Continuous flow catalytic partial hydrogenation of hydrocarbons and alcohols over hybrid Pd/ZrO2/PVA wall reactors

Abstract

• Wall reactors comprising Pd nanoparticles into an hybrid zirconia / polyvinyl alcohol layer are prepared. • Wall reactors are used in the catalytic partial hydrogenation reaction of unsaturated hydrocarbons in the liquid phase. • Monoenes are obtained with excellent selectivity for dienes and alkynes, respectively, under continuous flow conditions. • Minimal amounts of catalyst and mild reaction conditions are required in hydrophilic solvents. • Neither metal leaching nor need of additives is observed. Catalytic hydrogenation reactions of functionalized hydrocarbons are of utmost interest in the fine-chemicals industry. Current hurdles relate to catalyst selectivity and stability, which often require use of sophisticated catalysts and/or the use of considerable amount of toxic additives. For practical applications, processes intensification would also be needed in terms of reagents/catalyst separation, improved space-time-yield productivity. We have shown that catalytic wall reactors comprising a zirconia/polyvinyl alcohol/Pd hybrids layered onto an inert solid support can be easily engineered and used in the liquid phase continuous flow partial hydrogenation reaction of alkenes and alkynes. Films of typical 0.5–1.5 nm thickness and containing ca. 10% wt palladium nanoparticles of 3.6 ± 0.9 nm size (TEM) provided good conversion and selectivity (88–99%) in the partial hydrogenation of 1,5- cyclooctadiene and 3-hexyn-1-ol over ca. 1 mg hybrid catalyst, under very mild flow conditions, i.e. residence times 150–180 s and room temperature. The catalysts showed remarkable resistance over prolonged time on stream, with neither metal leaching detected nor additives or regeneration steps required for use in hydrophilic solvents.