Revealing complex catalytic reaction mechanisms by in

Revealing complex catalytic reaction mechanisms by in-situ
hard X-rays techniques
Gian Luca Chiarello
Dipartimento di Chimica, Università degli Studi di Milano, Milano, Italy
Determination of the structure vs activity relationships, including the mechanism of reaction and the
redox dynamics under real working condition, is a crucial task in heterogeneous catalysis for catalyst
design and performance improvement. A deeper insight in this contest can be acquired combining insitu time-resolved X-ray absorption spectroscopy (XAS) and diffraction (XRD). These two
techniques are complementary each other and available only in synchrotron light facilities. Indeed,
XAS is element specific and reveals short-range order, whereas XRD is a bulk technique and reveals
long-range structural order. During these lectures, a brief description of Synchrotron facilities will be
presented, including: i) basic relativistic phenomena responsible for synchrotron light emission; ii)
beamline and their typical instrumentations; and iii) fundamental of XAS (including both XANES
and EXAFS). Furthermore, the new “modulated excitation extended X-ray absorption fine structure
spectroscopy (ME-EXAFS)” technique, recently developed by us [1,2] will be explain, demonstrating
its powerful application in enhancing the sensitivity of EXAFS for catalytic applications. Several
examples will be finally presented and discussed, emphasizing the key role of these hard X-ray
techniques in the determination of the structure vs activity relationship, such as: selective reduction
of NOx with H2 in presence of excess O2 on Pd/LaCoO3 [3,4]; role of ceria-zirconia in three way
catalysts [5]; effect of noble metal modification of TiO2 in photocatalytic H2 production [6,7], CO
reduction with H2 to produce alcohols on Mo2C [8], Cu-Ni [9] and Ga-Ni alloys [10].
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