Selective hydrocracking of 1-methylnaphthalene to benzene/toluene/ xylenes (BTX) over NiW/Beta bifunctional catalyst: Effects of metal-acid balance

The hydrocracking catalyst is characteristic of bifunctional catalyst mainly requiring metal-acid balance, which includes metal-acid ratio and metal-acid proximity. Here, we screened and clarified the optimal metal-acid balance on 1-methylnaphthalene (1-MN) hydrocracking by adjusting metal-acid ratio (nM/nA) via physically mixing the gamma-Al2O3 supported NiW samples and Beta zeolite with different acidity (denoted as NiW/AB(x) and x presents the molar ratio of SiO2/Al2O3 for Beta zeolite). NiW/AB(60) catalyst with a nM/nA of 0.40 showed the highest BTX selectivity (14.4 %) at a 1-MN conversion of 76.6 %, suggesting an optimal site balance between the metal sulfide site and medium-strong acid sites (ca. 1:2.5). Also, four different metal-acid proximities with centimeter, millimeter, micrometer and nanoscale distances were compared. The nanoscale proximity enabled the highest BTX selectivity (19.6 %) as compared to the microscale (14.4 %), millimeter scale (12.4 %) and centimeter scale (7.1 %) catalysts, confirming that the selectivity of BTX benefited from the fast diffusion for transporting reaction intermediates between metal and acid sites. Thus, we realized a nM/nA of 0.40 and a nanoscale site proximity for improving the reactivity and selectivity of 1-MN hydrocracking. This work not only presents an elegant showcase of achieving the synergistic effects of bifunctional catalyst, but also provides a rational approach for enhancing the catalytic performance of hydrocracking and beyond.