Pd/oCNT Monolithic Catalysts for Continuous-Flow Selective Hydrogenation of Cinnamaldehyde

Chemical engineering optimization from a batch processto continuousflow in liquid-phase hydrogenation brings a significant improvementin efficiency. However, its further application is limited due tothe severe pressure drop and tube blockage problems in a powder-formcatalyst fixed-bed reactor, especially for nanocarbon-supported catalysts.In this work, spherical monoliths containing oxygenated carbon nanotube(oCNT)-supported Pd nanoparticles (ca. average size of 2 mm) are fabricatedvia an in situ gelation method and applied for cinnamaldehyde (CAL)selective hydrogenation in a continuous-flow system. The simulatedresults by the computational fluid dynamics-discrete elementmethod (CFD-DEM) coupled method show that the pressure dropof the monolith catalyst bed is maintained within 0.4 Pa. The Pd/oCNTmonolithic catalyst exhibits excellent CAL conversion of 85.8% andhydrocinnamaldehyde (HCAL) selectivity of 93.5% within a high weighthourly space velocity (WHSV) of 0.012 s(-1) at mildreaction conditions (30 & DEG;C, 3 bar). The catalyst maintains robustcatalytic activity and HCAL selectivity (>93%) under varied reactiontemperatures (30/60 & DEG;C), H-2 partial pressures (3-10bar), and WHSVs (0.012-0.184 s(-1)) and a stablereaction activity for more than 60 h time on stream, revealing thepossibility in industrial hydrogenation reactions. The catalytic activityof the monolithic catalyst is determined by the surface propertiesof the carbon nanotubes and the chemical interactions between Pd nanoparticlesand supports. The oxygenated functional groups and surface defectson oCNTs are beneficial for strong chemical interaction with Pd species,which forms abundant electron-deficient Pd & delta;+ speciesto facilitate C C hydrogenation. This study puts forward insightsinto and perspectives for selective hydrogenation reactions in bothelectronic structure tuning of the active phase at the atomic scaleand fabrication of monolithic catalysts at the macroscopic scale.