Engineering the site-accessibility for robust, continuous flow-through hydrogenation of styrene

Abstract

The evolution of micro-scale chemical factories operating under flow conditions has fueled growing interest in designing new catalytic materials capable of sustaining multiphasic reactions with enhanced kinetics and selectivity over extended periods. Unlike batch-mode, the flow-through configuration demands continuous catalytic interfacial engineering stretching from the micro-scale of the active site to the macro-scale of the reactor geometry. Here, we address this multi-scale, multiphasic challenge by demonstrating a macro-scale, shape-tunable carbon monolith, chemically decorated at the microscale with well-defined nickel (Ni) nanoparticles. The resulting Ni-monolith is both processable and mouldable into desired geometries, offering precise control, high selectivity, and excellent yield for the catalytic mono-hydrogenation of styrene under continuous flow conditions over prolonged durations. Through kinetic analysis, we reveal that the outstanding performance of the granulated Ni-on-monolith (NOM-G) catalyst is enabled by a transition in the rate-determining step from half-hydrogenation of styrene to complete hydrogenation forming ethylbenzene. Additionally, the engineered turbulent flow channels within the NOM-G monolith significantly enhance the interfacial accessibility of reactants to active sites, sustaining high yields over extended timescales. As a result, the system delivers one of the highest space-time yields (231 g L⁻¹ h⁻¹) reported thus far and establishes the viability of multiphasic reactions through flow.