C-1-C-4 primary carboxylic acids were selected as model compounds to observe the nature and stability of bio-oil adsorption in zeolite HZSM-5 via DFT-D2 theoretical calculation. Adsorptions with and without solvents of water, dimethyl sulfoxide, methanol, and ethanol were studied. The most stable adsorption configuration is hydrogen bonding (HB) through the carbonyl oxygen of acid over the Bronsted acid site of zeolite with the strong energies range from -133.2 to -154.8 kJ/mol. Partial transfer of the Bronsted proton to the acid was observed. Strength of intramolecular-zeolite acid site interaction increases in the order: carbonyl oxygen HB > hydroxyl oxygen HB > CH3 physisorption. The vdW interactions increase notably with the size of the acids. The adsorption energies are significantly reduced by solvation effect. [GRAPHICS] .