Pure shift, a novel nuclear magnetic resonance (NMR) spectroscopy technique is here applied to analyze the hydrogenation/hydrogenolysis products of the biomass-derived platform compounds. The complex and very overlapped 1H NMR signals of the model mixtures from several biomass hydrogenation/hydrogenolysis reactions, such as glucose hydrogenation, sorbitol hydrogenolysis, levulinic acid (LA) formation, tetrahydrofurfuryl alcohol hydrogenolysis, and a real reaction system, were successfully analyzed and assigned by suppressing homonuclear couplings. Thus, we can clearly achieve component analysis and distinguish most signals according to one-dimensional (1D) pure shift obtained by chirp excitation (PSYCHE) spectra. For sophisticated mixtures, e.g., α-d-glucose, sorbitol, and mannitol, or LA, γ-valerolactone, and 2-methyltetrahydrofuran, and finally the real reaction mixture, the 1D total correlation spectroscopy (TOCSY)-PSYCHE approach was used as a supplementary tool to obtain full signals in one component. This allowed us to further resolve the signals where the PSYCHE technique failed to distinguish the signals sufficiently. The results demonstrated that the combined use of 1D PSYCHE and 1D TOCSY-PSYCHE techniques successfully analyzed various catalytic hydrogenation/hydrogenolysis mixtures and enabled us to provide precise signal assignments. Therefore, the pure shift NMR tool (a combination of 1D PSYCHE and 1D TOCSY-PSYCHE) can significantly simplify and successfully be used to assign the NMR spectra of the biomass-derived complex mixture, such as hydrogenation/hydrogenolysis reaction mixtures.

Solvent provides additional degrees of freedom to regulate catalyst reactivity in liquid-phase heterogeneous catalysis, but it is still a challenge to have insight into the multifaceted solvent effects. Herein, a remarkable promotional effect of water in maleic acid (MAc) hydrogenation to succinic acid (SAc) was observed. Kinetic studies showed that the apparent activation energy in water was much lower than in organic solvents. A series of isotope-labeling experiments were designed, and the products were analyzed by NMR ( 1 H, 13 C, 2 H, and DEPT135 spectra). The results showed that D 2 O participated in MAc C�C hydrogenation and 34.7% of SAc was deuterated. The structures of these deuterated compounds were further confirmed by electrospray mass spectrometry (ESI-MS). The detailed mechanism of water participating in MAc C�C hydrogenation was studied by quasi-in situ mass spectrometry experiments. The results showed that H 2 exchanged with D 2 O and formed the HD 2 O* transition state over the active site of Pd. Quantitative 13 C NMR demonstrated that 46.2% of SAc was generated through the HD 2 O* transition state pathway. Based on these results, a rational mechanism of MAc hydrogenation in aqueous solution was proposed. Finally, a recyclability experiment showed that Pd/C had much better stability in water than in organic solvents.