Thermodynamic and kinetic problems are examined, as encountered in the design of catalytic devices for the removal of pollutants in the ppm range, i.e., for ultrapurification. The customary approximations used in catalytic reaction engineering are examined and found to be unreliable over wide ranges of process variables. To circumvent the uncertainty created by risky extrapolations of design rate equations, the method of microkinetic analysis suggests itself. But its application relies on a database of rate constants that must be accumulated through extensive scientific work. In the meantime, it is noted that the rate of removal of pollutants in ultrapurification must be first order with respect to pollutant concentrations, as the rate depends linearly on the thermodynamic potential for reaction.