Red mud supported Ni-Cu bimetallic material for hydrothermal production of hydrogen from biomass

Exploring efficient and reliable catalysts to achieve gasification of biomass waste is a promising research endeavour. In this study solid waste red mud (RM, an inexpensive and efficient support) loaded Ni-Cu metals (Ni-Cu/RM) was used to catalyze hydrothermal gasification of cotton stalk at 340–400 ℃ and 16–30 MPa. In the presence of Ni-Cu/RM catalyst, 21.88 mmol/g H2 yield with 79.89% carbon balance was achieved, increased by 22.8 times under the optimized conditions (380 ℃ for 5 min) based on orthogonal experiments. Under the optimal conditions, H2 yield with neat Ni and Ni/RM loaded on RM is 0.96 and 12.94 mmol/g, respectively due to the specific surface area soaring by 72.0 times from 0.7 to 50.5 m2/g. With Ni-Cu/RM bimetallic catalyst, H2 yield jumped from 3.41 to 21.88 mmol/g, 6.7 times higher than that neat Ni, or reached 84% with Ni-Cu/Al2O3 if Al2O3 was as support. It is further found that Cu promoted the dispersion of Ni on red mud with surface area rising from 50.47 to 73.42 m2/g together with forming Ni-Cu alloy (alkalinity of Ni-Cu/RM rose to 285.65 from 172.21 μmol/g for Ni/RM) enhanced H2 generation. When temperature grew from 340 ℃ to 400 ℃ (supercritical), H2 yield improved by 3 times from 9.21 to 28.50 mmol/g. Red mud is an ideal candidate for replacing the commercial support Al2O3.