Enhancement of biohydrogen production and low coke formation by applying Ni/ZrxCe1-xO2 catalyst in steam gasification of spent coffee ground in monolithic reactor

Abstract

To produce H2-rich gas, steam gasification of spent coffee grounds is performed in this study by applying ZrxCe1-xO2 supports (x = 0.2, 0.6) in a monolithic reactor. Compared with conventional Ni/γ-Al2O3, Ni/ZrxCe1-xO2 catalysts offer higher gas yields and H2 generation. In particular, Ni/Zr0.6Ce0.4O2 exhibits the highest gas yield (86.32 wt%), H2 selectivity (56 vol%), and low coke formation owing to its favorable Ni dispersion, high oxygen mobility, and completely homogeneous nanometer-sized morphology. A significant increase in gas yield was observed in the monolith reactor (M@Ni/Zr0.6Ce0.4O2) compared to the fixed bed reactor (F@Ni/Zr0.6Ce0.4O2), from 74.85 wt% to 86.32 wt%. H2 selectivity (56.87 vol%) is also increased, which can be associated with the unique properties of the monolithic reactor. This phenomenon is attributed to the increase in residence time and the amount of mass and heat transfer between the catalyst and vapor, which favorably direct the selectivity toward H2. The use of metal-oxide composite supports, especially Ni/Zr0.6Ce0.4O2 catalyst, effectively alleviated coke formation (0.7 wt%), whereas the amount of coke produced by Ni/γ-Al2O3 (2.4 wt%) was more than three times higher. Overall, exploiting the remarkable benefits of ZrxCe1-xO2 (x = 0.2, 0.6) composite oxides as supports for Ni catalyst and monolithic reactors would have an emerging outlook for H2 generation via gasification technology.