The water-gas shift (WGS) reaction is a well-known step for upgrading carbon monoxide to hydrogen in the production of synthesis gas. For more than 90 years after its first industrial application, many issues in respect of the catalyst, process configuration, reactor design, reaction mechanisms and kinetics have been investigated. More recently, a renewed interest in the WGS reaction carried out in hydrogen perm-selective membrane reactors (MRs) has been observed because of the growing use of polymeric electrolyte membrane (PEM) fuel cells that operate using high-purity hydrogen. Moreover, MRs are viewed as an interesting technology in order to overcome the equilibrium conversion limitations in traditional reactors.This article reviews the most relevant topics of WGS MR technology -catalysis and membrane science. The most used catalysts and relevant progress achieved so far are described and critically reviewed. The effects of the most important parameters affecting the WGS in MRs are detailed. In addition, an overview on the most used membranes in MRs is also presented and discussed. 

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In this paper the catalytic performances for the low-temperature water-gas shift reaction of Au/TiO 2 type A (from World Gold Council), Au/CeO 2 (developed at UPV-CSIC), CuO/Al 2 O 3 (from BASF), and CuO/ZnO/ Al 2 O 3 (from REB Research & Consulting) have been compared. The catalysts were characterized by different techniques such as Raman spectroscopy, BET surface area measurements, temperature-programmed reduction, and high-resolution transmission electron microscopy, which gave additional information on the redox properties and textural and morphological structure of the investigated samples. The performances of these catalysts were evaluated in a wide range of operating conditions in a micro packed-bed reactor. It was observed that the presence of reaction products in the feed (CO 2 and H 2 ), as well as CO and H 2 O feed concentrations, have significant effects on the catalytic performances. With a typical reformate feed the Au/CeO 2 catalyst reveals the highest CO conversion at the lowest temperature investigated (150°C). However, while in the long tests performed the CuO/ZnO/Al 2 O 3 catalyst showed a good stability for the entire range of temperatures tested (150-300°C), the Au/CeO 2 sample clearly showed two distinct behaviors: a progressive deactivation at lower temperatures and a good stability at higher ones. The selection of the best catalytic system is therefore clearly dependent upon the range of temperatures used.