Preparation of a novel bimodal catalytic membrane reactor and its application to ammonia decomposition for COx-free hydrogen production

A novel bimodal catalytic membrane reactor (BCMR) consisting of a Ru/γ-Al2O3/α-Al2O3 bimodal catalytic support and a silica separation layer was proposed. The catalytic activity of the support was successfully improved due to enhanced Ru dispersion by the increased specific surface area for the γ-Al2O3/α-Al2O3 bimodal structure. The silica separation layer was prepared via a sol–gel process, showing a H2 permeance of 2.6 × 10−7 mol Pa−1 m−2 s−1, with H2/NH3 and H2/N2 permeance ratios of 120 and 180 at 500 °C. The BCMR was applied to NH3 decomposition for COx-free hydrogen production. When the reaction was carried out with a NH3 feed flow rate of 40 ml min−1 at 450 °C and the reaction pressure was increased from 0.1 to 0.3 MPa, NH3 conversion decreased from 50.8 to 35.5% without H2 extraction mainly due to the increased H2 inhibition effect. With H2 extraction, however, NH3 conversion increased from 68.8 to 74.4% due to the enhanced driving force for H2 permeation through the membrane.