Boosting Catalytic Selectivity through a Precise Spatial Control of Catalysts at Pickering Droplet Interfaces

Abstract

Exploration of new methodologies to tune catalytic selectivity is a long-sought goal in catalytic community. In this work, oil–water interfaces of Pickering emulsions are developed to effectively regulate catalytic selectivity of hydrogenation reactions, which was achieved via a precise control of the spatial distribution of metal nanoparticles at the droplet interfaces. It was found that Pd nanoparticles located in the inner interfacial layer of Pickering droplets exhibited a significantly enhanced selectivity for p-chloroaniline (up to 99.6%) in the hydrogenation of p-chloronitrobenzene in comparison to those in the outer interfacial layer (63.6%) in pure water (68.5%) or in pure organic solvents (46.8%). Experimental and theoretical investigations indicated that such a remarkable interfacial microregion-dependent catalytic selectivity was attributed to the microenvironments of the coexistence of water and organic solvent at the droplet interfaces, which could provide unique interfacial hydrogen-bonding interactions and solvation effects so as to alter the adsorption patterns of p-chloronitrobenzene and p-chloroaniline on the Pd nanoparticles, thereby avoiding the unwanted contact of C–Cl bonds with the metal surfaces. Our strategy of precise spatial control of catalysts at liquid–liquid interfaces and the unprecedented interfacial effect reported here not only provide new insights into the liquid–liquid interfacial reactions but also open an avenue to boost catalytic selectivity.

Spatial Localization of Two Enzymes at Pickering Emulsion Droplet Interfaces for Cascade Reactions

“…NH 2 /C 8 /JMSNs were prepared according to our previous methods, [11b,c] and scanning electron microscopy (SEM) images show a morphology of discrete nanosheets with a thickness of nearly 40 nm (Figure S1c). Transmission electron microscopy (TEM) images further showcase that ordered mesochannels were perpendicular to the nanosheets (Figure S1g).…”

Thermo-Switchable Pickering Emulsion Stabilized by Smart Janus Nanosheets for Controllable Interfacial Catalysis

“…1−4 Apart from stabilizing the Pickering emulsion to maximize the oil/water interface for mass transfer, solid emulsifiers behave as interfacial catalysts simultaneously in PIC, which makes the enlarged oil/water interface to be a reaction interface for efficient aqueous catalysis. 5,6 Amphiphilic Janus materials, composed of one hydrophobic side and another hydrophilic, have recently emerged as attractive solid emulsifiers in PIC owing to their excellent surface activity. 7−9 In particular, the amphiphilic Janus nanosheets (JNSs) with a highly anisotropic shape are restricted to rotate at the oil−water interface, which makes the Pickering emulsion extremely stable for efficient interfacial catalysis.…”

“…Pickering interfacial catalysis (PIC) has received considerable attention in recent years, since it empowers water-incompatible organic catalysis to be highly efficient in water. − Apart from stabilizing the Pickering emulsion to maximize the oil/water interface for mass transfer, solid emulsifiers behave as interfacial catalysts simultaneously in PIC, which makes the enlarged oil/water interface to be a reaction interface for efficient aqueous catalysis. , Amphiphilic Janus materials, composed of one hydrophobic side and another hydrophilic, have recently emerged as attractive solid emulsifiers in PIC owing to their excellent surface activity. − In particular, the amphiphilic Janus nanosheets (JNSs) with a highly anisotropic shape are restricted to rotate at the oil–water interface, which makes the Pickering emulsion extremely stable for efficient interfacial catalysis. − Unfortunately, the super-stability of the Pickering emulsion makes the detachment of the JNSs from the oil/water interface very hard. , Harsh conditions, such as dialysis, electrophoresis, or supercentrifugation, are often required to demulsify the emulsion and recover the catalytic JNSs, which inevitably results in high energy consumption and/or produces undesired byproducts. − Therefore, a convenient approach to control the emulsification and demulsification of Pickering emulsions on demand is highly desirable in PIC, but it has remained challenging to date.…”

CO2-switchable emulsions with controllable size and viscosity

“…28,29 Compared with conventional emulsions, Pickering emulsions have much higher stabilities due to nearly irreversible adsorption of surface-active particles at the oil-water interface. 30 However, the high stabilities of Pickering emulsions always cause difficulties during demulsication, which might hinder their applications in which temporary stability is needed, such as in emulsion catalysis, 31,32 enzymatic catalysis 33 and emulsion polymerization. 34 Recently, oil-in-dispersion (OID) emulsions stabilized with similarly charged surfactants and nanoparticles have been reported, 35 in which the surfactants were adsorbed at the oilwater interface and the nanoparticles remained in the aqueous phase.…”

“…28,29 Compared with conventional emulsions, Pickering emulsions have much higher stabilities due to nearly irreversible adsorption of surface-active particles at the oil–water interface. 30 However, the high stabilities of Pickering emulsions always cause difficulties during demulsification, which might hinder their applications in which temporary stability is needed, such as in emulsion catalysis, 31,32 enzymatic catalysis 33 and emulsion polymerization. 34…”