Understanding the mechanism of catalytic fast pyrolysis by unveiling reactive intermediates in heterogeneous catalysis

Abstract

Catalytic fast pyrolysis is a promising way to convert lignin into fine chemicals and fuels, but current approaches lack selectivity and yield unsatisfactory conversion. Understanding the pyrolysis reaction mechanism at the molecular level may help to make this sustainable process more economic. Reactive intermediates are responsible for product branching and hold the key to unveiling these mechanisms, but are notoriously difficult to detect isomer-selectively. Here, we investigate the catalytic pyrolysis of guaiacol, a lignin model compound, using photoelectron photoion coincidence spectroscopy with synchrotron radiation, which allows for isomer-selective detection of reactive intermediates. In combination with ambient pressure pyrolysis, we identify fulvenone as the central reactive intermediate, generated by catalytic demethylation to catechol and subsequent dehydration. The fulvenone ketene is responsible for the phenol formation. This technique may open unique opportunities for isomer-resolved probing in catalysis, and holds the potential for achieving a mechanistic understanding of complex, real-life catalytic processes.

Threshold Photoelectron Spectroscopy of IO and HOI

“…Detecting electrons and ions in coincidence permits to record photoion mass‐selected threshold‐photoelectron spectra (ms‐TPES) of reactive molecules and to distinguish isomers, even when the differences in the IE are small or when a large number of species is present . Combined with synchrotron radiation, PEPICO has been established as an analytical tool to monitor gas‐phase kinetics, combustion reactions and catalysis …”

The Curious Case of Ketene in Zeolite Chemistry and Catalysis

“…Fulvenone ketene was first identified by van Bokhoven et al. as being responsible for the formation of phenol during CFP of guaiacol (Figures a,b) using imaging photoelectron photoion coincidence spectroscopy (iPEPICO) with synchrotron radiation . Zeolite promotes demethylation of guaiacol to form catechol, which then hydrolyzes to 6‐fulvenone (Figure c).…”

“…Ketene has also been detected during zeolite‐mediated catalytic fast pyrolysis (CFP)—another promising technology that lacks mechanistic information (Figure ) . Fulvenone ketene was first identified by van Bokhoven et al.…”

Overcoming the Inertness of Iridium(III) in a Facile Single‐Crystal to Single‐Crystal Reaction of Iodine Vapor with a Cyclometalated Chloride Monomer

“…Direct observations of chemical reaction intermediates are very desirable as they provide crucial information about the reaction mechanisms that is especially important for catalytic processes . Single‐crystal to single‐crystal (SCSC) reactions, in combination with X‐ray diffraction analysis, are a very powerful tool to obtain comprehensive structural data on chemical species involved in the reactions, and to give insights into the dynamics of their mutual transformations .…”

“…The resultsp rovide excellent opportunities to modulate the geometry and kinetic properties of cyclometalated iridium(III) complexes that may be very promisingi n catalysis and design of anticancer agents.Direct observations of chemical reactioni ntermediatesa re very desirable as they provide crucial information about the reaction mechanisms that is especially important for catalytic processes. [1][2][3] Single-crystal to single-crystal (SCSC) reactions, in combination with X-ray diffraction analysis, are av ery powerful tool to obtain comprehensive structurald ata on chemical species involved in the reactions, and to give insights into the dynamics of their mutual transformations. [4][5][6][7][8] Still, for discrete molecular organometallic complexes, SCSC reactions involving ligand exchange are rare, [9][10][11][12][13][14][15][16] because the formationo rc leavage of metal-ligand bonds is usually accompanied by the loss of crystallinity.…”