Metal-supported catalysts are the cornerstone of many large-scale industrial processes currently used to produce fertilizers, fuels, paints, solvents, pharmaceutical active ingredients, and agrochemicals. The ever-increasing degree of sophistication and control over the metal cluster nano-architecture, chemistry, and electronic properties have enabled the development of a wealth of materials with controlled catalytic selectivity and activity. These metal clusters, however, can undergo surface reconstruction, poisoning, lixiviation, coking, and sintering in the presence of liquid environments (e.g. aqueous environments). This greatly limits the utilization of these tailored-design catalysts at the industrial scale for processing complex feedstocks such as biomass, in which the presence of water is unavoidable. To overcome these limitations, we have developed polymer over-coatings on the catalyst that can act as “co-solvents” to simultaneously; 1) control the selectivity and activity of the catalyst towards the desired product to maximize atom-efficiency of the process, and 2) prevent catalyst deactivation by preventing the sintering, lixiviation, and poisoning. In this contribution, we will discuss the effects of thermo-responsive polymer brush chemistry (poly(N-isopropylacrylamide) on the molecular transport using in-situ Attenuated Total Reflectance Infrared Spectroscopy (ATR-IR) to uncover the mechanisms of diffusion on membranes containing thermo-responsive polymer brushes that resemble that of egg-shell catalysts. Our results reveal that, contrary to the common knowledge on stimulus-responsive catalysis where at high temperatures mass transport limit diffusion due to the collapse of the polymer and subsequent pore blockage of the catalyst, in large pores (200 nm) the collapse of the polymer opens the pores allowing faster diffusion. Also, adsorption and diffusion of the probe molecule (CO) to the active sites (Pd/Al2O<sub>3</sub>) seems to depend on the polymerization time (i.e. polymer thickness).

In-situ ATR-IR spectroscopy of CO chemisorption on bio inspired catalyst in liquid environment

ACS Fall 2021

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