Oxidation of CO in hydrogen-rich gas using a novel membrane combined with a microporous SiO 2 layer and a metal-loaded γ-Al 2O 3 layer

Abstract

In order to prepare metal-loaded catalyst membranes for CO oxidation, γ-Al 2O 3 layers were formed on porous α-Al 2O 3 support tubes (1.7 mm i.d., 2.1 mm o.d.) using a sol–gel technique. The layers were then impregnated with Pt, Ru, Ni, Co and Rh, using aqueous solutions of H 2PtCl 6, RuCl 3, Ni(NO 3) 2, Co(NO 3) 2 and RhCl 3, respectively, and calcined in air at 573 K. A gaseous mixture of H 2, CO and O 2 was permeated through these membranes, and their activities were determined with respect to CO oxidation at 423–523 K. The CO oxidation activity was the highest for the Rh/γ-Al 2O 3 membrane. Based on the report that the CO oxidation activity was much reduced for higher concentrations of CO than the threshold value, a membrane was developed by forming a microporous silica layer on the Rh/γ-Al 2O 3 membrane. By the selective permeation with no feed of O 2, the CO concentration of 50,000 ppm on the feed side could be decreased to 610–2700 ppm. When O 2 was added to the feed, the CO concentration was further decreased. Thus, the composite membrane, which was developed in the present study, can play dual roles: H 2-selective permeation with a high H 2/CO separation factor, and catalytic oxidation of CO which leaked through the microporous silica layer.