3D printed nickel-copper modified CaNaX and NaX zeolites obtained from coal fly ash for sustainable levulinic acid hydrogenation

Coal fly ash zeolites with Na(Ca)X structure with different Ca and Fe content were synthesized by ultrasound-assisted double stage fusion-hydrothermal synthesis. Bimetallic Ni-Cu supported catalysts with different nickel (5–10 wt%) and copper (2.5–5 wt%) content were prepared by post-synthesis incipient wetness impregnation. 3D printing technique was applied for the catalysts preparation after modification with metal precursors. The catalysts were characterized by X-ray powder diffraction (XRD), Temperature programmed reduction with derivative thermogravimetry (TPR-DTG), N₂ physisorption and Transmission electron microscopy (TEM). It was found that crystalline Ni_xCu_y intermetallic nanoparticles with different x/y ratio were formed in the reduced catalysts and they affected the reducibility and catalytic performance of the active nickel phases. The 3D printed catalysts were studied in the lignocellulosic biomass-derived levulinic acid (LA) to γ-valerolactone (GVL). It was found that the presence of NiCu alloy rich of nickel on the 3D printed catalysts favors their catalytic performance in the studied reaction. The preservation of the zeolite structure was detected for all 3D printed samples, which has a positive influence on the metal dispersion registered in the 3D spent catalysts. The 3D printed 10Ni5Cu/NaCaX catalyst showed the highest LA conversion and high GVL yield at 200 °C reaction temperature but more stable catalytic performance was registered for the 10Ni5Cu/NaX catalyst in 4 reaction cycles. The preservation of zeolite structure and metal dispersion in 3D printed 10Ni5Cu/NaX catalyst resulted in stable catalytic activity in the studied reaction indicating its potential for practical application.