Described herein are solid acid catalysts and the methods for catalytically preparing alpha, beta-unsaturated carboxylic acids and/or esters thereof. In one aspect, a zeolite catalyst may be used. Thecatalyst may, in certain embodiments, be modified to improve the selectivity and/or conversion of a reaction. For instance, a catalyst may be modified by ion exchange to achieve a desirable acidity profile in order to achieve high level of conversion of reactants and selectivity for desirable products of the catalytic reaction. In another aspect, a variety of feed stocks (e.g., starting compositions) may be used including an alpha-hydroxycarboxylic acid, an alpha-hydroxycarboxylic acid ester, a beta-hydroxycarboxylic acid, a beta-hydroxycarboxylic acid ester, cyclic esters thereof (e.g., lactide), and combinations thereof.