Pd/Zn/C-N催化CO_(2)加氢合成甲醇性能研究

The Study of CO_(2) Hydrogenation to Methanol over Pd/Zn/C-NCatalysts

利用Zn2+和2-甲基咪唑自组装形成的ZIF-8, 800℃N2氮气气氛下焙烧得到Zn/C-N载体.采用NaBH4还原法将不同含量Pd负载于Zn/C-N上焙烧后得到Pd/Zn/C-N催化剂, ICP测得Pd实际负载量为0.02%、0.05%、0.1%、0.3%.负载Pd后,由于Pd氢溢流作用, ZnO表面还原温度降低,氧空穴增加,更有利于CO_(2)解离吸附,因此Pd负载量越高,催化剂CO_(2)转化率越高.甲醇选择性受Pd纳米颗粒大小显著影响,小颗粒Pd与ZnO相互作用更强,更有利于甲醇生成,其中0.02%Pd/Zn/C-N催化剂在275℃, 2 MPa反应条件下, Pd/g上甲醇时空收率最高, STYMeOH值为11.0 mol/(g Pd·h).

ZIF-8 was formed by self-assembly of Zn^(2+)and 2-Methylimidazole.The Zn/C-N support are obtained by calcining at N_(2) atmosphere at 800℃for 5 h.Pd was loaded onto Zn/C-N by using NaBH_(4) reduction method.The actual loading amount of Pd measured by ICP-OES were 0.02%,0.05%,0.1%and 0.3%.After loading Pd,the reduction temperature of surface ZnO decreased and oxygen vacancies increase due to Pd hydrogen spillover,which is more conducive to CO_(2) dissociation and adsorption.Therefore,the higher the Pd loading,the higher the CO_(2) conversion rate of the catalyst.The methanol selectivity is significantly affected by the size of Pd nanoparticles,and the interaction between small Pd particles and ZnO is stronger.This is more beneficial to generate methanol.The performance of the 0.02%Pd/Zn/C-N catalyst is the best at 275℃and 2 MPa,and the methanol space-time yield is 11.0 mol/(gPd·h).