Spent coffee ground-derived biochar with trimodal porosity: green biochar supported highly dispersed TiO2 and Nb2O5 nanoparticles as an efficient novel catalyst for lactic acid synthesis

Abstract

Lactic acid obtained from cellulose over heterogeneous acid catalysts is one of the key areas in bioeconomy. Herein, we develop a series of biochar-supported nano-titanium–niobium oxides (with 10% Ti and 0.25 to 15% Nb) prepared via wet impregnation and evaluate their performances in cellulose conversion to lactic acid. We report for the first time a biochar which displays trimodal (micro-, meso-, and macro-) porosity and high surface area due to the synergistic effect between lanthanum and zinc during the carbonization of spent coffee grounds. The successful impregnation of Nb and Ti species on the surface of the biochar was confirmed by XRD, TGA, XPS, AFM, SEM-EDS, and STEM-EDS. The presence of niobia and titania generated a significant increase in the catalyst's acidity as noticed by NH₃-TPD and, subsequently, improved the lactic acid yield from 1.6% (for 10% Ti/AC) to 14% (for 10% Ti–0.5% Nb/AC). Furthermore, the high-water tolerance of niobium and titanium species allowed the biochar-supported nano-titanium–niobium oxides to be recycled three times without a significant loss in their catalytic activity.