Water–gas shift reaction in a Pd membrane reactor over Pt/Ce0.6Zr0.4O2 catalyst

Abstract

A water–gas shift (WGS) Pt/Ce 0.6 Zr 0.4 O 2 catalyst has been prepared, which exhibits much faster kinetics than conventional high-temperature ferrochrome catalysts in the temperature range most suitable for operation of WGS Pd membrane reactors, i.e. above 623 K. The performance of the Pt catalyst was tested in a reactor furnished with a supported, 1.4 μm thick high-flux Pd membrane using feeds obtained by autothermal reforming of natural gas. CO conversion remained above thermodynamic equilibrium up to feed space velocities of 9100 l kg −1 h −1 at 623 K, P total = 1.2 MPa and steam-to-carbon ratio S/C = 3, but H 2 recovery decreased from 84.8% at GHSV = 4050 l kg −1 h −1 to 48.7% at the highest space velocity. This rapid decline of separation performance is attributed to slow H 2 diffusion through the catalyst bed, suggesting that external mass flow resistance has a significant impact on the H 2 permeation rate in such membrane reactors. This could be minimized by the development of WGS catalysts with even faster kinetics which would allow further reduction of the catalyst bed height.