Yingqing Zhao,Rui Liu,Christian Marcus Pedersen,Zhenzhou Zhang,Zhaohui Guo,Honghong Chang,Yingxiong Wang,Yan Qiao
Lactic acid (2-hydroxypropionic acid, LA) can be produced from abundant and renewable biomass resources via chemocatalytic processes, which exhibited high potential for meeting its tremendous demand in a wide range of applications. The basic Ba(OH) 2 could efficiently catalyze the conversion of d -glucose into LA. In the present study, by utilizing various NMR techniques including, chemical shift titration, 2D diffusion ordered spectroscopy (DOSY) analysis, heteronuclear singular quantum correlation ( 1 H– 13 C HSQC), the binding sites and catalytic interaction between d -glucose and catalyst were clarified. The experimental results by NMR and electrospray ionization mass spectrometry (ESI–MS) were used to explore the reaction mechanism. Experimental results disclosed that the catalyst, Ba(OH) 2 , may exist in the form of [Ba(OH)(H 2 O) 2 ] + under the reaction condition. The OH – of [Ba(OH)(H 2 O) 2 ] + is attached to the C5-O of d -glucose, and Ba 2+ is connected to the C1-O of d -glucose. Herein, we suppose that Ba(OH) 2 and d -glucose interact and form a complex, d -glucopyranose-[Ba(OH)(D 2 O) 2 ] + . Furthermore, when the reaction was performed in D 2 O, we were surprised to find that LA underwent varying degrees of deuteration. The reaction mechanism, binding sites and deuteration of the product have shed light on the efficient conversion of biomass to LA.
Dual active sites from acidic zeolite and Pd are not only capable of catalyzing multiple type of reactions, but could also generate unique functions owing to the synergy between metals and acidic sites. However, there are only a few reports on the investigation of the synergy of acid/Pd dual sites in TS-1. Herein, TS-1 confined Pd catalyst with mesoporous silica shell (Pd@TS-1 @meso-SiO 2 ) has been successfully synthesized and its synergy effect contributes to the enhanced conversion rate (19.2%) and selectivity (74.7%) on styrene oxidation . The interaction between Pd and TS-1 has been investigated by EPR and 1 H NMR techniques, the experimental measurements show an obvious change in the signal distribution of weakly acidic terminal hydroxyls and hydrogen-bonding silanols. The schematic illustration of selective styrene oxidation in the model of Pd@TS-1 @meso-SiO 2 is proposed to clarify the synergistic effect on styrene oxidation between TS-1 and Pd nanoparticles at an atomic-/nanoscale.
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