Ni/CeO_(2)@ZIF-8核壳结构催化剂的制备及其RWGS反应性能研究

Preparation of Ni/CeO_(2)@ZIF-8 core-shell catalyst and its RWGS reaction performance

利用液相浓度控制成核法制备了ZIF-8包覆的Ni/CeO_(2)核壳结构催化剂,通过一系列表征技术,研究了ZIF-8壳层对催化剂物理化学性质的影响,并进一步探究引入ZIF-8对于催化剂上的RWGS反应性能与路径的影响。结果表明,ZIF-8壳层能够增大催化剂的比表面积,减弱加氢能力和对CO的吸附强度,在300℃,0.1 MPa,GHSV=6 L/(g·h)和CO_(2)∶H_(2)=1∶3的反应条件下,核壳结构催化剂上的CO选择性提升了60.3%。ZIF-8包覆前后的Ni基催化剂上的反应中间物种不同,生成CO的主要中间体为羧酸盐而CH_(4)则为甲酸盐,ZIF-8壳层的存在抑制了羧酸盐进一步加氢转化为甲酸盐,从而抑制了甲烷化副反应进行,提高了RWGS反应的CO选择性。

The ZIF-8-coated Ni/CeO_(2) core-shell catalysts were prepared using a liquid phase concentration controlled nucleation method.The effects of the ZIF-8 shell on the physicochemical properties of the catalysts were investigated by a series of characterization techniques,and the effects of introducing ZIF-8 on the performance and pathways of the RWGS reaction on the catalysts were further explored.The results showed that the ZIF-8 shell could increase the specific surface area of the catalysts,while weakening the hydrogenation capacity and the adsorption strength of CO,and the CO selectivity was enhanced by 60.3% under the reaction conditions of 300 ℃,0.1 MPa,GHSV=6 L/(g·h) and CO_(2)∶H_(2)=1∶3.The intermediate species in the reaction on the Ni-based catalysts before and after ZIF-8 coating were different.The main intermediate for CO was carboxylate while the bridged formate was for CH_(4).The presence of the ZIF-8 shell inhibited the further hydrogenation of the carboxylate to formate intermediate species,thus inhibiting the methanation reaction from proceeding and improving the CO selectivity of the RWGS reaction.