Nowadays, there has been an increasing interest in tailoring catalysts with stimuli-responsive polymers to improve their selectivity, stability, and recyclability in liquid environments[1,2]. To create this materials the external surface of the catalyst is functionalized with polymer brushes that can undergo reversible conformational transitions from solvated state or “collapse” state depending on the conditions of the reaction environment (e.g. pH, temperature, solvent polarity). In the solvated state the catalytic active sites are easily accessible to molecules in the liquid and as a result the reaction can take place. Upon conformational transition to the “collapse” state the polymers form a dense layer at the surface of the catalyst that limits molecular diffusion of reactants to the active site[3]. The vast majority of the existing reports are focused on the utilization of this strategy to control either the dispersability of nano-catalysts in liquid environments or the molecular transport towards the active sites assuming that the polymer cannot modify the surface reaction energetics. To challenge this idea, we have developed a family of catalysts that are free of mass transport limitations to investigate the interplay between the stimuli-responsive polymer brushes attached to the catalyst and solvation environment near the active sites using nitrobenzene hydrogenation as probe reaction. For this purpose, we employed poly(n-isopropyllacrylamine), a typical thermoresponsive polymer that exhibits a sharp change in solubility at temperatures above 32 °C, to create a coating on Pd/SiO2 catalyst. The polymer coated catalyst shows a higher selectivity to P-aminophenol and a lower activation energy compared with the normal Pd/SiO2 catalyst. These results will be instrumental in the development of new mechanisms that could understand the solvation effect of polymer on a catalytic hydrogenation reaction.

Fine-Tuning of Solvation Environments in Liquid Phase Reactions Using Polymer-Modified Metal-Supported Catalysts

ACS Fall 2021

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