A process for regenerating catalysts that have been deactivated or poisoned during hydrogenation of biomass, sugars and polysaccharides is described, in which polymerized species that have agglomerated to catalyst surfaces can be removed by means of washing the catalyst with hot water at subcritical temperatures. A feature of the process regenerates the catalysts in situ, which allows the process to be adapted for used in continuous throughput reactor systems. Also described is a continuous hydrogenation process that incorporated the present regeneration process.