THE CHEMISTRY OF METHANE REFORMING WITH CARBON-DIOXIDE AND ITS CURRENT AND POTENTIAL APPLICATIONS

The reforming of CH4 with CO2 produces synthesis gas with a lower H-2/ CO ratio than that generated by the widely employed steam/CH4 reformin g reaction. The two reactions have similar thermodynamic characteristi cs except that in the case of CO2/CH4 reforming there is a greater pot ential for carbon formation, primarily due to the lower H/C ratio of t his system, Thermodynamic analysis of the CO2/CH4 reforming reaction s ystem shows that carbon formation is possible over a wide range of rea ction conditions of possible commercial interest, Whilst technology ha s been developed to enable CO2/CH4 and steam/CH4 reforming to be carri ed out simultaneously, the former reaction has to date had no signific ant commercial application by itself. However, there is now renewed in terest in C-1-chemistry to produce chemicals and fuels requiring synth esis gas with a 1/1 H-2/CO ratio. Conducted in the absence of steam/CH 4 reforming, CO2/CH4 reforming has a number of major advantages over a lternative chemical reactions for the thermochemical storage and trans mission of renewable energy sources such as solar energy. Hence it is likely to become an increasingly important industrial reaction in the future. A review of the literature on the catalysis of CO2/CH4 reformi ng shows that Group VIII metals, when distributed in reduced form on s uitable supports, are effective catalysts for this reaction. Rh appear s intrinsically to be the most suitable, and considering the relative material costs, Ni catalysts deserve closer attention. In the latter c ase the emphasis should be on developing catalysts which are capable o f carbon-free operation under practical reaction conditions. Of the va rious supports studied to date, alumina and magnesia or combinations t hereof are most promising. Analysis of the reaction mechanism indicate s that the effective catalysts are those metal-support combinations wh ich actively dissociate CH4 into CHx residues including carbon, whilst at the same time also activating CO2 to generate CO and an adsorbed O species on the catalyst surface. The O thus produced is consumed in t he conversion of CH2 and C to CO. Net carbon formation becomes a probl em when the CH4 dissociation and CO2 activation steps are out of balan ce. Considering the current status of catalyst development and the lik ely future large-scale applications for CO2/CH4 reforming, significant scope exists for further work in optimising both catalysts and reacto r design for this reaction.