Enhanced production of phenolics and aromatics from raw bio-oil using HZSM-5 zeolite additives for PtPd/C and NiW/C catalysts

This study delves into the performance of a Pt-Pd and a Ni-W catalyst supported on a phosphorus-containing activated carbon (ACP) in the hydrodeoxygenation (HDO) of raw bio-oil, as well as the enhancement of phenolic and aromatic product yields produced by incorporating physically mixed HZSM-5 zeolites (20 wt%) of different Si/Al ratio (15 and 140 in zeolites Z15 and Z140, respectively) in the catalytic bed. The HDO runs have been conducted in a fixed bed reactor at: 450 °C; 65 bar; space time, 0.15 gcat h g−1bio-oil; 90 ml min−1 H2; and time on stream up to 6 h. After a fast initial deactivation due to coke deposition the catalysts reached a pseudosteady state at which the carbon product yields are higher than in fresh catalyst conditions. The NiW catalyst provided yields of 42.3 wt% liquid carbon products (in a dry bio-oil basis), yielding 5.3 wt% phenolic and 12.3 wt% aromatic product yields. The NiW + Z140 combination was the most efficient catalyst (with a 47.3 wt% carbon production, including 6.8 wt% phenolics and 15.5 wt% aromatics) as a consequence of this low-acidity zeolite promoting the synergy with the dehydrogenation activity of metallic sites by favoring the acid-catalyzed cracking reactions of the bio-oil oxygenates, while simultaneously limiting gas product and coke formation. Two types of coke were detected, of thermal origin and catalytic coke, with the formation of the latter being dependent on the acidity of the zeolite.