The Catalyst Review February 2020 - 18

MOVERS & SHAKERS
Jiahan Xie, PhD
Research Scientist Specialist, Catalysis Department, Braskem America, Inc.
Jiahan received his bachelor's degree in chemistry from Peking University in 2013 and completed his doctoral degree
at the University of Virginia in 2017 under the supervision of Prof. Robert J. Davis. His doctoral research focused
on a fundamental understanding of heterogeneous catalysts to upgrade biomass-derived chemicals via selective
oxidation. His mechanistic findings on oxidation reaction and catalyst deactivation provided essential insights on
the rational optimization of the catalytic system. In 2018-2019, he joined the laboratory for science and applications
of catalysts at the University of California, Berkeley, as a postdoctoral researcher. There he continued to explore
the effect of microporous environment on reactivity and diffusion during dehydrocyclodimerization of light alkanes on metal-acid
bifunctional catalysts. His catalysis research continued after joining Braskem, with a more industry-oriented goal to develop reactive
and robust catalysts to produce intermediates and chemicals following disciplines of sustainable development. He can be reached
at: jiahan.xie@braskem.com.

The Catalyst Review asked Dr. Xie to share his insights regarding solvation effects and
characterization challenges for catalysts in the liquid phase.
Polymers have been broadly utilized in both heavy and light industry due to their tailorable properties. However,
disposal issues, as well as prerequisite use of fossil fuel feedstocks, has caused societal concerns related to sustainability.
Currently, considerable efforts are being made to recycle or reuse the polymer waste. In addition to recycling, the use
of renewable feedstock, such as biomass, aids in the overall sustainability of these materials. Biomass can be converted
to various polymers via catalytic functionalization and subsequent polymerization, in which oxygenate molecules are
commonly involved. Because of their relatively high melting point, the catalytic conversion of oxygenates is usually
performed in the liquid phase under mild reaction conditions. Compared to catalysis in the gas phase, the liquid-phase
environment brings both opportunities in tuning the catalytic system via enhanced non-covalent interactions as well as
challenges in identifying active sites and surface species.
During reactions in the liquid phase, the enhanced non-covalent interactions among reactant, intermediate, solvent,
and catalyst framework can significantly influence the energies of the various states along the reaction coordinate. This
so-called "solvation effect" creates an extra dimension in which the catalytic system can be optimized to achieve desired
reactivity and product selectivity. The rational design of the catalytic system relies on the mechanistic understandings of
catalytic reactions. In order to investigate the reaction mechanism, the active sites and surface species are usually probed
by microscopy and spectrometry. Combined with these characterization results, kinetics and theoretical computation can
provide further insights into the reaction path. Traditionally, spectroscopic and microscopic studies are performed ex-situ,
which may be misleading because of potential structural and compositional changes of catalysts during the reaction.
Admittedly, recent instrumental development has made it possible to characterize the catalyst at the atomic level under
working conditions. These in situ characterization techniques, however, have many limitations in the liquid phase because
of the interference of solvent molecule signals. In order to address these issues, research has focused on exploitation
of element-specific techniques, such as X-ray adsorption spectroscopy, to minimize the noise from the solvent, as
well as the development of surface-sensitive methods, such as attenuated-total-reflection infrared spectroscopy and
surface-enhanced Raman spectroscopy, to amplify the signals of active sites and surface species. These advances have
facilitated the mechanistic understanding of the solvation effect during dehydration, ring-opening, and dehydrogenation
reactions that are involved in the transformation of biomass to polymers. Based on these understandings, the rational
design of non-covalent interactions is anticipated to play an increasingly important role in tuning the reactivity and
product selectivity in conjunction with existing methods of tuning catalyst composition and structure, as well as reaction
conditions.

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The Catalyst Review

February 2020

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The Catalyst Review February 2020

Table of Contents for the Digital Edition of The Catalyst Review February 2020