Abstract
The external surface of the H-Mordenite (MOR) was modified with lanthanide oxides such as CeO2, La2O3, Pr2O3, Sm2O3, Dy2O3, and Yb2O3, to investigate the deactivation of external acid sites. It is confirmed that the modification with the oxides prevents the isomerization of 2,6-diisopropylnaphthalene (DIPN) during the isopropylation of naphthalene (NP). The oxides accumulated on the MOR surface deactivated the acid sites with keeping catalytic activities of the isopropylation when their loadings are in the range of 5–10 wt%; however, the differences in the activities were observed when the loading was increased to 20–30 wt%: CeO2 gave a high activity with a high selectivity for 2,6-DIPN, and Sm2O3 maintained moderate activities, whereas the other oxides lost the activities. The differences of the modified MORs are ascribed to the morphologies of mesopores formed by the accumulation of the oxides. CeO2 is accumulated as segregated nano-sized crystallites, and the pore-entrances of MOR are opened through their mesopores for the access of NP and its products, and the isopropylation occurs in the channels with a high selectivity for 2,6-DIPN without a significant loss of the activities. However, La2O3 is accumulated as amorphous glassy oxide with a low surface area, leading to the loss of the activities by disturbing the access of NP to MOR pores. Further, amorphous glassy Sm2O3 also supports the selective formation of 2,6-DIPN as the mesopores allow the access of NP to MOR channels.
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•Effective deactivation of external acid site of MOR with lanthanide oxides.•CeO2 enhanced the selectivities for 2,6-DIPN. La2O3 disturbed the catalysis of MOR.•Differences of CeO2 and La2O3 on MOR surfaces are due to textural properties.•CeO2 keeps MOR pores open through accumulated segregated crystals.•La2O3 chokes pores through accumulated glassy oxides.