卤素负载锌-腺嘌呤骨架材料的构建及无助剂催化CO_(2)环加成反应

Halogen-rich zinc-adeninate framework construction and its catalytic performance on CO_(2)cycloaddition without cocatalyst

富氮型金属有机骨架材料(MOFs)具有良好的CO2捕集性能,但其CO2催化性能常需添加带氢键或亲核基团的助催化剂。以硝酸锌-腺嘌呤-异烟酸[Zn(NO3)2-Ad-Int-DMF]构建稳健的骨架材料,发现其催化合成碳酸丙烯酯(PC)收率不足2%;尝试选型锌盐前体引入亲核卤素,在DMF溶剂中部分卤代锌盐不能络合结晶成MOFs,而形成的ZnI_(2)-Ad-Int-DMF收率提升至19.5%;溶剂由DMF调变为H2O-DMF混合溶剂,H_(2)O的引入避免了卤素对金属和配体间络合的影响,使得以ZnCl_(2)、ZnBr_(2)和ZnI_(2)为前体均能晶化成MOFs,其热分解起始温度(Tonset,434℃)明显高于ZnI_(2)-Ad-Int-DMF(280℃),而比表面积(<14 m^(2)/g)明显小于后者(571 m^(2)/g),造成活性低于后者。通过CO_(2)吸附脉冲和UV-Vis漫反射推测I-由于与Zn碱位的相互作用而均匀吸附于骨架上。进而,在无助剂、无溶剂工况下对CO_(2)环加成反应进行活性评价。温度升高显著提升PC产率,140℃下ZnI_(2)-Ad-Int DMF催化产率可达98.5%,但由于吸附在骨架上的卤素在高温、溶剂环境下会脱落,造成重复性实验中活性下降,而该类MOFs在反应前后骨架保持稳定,未造成坍塌或明显孔堵塞现象。后续如能强化卤素的吸附或温和化反应条件,则具有良好的应用潜力。

N-Rich metal organic framework materials(MOFs)have good CO2 capture performance,but their CO_(2)catalytic performance often requires the addition of co-catalysts with hydrogen bonds or nucleophilic groups.In this work,a stable Zn(NO_(3))_(2)-Ad-Int-DMF(Ad=adenine,Int=isonicotinic acid)framework was constructed,and showed low activity(<2%)on propylene carbonate(PC)synthesis.Zinc halide precursors were selected to bring in nucleophilic halogen,only ZnI_(2)-Ad-Int-DMF was crystallized in DMF solvent,and its activity reached 19.5%.Then,the solvent was modulated from DMF to H2O-DMFmixed solvent,MOFs could be constructed from all of ZnCl_(2),ZnBr_(2)and ZnI_(2).After the introduction of H2O,metal could be coordinated with organic ligands without halogen interference.These MOFs grown in H2O-DMF showed an obviously higher initial decomposing temperature(Tonset,434℃)and smaller BET(<14 m2/g)than the one in DMF(280℃,571 m2/g),consequently with lower activity.Then,it was speculated that iodine was adsorbed uniformly on alkaline Zn in the framework according to the CO_(2)pulse adsorption and UV-Vis diffuse reflectance spectra.The activity evaluation was tested on CO_(2)cycloaddition under no cocatalyst and no solvent.The activity was promoted significantly with temperature increasing,the yield for ZnI2-Ad-Int-DMF could reach 98.5%at 140℃.The halogen would fall from the framework under high temperature and solvent environment,which lead to the decrease of activity in the repeatability test.Nonetheless,the framework kept stable before and after reaction,no collapse and remarkable pore blocking were happened.If the halogen adsorption could be strengthened or reaction condition got milder,it would exhibit a good application potential.