Paving the way towards an eco- and budget-friendly one-pot catalytic conversion of cellulose and lignocellulosic residues into ethylene glycol over Ni–W/CNT catalysts

Abstract

The increasing demand for ethylene glycol (EG) for the manufacture of polyester fibers and resins in the plastic industry and as antifreeze in the automotive industry, together with the urge to replace fossil resources by renewable alternatives, leads today's society for the search of new sustainable processes like EG production from biomass. However, although many studies have been conducted on the catalytic conversion of cellulose to EG, the main issue that remains a challenge is to achieve adequate catalyst stability. To fulfil this gap, herein, a series of Ni–W-based catalysts supported on carbon nanotubes (CNT) were prepared and characterized by several techniques (TG, SEM, EDS, XRD, ICP and N2 adsorption). Cellulose was initially used as model feedstock for a comparative study on its reaction pathways, which effective control is fundamental to maximize EG production. In this work, cellulose was completely converted over Ni–W/CNT catalysts producing an EG yield over 50% after 5 h. The notable performance was attributed to the equilibrium between retro-aldol condensation and hydrogenation reactions achieved through the optimal conjugation of nickel and tungsten active sites. The best catalyst was then evaluated for EG direct production from lignocellulosic residues, such as eucalyptus wood, corncob and cotton wool. Unprecedented EG yields up to 46% were directly attained from the lignocellulosic wastes in just cheap and non-toxic water in the presence of pressurized hydrogen, under mild conditions and using promising environmentally friendly and cost-effective earth-abundant metal catalysts in replacement of noble metals (e.g. Ru). The catalysts presented good stability in hydrothermal conditions during repeated use for at least 6 cycles, demonstrating a promising outlook for future developments. Accordingly, 20%Ni–20%W/CNT is here presented as a potential cost-effective catalyst solution for the mandatory reduction of the dependence on petroleum.