Carbon Routes in Carbon Dioxide Reforming of Methane

Abstract

Over the past few years, the carbon dioxide reforming of CH4 has attracted interest from both environmental and industrial perspective. From the environmental point of view, CO2 and CH4 being “harmful” greenhouse gases, the reaction provides a method of disposing of these gases. From the industrial point of view the reaction is attractive since it produces synthesis gas with a lower H2/CO ratio than does either partial oxidation or steam reforming. However, compared with the two last processes, the so called “dry reforming” presents substantially higher risk of catalyst deactivation due to carbon deposition via methane decomposition and via CO disproportionation. Options to reduce coke build up include: i) coupling with steam reforming , ii) coupling with partial oxidation, and iii) use of catalysts which minimize the rate of coking. Thermodynamic calculations indicate that at temperatures higher than 950°C deposition of carbon can be avoided. However, lower reaction temperatures are desirable for industrial applications. In the CO2 reforming of CH4, the carbon deposition sequence generally reported for various metals is the following: Ni ≫ Pt > Ru. It is however, worthwhile to develop improved, stable and effective nickel-based catalyst, also because of the high cost of noble metals. To perform this correctly an advanced knowledge of the reaction mechanism including all the steps dealing with coke formation is required. This paper reviews the main fundamental aspects of the dry reforming reaction focussing at the various carbon routes that determine the fate and performance of any nickel or noble metal based catalyst.