Graphene-Supported Fe/Ni, β-Mo2C Nanoparticles: Experimental and DFT Integrated Approach to Catalyst Development for Synergistic Hydrogen Production through Lignin-Rich Biomass Reforming and Reduced Shale Gas Flaring

Biomass-flare gas synergistic coprocessing is a novel energy conversion technology that aims at harnessing an abundant renewable energy source: biomass and mitigate shale gas flaring. p-Cresol is used to represent lignin- and biomass-derived oxygenates for performing experimental and molecular reaction engineering of methane-assisted hydrodeoxygenation (HDO), hydrogenolysis reforming. The reaction pathway was also demonstrated on complex feedstocks like lignin and biomass, which contain a wide range of oxygenates in their composition. Novel in situ catalyst synthesis using a biomass precursor was achieved through pyrolysis to yield graphene nanosheet (GNS)-supported transition metal (TM) and Mo2C nanoparticles. Experimental work and density functional theory (DFT) modeling calculations were performed for methane-assisted p-cresol reforming using Fe, Ni, Mo2C, Fe-Mo2C, Ni-Mo2C, and Pd-Mo2C supported on GNS. Detailed mechanistic investigation of the methane-p-cresol synergistic reaction experimentally and through DFT-based molecular simulations helped ascertain the unique reaction pathway occurring on bifunctional (dual) active site-TM-doped beta-Mo2C. Without TM doping, Mo2C is equally effective as Fe-Mo2C-GNS and Ni-Mo2C-GNS for CH4 dissociation and p-cresol HDO but presents a significantly higher barrier for H-2 (1.7 eV vs 1.15, 1.13 eV) and CO (3.67 eV vs 2.87, 2.80 eV) gas-phase desorption. Dual active sites are required for hydrogen-rich syngas production through methane-assisted p-cresol reforming as validated by experiments, DFT calculations, and microkinetic modeling. Lignin and hardwood biomass both having a higher O/C weight ratio compared to p-cresol (0.46, 1.09 vs 0.19) were coprocessed with CH4 over Fe-Mo2C-GNS, Ni-Mo2C-GNS, and Pd-Mo2C-GNS catalysts. Fe-added Mo2C nanoparticles dispersed in the graphene support were found to be highly active for simultaneous CH4 activation and extensive HDO of p-cresol, lignin, and hardwood biomass. Higher HDO conversion and H-2/CO ratios were obtained from CH4-assisted lignin/biomass reforming over Fe-Mo2C-GNS. Up to 99% hydrogen present in lignin could be valorized as syngas with a concentration of >65%.