Atomic Scale in‐situ Studies of Catalytic Reactions between Iron Clusters and Single‐walled Carbon Nanotubes
Authors: Cao Kecheng , Biskupek Johannes , Chamberlain Thomas W. , Khlobystov Andrei N. , Kaiser Ute 
Published: December 2016

Atomic Scale in‐situ Studies of Catalytic Reactions
b
etween
Iron
Clusters and
Single‐walled Carbon Nanotubes

Kecheng Cao(1), Johannes Biskupek (1), Thomas W. Chamberlain(2), Andrei N. Khlobystov (2) and Ute Kaiser (1)

[1] Electron Microscopy of Materials Science, Central Facility for Electron Microscopy, Ulm University, Albert Einstein Allee 11, Ulm 89081, Germany

[2] School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom

Metal nanoparticle catalysts play an important role in the field of catalytics. Understanding the reaction between metal nanoparticles (MNPs) and carbon at the atomic scale contributes to the design of highly efficient catalysts. Single‐walled carbon nanotubes (SWNTs) with the characteristics of heat resistance, cleanness and transparency areideal nano‐test tubes for MNPs to study their catalytic properties in‐situ. Moreover, with the aid of the powerful aberration‐corrected high‐resolution transmission electron microscopy (AC‐HRTEM), several kinds of MNPs are filled into SWNT and have been investigated their reactions with SWNT.The transition metals are varied along groups as well as periods of the periodic table of elements, and characterized systematically to track their interactions with the electron beam and the carbon special environment
1‐4
. Among them, Os and Ni nanoparticles exhibit the ability of cutting SWNT under electron beam irradiation
2, 3
. But iron nanoparticles with Fe
3
C structure are much more stable that no significant reactions are observed between Fe
3
C and SWNT
4
.

In this study we present in‐situ irradiation experiments of sub‐nanometer sized α‐ Fe clusters enclosed in SWNTs by means of low‐voltage AC‐HRTEM. The Fe nanoparticles show different structure to the previously published experiments on Fe
3
C nanoparticles
4
, and are observed to be unstable under e‐beam irradiation at 80 kV. In our experiments, the particular technique of HRTEM combines imaging tool and irradiation source in one integral experiment. Here, SWNTs are initially filled with Fe
3
(CO)
12
molecules and then irradiated by election‐beam with acceleration voltage 80 kV in TEM. α‐ Fe nanoparticles are obtained in the lumen of SWNTs. Being irradiated, α‐ Fe nanoparticles keep changing shape and restructuring the geometric construction of SWNT and ultimately cut it into two parts. Additional experiments regarding the stability under e‐beam irradiation at much lower voltages down to 20 kV will be carried out to study influences of knock‐on damage and ionization effects. Figure 1 shows a time series of the cutting process. . Thus we confirm that two kinds of clusters, α‐ Fe nanoparticle and Fe
3
C can be obtained by breaking the Fe
3
(CO)
12
molecules in SWNT and they exhibits distinct catalytic activities that Fe
3
C is stable but α‐ Fe nanoparticle can cut SWNTs. The experiments were conducted using a C
S
‐corrected FEI Titan 80‐300 operated at 80 kV. The dose rate was 1.4*10
6
e
‐
/s*nm
2
and the exposure time was 1.0 second.