Evaluation of High-Loaded Ni-Based Catalysts for Upgrading Fast Pyrolysis Bio-Oil

Abstract

The catalytic activity of high-loaded Ni-based catalysts for beech wood fast-pyrolysis bio-oil hydrotreatment is compared to Ru/C. The influence of promoter, temperature, reaction time, and consecutive upgrading is investigated. The catalytic activity is addressed in terms of elemental composition, pH value, H2 consumption, and water content, while the selectivity is based on the GC-MS/FID results. The catalysts showed similar deoxygenation activity, while the highest hydrogenation activity and the highest upgraded oil yields were obtained with Ni-based catalysts. The elemental composition of upgraded oils was comparable for 2 and 4 h of reaction, and the temperature showed a positive effect for reactions with Ni–Cr and Ru/C. Ni–Cr showed superior activity for the conversion of organic acids, sugars and ketones, being selected for the 2-step upgrading reaction. The highest activity correlates to the strength of the acid sites promoted by Cr2O3. Consecutive upgrading reduced the content of oxygen by 64.8% and the water content by 90%, whereas the higher heating value increased by 90.1%. While more than 96% of the organic acid content was converted, the discrepancy of aromatic compounds quantified by 1H-NMR and GC-MS/FID may indicate polymerization of aromatics taking place during the second upgrading step.