Abstract
Transforming hazardous and difficult-to-process waste materials, like spent Ni-MH batteries and aluminium foil, into nanocatalysts (NCts) provides a sustainable solution for resource management and reducing environmental impact. This study demonstrates a novel approach by extracting nickel sulfate (NiSO(4)·xH(2)O) from battery waste and subsequently converting it into Ni(OH)(2) hydrogel precursors using l-glutamic acid. Waste aluminium foil was processed into alumina (Al(2)O(3)), and combined with Ni(OH)(2) to synthesize Ni/η-Al(2)O(3) NCts with 4% and 8% Ni loading. Characterization through XRD/SAED, STEM/EFTEM, and EELS revealed a disordered cubic structure of η-Al(2)O(3), with well-dispersed Ni particles, making it effective for CO(2) hydrogenation. The 8-Ni/η-Al(2)O(3) exhibited the best catalytic performance, with CH(4) selectivity of 99.8% and space time yield (STY) of 80.3 mmol(CH(4)) g(cat) (-1) h(-1) at 400 °C. The CO(2) methanation mechanism over Ni/η-Al(2)O(3) NCts was further explored using operando DRIFTS aligned with GC + MS. The operando investigation suggested a preferential associative CO(2) methanation pathway, involving sequential adsorption and hydrogenation of CO(2) to hydrogen carbonates on Ni/η-Al(2)O(3), and their transformation into formate and methoxy intermediates leading to methane. Finally, to complete the upcycling/recycling loop, the spent Ni/η-Al(2)O(3) NCts were recycled into Ni and Al precursors. These findings underscore the potential of upcycling waste materials for synthesizing sustainable, high-performance NCts, and offer insights into the CO(2) methanation mechanism.