Tailored acidity of silylated Pt/USY catalysts to regulate catalytic performances for phenol hydrogenation

Pt-based catalysts supported on acidic zeolites are intensively utilized for selective hydrogenation reactions; yet the interplay between zeolite acidity and metal sites remains important research topics, because zeolites feature adjustable acidity (Brønsted/Lewis), strong (hydrothermal-)stability, and highly-ordered porosity for nanoconfinement and shape selectivity. This study systematically identifies the contribution of Brønsted (B) acids and Lewis (L) acid sites in Pt/USY catalysts tailored by controlled introduction of diethoxydimethylsilane (DEDMS, 0-5.0% wt) for phenol hydrogenation to cyclohexanol and cyclohexanone. The modification declined B acid sites (from 145.8 over 1%Pt/USY-1 to 14.7 μmol/g over 1%Pt/5.0%DEDMS-USY) and L acid sites (from 129.3 to 38.4 μmol/g). The reduction in B acid sites considerably suppressed phenol adsorption and thus decreased its conversion from 100% (1%Pt/USY-1) to 19.0% (1%Pt/5.0%DEDMS-USY-1), and the reduction in L acid sites primarily suppressed the cyclohexanone adsorption and thus increased its selectivity from being undetectable (1%Pt/USY-1) to 57.7% (1%Pt/5.0%DEDMS-USY). The silylation could effectively tailor the catalytic activity and selectivity of Pt/USY catalysts and provides valuable insights for designing bifunctional catalysts in selective hydrogenation.