Catalysts coated with stimuli-responsive polymers can improve selectivity, stability, and recyclability in liquid environments. The stimulus-reponsive polymer covalently bonded on the catalyst surface 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). The vast majority of the existing reports are focused on the utilization of these polymers 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. In this contribution, we have challenged this idea by developing catalysts that operate in the kinetic regime regarless of the reaction conditions employed. This allow us to extract fundamentally relevant kinetic information about the solvation effects of the polymer in its swollen and collapsed states. To investigate the interplay between the stimuli-responsive polymer brushes attached to the catalyst and solvation environment near the active sites we have employed both nitrobenzene and nitrite hydrogenation reactions as probes. 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/SiO<sub>2</sub> catalyst. The polymer coated catalyst shows a a lower activation energy compared with the normal Pd/SiO<sub>2</sub> catalyst for both reactions particularly in the temperatures in which the polymer is swollen. These results will be instrumental in the development of new mechanisms that could understand the solvation effect of polymer on a catalytic hydrogenation reaction.

Exploring solvation effects on polymer modified metal-supported catalysts

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ACS Fall 2022

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