We have investigated heterocatalytic reactions of isosorbide (IS), a crucial platform molecule with industrial applications. Mainly, we have looked at the isomerization of IS to its less abundant isomers, isoidide and isomannide, with a special focus to understanding the indispensable role of hydrogen. The isomeriztion is a potential route in any reaction that involves dehydorgenation of IS, i.e. amination, and thus needs in depth understanding to aid in our attempts to valorize IS into other useful chemicals. The isomerization reaction takes place in the presence of aqueous solvent, up to 50 bar pressure of hydrogen and temperature as high as 200 ℃ using carbon-supported ruthenium catalyst. Using periodic density functional theory, we have investigated the potential energy surface for the isomerization of IS both in the absence and the presence of hydrogen. Our results indicate that a coverage of hydrogen on the catalyst surface plays an important role in destabilizing the otherwise very stable reaction intermediates thereby reducing the overall barriers involved in the reaction. As a second step, we have characterized the surface state of the catalyst under experimental conditions of temperature and pressure using ab initio atomistic thermodynamics. Our findings reveal that in the absence of any hydrogen, the surface can get (partially-)oxidized even by the mere presence of water. This further signifies a potential role of hydrogen as a protecting agent in the isomerization reaction. Finally, using kinetic modelling, we have investigated the amination reaction of IS with a view to understanding the potential poisoning of the catalyst surface by NHx species.