Model Catalytic Studies of the LOHC System 2,2′-Bipiperidine/2,2′-Bipyridine on Ni(111)

N-heterocyclic compounds such as octahydroindole and dodecahydro-N-ethylcarbazole have been proposed as suitable liquid organic hydrogen carriers for chemical hydrogen storage. Following these studies, we focused on hydrogen-rich 2,2'-bipiperidine with a hydrogen storage capacity of 7.1 wt % and hydrogen-lean 2,2'-bipyridine. Both were adsorbed on Ni(111), and the temperature-induced reaction mechanism and decomposition were studied. The reaction was investigated using synchrotron-based XPS, NEXAFS, and TPD experiments. Upon adsorption, the formation of a flat-lying chemisorbed layer is observed. Above 370 K, 2,2'-bipyridine is dehydrogenated in the alpha-position to the nitrogen atoms to form an alpha-2,2'-bipyridyl species with a tilted adsorption geometry. The hydrogen-rich 2,2'-bipiperidine is partially dehydrogenated above 180 K and deprotonated at the nitrogen atoms above 250 K. Above 320 K, alpha-2,2'-bipyridyl is formed, which is accompanied by a byproduct that is partially dehydrogenated at the carbon atoms. Above 400 K, we observe the decomposition of the alpha-2,2'-bipyridyl species.

Automated summary

N-heterocyclic compounds have been proposed as suitable liquid organic hydrogen carriers for chemical hydrogen storage. The adsorption and reaction mechanisms of hydrogen-rich 2,2'-bipiperidine and hydrogen-lean 2,2'-bipyridine on Ni(111) were studied using synchrotron-based XPS, NEXAFS, and TPD experiments. The temperature-induced dehydrogenation and decomposition processes of these compounds were observed, providing insights into their behavior as potential hydrogen storage materials.