Abstract
Herein, a defective zeolite-carbon (CFR@HZSM-5) nanocomposite-supported nano-scale Pd catalyst (Pd/CFR@HZSM-5) was facilely synthesized for selective "H2-free" hydrodeoxygenation (HDO) of vanillin (VL) under mild conditions. The optimal Pd/CFR@HZSM-5(2:1) catalysts show excellent activity (the 99% yield to 2-methoxy-4-methylphenol) and high turnover frequency in polymethylhydrosiloxane at 60 degrees C. According to spectral analysis, there is an abundant carbon defect structure on the surface of the CFR@HZSM-5 nanocomposite, which can provide unique sites for capturing Pd metal nanoparticles (NPs) and serve as active sites to promote the adsorption of substrates. The stable and high-dispersion Pd NPs are fastened with carbon atoms in the vacancy defect through strong electronic metal-support interactions, which improved the activity of VL HDO up to four times higher than that of other catalysts under mild conditions. The unique high-dispersion Pd structure and abundant surface defects of Pd/CFR@HZSM-5 catalysts are significant features to brilliant catalytic activity for biomass-derived molecule HDO. Meanwhile, the abundance of acidic sites in the composite carrier catalyst replaces the use of acidic additives in previous catalytic systems. The optimal Pd/CFR@HZSM-5(2:1) catalysts showed good recovery even after five uses. The catalytic system was also applied for various biomass HDO models under mild conditions. This methodology opens new ideas for designing catalysts with high activity and high efficiency for selective HDO of biomass under green and mild conditions.