catalysts with a good catalytic activity gives rise to high conversions at high values of volumetric hourly space velocity, making it possible to produce large amounts of syngas. Of the catalysts evaluated the most suitable for the microwaveassisted dry reforming of methane proved to be mixtures of carbonaceous material and metal catalyst. The carbon material should be microporous and have a good reactivity towards CO2. The metal catalyst with the best catalytic activity is Ni/alumina. Energy consumption in the process of microwave-assisted reforming of methane with CO2 is estimated to be 4.6 kW·h per m3 of H2, which is a promising value compared to the energy consumption in the steam reforming of methane. Therefore, the