Preparation Of Zn And Fe Single-atom Catalysts By Ball Milling And Their Catalytic Performance

Since the beginning of the twenty-first century,energy and environment are two big problems for scientists.Utilizing new energy and controlling environmental pollution are the focus of scientific research.Single-atom catalysts（SACs）have attracted much attention because of their excellent performance in the field of heterogeneous catalysis with 100%atomic utilization.We synthesized ZIF-8 by ball milling,and used it as a template to prepare a series of SACs and double-atom catalysts（DACs）.Among them,Zn SACs can be used to catalyze the hydrogen production of silane,and Fe SACs and Fe DACs can be used to catalyze the decomposition of hydrogen peroxide。The specific works are as follows:（1）ZIF-8 was obtained by ball milling with zinc oxide and 2-methylimidazole as precursors,and calcined at 700℃to obtain Zn SACs,and the Zn loading was as high as 28.3wt%.The Zn species were atomically dispersed and its coordination structure was also identified by various characterization methods.It was employed to catalyze the production of hydrogen with silane and alcohol.The catalysts showed superior catalytic properties that the reaction between phenylsilane and methanol can be full converted within 30 min,and the catalyst retained its activity after 5 cycles.The catalytic activities(TOF=4944 h^-1)of Zn single-atom catalyst was 494 times higher than that of ZnO(TOF=10 h^-1)under the same conditions.The results above were clearly indicative of the great prospect of Zn SACs in the utilization of hydrogen energy.（2）The metal precursors can be encapsulated in the cavity of ZIF-8 during the synthesis process.Most of the Zn atoms escaped after high temperature calcination,and the target SACs can be prepared that the metal atoms occupied the original Zn site.Fe SACs exhibited the excellent catalytic performance in the decomposition of hydrogen peroxide,due to the similar structure with iron porphyrin.The TOF of Fe DACs（Fe₂/N-C）was twice higher than that of Fe SACs（Fe₁/N-C）,and 10-20 times higher than that of Fe NPs/N-C catalyst.At low concentrations of H₂O₂,the activity was similar to that of catalase（CAT）and much higher than commercially available Mn O₂.At high concentration of H₂O₂ or under strong acidity and strong alkaline conditions,CAT will be rapidly inactivated,while Fe₂/N-C and Fe₁/N-C still retained their activities.The catalyst can also be prepared on a large scale with good catalytic activity.Therefore,Fe₂/N-C and Fe₁/N-C were expected to become substitutes to replace CAT for removing residual hydrogen peroxide in textile,paper making and sewage treatment industries.（3）We found that commercially available ZnO can be used to efficiently catalyze the selective N-formylation of amines using silane and CO₂ under mild conditions.Under mild conditions（40℃,1 MPa CO₂）,it showed a very high conversion（98%）and selectivity（99%）for N-methylaniline.Compared with the reported catalysts,it can significantly reduce the cost of the reaction without the tedious catalyst synthesis process.