Enhanced bio-oil deoxygenation activity by Cu/zeolite and Ni/zeolite catalysts in combined in-situ and ex-situ biomass pyrolysis

The presence of oxygenated compounds in pyrolytic oil makes it highly acidic and unsuitable energy source for real-world applications. In-situ and ex-situ catalytic pyrolysis have been considered the most significant approaches to convert these oxygenated compounds into hydrocarbons or less oxygenated compounds, thereby increasing the carbon and hydrogen content in the bio-oil and improving its overall quality. A remarkable conversion of oxygenated compounds could also be achieved using a combined in-situ and ex-situ catalytic pyrolysis approach. Therefore, this study aimed to prepare Cu10%/zeolite and Ni10%/zeolite catalysts using a wet-impregnation method and investigate their potential for bio-oil upgrading in a combined in-situ and ex-situ catalytic pyrolysis mode and the results were compared with sole in-situ and ex-situ catalytic pyrolysis. In combined pyrolysis, Cu/zeolite was used in-situ and Ni/zeolite in ex-situ mode with four different catalyst to biomass (C/B) ratios (2, 3, 4 and 5). Interestingly, the results demonstrated that the combined pyrolysis with a C/B ratio of 5 achieved the highest deoxygenation activity ((similar to)98%) and total hydrocarbon production ((similar to)72%) as compared to sole in-situ (C/B ratio of 5) or ex-situ catalytic pyrolysis (C/B ratio of 3). It was further noticed that both the catalysts in sole in-situ pyrolysis promoted the formation of acids ((similar to)28% by Cu/zeolite with C/B ratio of 5) in the bio-oil, but a negligible proportion of acids ((similar to)1%) was obtained in sole ex-situ and combined pyrolysis mode. The major hydrocarbons detected in all the bio-oil samples were ethylidenecyclobutane, retene, fluorene, phenanthrene, and pyrene. The enhanced deoxygenation activity and hydrocarbon production by the catalysts can be attributed to the abundant acidic sites present inside the pores or on the surface of the catalysts that carried out major deoxygenation reactions, such as dehydration, decarboxylation, decarbonylation, aldol condensation, and aromatization. Overall, this study suggested that a combined in-situ and ex-situ catalytic pyrolysis approach could be advantageous for bio-oil upgrading as compared to sole in-situ or ex-situ catalytic pyrolysis mode.