The paper investigated the effects of molecular structures on the conversion of the carboxylic acids (formic acid, acetic acid, propionic acid and butyric acid) during the steam reforming reactions. In essence, molecular structures determined catalytic behaviors of the organics during the reforming reactions. The acids with a C–C bond were more stable than formic acid during the homogenous decomposition reactions. However, the steam reforming of formic acid was much easier than that of the heavier acids due to the absence of cracking of the C–C bond during reforming. The difficulty for reforming of the carboxylic acids increased with the increase of the length of the aliphatic carbon chain (from acetic acid to butyric acid). The carboxylic acids with a longer aliphatic carbon chain (propionic acid and butyric acid) also had a higher tendency towards coking than acetic acid and formic acid. The coke formed in steam reforming of formic acid was the lowest compared with other acids. The C–C bond and the number of C–C bond in the carboxylic acids affected the reactivity of the carboxylic acids, their tendencies towards the formation of coke and the properties of the coke. The coke had larger aromatic ring systems and oxygen–containing functionalities during steam reforming of acetic acid. The amorphous coke formed in reforming of acetic acid, while the fibrous coke formed during the reforming of the heavier carboxylic acids
