Embedding ruthenium nanoparticles in the shell layer of titanium zirconium oxide hollow spheres to catalyze the degradation of alkali lignin under mild condition

Abstract To catalyze the degradation of lignin in refractory wastewater efficiently, a new nanocomposite with Ru nanoparticles embedded on the surface of TiZrO4 hollow spheres was fabricated with three method a “sol-gel + calcination + vacuum-impregnation” template method, and the unique binary composition of TiZrO4/Ru prevented the aggregation of Ru and keep its high activity. During 3-h catalytic-oxidation at 160 °C and 2.0 MPa O2, 98% alkali lignin was degraded and 70% organic carbon was mineralized with the catalysis of TiZrO4/Ru, while the values were only 50% and 25% without analysts. The catalyst increased the catalytic-oxidation rate constant k1 (h−1) of alkali lignin from 0.282 h−1 to 1.175 h−1 because of high-efficiency hydroxyl radical production, as determined by EPR. LC-OCD showed that the catalyst decomposed alkali lignin with molecular weight 1–2 kDa to small molecules. Butyl acetate was the main intermediate product, which should be derived from the auto synthesis of butanol and acetic acid. In addition to high conversion efficiency, the catalyst had good stability with 95% capability after five cycles. In real biogas slurry treatment, an increase of biochemical to COD ratio from 0.28 to 0.51, with obvious decoloration, indicated TiZrO4/Ru enhanced the biodegradability of the refractory wastewater significantly.