Design, Fabrication, And Performance Investigation Of Formic Acid Dehydrogenation Catalysts

Hydrogen has been considered as one of the best alternative energy carriers to satisfythe increasing demands for an efficient and clean energy supply. Hydrogen can be convertedefficiently to produce electricity when it is combined with polymer electrolyte membrane(PEM) fuel cell technology. However, the safe and efficient storage and transfer of hydrogenis a challenge because of its low volumetric and weight energy densities. To solve thisproblem, formic acid can be used as a material for the storage of hydrogen, because it offershigh energy density, is non-toxic and can be safely handled at room temperature. Moreimportantly, formic acid can be produced from photocatalytic CO2hydrogenation. One of thekeys to the practical application of this system is to develop efficient and economicalcatalysts for further improving the kinetic and thermodynamic properties. In this thesis, themain results are divided into three parts as following:1. All catalysts previously synthesized for the dehydrogenation of formic acid arecomposed of noble metals, hindering their large-scale practical applications due to high costsand scarcity. In order to reduce the usage of noble metals and further improve the activity ofthe catalyst, we introduced non-noble metal Co into AuPd alloys. CoAuPd/C is synthesizedthrough a surfactant-free co-reduction method. Due to the electron transfer from Co atoms toAu and Pd atoms, the CoAuPd/C shows the superior activity and100%hydrogen selectivitytoward hydrogen generation from formic acid at room temperature. In addition, DNA wasused to functionalize graphene oxide (GO) and further to guide the growth of CoAuPd alloynanoparticles (NPs) on DNA-GO surface. We found that DNA can not only efficientlycontrol the growth of CoAuPd NPs, but also promote the good dispersion of theCoAuPd/DNA-rGO composite in water. As a result, the initial turnover frequency (TOF)over the CoAuPd/DNA-rGO composite is measured to be85.0mol H2mol catalyst-1h-1atroom temperature without any additives, which is almost1.9,6.4, and2.3times higher thanthose of CoAuPd/rGO composite, CoAuPd NPs, and CoAuPd/C under the same conditions,respectively. On the other hand, in order to further reduce noble metal usage, we designedand prepared a new catalyst, NiAuPd/C, using a co-reduction method without surfactant. Wefound that alloying of Ni with Au and Pd can modify the catalyst surface, resulting in anenhanced activity for formic acid dehydrogenation. 2. In order to improve the activity of atalyst and simplify the catalyst preparationprocesses, we developed the highly efficient hydrogen generation from formic acid/sodiumformate aqueous solution catalyzed by in situ synthesized Pd/C with citric acid. We foundthat sodium formate plays the role of both reducing agent and hydrogen source in our systemand citric acid can dramatically improve the activity of Pd/C for the dehydrogenation offormic acid. As a result, the conversion and TOF for decomposition of formic acid/sodiumformate system can reach the highest values ever reported of85%within160min and64mol H2mol catalyst-1h-1, respectively, at room temperature.3. Using ammonia solution as the N source, we successfully prepared a new N-dopedgraphene based catalyst, AuPd-CeO2/N-rGO hybrid at low temperature. We found that theincorporation of N atoms into reduced graphene oxide (rGO) is the key to the formation ofthe ultrafine and well-dispersed AuPd-CeO2nanocomposites (NC). As a result, theapplication of N-rGO dramatically improves the activity of AuPd-CeO2NC for hydrogengeneration from formic acid. The intial TOF over AuPd-CeO2/N-rGO hybrid is measured tobe52.9mol H2mol catalyst-1h-1without any additives at298K. On the other hand, wedevelop a green and facile sequential reduction route to prepare Au@Pd core-shell NPsgrowing on nitrogen-doped reduced graphene oxide (Au@Pd/N-rGO) by redox reactionsbetween Au3+, Pd2+and GO. As a result, the Au@Pd/N-rGO hybrid shows much higheractivity for formic acid dehydrogenation than that of the AuPd alloy nanoparticles/N-rGOand Pd/N-rGO hybrid. Its initial TOF is89.1mol H2mol catalyst-1h-1at room temperaturewithout any additives.