Engineering non-noble Ni/WOx-ZrO2 towards boosted fuels production by catalytic upcycling of polyethylene at mild conditions

Abstract

Chemical upcycling through catalytic hydrocracking to fuels has potential to mitigate the serious environmental issues caused by plastic waste. Herein, non-noble tungstate-zirconia supported nickel catalyst (Ni/WOx-ZrO2) with tunable Brønsted/Lewis (B/L) ratio was firstly proposed for the hydrocracking of low-density polyethylene (LDPE), which achieves hydrogenation/dehydrogenation on Ni sites and cracking/isomerization on WOx-ZrO2, respectively. Excellent 100 % LDPE conversion with 76.9 % liquid yield was achieved, which is comparable to noble Ru-based and Pt-based catalysts. Quantitative linear relationship between B/L ratio and hydrocracking performance was established, and the key to boost performance was keenly controlling the volcanic-shape relationship between surface WOx density and B/L ratio of catalyst. Moderate WOx surface density with higher B/L ratio enhances LDPE hydrocracking, and inhibits the hydrogenation of the primary products. However, excessive WOx polymerized and formed WO3 crystals, compensating acid sites and inhibiting LDPE hydrocracking. This work is of prime scientific and industrial significance to the rational design of catalysts for industrial plastic hydrocracking.