Oxidation of CO in hydrogen-rich gas using a novel membrane combined with a microporous SiO_2 lyer and metal-loaded #gamma#-Al_2O_3 layer

摘要

In order to prepare metal-loaded catalyst membranes for CO oxidatiion,#gamma#-Al_2O_3 layers were formed on porous #alpha#-Al_2O_3 support tubes(1.7min i.d.,2.1mm 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,respectiviely,and calcined in air at 573K.A gaseous mixture of H_2,CO and O_2 was permetaed through these membranes,and their ctivities were determined with respect to CO oxidatation at 423-523K.The CO oxidation activity was the highest for the Rh/#gamma#-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/#gamma#-Al_2O_3 membrane.By the selective permetion with no feed of O_2,the CO concentration of 50,000ppm on the feed side could be decreased to 610-2700ppm.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 esparation factor,and catalytic oxidatiion of CO which leaked through the microporous silica layer.