Impact of Acidity and Metal Particle Size on the Competitive Pathways of Benzyl Phenyl Ether Conversion to Aromatics and Cycloalkanes in a Nonpolar Solvent

This work investigates the role of the support and metal particle size in the performance of Pd-based catalysts for the hydroconversion of benzyl phenyl ether (BPE) in the liquid phase. Pd-based catalysts supported on different oxides (SiO2, TiO2, Nb2O5, Al2O3, ZrO2, and HZSM5) were synthesized by incipient wetness impregnation (particle size > 4 nm) and sol-immobilization methods (particle size < 4 nm). Different reaction pathways leading to aromatics, polyaromatics, or cycloalkanes have been evidenced, and the role of the support acidity and metal particle size on the competition between these pathways has been clarified. The acid sites of the support themselves promote the cracking of the Caliph–O bond of BPE, producing monoaromatic intermediates that react with each other to form polyaromatic dimers and trimers. Besides, hydrogenolysis of the Caliph–O bond takes place on the metallic Pd particles, producing toluene and phenol, but polyaromatics are still formed in a parallel pathway when the catalysts present large Pd particles. In contrast, on catalysts containing small Pd particles, this competitive pathway is suppressed. Moreover, toluene and phenol are hydrogenated, and completely deoxygenated cycloalkanes are obtained. These results stress the importance of the balance between metal particle size and support acidity for the production of cycloalkanes from aryl ethers. Finally, a reaction network that simultaneously takes into account the characteristics of the metal (particle size) and the support (acidity) is proposed.