Preparation And Properties Of Cu-ZnO-CeO₂/SiC Monolithic Catalyst For Hydrogen Production From Methanol Reforming

Due to the high calorific value and no pollution during combustion,hydrogen energy is deemed as the most promising energy source to replace fossil fuels.However,current methods of storing hydrogen are commonly expensive and insecure,thus hindering the development of hydrogen fuel cell vehicle.The technology of methanol steam reforming microreactor for hydrogen production has attracted extensive attention because of its low reforming temperature,high H₂ production,low CO content,as well as its ease of implementation for on-site hydrogen production.Therefore,it is expected to solve the present problems faced in the storage and use of hydrogen.In this technology,the preparation and performance study of monolithic catalysts in microreactors is the critical point.In this paper,porous Si C ceramic was used as the catalyst support and the Cu-Zn O-Ce O₂catalysts were directly loaded on the support by using loading different methods to prepare Cu-Zn O-Ce O₂/Si C monolith catalysts.The effects of different loading methods on the microscopic morphology,the loading strength and element composition of the monolithic catalysts were explored.Further,the prepared monolith catalysts were assembled into a microreactor to evaluate the catalytic performance in methanol steam reforming.The specific contents of the study were as follows:（1）Cu-Zn O-Ce O₂ catalysts have been supported on the porous Si C support by the impregnation method.It was found that the methanol conversion of the monolithic catalyst was only 88.9%at the reforming temperature of 360℃,and the monolithic catalyst would be dramatically deactivated after 18 h of time on stream.The reason is that the catalysts are unevenly distributed on the support,loading strength is low and the particle size was larger,resulting in bad catalytic performance.（2）In order to solve the problem of uneven distribution of catalysts on the support,Cu-Zn O-Ce O₂ catalysts were loaded on the porous Si C support by homogeneous precipitation method with urea as the precipitant.It can be observed that the catalysts prepared by the homogeneous precipitation method became a smaller particle size,a more uniform distribution and a larger specific surface area,which improved the catalytic activity.Methanol conversion of the monolithic catalyst reached 97.3%at the reforming temperature of 300℃,and its methanol conversion dropped to 68.4%after 20 h of reforming reaction.Moreover,compared with the impregnation method,although the catalytic effect was significantly improved,the problem of uniform distribution of catalysts needed further improvement due to the uneven heating distribution of the porous Si C support by the heating method of water bath.（3）Due to the good microwave absorption performance of Si C,the catalysts can be in-situ deposited on the porous Si C support by microwave-assisted homogeneous precipitation method.It was found that the catalyst particles were smaller and more evenly distributed on the support at the optimal urea content.The specific surface area of the particles increased from 1.78 m²/g to 11.82 m²/g,and the loading decreased by only 13%after 15 min of ultrasonic vibration.100%methanol conversion was achieved with the monolithic catalyst at a reforming temperature of290℃.After 32 h of time on stream,the methanol conversion remained at about 94%,showing higher catalytic activity.