Efficient conversion of ethylene glycol to indole by hydrophobic modified Pt/Al2O3 catalyst

To address the issue of water formation leading to the collapse of catalyst structure and diminished catalytic activity during the synthesis of indole via reaction of ethylene glycol and aniline, a series of hydrophobic Pt/Al 2 O 3 catalysts have been engineered through surface chemical modification. Herein, alkyltriethoxysilane and alkyl phosphonic acid were employed as modifiers to decorate the surface of Pt/Al 2 O 3 , preparing hydrophobic catalyst (Pt/Al 2 O 3 -R), and the quantity of these hydrophobic reagents were selectively regulated to ascertain the catalyst with optimal efficiency. In the course of this procedure, the catalyst Pt/Al 2 O 3 -0.03SiC 12 , which exhibited a water contact angle of 112° and an ethylene glycol contact angle of 62°, significantly enhanced the yield of indole to 72%. It has been established that variations in the alkyl chain length impact the hydrophobicity and wettability of ethylene glycol, collectively influencing the catalytic efficiency. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FT-IR) confirmed successful integration of the chemical modifier onto the Al 2 O 3 surface via Si-O bonds. Furthermore, XRD, TEM, and BET results indicate that although the surface hydrophobic modification has a certain impact on the metal-active center, whereas the hydrophobic microenvironment is highly effective for the conversion of ethylene glycol to indole. DFT calculations further supported this finding, showing reduced water adsorption energy on the modified Pt/Al 2 O 3 surface. This study highlights the role of alkyl chains in modulating hydrophobicity and substrate wettability in the context of indole synthesis, offering insights into the design of catalysts for other dehydration reactions.