Development of heterogeneous catalysts for hydrogen production from biomass derived formic acid

Hydrogen is increasingly used in a variety of applications and holds promise as a replacement for fossil fuels. Biomass derived formic acid represents an excellent renewable material for hydrogen storage. This thesis is devoted to an investigation of different catalysts aiming ultrapure hydrogen production from formic acid decomposition. Two research directions were considered: (I) decomposition of formic acid over Au catalysts supported on a selection of metal oxides, and (II) decomposition of formic acid over Ru, Pd and Pt catalysts supported on a variety of N-free and N-doped carbon materials. A series of characterization methods were applied to understand the promotion of the catalysts with the nitrogen incorporated into the carbon structure, which should be taken into the account when designing a catalyst for particular use. A study of ~2.5 wt.% Au catalysts supported on different metal oxides (Al2O3, ZrO2, CeO2, La2O3 and MgO) with the same mean Au particle sizes showed that alumina is the most efficient support for stabilization of Au species providing almost CO free hydrogen production for at least 16 h. High activity of Au catalysts was associated with acid–base properties of the support. N-doping of Ru catalysts supported carbon nanofibers (CNFs) demonstrated an increase of the rate of the formic acid dehydrogenation reaction and lead to an increase of the selectivity to hydrogen from 83 to 92%. The increase in activity was explained by coordination of the Ru species by pyridinic nitrogen located on the open edge of graphene layers of the herringbone type CNFs used. The effects of preparation variables, structure of the carbon supports (carbon nanofibers and porous carbon network), and surface functional composition on catalytic properties of the Pd and Pt catalysts were studied. Single Pd atoms and single Pt atoms on nitrogen-functionalized carbon materials, observed by aberration-corrected scanning transmission electron microscopy were found to contribute considerably to the catalytic activity, selectivity and did not affect the stability of the catalysts at least for 30 h in hydrogen production. XPS analysis proved the presence of Pd2+ ions in significant concentration even after treatment of the catalyst with H2 and interaction of Pd atoms with pyridinic nitrogen of the support was recognized.