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

Abstract

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 γ-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.