Utilization of gold-loaded ironbark biochar-based catalyst for catalytic upgrading of spent coffee grounds: reaction kinetics, products distribution, and mechanism

Abstract To reduce dependence on fossil fuels and limit environmental impacts, converting abundant and low-cost lignocellulosic biomass into renewable energy products is essential. While biomass-derived biochar is widely used in environmental and agricultural applications, its role as a catalyst or catalytic support has received far less attention. In this study, we develop a novel biochar-based catalyst and demonstrate its effectiveness in the catalytic pyrolysis of spent coffee grounds (SCG), leading to enhanced production of valuable hydrocarbons and phenols. This work reveals a new and underexplored application of biochar in sustainable energy and chemical generation. The adsorption method was adopted for the preparation of gold nanoparticles (AuNPs) loaded into ironbark biochar (IBBC) catalysts. The characterization by BET, XRD, FTIR, SEM-EDS findings confirmed the successful preparation of AuNPs-IBBC catalyst. SCG biomass, without-metal catalyst showed the lowest hydrocarbon production. However, incorporating the AuNPs-IBBC into the process led to an increase in the production of aromatics, as well as aliphatic hydrocarbons. The biochar surface functionalities coupled with gold increased the aromatics selectivity two-fold (from 4.5 to 9.9%) and phenols (from 2.4 to 5.5%) with the IBBC-BC1 catalyst. At 750 °C pyrolysis temperature with the BC1 catalyst, hydrocarbon production was the highest compared to other catalysts. The BC1 catalyst favored C4–C11 hydrocarbons with a selectivity of 6%. The BC1 catalyst has demonstrated an enhanced pore volume of 0.089 cm³/g, accompanied by an average pore diameter of 3.182 nm. TGA results showed significant weight reduction rates and increased thermal degradation rates after catalytic pyrolysis of SCG. Therefore, it could be suggested that gold-loaded biochar catalyst can upgrades the SCG biomass to produce value-added chemicals.