Abstract
A key challenge in studying the upgrading process for the thermochemical conversion of biomass, such as lignin, is to understand the underlying mechanisms of catalytic conversion at the atomic scale. In this study, a method combined with in situ 2H NMR and GC-MS was proposed for investigating the conversion of phenethyl phenyl ether (PPE) in the hydrotreating process, as catalyzed by Pd, Ru, and Pt loaded onto C or γ-Al2O3. The results indicated that Pd/γ-Al2O3 prefers to produce more ether bond-cleaved products, while Pt prefers to produce more hydrogenation products from PPE. Furthermore, based on this new strategy, a possible reaction mechanism of PPE with Pd/γ-Al2O3 was presented from the atomic point of view, showing the potential of this in situ detection method for reaction mechanism studies. Besides, mechanistic investigations by GC-MS were accomplished for the hydrothermal treatment of PPE for comparison with the new method. The results showed that the in situ 2H NMR combined with GC-MS provided a deeper understanding of the catalytic mechanism compared to GC-MS alone.
Highlights
Lignin is a waste material from the paper industry and a by-product from second-generation bio-ethanol production processes
We proposed a strategy of isotopic labeling combined with in situ 2H NMR monitoring and gas chromatograph (GC)-MS to detect and analyze the catalytic upgrading process of phenethyl phenyl ether (PPE)
This study proposed a novel reaction monitoring strategy which is high-pressure in situ 2H NMR and GC-MS for the upgrading process
Summary
Lignin is a waste material from the paper industry and a by-product from second-generation bio-ethanol production processes. Richter et al (2019) used in situ 13C NMR spectra to identify final products, intermediates, and by-products during the whole reaction, which in turn helped to reveal the TABLE 1 | Reported abundance of major linkages in softwood and hardwood lignin (Chakar and Ragauskas, 2004; Zakzeski et al, 2010). Isotope labeling combined with 2H NMR is another effective means for investigating the reaction mechanism. We proposed a strategy of isotopic (deuterium) labeling combined with in situ 2H NMR monitoring and GC-MS to detect and analyze the catalytic upgrading process of PPE. This research showed the potential of a high-pressure in situ 2H NMR monitoring method using isotopic labeling for studying the upgrading process of biomass model compounds
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