Preparation Of MOF-Derived Single-Atom Catalysts And Their Hydrogenation Performance

Single-Atom Catalysts?SACs?,because of their unique structure and electronic characteristics,the uniformly dispersed active sites of their atoms not only maximize the utilization of metal atoms,but also make it show in a variety of chemical reactions excellent catalytic performance.This article aims to develop a novel preparation method for SACs,select Metal-Organic Framework?MOF?with regular crystal structure as the carrier,and introduce metal active centers through in-situ synthesis to obtain catalyst precursors.Then,through the steps of calcination and reduction,MOF-derived SACs were prepared,and their selective hydrogenation performance was studied.The main content includes the following aspects:First,select MIL-53?Al?as the support of the catalyst precursor and prepare Rh@Al₂O₃@C SAC by in-situ synthesis.Through AC-HAADF-STEM,CO-IR,NMR and other characterization methods,it was found that Rh@Al₂O₃@C is uniformly dispersed in the form of a single atom on the Al₂O₃@C carrier,of which five-coordinated aluminum species?Al ^V?it can provide unsaturated coordination sites for metals,which is very important for achieving high dispersion of Rh atoms.In addition,Rh/?-Al₂O₃and Rh/C nanocatalysts prepared by the equal volume reduction method were used as comparative catalysts,and the selection of Rh@Al₂O₃@C SAC in m-chloronitrobenzene?m-CNB?application of m-chloroaniline?m-CAN?by reactive hydrogenation.It is worth noting that the TOF of Rh@Al₂O₃@C SAC is up to 2317 mol_m-CNB·mol_Rh^-1·h^-1,which is better than other heterogeneous catalyst systems under T=313 K and P_H2=20 bar.At the same time,the catalyst has good recycling performance,repeated use five times,can still maintain m-CAN selectivity at about 98%.NH₃-TPD and XPS for Rh@Al₂O₃@C found that the reason why it has such excellent performance is mainly due to the proper adjustment of the hydrogenation capacity of the catalyst through the formation of single atom metal centers and the presence of the stronger acid functional sites of the catalyst.Second,continues to expand the method of preparing SACs by in-situ synthesis.Ui O-66?Ce?with abundant lattice defect sites was used as the carrier of the catalyst precursor to prepare Pt@Ce O₂@C and Pt@Ce O₂SACs.Through the characterization of PXRD,HAADF-STEM and other characterization methods,it was found that SACs were successfully prepared,which shows that the in-situ synthesis method developed in this paper is not only applicable to the synthesis of MOF-derived SACs under hydrothermal reaction conditions,but also to the synthesis of MOF-derived SACs under simple reaction conditions in an oil bath?agitated for 20 min?.And no matter whether it is a reducing carrier or a non-reducing carrier,SACs can be prepared.In addition,the Pt/Ce O₂catalyst prepared by the equal volume impregnation method was introduced as a comparative catalyst,and the application of the Pt@Ce O₂SAC in the selective hydrogenation of phenylacetylene?PA?to styrene?ST?was investigated.Under the conditions of T=333 K,P_H2=20 bar and reaction time t=6 h,the Pt@Ce O₂SAC has a good ST selectivity of 77.3%.