The catalytic transformation over a HZSM-5 zeolite of key components of the liquid product obtained by the flash pyrolysis of biomass, namely, acetaldehyde, ketones (acetone and butanone), and acetic acid, has been studied, and great differences in reactivity and degradation to coke have been found. Acetaldehyde has a low reactivity to hydrocarbons, with a noticeable deactivation caused by coke deposition, which can be attributed to its capacity for oligomerization with the trimer trimethyltrioxane obtained as an intermediate product. The transformation of ketones [less reactive than the alcohols studied in part I of this work (see the preceding paper in this issue)] and of acetic acid (which gives rise to acetone as the primary product) mainly occurs through decarboxylation and, to a lesser degree, dehydration. Above 400 degreesC, this transformation gives olefins and aromatics according to a reaction scheme similar to that better known for the reaction of alcohols. The generation of coke (attenuated by the presence of water in the reaction medium) is more significant than in the corresponding process for alcohols, and it limits the formation of aromatics and increases the formation of olefins (intermediate products of the reaction scheme).