Role of Na in the dehydro-aromatization of 1,2-cyclohexanediol to catechol over the Na/Ni/HZSM-5 catalyst

Abstract

A series of Na- and/or Ni-modified HZSM-5 catalysts were employed in the dehydro-aromatization of 1,2-cyclohexanediol to catechol. The characterization of catalyst by XRD, N2-physisorption, FT-IR, NH3-TPD, H2-TPD, H2-TPR and FE-SEM showed that the Ni-loading over HZSM-5 zeolite generated the mesopores in the catalyst. The reduction to the Ni/HZSM-5 catalyst favored the formation of mesopores and also decreased largely both the acid property of strong acid sites and interaction between nickel species and HZSM-5 zeolite. The Na-loading to the Ni/HZSM-5 enabled the catalyst to be more easily reduced, and particularly, diminished the Brönsted acid sites, causing more large modifications to the catalyst than what the reduction process had done. The catalytic performance evaluation indicated that catechol could be only generated over the reduced Ni-containing catalysts but not over the pure HZSM-5 and unreduced Ni-containing catalysts. As high as 95.8% selectivity to catechol at 99.9 conversion of 1,2-cyclohexanediol was achieved over the reduced Na/Ni/HZSM-5 catalyst, while much lower selectivity to catechol was obtained, accompanied by the formation of large amounts of byproducts, over the reduced catalysts without the modification by Na. Accordingly, the modifications of Na to the pore structure, acidity and interaction between nickel species and HZSM-5 zeolite were responsible to the high performance of the reduced Na/Ni/HZSM-5 catalyst.