"The second law of thermodynamics describes why a catalyst does not change the chemical equilibrium of a reaction. Suppose there was such a catalyst that shifted an equilibrium. Introducing the catalyst to the system would result in a reaction to move to the new equilibrium, producing energy. [...] Then, removing the catalyst would also result in reaction, producing energy; i.e. the addition and its reverse process, removal, would both produce energy. Thus, a catalyst that could change the equilibrium would be a perpetual motion machine, a contradiction to the laws of thermodynamics." https://en.wikipedia.org/wiki/Catalysis

Adding and removing the catalyst are not processes in which work is done by or on the system - here again the operator is not involved in work production, as in the capacitor case:

"Liquid Dielectric Capacitor" http://www.youtube.com/watch?v=T6KAH1JpdPg

Accordingly, isothermal heat engines based on the property of catalysts to affect the forward and reverse reactions DIFFERENTLY can generate perpetual motion. For instance, in the picture below, A_2 perpetually flows towards the catalytic surface S1 while A flows towards the catalytic surface S2:

http://upload.wikimedia.org/wikipedi...SLTD-Fig1c.jpg

Pentcho Valev