Functions of local structural surrounding in activity of Ca-containing catalysts for vapor upgrading during biomass thermal decomposition

Abstract

The catalytic activity of calcium-containing complex oxides with perovskite structure (CaTiO3), brownmillerite structure (Ca2Fe2O5 and Ca2FeAlO5), spinel structure (CaAl2O4), and pseudowollastonite structure (CaSiO3) was compared to CaO for the upgrading of Oakwood fast pyrolysis vapors. Initial catalyst particle sizes range between 0.61 and 3.21 μm, while the BET surface area is between 0.2 and 8.7 m2/g. In contrast to CaO, the complex oxides compounds demonstrated negligible CO2 and H2O chemisorption during catalytic fast pyrolysis, thereby a low deactivation of catalysts, good structural and morphological stability and thus high reusage feasibility. Due to their unique features, Ca-containing catalysts were found to promote specific reaction pathways, such as the conversion of guaiacol to 3-methyl phenol, 4-ethenyl-2-methoxyphenol to 4-ethyl-2-methoxyphenol, 1-(4-hydroxy-3,5-dimethoxyphenyl)ethanone to 3,5-dimethoxy acetophenone and long chain carboxylic acids to acetic acid through a multitude of reaction routes including demethylation/demethoxylation, hydrogenation and hydrodeoxygenation, oxidative cleavage, and dehydration reactions. CaO and Ca2Fe2O5 promoted the alkylation reactions within the methoxy phenolics, whilst CaSiO3 promoted hydrogenation reactions. The formation of acetic acid was promoted over Ca2FeAlO5, CaAl2O4, and CaSiO3, while acetone, 2-butanone, new cyclic C5 ketones were revealed over CaO. The resulting ketonic fraction was noticeably affected by the use of Ca2Fe2O5 and CaAl2O4 catalysts.