Unconventional Pd@Sulfonated Silica Monoliths Catalysts for Selective Partial Hydrogenation Reactions under Continuous Flow

Abstract

Doubly functionalized, hierarchical‐porosity silica monoliths were synthesized by postgrafting of sulfonic groups and in situ growth of Pd nanoparticles in that order. PdNP of 3.1 nm size located in the mesopores of the material showed to be evenly distributed within 4.6 % wt Pd monoliths. The system was explored in the continuous‐flow, catalytic partial hydrogenation reaction of 3‐halogeno‐nitrobenzenes and 3‐hexyn‐1‐ol in the liquid phase, showing remarkable conversion, selectivity, and resistance under very mild conditions.

Continuous‐Flow Oxidation of HMF to FDCA by Resin‐Supported Platinum Catalysts in Neat Water

“…Within the above flow ranges, the spontaneous back‐pressure generated by the packed catalyst was approximately 2 bar, that is, a pressure drop of approximately 1 bar. As expected for such a flow system, at a given temperature, conversion and selectivity proved to be ruled by the residence time τ (the amount of time that the substrate spends inside the reactor, depending on the solution flow rate), and by the O 2 /substrate molar ratio (which depends on the O 2 flow rate). However, reproducible reaction patterns were observed.…”

“…To this purpose, the catalyst (60 mg) was packed into ag lass tube (50 mm length, 3mmi nternal diameter) ands crutinized under ac ombination of O 2 (0.8-8.0 mL min À1 )a nd solution flow rates (0.05-0.20 mL min À1 ), O 2 pressures, andH MF concentrations. Within the above flow ranges, the spontaneousb ack-pressure generated by the packed catalystw as approximately 2bar,t hat is, ap ressure drop of approximately 1bar.A se xpectedf or such af low system, [32] at ag iven temperature, conversion and selectivity provedt ob er uled by the residence time t (the amount of time that the substrate spends inside the reactor,d epending on the solution flow rate), [33,34] and by the O 2 /substrate molar ratio (which depends on the O 2 flow rate). However,r eproducible reaction patternsw ere observed.…”

Recent Progress in Continuous‐Flow Hydrogenation

“…Selective reduction of specific functional groups is important in synthesis. Barbaro and co‐workers reported unconventional Pd@sulfonated silica monolith catalysts that were synthesized by post grafting of sulfonic groups and in situ growth of Pd nanoparticles . The Pd nanoparticles (3.1 nm) were evenly dispersed in the mesoporous silica, yielding the Pd@MonoSil‐ArSO 3 monolith with 4.6 wt % Pd.…”

Low‐Temperature Continuous‐Flow Dehydration of Xylose Over Water‐Tolerant Niobia–Titania Heterogeneous Catalysts

“…[20,21] To circumvent these issues, different types of inorganic monoliths have been synthesized by spinodal decomposition showingi mproved resistancea nd rigidity. [52] Irrespective of the supported catalysta nd reaction, monolithic systemsh ave shown remarkable stability over prolonged reactiont imes, with no significant activity decay observed with up to 3days time-on-stream. [34] Despite their advantages, use of hierarchically porous inorganic monoliths in flow catalysis hasb een scarcely investigated so far,b eing essentially exploredf or HPLC applications.…”

“…[51] In terms of selectivity,t he Pd@SiO 2 monolith also performed better than Pd on conventional mesoporous silicai nt he partial hydrogenation reactiono f3 -hexyn-1-ol and 3-halogeno-nitrobenzenes, both under flow and batch conditions. [52] Irrespective of the supported catalysta nd reaction, monolithic systemsh ave shown remarkable stability over prolonged reactiont imes, with no significant activity decay observed with up to 3days time-on-stream. [46,50] All above findings show the advantages of unconventional inorganic monolithic catalysts compared with the classical heterogeneous ones.…”