Liu Mengyuan,Yan Wenjuan,Wu Jingwei,Wang Shu,Xia Qi,Fang Tianqi,Jin Xin
Selective oxidation of glycerol is one of the most promising routes to produce value-added fine chemicals from biomass. However, achieving good selectivity towards glyceric and lactic acids still remains a grand challenge in this field. A series of unique electronically coupled PtCo catalysts, supported on layered double hydroxides via co-precipitation method, was reported in this work, as they display tunable selectivity toward glyceric acid and lactic acid during glycerol conversion. It is found that the unusual electronic transfer from MgAl hydrotalcite support to cobalt species, leading to high electron binding energy of PtCo sites on catalyst surface. The presence of cobalt components contributes to synergistic enhancement of oxidation activity at electron deficient Pt sites and more critically, weakened Pt–O strength during glycerol conversion. Such unique electronic reconfiguration, as characterized by XRD and XPS spectroscopy, induces two alternative reaction pathways under different reaction temperatures. While Pt–O bonding strength is significantly weakened by strong Co–O affinity at relatively higher reaction temperature (100 °C), such effect is almost negligible at 50 °C. As a result, lactic acid selectivity of 67% was obtained at 100 °C, while glyceric acid selectivity of 65% was achieved at 50 °C, over the bifunctional PtCo/MgAl hydrotalcite catalysts. The design principles reported in this work offer alternative approaches for manufacturing cost-effective catalytic materials for glycerol conversion to various value-added carboxylic acids and derivatives. Graphic Abstract
Herein, a series of the Pt-based bimetallic catalysts (PtM x /SBA-15) are gained by using ultrasonic incipient wetness impregnation method (M = Co, Cu, Ni or Zn). The experimental results show that the catalytic performance (including catalytic activity (turnover frequency-TOF), selectivity to crotyl alcohol) of PtCo x /SBA-15 for catalyzing crotonaldehyde selective hydrogenation is the best among PtM x /SBA-15. Additionally, the ratio of Pt/Co in the PtCo x /SBA-15 catalysts is changed to successfully synthesize PtCo/SBA-15, PtCo 2 /SBA-15, PtCo 5 /SBA-15. It demonstrates that the selectivity of the PtCo x /SBA-15 catalysts for crotonaldehyde selective hydrogenation to crotyl alcohol is significantly improved with the increase of the Co content. The PtCo 5 /SBA-15 catalyst provides 83.8% conversion of crotonaldehyde, 94.3% selectivity to crotyl alcohol and TOF of 910.5 h −1 under mild reaction conditions (3.0 MPa H 2 , 80 °C and 2.0 h). And PtCo 5 /SBA-15 has much better catalytic performance (higher catalytic activity and selectivity to crotyl alcohol) than PtCu 5 /SBA-15, PtNi 5 /SBA-15 and PtZn 5 /SBA-15. The reasons are as follows: (1) PtCo alloy forms, which is conducive to crotonaldehyde adsorption and activation; (2) there is an appropriate synergy effect between Pt and Co, greatly improving the capacity of the catalyst activating hydrogen under mild conditions; (3) the electron transfers from Co to Pt, resulting in the increase of Pt electron density and decrease of Co electron density, then the Co sites are advantageous to C O group adsorption and activation and Pt sites for H 2 adsorbing and activating; (4) with the increase of the Co proportion in PtCo x /SBA-15, the synergy effect between Pt and Co in PtCo alloy strengthens and thus increases the selectivity of C O group hydrogenation.
The hydrogenation of nitroaromatics to aromatic amines is widely applied in the chemical, pharmaceutical, and agrochemical industries. However, the high cost of traditional precious metal-supported catalysts limits their industrial development. To address this, a PtCo alloy nanoparticle catalyst supported on CePO 4 (CePO 4 /PtCo) was designed. The catalyst exhibits high activity and selectivity for the hydrogenation of nitroaromatics under 60 °C and 5 bar H 2 , achieving 100 % conversion of p-nitrophenol and 98.2 % selectivity to aromatic amines within 50 min. Catalytic mechanism studies indicate that the multi-level modulation of active sites is achieved through the synergistic interplay of dual mechanisms: electron transfer within PtCo alloys and metal-support interactions between PtCo and CePO 4 . This multiple synergy enables precise electronic tuning of Pt sites, enhancing the adsorption capacity for nitroaromatics and reducing the reaction energy barriers of potential-determination steps. Meanwhile, the functional support CePO 4 adsorbs and activates the substrate, providing additional active sites for hydrogenation under hydrogen spillover. The multiple synergistic effects between the components of the catalyst revealed in this study provide new insights for the rational design of heterogeneous catalysts.
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