(560u) Hydrogen Donation from Bio-Acids over Carbon Nano Tube (CNT) Based Bi-Functional Catalysts: Density Functional Theory Study

Bio-acids (e.g. acetic acid and formic acid) have drawn considerable interest as alternative hydrogen source for in-situ hydrodeoxygenation of bio-oil to produce biofuels. However, their potential and decomposition mechanism as hydrogen donors have not been adequately explored. In this study, the decomposition pathways of bio-acids were investigated by DFT modelling with the emphasis on their performance on in-situ hydrogen donation. As promising green materials, metal supported on nitrogen doped carbon nanotubes (CNTs) was evaluated as catalysts for the decomposition of bio-acids. Adsorption modelling of acetic acid (AcOH) indicated Mo loading led to the highest adsorption energy compared to nine other transition metals, and N_p (pyridinic nitrogen doped)-CNT enabled the strongest binding to AcOH among a series of CNTs based supports, followed by intact CNT and N_g (graphitic nitrogen doped)-CNT. It was found that different doping types of nitrogen on CNT not only affected the adsorption of bio-acids, but also determined the catalysis performance and consequent reaction pathways of bio-acids decomposition. Modelling results indicated Mo/N-CNTs could significantly facilitated the decomposition of both bio-acids by lowering the reaction energy barriers, in comparison with the radical reactions without catalysts. The electron acceptor property of Mo/N_p-CNT gave rise to dissociative adsorption of both acids molecules, which significantly facilitated the decomposition of bio-acids, directly contributing to the hydrogen donation of formic acid (FA). Mo/N_p-CNT also enabled electron enrichment on both sides of C-CH₃ bond so that facilitated homolytic cleavage of in AcOH. The electron donation property of Mo/N_g-CNT made the hydrogen donation from lower fragments of methyl and hydroxyl much more facile, by arousing more electron enrichment to the hydrogen atoms, and resulted in eventual homolytic cleavage of the hydrogen atom. It can be concluded that FA performed better in hydrogen donation than that of AcOH, and Mo/N_g-CNT was supposed to be the most effective catalyst to facilitate the hydrogen donation from FA compared with Mo/Np-CNT and sole Mo catalyst.