Catalytic membrane in reduction of aqueous nitrates: operational principles and catalytic performance

The catalytic membrane with palladium–copper active component supported over the macroporous ceramic membrane, and a series of γ-Al2O3 supported Pd–Cu catalysts were prepared and investigated. In reduction of nitrate ions by hydrogen in water at ambient temperature, pronounced internal diffusion limitations of the reaction rate were observed for Pd–Cu/Al2O3 catalysts. The catalytic membrane with Pd–Cu active component deposited over the macroporous ceramic membrane support was employed to minimize the diffusion limitations. Multifold increase in the observed catalytic activity was registered for the catalytic membrane operated with the forced flow of the reaction solution through the membrane, as compared to the value achieved at the same conditions, but in the absence of the forced flow (i.e. when the membrane porous space was accessible to the reactants due to diffusion only). These improvements are attributed to the intensification of the intraporous mass transfer attainable with the reactants forced flow in the membrane pores. The concept of catalytic membrane reactors explored in this study offers a new means to improve catalytic performance in the processes where internal diffusion limitations must be minimized and the use of finely dispersed catalysts is not desired.