In this study, we report on the fabrication and operation of new hybrid membrane microreactors for gas-liquid-solid (G-L-S) reactions. The presented reactors consist of porous stainless steel tubes onto which carbon nanofibers (CNFs) are grown as catalyst support, all encapsulated by a gas permeable coating. Such reactors benefit from a controlled G-L-S interface of a membrane reactor and high surface area of carbon nanofibers as catalyst support. Preparation steps such as porous stainless steel hollow fiber fabrication, CNF growth on the stainless steel surface, palladium catalyst immobilization and an outer gas permeable polymeric coating steps are presented. The fabricated microreactors have high surface area, mechanical strength and catalytic activity for nitrite reduction in water. Results proved high nitrite reduction performance of these reactors, even without the presence of palladium (Pd) or additional hydrogen (H(2)) supply. Our results suggest intrinsic reductant properties and catalytic activity of the reactors, which make them very suitable for hydrogenation reactions. (C) 2011 Elsevier B.V. All rights reserved.