Supported
metal clusters are widely used in catalysis for many
important reactions. To understand the catalytic properties, in situ/operando characterization techniques,
such as X-ray absorption spectroscopy (XAS), provide essential details
of the size, shape, and chemical composition of the cluster and the
nature of the active sites. New-generation synchrotrons combined with
focusing beamlines provide high-flux-density X-rays for improved detection
sensitivity as well as higher time and spatial resolution. Understanding
the effects of a high-flux-density X-ray beam on the catalyst during
the actual measurement, whether XAS or another synchrotron-based technique,
is crucial. This is especially important for in situ and operando studies where both the high flux density
and reaction conditions can affect the catalyst structure. In this
work, we investigated the effect of the flux density on rhodium clusters
supported on Al2O3 at two different beamlines:
National Synchrotron Light Source II beamline 08-ID and Stanford Synchrotron
Radiation Light Source (SSRL) beamline 4-1. We show that the higher
flux density at beamline 08-ID causes the reduction of the highly
dispersed RhO
x
/Al2O3 catalyst, even at room temperature. Additionally, exposure to the
higher flux density X-rays at beamline 08-ID during in situ reduction results in significant agglomeration of the Rh clusters.
The final size of the Rh nanoparticles reduced at 310 °C is equivalent
to that of particles formed after the reduction at 600–650
°C in the absence of the beam. Significant beam-induced reduction
and agglomeration is also shown for Ni supported on beta zeolite during in situ reduction at an intermediate-flux-density beamline
9-3 at SSRL, indicating that beam-induced changes in heterogeneous
catalysts could be common at intermediate- and high-flux-density beamlines.
We provide precautions and recommendations for detecting and minimizing
beam damage during in situ/operando XAS measurements.
Dispersed Cr species supported on zeolite ZSM-5 were investigated in the context of catalytic ethane dehydrogenation. Probe molecule FTIR and XANES were used to characterize the nature of Cr sites...
The influence of zeolite heteroatom composition on the electron density and catalytic activity of a supported Ni cation is examined. Ni-[X]-Beta catalysts, where X = Al, Ga, Fe, or dealuminated,...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.