Abstract
Biomass-derived carboxylic acids (e.g. acetic acid AcOH and formic acid FA) are a green and low-cost hydrogen source to replace hazardous H2 gas in in-situ hydrogenation processes. To date, bio-acids dehydrogenation has been mainly conducted using noble metal catalysts which would negatively impact the process economy, thus development of efficient non-noble metal catalysts for this purpose is highly desirable. In this study, the performance of transition metals supported on nitrogen doped carbon nanotubes was thoroughly evaluated by computational modelling based on Density Functional Theory (DFT). Results revealed that, out of the 10 selected transition metal candidates, molybdenum (Mo) was most active for binding AcOH and a combination of Mo and nitrogen doping significantly enhanced binding to the carboxylic acid molecules compared to pristine carbon nanotubes (CNTs). The newly designed Mo/N-CNT catalysts considerably facilitated the bio-acids decomposition compared to the non-catalytic scenarios by lowering energy barriers. FA distinctly outperformed AcOH in hydrogen donation over Mo/N-CNT catalysts, through its spontaneous cleavage leading to facile hydrogen donation.
Highlights
The rapid economic growth and increase in the global population have accelerated the consumption of fossil resources
Mo and Pt supported on Np-carbon nanotubes (CNTs) exhibi ted the strongest AcOH binding energy (1.76 eV), implying that they are probably more catalytically active than other transition metals selected in activating carboxylic acids
It is found that Np-CNT and Ng-CNT exhibit different acid and base ef fects on AcOH adsorption only in the presence of Mo, which can be attributed to the synergistic effects between N and Mo atoms, in line with the reported results in the literature [40,53]
Summary
The rapid economic growth and increase in the global population have accelerated the consumption of fossil resources. This has resulted in an unprecedented increase in the level of CO2 and other greenhouse gases (GHG) emissions, threatening the future of our planet by contributing to global warming [1]. Alternative sustainable feedstocks are needed to meet the demands for organic chemicals and fuels. Non-edible and waste biomass such as lignocellulose and tri glycerides are considered a sustainable source of carbon that can be used to produce green and low-cost chemicals and fuels. Lignocel lulosic biomass has high oxygen content, itself or its derivative has to undergo some deoxygenation steps to be converted to the desired products [2]. Deoxygenation is conducted via hydro genation using precious metal-based catalysts and molecular H2
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