Removal of CO from Hydrogen Fuel by Using Platinum-Loaded Zeolite Catalytic Membranes

在多孔α-Al 2 O3载体管上制备了Y型分子筛膜，并与Pt进行了离子交换。负载Pt的Y型沸石膜被用作用于CO氧化的催化膜，CO以10000 ppm的浓度混合在氢气中。CO和O_2穿过无缺陷膜的平均停留时间比H_2至少长10倍。这导致CO在其渗透通过膜期间的选择性氧化。当O_2流量为CO流量的1.2倍时，反应温度为523 K时，渗透侧的CO浓度降至检测限（8 ppm）以下。在另一个实验中，在多孔α-氧化铝支撑管上制备了Rh负载的γ-Al_2O_3膜，并进一步涂覆了高H_2选择性的SiO_2膜。当H_2、CO和O_2的混合物为进料（CO浓度= 50000 ppm）时，CO渗透通量随着O_2进料速率的增加而降低，在523 K时CO浓度小于48 ppm。这些在非常短的接触时间内的高CO氧化产率可以归因于在阈值CO浓度处具有最大值的独特速率表达式。因此，需要长的反应时间以获得非常高的CO转化率。然而，当使用膜粗略地分离CO时，由于CO浓度通过膜渗透而降低到接近阈值，因此所需的反应时间急剧缩短。

A Y-type zeolite membrane was formed on a porous α-alumina support tube, and then ion-exchanged with Pt. The Pt-loaded Y-type zeolite membrane was used as a catalytic membrane for use in the oxidation of CO, which was mixed in hydrogen at a concentration of 10000 ppm. The mean residence time of CO and O_2 for crossing the defect-free membrane was estimated to be at least 10 times longer than that of H_2. This resulted in the selective oxidation of CO during its permeation through the membrane. When the flow rate of O_2 was 1.2 times that of CO, the CO concentration on the permeate side at a reaction temperature of 523 K was decreased below the limit of detection (8 ppm). In a separate experiment, a Rh-loaded γ-Al_2O_3 membrane was prepared on a porous α-alumina support tube, and was further coated with a highly H_2-selective silica membrane. When a mixture of H_2, CO and O_2 was feed (CO conc. = 50000 ppm), the CO permeation flux decreased with increasing O_2 feed rate, and the CO concentration to less than 48 ppm at 523 K.These high CO oxidation yields in very short contact times can be attributed to the unique rate expression which has a maximum at the threshold CO concentration. Thus, a long reaction times is required in order to attain a very high CO conversion. When CO is roughly separated using a membrane, however, the necessary reaction time is shortened drastically because the CO concentration is decreased nearly to the threshold values by permeation through the membrane.