A Kinetic Model of Furfural Hydrogenation to 2-Methylfuran on Nanoparticles of Nickel Supported on Sulfuric Acid-Modified Biochar Catalyst

Lignocellulosic biomass can uptake CO₂ during growth, which can then be pyrolysed into three major products, such as biochar (BC), syngas, and bio-oil. Due to presence of oxygenated organic compounds, the produced bio-oil is not suitable for direct use as a fuel and requires up-grading via hydrodeoxygenation (HDO) and hydrogenation. This is typically carried out over a supported metal catalyst. Regarding circular economy and sustainability, the BC from the pyrolysis step can potentially be activated and used as a novel catalyst support, as reported here. A 15wt% Ni/BC catalyst was developed by chemically modifying BC with sulfuric acid to improve mesoporous structure and surface area. When compared to the pristine Ni/BC catalyst, sulfuric activated Ni/BC catalyst has excellent mesopores and a high surface area, which increases the dispersion of Ni nanoparticles and hence improves the adsorptive effect and thus catalytic performance. A liquid phase hydrogenation of furfural to 2-methylfuran was performed over the developed 15wt% Ni/BC catalyst. Langmuir–Hinshelwood-Hougen-Watson (LHHW) kinetic type models for adsorption of dissociative H₂ were screened based on an R² value greater than 99% demonstrating that the experimental data satisfactorily fit to three plausible models: competitive (Model I), competitive at only one type of adsorption site (Model II), and non-competitive with two type of adsorption sites (Model III). With a correlation coefficient greater than 99% between the experimental rates and the predicted rate, model III, which is a dual-site adsorption mechanism involving furfural adsorption and hydrogen dissociative adsorption and surface reaction, is the best fit. The Ni/BC catalyst demonstrated comparative performance and significant cost savings over previous catalysts, a value of 24.39 kJ mol^-1 was estimated for the activation energy, -11.43 kJmol^-1 for the enthalpy of adsorption for H₂, and -5.86 kJmol^-1 for furfural. The developed Ni/BC catalyst demonstrated excellent stability in terms of conversion of furfural (96%) and yield of 2-methylfuran (54%) at the fourth successive experiments. Based on furfural conversion and yield of products, it appears that pores are constructed slowly during sulfuric acid activation of the biochar.