Hydrotreatment of wood-based pyrolysis oil using zirconia-supported mono- and bimetallic (Pt, Pd, Rh) catalysts

Fast pyrolysis oil (PO), the liquid product of fast pyrolysis of lignocellulosic biomass, requires upgrading to extent its application range and for instance to allow for co-feeding in an existing oil-refinery. Catalytic hydrotreatment reactions (350 °C, 20 MPa total pressure, and 4 h reaction time) with mono- and bi-metallic metal catalysts based on Rh, Pt, Pd on a zirconia support were performed in a batch set-up. Pd/ZrO2 showed the highest activity, followed by Rh/ZrO2. Upgraded oils with the best product properties were obtained with Rh/ZrO2. For this catalyst, the TGA residue, which is a measure for coking tendency, was 13.4 wt% and the Mw of the upgraded oil (748 g/mol) was lowest. All noble metal catalysts showed higher activities per gram of metal than the benchmark catalyst CoMo/Al2O3. Hydrotreatment reactions at variable batch times were performed to gain insights in reaction pathways and showed the involvement of competitive hydrogenation/hydrocracking and polymerisation pathways. Temperature programmed oxidation (TPO) measurements of spent catalysts showed the presence of carbonaceous deposits on the catalyst (2–6 wt%). These deposits may be removed by oxidation at temperatures lower than 600 °C without changing the morphology of the catalyst.

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► Noble metal catalysts on ZrO2 were tested for hydrotreatment of pyrolysis oil.
► The catalysts are more active on a metal basis than the benchmark CoMo/Al2O3.
► Rh/ZrO2 gave a product oil with the lowest tendency for coking (TG residue).
► A reaction network is proposed and involves repolymerisation and hydrogenation.
► Carbonaceous deposits on spent catalysts can be removed by an oxidation step.