Feasible coupling of CH4/H2 mixtures to H2 storage in liquid organic hydrogen carrier systems

Abstract

The cheap CH4-containing hydrogen mixtures are available in petrochemical industry and nevertheless, their usage is limited because of economic issue. We herein demonstrate the impacts of CH4 fraction (fCH4) in CH4/H2 mixtures on the essential steps for liquid organic hydrogen carrier (LOHC) systems. In the preparation of Ru/Al2O3 catalysts by thermolysis in CH4/H2 mixtures, the fCH4 affects the content of carbon formed by methane decomposition but not the size of Ru nanoparticles, indicating that it should be avoided to use a CH4/H2 mixture with the fCH4 of higher than 30%. When CH4/H2 mixtures are used for the hydrogenation of monobenzyltoluene, the higher fCH4 reduces the catalytic activity, particularly at high temperatures and H2 partial pressures because of competitive adsorption of CH4 and H2 on the Ru surface. Such an effect of CH4 is lessened under mild conditions, which is confirmed by the experiments using the same CH4/H2 mixture for both catalyst preparation and hydrogenation reaction. Therefore, it is feasible to use the CH4/H2 mixture of up to 30% fCH4 for the preparation of Ru/Al2O3 and for stable H2 storage performance at lower temperatures and H2 partial pressures, thus enabling to couple the CH4/H2 mixture to LOHC systems.