Based on our mechanistic investigations, as well as the previously reported mechanistic work for molecular systems, a possible mechanism involves a number of hydrogenation and dehydrogenation steps resulting in a temporary cleavage of the ester group linkage via hemiacetal formation and its subsequent dissociation (Fig. ). Dehydrogenation of the resulting alcohol group followed by hydrogenation of the initial aldehyde yields a new hemi-acetal, whose dehydrogenation finalizes the HTEM sequence.