(458b) Understanding the Effect of Organic Coatings on 4-Nitrostyrene Hydrogenation Selectivity over Pt Catalysts

The use of organic coatings has been shown to provide selectivity control on supported metal catalysts for hydrogenation reactions with multiple reducible groups in the same molecule. The reduction of substituted nitroarenes to anilines is an industrially relevant example where organic coatings have enhanced selectivity, but the mechanisms by which these coatings influence selectivity are poorly understood. Typically, short-chained coatings (18 carbon atoms or less) are used, however, this work explored longer chains of ion-conducting polymers (ionomers) as organic coatings. Ionomers are commonly used in electrochemistry for ion transfer across electrochemical cells. This study aimed to evaluate ionomers as long-chained organic coatings for selectivity control in a thermochemical system. Specifically, the hydrogenation of 4-nitrostyrene was investigated over Pt-based metal oxide-supported catalysts to understand the effects of different coatings on product selectivity and reaction rates. This reaction is of interest due to the distinct nitro and vinyl functional groups on 4-nitrostyrene, each requiring different surface environments for optimal reactivity. 4-Nitrostyrene hydrogenation reactions were performed in a batch reactor using uncoated, ionomer coated, alkane thiol coated, and phosphonic acid (PA) coated catalysts. The coating density of alkane thiols and PAs were varied. Product selectivity for each coated catalyst was evaluated against the uncoated catalyst product distribution. Changes in selectivity were observed for all coated catalysts, with thiol coatings shifting selectivity towards 4-aminostyrene and both ionomer and PA coatings shifting towards 4-ethylnitrobenzene. It was observed that selectivity toward 4-aminostyrene with thiol coatings increased proportionally with their coating densities. These changes were attributed to the identity of the adsorption sites modified by different coatings, underscoring how selection of appropriate organic functionality can be used to tune catalyst selectivity. These results shed light into how ionomers can be utilized in thermochemical systems.