(584cr) Aryl-Bridged Polysesquioxane As a Support for Palladium-Catalyzed Selective Hydrogenolysis of Acetophenone: Valorizing Byproducts from Propylene Oxide Synthesis

Propylene oxide (PO) is an essential feedstock for producing various industrial chemicals. Although several synthesis routes exist, the predominant method is the ethylbenzene co-oxidation process (PO/SM), which simultaneously produces PO and styrene monomers (SM). A major drawback of the PO/SM process is the formation of acetophenone (AP) as the main byproduct, which undermines feedstock utilization. To address this issue, AP is typically subjected to catalytic hydrogenation to yield α-methylbenzyl alcohol (α-MBA) and ethylbenzene (EB), which can be recycled back for PO synthesis process. However, this method suffers from the formation of undesired over-hydrogenated products.

In this study, palladium catalysts supported on Aryl-bridged polysilsesquioxanes (ABPS), an organic–inorganic hybrid silica, were developed for enhanced AP conversion and EB selectivity. ABPS supports of different pore size were synthesized via sol–gel processing of bis(trimethoxysilylethyl)benzene in different solvents. The palladium catalysts were characterized using nitrogen physisorption, XPS, TEM, and NMR techniques. Hydrogenation reactions were performed in an autoclave reactor at 150°C and 50 bar H₂ pressure, and the reaction samples were analyzed using GC-MS.

The nitrogen physisorption results suggested that the ABPS support synthesized using acetonitrile (ABPS-A) has a higher surface area and larger pore diameter compared to those of the ABPS support synthesized using tetrahydrofuran (ABPS-T). The increased pore size in ABPS-A resulted in increased Pd particle size, as confirmed by transmission electron microscopy (TEM). The kinetic studies revealed that although both Pd/ABPS-A and Pd/ABPS-T catalysts achieved almost complete conversion within the first 15 min of the reaction, the Pd/ABPS-T catalyst (with smaller Pd size) was more selective for ethylbenzene, an HDO product, than Pd/ABPS-A. These results demonstrate the efficiency of our catalysts for hydrodeoxygenation without ring hydrogenation and highlight the impact of palladium particle size on HDO activity. Consequently, our Pd/ABPS catalysts emerge as promising candidates for selective catalytic hydrogenolysis of acetophenone