Investigation of Nb2O5 and Its Polymorphs as Catalyst Supports for Pyrolysis Oil Upgrading through Hydrodeoxygenation

Mild catalytic hydrogenation is an interesting processto upgradeand stabilize raw fast-pyrolysis oil, allowing higher ratios of bio-oilto be coprocessed in conventional refineries. In the search for hydrodeoxygenation(HDO) catalysts with high activity, high selectivity, and long-termstability, Nb2O5-supported catalysts are stressedowing to their water-resistant acid sites. Due to the Nb2O5 polymorphism, its properties such as acidity, morphology,and crystalline structure are adjustable. This study evaluated thesuitability of Nb2O5 as a catalyst support andthe impact of its different polymorphs on the upgrading of pyrolysisoil. Four different Nb2O5 polymorphs were preparedby thermal treatment of niobic acid, and nanostructured Nb2O5 was prepared by hydrothermal synthesis with niobiumoxalate. The supports were wet impregnated with Pd (1 wt %) and appliedfor the upgrading of the light phase of beech wood fast-pyrolysisoil (FPO-LP) in a batch reactor, pressurized at 80 bar H-2 (room temperature), and heated to 250 & DEG;C for 2 hours. The activityand selectivity of catalysts and the dominant reaction pathways wereaddressed in terms of upgraded product properties (elemental composition,water content, functional groups via H-1-NMR, and chemicalcomposition via GC-MS/FID), H-2 consumption, generatedgases, deoxygenation degree, and catalyst deactivation via coke formation.Nb2O5 showed outstanding potential as a catalystsupport for FPO-LP HDO, taking into account the improved propertiesof the upgraded oil, such as higher carbon content and lower waterand oxygen contents. The polymorphs without thermal treatment (Pd/TT & A-Nb2O5) or with a low-temperature thermal treatment(Pd/TT & A-Nb2O5) presented higher activitythan the one obtained at high temperature (Pd/M & T-Nb2O5). The high stability of the Pd/A-Nb2O5 was demonstrated by regeneration and re-use. Finally, thenanostructured TT-Nb2O5 presented a remarkableactivity toward hydrogenation and hydrogenolysis, owing to its higheracidity and surface area, resulting in the most improved oil.

Automated summary

This study evaluated the impact of different Nb2O5 polymorphs on the upgrading of pyrolysis oil and concluded that un- or low-temperature treated polymorphs showed higher activity and potential as catalyst supports. Furthermore, the nanostructured TT-Nb2O5 exhibited remarkable activity towards hydrogenation and hydrogenolysis, resulting in improved oil quality.