Scale-up Biopolymer-Chelated Fabrication of Cobalt Nanoparticles Encapsulated in N-enriched Graphene Shells for Biofuel Upgrade with Formic Acid

Both exploring high-performance catalytic materials from non-edible lignocellulosic biomass and selective hydrodeoxygenation of bioderived molecules will enable the value-added utilization of renewable feedstocks to replace rapidly diminishing fossil resources. Herein we developed a scale-up and sustainable method to fabricate gram-quantities of highly dispersed cobalt nanocatalysts sheathed in multilayered N-doped graphene (Co@NG) by using biomacromolecule carboxymethyl cellulose (CMC) as raw material. The ionic gelation of CMC, urea and Co2+ ions lead to the uniformly dispersion and chelation of different species, consequently resulting in the formation of high distributed Co nanoparticles (NPs) (10.91 nm) with N-enriched graphene shells in solid-state thermolysis process. The usage of urea as non-corrosive activation agents can introduce a porous belt-like nanostructure and abundant doped nitrogen. Among all the prepared catalysts in this work, the optimized Co@NG-6 with the largest specific surface area (627 m2 g−1), the most and strongest basic sites, the highest proportion of pyridinic-N (37.6%) and mesopore exhibited excellent catalytic activity (99% yield of 2-methoxy-p-cresol) for base-free transfer hydrodeoxygenation (THD) of lignin molecule vanillin using bioderived formic acid (FA) as H source at 160 °C for 6 h. The poisoning tests and electron paramagnetic resonance spectra (EPR) verified that the strong interaction between N atoms and encapsulated Co NPs provided synergistic effects, which were essential for the outstanding catalytic performance of Co@NG-6. The deuterium kinetic isotope effect study clearly demonstrated the formation of Co-H- via β-hydride elimination and protonation was rate-determining step, and the protic N-H+ and hydridic Co-H− were considered to be active intermediate species in THD reaction. Furthermore, Co@NG-6 was highly stable for recycling owing to graphene shells preventing Co NPs from corrosion and aggregation.