Biomass and its derivatives are abundant and can be converted into high, value-added chemicals and fuels. This process is envisioned as a potential green avenue to bring down the dependence on traditional fossil resources.
Pyrolysis of lignocellulose is one such process that has turned into a green and cost-effective means for mass production of bio-oils to replace fossil fuels. Yet, the bio-oils produced in this way have oxygen-rich contents and, thus, exhibit relatively low energy density. This can result in damage to engines. Therefore, catalytic hydrodeoxygenation (HDO) is used to upgrade bio-oils with high energy density by selectively eliminating oxygen contents.
Vanillin, a direct lignocellulose pyrolysis product, can be upgraded to 2-methoxy-4-methylphenol (MMP) by HDO. The resultant MMP has extensive applications as a high energy density fuel and also as a vital intermediate to produce fragrances and drugs. Therefore, creating effective nonprecious metal catalysts that can selectively HDO vanillin to MMP in water is essential.
The synergetic effect of the alloyed nanoparticles (NPs) based catalysts is favorably employed to significantly increase the catalyst performance for advancing biomass and biomass-derivatives to fuels and chemicals of high value. Normally, the group VIII metals (Ni, Rh, Ru, Pt, Pd) have greater catalytic activities for the hydrogenation of unsaturated C=O bonds and C=C bonds.
Thus, non-precious Ni-based catalysts are largely used to catalyze HDO reactions; however, they exhibit limited selectivity toward oxygen-free products. To improve the deoxygenation activity and selectivity of Ni-based catalysts, combining Ni with other metals to create alloy NPs is an effective strategy.
Researchers headed by Professor Huijun Zhao from Institute of Solid State Physics, HFIPS, CAS, China announced the controllable synthesis of distinct Ni-Co alloy NPs confined by N-doped carbon nanotubes (N-CNTs) and their application as effective HDO catalyst to convert vanillin, its derivatives and other aromatic aldehydes to the corresponding MMPs and deoxygenated products.
The findings indicate that the as-synthesized Ni-Co alloy NPs catalyst ([email protected]/CMF) can fully transform vanillin to MMP with a 100% selectivity under mild reaction conditions, outshining the reported high-performance nonprecious HDO catalysts.
Remarkably, the catalyst showcases superior HDO catalytic performance towards a broad spectrum of vanillin derivatives and other aromatic aldehydes with 100% conversion efficiency and high selectivity (91.5%–100%).
The DFT calculations and experimental results substantiate that the accomplished outstanding HDO catalytic performance is because of the highly promoted selective adsorption and activation of C=O, and desorption of the activated hydrogen species by the synergism of the alloyed Ni-Co NPs. The observations of this research put forth a novel strategy to design and create efficient transition metal-based catalysts for HDO reactions in water.
Wang, D., et al. (2021) Encapsulated Ni-Co alloy nanoparticles as efficient catalyst for hydrodeoxygenation of biomass derivatives in water. Chinese Journal of Catalysis. doi.org/10.1016/S1872-2067(21)63828-7.