Molecular pumps move molecules against the free energy gradient associated with concentration or pressure, while the catalytic pumps described here aim to advance the extent of reaction against the chemical potential associated with chemical reaction equilibrium. Molecular pumps utilize the ratchet mechanism, while the catalytic pump utilizes the ratchet mechanism plus the addition of a surface reaction as one of the free energy profile transition states. Similarly, molecular pumps utilize external energy sources (e.g. ATP in biological membrane transport), while catalytic pumps oscillate binding energy by a variety of proposed methods as described in Figure (e.g., oscillating surface strain or electric field).