We have studied the single-step catalytic conversion of biomass-derived aliphatic carboxylic acids to linear olefins via tandem hydrogenation/dehydration reactions. Hexanoic acid was converted to a mixture of hexenes (92.0% selectivity) over silica–alumina supported Cu nanoparticles. Remarkably, we observed a rapid selectivity switch to 99.8% hexane once carboxylic acids were fully consumed, with similar results using butanoic acid derived from biomass using consolidated bioprocessing. Based on intermediate, desorption, and in situ spectroscopy studies, we propose that the presence of a small amount of carboxylic acid on the catalyst surface leads to a dramatic decrease in overhydrogenation of olefins.