Catalytic Transformation of Greenhouse Gases in a Membrane Reactor
Supported Ni and Rh catalysts were developed for the reforming of two greenhouse gases, methane and carbon dioxide to syngas (a mixture of hydrogen and carbon monoxide). This is an endothermic, equilibrium limited reaction. To overcome the thermodynamic limitations, a commercially available porous membrane (Vycor glass) was used in a combined reactor-separator configuration. This was to selectively remove one or more of the products from the reaction chamber, and consequently shift the equilibrium to the right. However, the separation mechanism in this membrane involved Knudsen diffusion, which provided only partial separations. Consequently, there was some transport of reactants across the membrane and this led to only marginal improvements in performance. To overcome this limitation, a new membrane was developed by modifying the Vycor substrate by the chemical vapor deposition of a silica precursor. This new membrane, termed Nanosil, provided high selectivity to hydrogen at permeabilities comparable to the support material. Application of this membrane in the combined reactor-separator unit provided higher conversions than that obtained using the Vycor membrane.