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Micro-pyrolyzer screening of hydrodeoxygenation catalysts for efficient conversion of straw-derived pyrolysis vapors

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Abstract

Catalyst screening at micro-scale was performed for atmospheric hydrodeoxygenation (HDO) of fast pyrolysis vapors from biomass (wheat straw). The performance of TiO2-supported Pt and MoO3 catalysts and ZrO2 and TiO2-supported WO3 catalysts was compared to industrial Mo- and NiMo based catalysts. In addition, the HDO activity of an industrial HZSM-5/γ-Al2O3 extrudate promoted by MoO3 was investigated. In comparison with unpromoted acidic catalysts such as HZSM-5/γ-Al2O3, decreased deactivation rates and coke yields were obtained with catalysts that are active in HDO. Mo-based catalysts showed a higher selectivity to aromatics compared to aliphatics, while vapor upgrading with Pt/TiO2 favored aliphatics, thereby achieving the highest effective hydrogen index of the non-condensed vapors amongst the tested catalysts. Bulk WO3 was active for deoxygenation (23 % oxygen removal), albeit to a lesser extent compared to bulk MoO3 (37 % oxygen removal). Compared at the same mass of bulk transition metal oxide, the TiO2-supported WO3 and MoO3 catalysts obtained nearly complete deoxygenation (86–96 % oxygen removal), again with the supported MoO3 being more active compared to supported WO3 catalyst. For the production of renewable fuels and/or chemicals from biomass via HDO of pyrolysis vapors the catalyst cost directly influences the economy and sustainability of the process. Therefore, this study further investigated red mud, an abundantly produced industrial waste from aluminum industries, and bog iron as two low-cost transition metal catalysts that are rich in iron. These two catalysts were tested at 4 times higher loading (8 mg) than the high-performing catalysts (2 mg). Under these conditions, an oxygen removal of 51 % and 61 % at vapor carbon yields of 22 wt% C and 14 wt% C were obtained for bog iron and red mud, respectively. Both catalysts showed a high selectivity to monoaromatics and ketones. However, bog iron obtained a higher yield of ketones compared to red mud. In addition, phenolics were converted completely by red mud, indicating a higher activity compared to bog iron.